f% ENGINEERING universe ^J;t'i 01 URBAMA, ILLINOIS. 61801 CIVIL ENGINEERJ^STUDIES SANITARY ENGINEERING SERIES NO. 39 £28 Ii65c no .35 THE ion-EXCHANGE REACTIONS OF RADIOACTIVE IONS WITH SOILS AND EFFECTS OF ORGANIC COMPOUNDS CONFERENCE H By - \9B9 BONG TAICK KOWN A lU .iiUiS BEN B. EWING Principal Investigator FINAL REPORT PROJECT A-004-ILL Supported by UNIVERSITY OF ILLINOIS WATER RESOURCES CENTER with funds from OFFICE OF WATER RESOURCES RESEARCH U.S. DEPT. OF THE INTERIOR Agreement No. 14-01-0001-907 DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF ILLINOIS URBANA, ILLINOIS OCTOBER, 1966 ■ggA g LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 628 I£65c no. 39 d& & ENGINEERING LIBRARY BKIgEEREKG UBi&ffl The person charging this material is re- sponsible for its return on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN L161— O-1096 THE ION-EXCHANGE REACTIONS OF RADIOACTIVE ONS WITH SOILS AND EFFECTS OF ORGANIC COMPOUNDS AGRICULTURE RECEIVED by Bong Taick Kown NOV IS 1966 ESS® Ben B. Ewing Principal Investigator Final Report Project A-004-ILL Supported by University of Illinois Water Resources Center with funds from Office of Water Resources Research U.S. Dept. of the Interior Agreement No. 14-01-0001-907 Department of Civil Engineering University of Illinois Urbana, I 1 1 i nois October 1966 t ) > ' 3 ' ENGlNfc&WMi U- THE ION-EXCHANGE REACTIONS OF RADIOACTIVE IONS WITH SOILS AND EFFECTS OF ORGANIC COMPOUNDS Bong Taick Kown, Ph„Do Nuclear Engineering Program University of Illinois, 1966 The ion-exchange reactions of radionuclides with soil minerals and the effects of various water-soluble organic compounds on the reac- tions were investigated,, Various theories concerned with ion-exchange reactions were examined for their practicability in predicting the equilibrium distribu- tion of radionuclides in a soil environment „ The effects of various water-soluble organic compounds on the ion-exchange reactions of a radio- nuclide with soil minerals (Mississippi montmorillonite and Fithian Illite) were studied using organic compounds selected from the groups which are known to be present in the natural environment and in certain wastes discharged from nuclear facilities,, The organic compounds include those which interact with metal ions (both the radionuclides and the com- peting counter ions) and others which may interact with soil particle surfaces „ The effects of the interactions of organic compounds with counter ions were examined using chelating agents 9 citrate 9 tartrate 8 and EDTAo Several soil-sorptive organic compounds (methylamine 9 dodecylaminej, methylene blue g and arginine) were used to determine the effects of organic adsorption on the ion-exchange properties of soil minerals „ Or- ganic compounds extracted from ground water and surface soils were also used to Investigate the effects of these extracts and to compare the Digitized by the Internet Archive in 2013 http://archive.org/details/ionexchangereact39kown capacities and the selectivity of soil exchange media. The experimental results indicated that certain organic compounds were irreversibly ad- sorbed on soil particle surfaces and had considerable effects on their ion-exchange parameters. Irreversible adsorption of organic compounds not only reduced the effective exchange capacities, but also changed the selective properties of the exchange media. In general, the selectivity for a cation in preference to others increased as soil particle surfaces were covered with organic compounds « The experimental results with natural organic extracts indicated that the effects of the extracts were similar to those of weak chelating agents. The degree of the effects was somewhat less than that of pure chelating agents used As a result of the inefficient method of extrac- tion used, the extracts are believed to contain only a small fraction of the natural organic compounds present in the original sample. Ill ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to all those whose assistance helped in bringing this work to successful comple- tion. The author is indebted to his advisor, Professor Ben B. Ewing, for his guiding assistance in the research and the writing of this thesis „ Special acknowledgements are also extended to Dr„ Richard Engelbrecht and Dr Marvin Wyman and all the personnel in the Sanitary Engineering Lab- oratory who have helped to make this work possible. The work upon which this publication is based was supported in part by funds provided by the United States Department of the Interior as authorized under the Water Resources Research Act of 1964 , Public Law 88-379 „ IV TABLE OF CONTENTS Page AL.i\lN UWJjEj UL3rjri£jiNlo o o o o o o o o o o o o o o o o o o n o o o o 1X1 ulu 1 Ui 1 ri.i.> LjILi Oo oooo ooeooo0o« ooeoo«Beft«ooeoVH J_jlt> 1 wi I IbUKuO O o o O O o oVlll J., d llN i rvuUUL 1 J.U.H oooooo oooooooooo oo o o o o • o o 00 1 lolo Purpose and Scope of the Investigation, . . . . • . . • . . 3 2, THEORY AND MECHANISM OF ION EXCHANGE, .............. 6 2.1. Theory of the Ion-Exchange Phenomena, ........... 6 2.1.1, The Double-Layer Theory .............. 6 2.1.2, The Donnon Membrane Theory, .,,,,„..„.,. 6 2.1.3, The Crystal Lattice Theory. ............ 9 2.1.4, The Ion-Exchange Theory of Soils. ......... 10 2.2. Ion-Exchange Equilibrium and Terminology, ......... 11 2.3. Evaluation of Ion-Exchange Equilibrium. ..,,,.,,„, 14 2,3,1, The Mass-Action Expression of Ion-Exchange ASaCX lOll So o o o o o o o o o o o o lO 2.4. Ion-Exchange Reactions of Heterogeneous Clay Mixtures . . . 22 2.5. Ion-Exchange Equilibrium in a Multicomponent System , „ . „ 24 2.6. Effects of Organic Compounds on Ion-Exchange Reactions or v-iciy iiiTiGxcixSo 000000000000000000000 ^o 2.6.1, Ion-Exchange Equilibria of Clay Minerals in the Presence of Sequestering Agents ........ 26 2.6.2, Adsorption of Organic Compounds on Clay Minerals and Its Effects on Ion-Exchange Properties of These Clay Minerals ......... 29 2.6.2.1. Organic Adsorption on Clay Surfaces ... 29 2.6.2.2. Effects of Adsorbed Organic Compounds on Properties of Clay Minerals, , . , , . 30 Page 3, MATERIALS AND EXPERIMENTAL PROCEDURE, .............. 35 O o -1 - o lIuLCildlb UbCUc • B • 4 ft O O J 3 1»1. Properties of Clay Minerals ...... ...... 35 3.1.1.1. Montmorillonite . 36 O o 1 a i ii ^ o 111116 o e o o o o o o o o o o o o o o o o O / 3ol,l 3c Treatment of Clay Minerals. , . , , . „ . 39 3.1.2. Organic Compounds Used, .............. 41 3,l 2ol. Pure Organic Compounds. ..,,.,... 41 3.1. 2. 2, Mixture of Organic Compounds in Natural Environments. .......... 41 3,2. Experimental Procedure , .................. 45 3.2.1. Analytical Methods and Equipment. ,..,...,, 45 3.2.2,, Ion-Exchange Reactions. .............. 46 3o2„2„l Exchange Capacity ............ 46 3 2o2o2„ Equilibrium Constants . . . ...... . 48 3o2.2o3„ Equilibrium Reactions of Hetero- geneous Clay Mixtures „ . . , . „ . „ „ , 50 3,2„2 4„ Ion -Exchange Equilibrium in a Multicomponent System . „ . „ „ . . . . . 51 3.2.2.5,, pH Effects on Ion-Exchange Equilibria . , 52 3.2 2o6„ Effects of Sequestering Agents on Ion-Exchange Reactions of Clay 1 * JLX1 wX d _L Ooooooooooooooooyo J t 3 2o2„7„ Effects of Adsorbed Organic Compounds on Ion-Exchange Reactions of Clay jl_LI.ic2XciJLoo e o o o o o o o o o o o a 9 a o 00 3„2„2o8„ Effects of Natural Organic Compounds on Ion-Exchange Reactions of Clay i 1 111"! el X. cSooooooooooooooooo DO VI Page 4. ION-EXCHANGE EQUILIBRIUM IN ABSENCE OF ORGANICS; RESULTS AND DISCUSSION e ». o . o ............... . 59 4.1. Treatment of Clay Minerals „ . . . . . . . . . . . . . , . . 59 4.2. Determination of the Cation Exchange Capacities ,..,.. 59 1.3. Behavior of Hydrogen Ions in Clay Ion-Exchange KGuCriOnS 000000000000000*000000000 DO 4.4. Determination of Equilibrium Constants, .......... 68 4.5. Ion-Exchange Equilibria of Heterogeneous Clay Mixtures. , , 81 4.6. Ion-Exchange Equilibrium in a Multicomponent System .... 82 5. ION-EXCHANGE EQUILIBRIUM IN PRESENCE OF ORGANICS; RESULTS AND DISCUSSION. ...................... 90 5.1. Effects of Sequestering Agents on Ion-Exchange Reactions of Clay Minerals. ................ 90 5.2. Adsorption of Organic Compounds and Effects on the Clay Ion-Exchange Properties. ............... 106 5o2„l. Adsorption of Methylene Blue and Its Effects on the Clay Ion-Exchange Properties ........ 106 5.2.2. Adsorption of Amine Compounds and Effects on the Clay Ion-Exchange Properties. ......... 115 5.2.3. Adsorption of Arginine and Effects on the Clay Ion-Exchange Properties. ........... 131 5o2.4„ Adsorption of Sucrose and Effects on the Clay Ion-Exchange Properties. .......... . 135 5.3. Effects of Natural Organic Compounds on Ion-Exchange Reactions of Clay Minerals. ................ 136 6. SUMMARY AND CONCLUSIONS .................... • 140 DlDJjl'Jlii J\/i JT il I oooooqoooooooooooooooqoooooooJLH'O APPENDIX - SYMBOLS USED .........<............... 148 V lino O O O O O O O O O O O O qXOU Vll LIST OF TABLES Table Page 1 APPROXIMATE PURITY OF CLAY MINERALS USED, „ „ . . . „ . . . 36 2 CHEMICAL AND PHYSICAL PROPERTIES OF ORGANIC ANIONS. .... 42 3 CHEMICAL AND PHYSICAL PROPERTIES OF ORGANIC CATIONS . „ . . 43 4 MEASUREMENT OF CONDUCTIVITY AND pH OF CLAY MINERAL oUO-T.LiiNoJ_vv.lNo o o o o o o o o o o o o o o o o o o o o o o o o Q \V 5 EXCHANGE CAPACITIES OF CLAY MINERALS. . ......... . 62 6 EQUILIBRIUM CONSTANT OF MONTMORILLONITE FOR THE EXCHANGE BETWEEN Sr ++ AND H + „ .... . . ........ . 66 7 INFLUENCE OF HYDROGEN ON THE EXCHANGE EQUILIBRIUM CONSTANTS OF MONTMORILLONITE. . . . . ... , . , .... . 67 8 THE VALUE OF EQUILIBRIUM CONSTANTS FOR THE EXCHANGE BETWEEN Sr ++ =Ca ++ AND Sr ++ -Mg ++ .............. 70 9 THE VALUE OF EQUILIBRIUM CONSTANTS FOR THE EXCHANGE BETWEEN Na + AND Sr ++ . . „ „ . „ „ „ . . „ . „ „ . „ . „ . . 71 10 EXPERIMENTAL CONDITIONS FOR EXCHANGE EQUILIBRIA IN MULTICOMPONENT SYSTEM. . . . „ . , . ... . . . . . 89 11 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF CITRATE ON CLAY ION-EXCHANGE REACTIONS. . „ . . . . . . . . 97 12 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF TARTRATE ON CLAY ION-EXCHANGE REACTIONS .......... 99 13 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF EDTA ON CLAY ION-EXCHANGE REACTIONS „ „ . . , , . „ . „ . . 99 14 EQUILIBRIUM CONSTANTS FOR THE EXCHANGE BETWEEN INORGANIC AND ORGANIC CATIONS . „ .... . . . ...... 125 VI 11 LIST OF FIGURES Figure Page 1 DIAGRAMATIC SKETCH OF THE STRUCTURE OF MONTMORILLONITE. . . 38 2 DIAGRAMATIC SKETCH OF THE STRUCTURE OF MUSCOVITE TYPE 1 Jj L 1 1 Ij o o O O O O O O O O O O O O O O O O 4 i' J 3 ION EXCHANGE CAPACITY OF CLAY MINERALS AS A FUNCTION OF THE COUNTER ION CONCENTRATION. . . . . . . , . . . . . . 61 4 EFFECTS OF H + AND OH~ IONS ON EXCHANGE CAPACITY OF \^ ij-ri X i i _L IN ill XvrlijO ooooooooooooooooooooooe DH 5 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE, Ca ++ , AND Sr ++ , ........... 72 6 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Sr ++ , AND Ca ++ „ „ . . „ „ „ „ . „ . . „ . . . 73 7 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE s Mg ++ , AND Sr ++ . . „ . . „ . . , , . . . . 74 8 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE 9 Sr ++ , AND Mg ++ „ „ . „ „ „ „ „ . . . . . . , „ 75 9 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE , Na + , AND Sr ++ „ , . . „ . , „ . . , . 76 10 CORRECTED EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE, Na + , AND Sr ++ . 000,000 77 11 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Na + , AND Sr ++ . . . . . . . , . 78 12 CORRECTED EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Na + , AND Sr ++ . , . , „ . . . . . . , . 79 13 EFFECTS OF IMPURITY OF CLAY ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ , AND Na + 0000000000.00, 83 14 EQUILIBRIUM CONSTANTS OF A CLAY MIXTURE AS A FUNCTION OF THE COUNTER ION CONCENTRATIONS . „ . . „ . . . , . . , „ 84 15 ION EXCHANGE EQUILIBRIUM OF MONTMORILLONITE WITH THREE COMPETING COUNTER IONS . „ . . , . . . . . 86 16 ION EXCHANGE EQUILIBRIUM OF MONTMORILLONITE WITH FOUR COMPETING COUNTER IONS 0.00000000,00000 87 IX Figure Page 17 ION EXCHANGE EQUILIBRIUM OF ILLITE WITH THREE COMPETING COUNTER IONS„ ............... 88 18 EFFECTS OF CITRATE ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. . . . . . 93 19 EFFECTS OF TARTRATE ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. ..... 94 20 EFFECTS OF EDTA ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. ........... 95 21 EFFECTS OF CHELATING AGENTS ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. ..... 96 22 ADSORPTION OF CITRATE ON CLAY MINERALS. .......... 102 23 ADSORPTION OF CHELATING AGENTS ON CLAY MINERALS ...... 103 24 ADSORPTION OF CITRATE ON CLAY MINERALS AS A FUNCTION . / F I \ d \sJL r\ LJ lJLj Uooooooooooooooooooooooq-L-^-'H" 25 ADSORPTION OF METHYLENE BLUE ON MONTMORILLONITE AND EFFECTS ON EXCHANGEABLE CATIONS, Sr ++ ........... 109 26 ADSORPTION OF METHYLENE BLUE ON ILLITE AND EFFECTS ON EXCHANGEABLE CATION , Sr ++ . ............... 110 27 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER I0NS 9 Sr ++ AND Ca ++ , FOR Ca-MONTMORILLONITE .... Ill 28 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS s Sr ++ AND Ca ++ , FOR Ca-ILLITE ....... 112 29 EFFECT OF METHYLENE BLUE ON ION EXCHANGE EQUILIBRIUM L v ) 1 \ O 1 l'\ IN J-Oooooooooooooooooooooo o o o o -J — L O 30 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na + , FOR Na-ILLITE, ....... 114 31 Sr ++ LEACHING FROM Sr-CLAY BY ORGANIC CATIONS ....... 118 32 ADSORPTION OF ORGANIC CATION ON MONTMORILLONITE ...... 119 33 ADSORPTION OF ORGANIC CATION ON ILLITE. ..... ..... 120 34 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Na + , METHYLAMINE, AND CLAY MINERALS. .......... 121 Figure Page 35 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Sr ++ , ORGANIC CATIONS, AND CLAY MINERALS . ...... 122 36 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Sr ++ , DODECYLAMINE, AND MONTMORILLONITE ....... 123 37 EFFECTS OF ADSORBED METHYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Ca ++ „ . . . . „ „ . „ , , . . . . . 127 38 EFFECTS OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr++ AND Ca ++ . „ . . . . . <> . . . . » . . . 128 39 EFFECTS OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Mg ++ . ............... 129 40 EFFECT OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na + ....... 130 41 EFFECTS OF ADSORBED ARGININE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Mg ++ . ............... 132 42 EFFECTS OF ADSORBED ARGININE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na+ WITH MONTMORILLONITE. ..... 133 43 EFFECTS OF ADSORBED ARGININE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na + WITH ILLITE . . . . . . . . . . 134 44 EFFECTS OF SOIL ORGANIC EXTRACTS ON DISTRIBUTION OF COUNTER IONS 00000000000.000000000 137 45 EFFECTS OF GROUND WATER ORGANIC EXTRACTS ON DISTRIBUTION OF COUNTER IONS ... ........... . 138 lo INTRODUCTION Radioactive contaminants created by nuclear processing plants or by bomb tests may enter the soil environment as fallout materials, as low-level wastes being disposed into the environment, or as a result of accidents whereby storage facilities or processing plants release them„ As the magnitude of the nuclear industry grows, the problems of nuclear waste treatment and contamination of the environment with radioactive waste are inevitable „ Transport of these radionuclides through soil media is a consequence of the movement of transporting water, but they are also retained by adsorptive properties of the soil media The role of nat- ural soil media in retaining or transporting radionuclides is becoming increasingly important „ In the interest of water supply and food pro- duction from soils „ greater care and precision will be required to evaluate the fate of radionuclides in the soil environment It is a well established fact that the ion-exchange properties of soil materials play important roles in retaining or transporting the radionuclides released into a soil environment „ Ion-exchange reactions 90 137 of hazardous radionuclides such as Sr and Cs with soil and its clay fraction have been studied by many investigators not only for the purpose of investigating the fate of the radionuclides g but also for the treatment of radioactive waste by exchange adsorption „ Equilibrium distribution of radionuclides released into the soil environment are controlled by various chemical and physical conditions of the environment „ Of many possible factors which may govern the ion- exchange reactions of soil materials, the presence of various inorganic salts, the pH of the environment, and properties of clay fraction of soil materials are important and have been studied for their effects „ Various theories involved in ion-exchange reactions of soil materials have been developed „ Within the frame of conditions assumed for their development, the theories are satisfactory; however, universal application of these theories for actual soil environments is limited because of the complexity of over-all reactions involved in the natural soil environment o In order to be able to predict more accurately the equilibrium distribution of radionuclides disposed into the soil environment, further study of the fundamental mechanisms of soil ion exchange and other possible factors which may affect the ion-exchange reactions of soil media is needed, One of the areas in which further investigation is needed for a better understanding of soil ion-exchange reaction is the effects of water- soluble organic compounds present in the system „ It is a known fact that (2) . . natural water and certain wastes discharged from nuclear facilities contain many types of dissolved organic compounds „ Furthermore , natural soils contain humus type organic compounds which are either the degradation products of vegetable matter or the products of microbial synthesis „ (3) Stevenson and his co-workers have shown the presence of various amino acids adsorbed on soil particles „ Though considerable research work has been conducted with regard to ion-exchange reactions between radionuclides and soil exchange media, these studies were generally performed with ideally simplified systems containing soils and distilled water solutions in the absence of any organic compounds The interactions of individual organic constituents in a natural soil environment and their effects on the ion-exchange properties of the soil environment have not been studied „ To have a better understanding of what happens to radionuclides when they enter the natural soil environment, a knowledge of over-all reactions including the interactions of the organic compounds with soil constituents and their effects on the ion-exchange reaction is needed „ lolo Purpose and Scope of the Investigation There now exists a large amount of data on ion-exchange properties of soil materials „ In general, these data have been obtained from ideally simplified systems „ These data alone are inadequate for the prediction of the actual equilibrium distribution of radionuclides re- leased into a soil environment, for in a natural soil environment various other interactions may affect the ion-exchange reactions , One such area in which further Investigation is needed is the effect of dissolved organic compounds „ It has been shown that in a natural soil environment there are (2) present various organic compounds which may interact with both com- peting counter ions and the soil exchange media „ Some of the organic compounds present in natural water are believed to be mult i -hydroxy - carboxylic compounds which may readily interact with metal ions present in the system The extraction of proteins and amino-acid-type organic (3) compounds from natural soil materials indicates the presence of soil- sorptive organic compounds in the natural soil environment „ Recently, ORNL and NRTS ' in their investigations of ion-exchange properties of radioactive wastes with soil media included the study of the effects of various complexing agents present in their wastes . It is the purpose of this investigation to study the mechanism of soil ion exchange and the effects of various organic compounds Organic compounds selected for the investigation were chelating agents, a polar compound, organic cations, and organic extracts from natural water and surface soil materials „ On the basis of their interaction, these organic compounds are grouped into two categories, one which inter- acts with counter ions and the other which interacts with soil particle surfaces o To examine the mechanism of soil ion exchange and the applica- bility of present theories, ion-exchange reactions of various counter ions with soil minerals (montmorillonite and illite) were first studied in the absence of organic compounds The studies included the determination of soil ion-exchange parameters and the applicability of data obtained from simple systems to more complex systems „ The interactions of counter ions (Na , Ca , Mg , and Sr ) with chelating agents and their effects on ion-exchange reactions were studied by batch equilibrium-type experiments with tartrate, citrate, and EDTA The laboratory findings were examined in terms of existing theories concerning ion exchange and metal chelate chemistry „ Several organic compounds having cat ionic properties (methyl - amine g, methylene blue 8 dodecylamine, and arginine) were used to study adsorption and its effects on the ion-exchange properties of soil min- erals o The relative selectivity of soil minerals for the organic cations with respect to inorganic counter ions (Na and Sr ) was determined „ The effects of adsorbed organic compounds on the ion-exchange properties of soil minerals were examined in terms of changes in the exchange parameters o In order to compare the effects of various pure organic com- pounds with those of organic compounds present in the natural environment, organics extracted from ground water and surface soils were also used in the investigation . The effects of the extracts were examined in terms of changes in distributions of counter ions in the presence of the extracts. 2. THEORY AND MECHANISM OF ION EXCHANGE 2.1. Theory of the Ion-Exchange Phenomena The various explanations that have been proposed for the ion- exchange phenomena have been widely divergent. These explanations may be grouped into three theories : (1) the double-layer theory, (2) the Donnon membrane theory, and (3) the crystal lattice exchange theory. 2.1.1. The Double-Layer Theory (7) The double-layer theory , developed as an explanation of the electrokinetic properties of colloids, has been considered as an explanation for the various phenomena associated with ion exchange. The double-layer model of charged colloids consists of an inner fixed layer with a diffuse and mobile outer layer of charges. The ions present in the diffuse outer layer of a colloid extend into the external liquid medium. It may be considered that the concentration of the ions consti- tuting the diffuse outer layer is varying continuously and depends on the concentration and pH of the external solution. If the concentration of the ions in the external solution is changed by addition of a foreign ion, the equilibrium is upset and a new equilibrium is obtained. Some new ions will enter the diffuse outer layer, exchanging the ions previously held in this layer. The capacity of the diffuse outer layer depends on the concentration and pH of the external solution. 2.1.2. The Donnon Membrane Theory A special case of the Donnon membrane theory ' has been applied to explain the ion-exchange phenomena occurring in various exchange media. The Donnon membrane theory pertains to the unequal dis- tribution of ions on two sides of a semipermeable membrane, one side containing an electrolyte, one of whose ions is not able to diffuse through the membrane, Bauman and Eichhorn , applying a Donnon mem- brane equilibrium approach, considered an ion-exchange medium as a very concentrated solution of functional groups separated from the surrounding solution by a semipermeable membrane. The functional groups (exchange media) are considered as the non-diffusible ions. For the solution containing electrolyte AX, the chemical poten- tial of electrolyte AX at equilibrium must be the same at both sides of the membrane. U AX = "L + R T lr a AX U AX ■ U AX = U AX + R T ln a AX> i2 - X) where a and a refer to the activities of the electrolyte AX in the AX AX exchanger and solution phases, respectively. In the first approximation, the standard chemical potentials — p o (U. and U ) of the electrolyte AX are considered as being equal on both sides, so that at constant temperature Equation (2-1) may be reduced to a AX ~ a AX» (2 " 2) which can> be written in the form, a A a x = a A a r (2-3) Equation (2-3) shows the fact that in the exchange medium with high exchange capacity (a > a ) the invasion of negative ion, X, is small. For the system containing the ion exchanger in ionic form B, and sur- rounded by the solution with another electrolyte BX, the ionic distribu- tion of electrolyte, BX, follows the same rule as AX. a B a x = a B a x (2-4) After eliminating the anion, X, which is common to both cations, A and B, the relationship of the cation A to cation B is, V = *A *B S B For a pair of ions of unequal valence, such as Na and Ca , the relation- ship is (I Ca ) (a X )2 = (a Ca ) (a X )2 and (a Na> ( V (2 " 5) After eliminating the anion, X, the relationship becomes, (a Ca> < a Ca> These relationships simply state that the exchange of ions must take place until the activity ratios are equal in both phases. The accuracy of the Donnon membrane theory for the description of an ion-exchange equilibrium is questionable because it does not consider any of the physical forces involved in the ion-exchange process; however, the Donnon concept clearly explains the inability of free electrolyte to enter the exchanger phase, the effect of valence, and the effects of concentrations. 2.1. 3o The Crystal Lattice Theory The concept of the nature of ionic solids has been applied to silicate minerals exhibiting the ion-exchange phenomena. An ion at the surface of a crystal is subject to less attractive forces than a similar ion beneath the crystal surface. If placed in a highly polar medium such as water, the net attractive forces binding the surface ion to the crystal are diminished to such a degree that the exchange of this ion is possible. The exchangeability of the surface ions depends on the nature of the binding force, the ion's charge, concentration, size, solubility, as well as its accessibility to the surface. The exchange of ions in silicate minerals ' such as zeolite and clay minerals is quite similar to that of the crystal lattice ions. The exchangeable cations on silicate minerals are there to balance the positive charge deficiency created by the imperfect crystalinity of these silicate minerals. Nonetheless these exchangeable cations on sili- cate minerals occupy essential lattice sites. 10 All the ion-exchange theories are quite similar in that the exchange of ions must satisfy the law of electroneutrality,, The differ- ences are the position and the origin of the exchange sites „ The crystal lattice exchange theory assumes a fixed number of exchange sites that must be satisfied regardless of changes in the concentration or the pH of the external solution „ However, in the double-layer theory this is not true since the diffuse outer layer depends on both concentration and pH„ In a certain system both types of exchange may occur simultaneously, the quantity depending on the nature of the exchange medium,, The Donnon mem- brane theory does not conflict with either the crystal lattice theory or the double-layer theory, but merely offers a quantitative relationship for an exchange process „ 2 lo 1 +. The Ion-Exchange Theory of Soils Numerous experimental results indicate that the ion-exchange properties of soils depend on the activities of the clay fraction,, Both the crystaline structure and the micro-size of clay minerals contribute (13) to the magnitude of the ion-exchange properties «, Grim cites three causes of the cation exchange properties ; (1) broken bonds, (2) lattice substitution, and (3) replacement of hydrogen from exposed hydroxyl groups o Broken bonds around the edge of silicate alumina units give rise to unsatisfied charges, which are balanced by adsorbed cations „ The number of broken bonds is increased by breaking the particle into smaller pieces ; hence, the exchange capacity is increased as the particle size decreases o In illite, chlorite, kaolinite, and holloysite minerals, 11 broken bonds are the major contributor to the exchange capacity,, Substitution of aluminum for silicon in the tetrahedral sheet and substitution of lower valence cations, particularly magnesium, for trivalent aluminum in the octahedral sheet result in unbalanced positive charge deficiencies, which are balanced by adsorbed cations. In mont- morillonite and vermiculite, substitution within the lattice structure gives rise to the major portion of their exchange capacities. The hydrogen of exposed hydroxyl groups in the basal cleavage or around the broken edge of clay minerals may be exchangeable by other cations. This type of exchange site may be sensitive to environmental conditions, particularly the pH of the solution, 2.2, Ion-Exchange Equilibrium and Terminology Ion-exchange equilibrium is attained when an ion exchanger is a+ placed in an electrolyte solution containing a counter ion (A ) which is different from that (B ) in the exchanger. At equilibrium, both the a+ exchanger and the solution contain both competing counter ions, A and B , The ion exchange reaction is, as a rule, reversible. Thus it makes no difference from which side equilibrium is approached; that is whether A is exchanged for B or B for A For the description of an ion-exchange equilibrium in which a moles of counter ion B are being exchanged by b moles of counter ion A a+ , b A a+ + a B-clay t a B b+ + b A-clay, (2-7) 12 the so-called selectivity coefficients, the mass-action equilibrium con- stants, and the thermodynamic equilibrium constants are often used The selectivity coefficient, Ko AB The concentration ratio of two competing counter ions in the exchanger is usually different from that in the solution; as a rule, the exchanger selects one specie in preference to the other. This selectivity of the exchanger is often described by the selectivity coefficient „ The selectivity coefficient is defined by m. , m AB m. — A m„ where m and m are the normal concentrations of counter ion A in the A A exchanger and the solution phases, respectively „ Molar concentrations of the counter ions are often used in the place of normal concentration,, The use of molar concentration does not change the value of Ko. n0 AB Frequently the term "equilibrium constant" is used for the selectivity coefficient „ However s the selectivity coefficient is not constant but depends on the experimental conditions „ The degree of con- stancy of the selectivity coefficient depends on the nature of the ex- changer o For certain exchangers, such as montmorillonite and illite used in this investigations, it has been found that the selectivity coefficients are fairly constant over a wide range of counter ion concentrations In certain practical applications the ion-exchange equilibrium is conven- iently expressed in terms of the distribution coefficients of the counter ionso The distribution coefficient is defined by 13 Kd„ = -A. A m A In terms of the distribution coefficients, the selectivity coefficients can be expressed as Kd A K °AB = Kd~' B t The mass-action equilibrium constant, Ko AB For the ion-exchange reaction, which is governed by the law of mass-action, the equilibrium condition is often described in terms of the mass-action equilibrium constant, K° AB = <£)" <^V (2-9) where a , a and a , a are the activities of the counter ions, A and A B A B B , in the exchanger and solution phases, respectively „ The mass-action equilibrium constant and the selectivity coefficient are interrelated by •Sb = Ko ab ( 77 )b ( ^> a < 2 - 10) A ^B — a+ where y a and y a represent activity coefficients of the ion A in the exchanger and solution phases , respectively „ It is important to note that the mass-action equilibrium con- j stant, Ko, applies to the system only if the ion-exchange reaction is AB governed by the law of mass-action „ As will be discussed in a later section, the exchange reactions of montmorillonite and illite used in 14 this investigation do indeed follow the law of mass-action„ The thermodynamic equilibrium constant, Kth In theoretical studies thermodynamic equilibrium constants are often used, which represent true thermodynamic characteristics of the ion- exchange reaction and have truly constant values depending only on temperature o This quantity is defined by the thermodynamic relation, AG° = - R T In Kth where AG is the standard free energy change of the ion-exchange reaction which includes the exchange of counter ion B by A , and the sorption and desorption of solvents and electrolytes „ 2„3o Evaluation of Ion-Exchange Equilibrium For the ion-exchange reaction in which the exchange of a moles of counter ion B by b moles of counter ion A is accompanied by desorp= tion of :f moles of electrolyte BX and sorption of g moles of electrolyte AX and h moles of the solvent, the free-energy change of the total + (14) . system is. AG = AG° + R T In (— ) b (— ) a - R T (^) f S A a D a BX JO 3 a + R T In (— ) g + R T In (—) h (2-11) a AX 3 w 15 At equilibrium the total free energy change becomes zero. Thus Equation (2-11) becomes, AG° = - R T In Kth AR r T in » (2.U, no a. "»* ~ ™ ^z,,. a A a B a BX AX Equation (2-11) contains only thermodynamically defined quantities and represents the true equilibrium reaction. It reflects all the possible effects of the various factors which may be accompanying the exchange of the counter ion B by A , If the sorption of electrolyte and changes in swelling resulting from the adsorption of the solvent can be neglected, the thermodynamic equilibrium constant is reduced to the mass-action equilibrium expression, A a B For many years, ion-exchange equilibria have been the subject of numerous experimental and theoretical investigations. The most 16 appropriate means of describing an ion-exchange equilibrium is by thermo- dynamics o Many investigators have attempted to describe an ion-exchange equilibrium by thermodynamic treatment ' ; however, the practical application of such a treatment is restricted because the quantities involved can not be determined by independent measurement nor can they be predicted without using non-thermodynamic assumptions „ Though the rig- orous thermodynamic treatment is correct and universal, it yields little information about the actual physical causes of the ion-exchange phenomena to which the treatment is applied. Therefore, models with particular properties resembling those of the exchanger have been introduced for deriving equations that reflect the action of the various physical forces. With such models the effects of particular properties of an exchanger can be analyzed. However, every committment of a model with particular properties means a deviation from rigorous thermodynamics, and equations developed from the model can only be applied to a system with identical properties. Furthermore, ion-exchange reactions of an exchanger depend on a variety of forces, which makes any theoretical treatment using a model with all the physical forces unmanageably complex. Even though none of the theoretical treatments of an ion- exchange process derived from a model have been satisfactory for practical application, it is of interest to examine the effects of particular properties of an ion-exchanger on the behavior of the system. The first model that reflects any of the particular properties of an ion-exchanger (17) was introduced by Gregor According to his model, an ion exchanger is a network of elastic springs. When the exchanger swells, the network is stretched and exerts a pressure on the internal pore, and the swelling 17 pressure in the exchanger affects the ion-exchange equilibrium Gregor, from his elastic spring model of an ion exchanger, derived the relation, Kth AB = R T l„ (!V (!*)* A a B = tt (a v B - b v A ) (2-14) where it is swelling pressure and v , v are partial molar volumes of the A a+ , _b+ counter ion A and B „ The practical application of Equation (2-14) is restricted by- difficulties of evaluating the activity coefficients, tt, v , and v . Qualitatively Gregor 's model and his equation explain the selectivity sequence of the alkali ions (Li < Na < K < Rb < Cs ) , which is in the same sequence as that of decreasing hydrated volume „ (18) Pauley has interpreted the selectivity of an ion exchanger in terms of a simple model, whose essential feature is the electrostatic attraction between the counter ions and the fixed ionic sites of the exchanger,, Assuming that all the counter ions in the exchanger are found at their distance of closest approach to the fixed ionic sites of the exchanger 9 from Coulomb's law the ion-exchange equilibrium constant for univalent counter ions is expressed as, l„ K th . ccJL-JU, (2-15) d B d A where d and d are the distance of closest approach between the counter ions and the fixed ionic sites of the exchanger 18 According to Equation (2-15), the counter ion with the smaller d value is preferred, Pauley's equation explains the selectivity series of alkali ions (Li < Na < K < Rb < Cs) , which is the same as the series of the Debye-Huckel parameter, d , for the alkali ions There is no doubt but that the situations in actual systems are much more complicated by interactions other than simple electrostatic reactions „ 2o3 l„ The Mass-Action Expression of Ion-Exchange Reactions Many theoretical approaches and models have been developed and used for the description of the equilibria existing between ion- exchangers and electrolyte solutions; however, a universally applicable solution does not exist „ In all cases, one uses either a selectivity coefficient or a mass-action equilibrium constant, both of which may be corrected somewhat to give an acceptable equilibrium constant „ The reversibility of the ion-exchange process, coupled with the equivalence of the exchange, has indicated the possibility of applying the law of mass-action, particularly for the exchangers with rigid structures 9 such as zeolites and clay minerals, both of which display negligible changes in adsorption of solvents and electrolytes „ The mass- action equilibrium constant for the reaction where b moles of the counter ion A is replacing a moles of the counter ion B may be written in the form of, 19 a A,b a B,a A a B . ( _A,b { _B,« ( Jk,,b ( _B } a A tn B A Y B I A) ( Y B) a Investigators generally agree that the solution phase activity correction factor may be approximated by, (?B) a (T« BX) Ubtl) a ( y A) b (Tl AX) (aa+D b where y ± Ay and y ± „ y are the mean activity coefficients of electrolytes AX and BX, and za and zb are the valences of the counter ions, A and B . The mean activity coefficient of a pure electrolyte can be calculated from the Debye-Huckel expression, - A (Z Z ) /F In y ± = (2-18a) 1 + BXd /l with the ionic strength, I = 1/2 Z m. Z. (2~18b) . 1.8246 x 10 6 _ 50.29 x 1Q 8 A = 3 /2 — -t B = I/O where D is the dielectric constant and T the absolute temperature. For most practical purposes Equation (2-18a) can be approxi- mated by, 20 0.511 (Z Z ) /T In y ± = - — - (2-19) 1 + 0„329 x 4.0 /T where the average effective diameters of counter ions are taken to be o ° 4.0 A , and constants are evaluated at the temperature of 25 C. Since an ion-exchange reaction always involves more than one electrolyte, the mean activity coefficients must be for a mixed electro- lyte; however, there being a lack of means for determining the activity coefficients of mixed electrolytes, certain approximations are necessary. In this investigation, the mean activity coefficients of mixed electro- lytes, A X and B Y, , are computed under two assumed conditions; (a) the J * x a y b' r activity coefficients of the two cations do not show mutual interference and the values of the coefficient are the same as those for either of the pure, individual electrolytes; (b) the activity coefficients do not show mutual interference, but the values are the same as those of the pure electrolytes having the total electrolyte concentrations. The difference in the two assumptions is in the value of the ionic strength, and the actual values of the activity coefficients will lie between these two values. Under the second assumption, the activity coefficients of the counter ions of the same valence in the same solution are identical, and the ratio of the activity coefficients becomes unit\r„ There have been many attempts to evaluate the activities of the exchanger phase, correlating the activities with the quantities that are accessible by independent measurement. However, there is no general agreement concerning the activities of the exchanger phase. The first approach to evaluating these activities was given by Vansellow , who considered the exchanger phase as a completely miscible, ideal mixture, 21 and the activity. of each component as being equal to its mole fraction in the exchanger With this assumption employed, the activity ratio of counter ions in the exchanger phase is, _ (-Ji_) b (a A> ^ + C B <2-20a) and the ratio of the activity coefficients becomes. — . A (m c ) m A + m + m = C„EoC , (2=24c) where all the cations are assumed to be the same valences „ 25 ( 26 ) Rearranging these equations , one can obtain the following expressions ' , which permit computation of the distribution coefficients, Kd, of each cat ion . „. (C.E.C.) Ko flB Ko AC Kd A = - — - , (2-25a) A m B K °AC + m C K °AB + m A K °AB K °AC (C.E.C.) Ko Kd n = — v - — ~ r - — , (2-2 5b) B m„ Ko Art + m^ Ko AT , + m A Ko AT , Ko ' B AC C AB A AB AC (C.E.C.) Ko Kd. = — ^ v T5 '• (2-2 5c) C m B K °AC + m C K °AB + m A K °AB K °AC If cation A is in trace concentration, Equation (2-25a) reduces to « (C - E - C - )K °AB KO AC Kd A = — ■ — - — . (2-25d) A m B K °AC + m C K °AB In the case of unsymmetrical exchange s in which the valences of the cations involved are not the same, the mathematical expressions for the system become more complicated. However, the manner of analyzing the system is similar. 2.6. Effects of Organic Compounds on Ion-Exchange Reactions of Clay Minerals In general, deviation from an ideal ion-exchange equilibrium may be due to the interactions among the various components present in the system. These interactions can be either between one component and 26 others in the external solution phase , such as the formation of organic complexes of metal ions, or it can be the interaction between one compo- nent and the solid exchanger , Effects of organic compounds on the ion-exchange reaction of soil minerals may be divided into two groups, one in which organic com- pounds interact with inorganic counter ions, especially metal ions, and the other in which the organic components may interact with soil mineral surfaces and thereby affect the ion-exchange properties of the soil minerals o The interaction of a certain organic cation with soil surfaces may be a simple ion-exchange reaction without affecting the soil exchange properties, or it may be that in the process of the exchange adsorption the soil's ion-exchange properties change 2 6olo Ion-Exchange Equilibria of Clay Minerals in the Presence of Sequestering Agents In general 9 cation-exchange equilibria are strongly affected (14) by the interaction " of counter ions with other components in the solu- tion phase o The interactions of cations with anions in the solution phase are particularly important, because anions are rather efficiently excluded from the solid exchanger phase, and thus the effects of these interactions in the solution phase are not compensated by that of similar interaction in the solid exchanger phase „ The exchanger, in general, prefers those cations that associate less strongly with anions „ This rule is illus- trated by a typical example „ Cation exchangers prefer other cations to ++ Hg if the solution contains CI , which form insoluble HgCl^o Among other possible interactions of cationic radionuclides in 27 a soil environment s the formation of water soluble chelated compounds (sequestered compounds) is one of the most important reactions in regard to their transport through the soil medium, because the formation of water soluble chelated compounds of these radionuclides inhibits their adsorp- tion on soil minerals o The formation of chelated compounds results in the inactivation of the counter ions by forming either neutral or even negatively charged metal chelates „ The degree of the inactivation of a counter ion by a sequestering agent depends on the nature of the agent and the counter ion The general theoretical treatment of an ion-exchange equilibrium is valid whether or not chelated products are formedo The formation of chelated compounds can be treated as an additional s distinct reaction „ The quantitative treatment of the ion-exchange equilibrium in the presence of sequestering agents is based on the known relations for the equilibria of the various chelated compounds , For a simple system in which the counter ions s A and B , are in equilibrium with an ion exchanger in The presence of sequestering agent 9 Y y , which forms chelated compound AY a j with only cation A and does not interact with the exchanger g the distribution of the counter ion A has to satisfy the following simul= taneous equations 9 .— .b , .a (m ) (m ) Ko ab - — b 7r-r> (2 = 26a) (m A ) (m B ) and (m AY ) K - 7 ■ ■ ■ . ■ ■ ■ - i . 9 (2=26b) AY (m ) (m v ) 9 28 where K is the stability constant of the chelate compounds, AY, and m is the ionic concentration of organic ligand, Y y , in the solution,, Rearranging these equations in terms of the effective distribution coef- ficient s Kd, that is s the ratio of the cation A in the exchanger phase to its total concentration in the solution phase, the following expression is obtained^ m B al I — m A L. Kd. = A = ■ ; , „ g (2-27) AB m B j A m A + m AY X + m Y K AY which shows the effect of the sequestering agent 9 Cm v ) 9 on the effective distribution coefficient s Kd. The case in which both cat ions 9 A and B , form chelated com- o v~ pounds with Y J is more complicated This situation occurs 8 for example, o ++ + + m the ion=exchange reaction of the counter ion pair Sr =Ca in the presence of a sequestering agent „ Equation (2-26) remains unchanged even if the competing counter ion B forms a chelated compound „ An exactly analogous relation holds for the effective distribution coefficient of _ L KO BA ( ^i ' The ratio of two effective distribution coefficients gives the ++ ++ effective selectivity coefficient for the counter ion pair Sr =Ca in the presence of sequestering agents „ 29 - (Kd A )b AB (Kd B ) a (1 + m K ) a - K °AB * L - £ V' <2 " 29) (1 + m y K AY ) where Ko refers to the effective selectivity coefficient, and K and Ad BY K Y are the stability constants of the chelate BY and AY„ It should be noted that in the derivation of these euqations several assumptions are made; (1) sequestering agents do not interact with the solid exchanger , (2) sequestering agents form only one type of sequestered compound with each cation, and (3) the sequestered cations do not compete for the ion-exchange sites „ In actual practice, the situa- tion becomes much more complicated by the fact that certain agents do indeed interact with the solid exchanger, as will be shown in a later section, and in general sequestering agents form more than one type of sequestered compound with each cat ion „ In addition , the stability of the sequestered compounds depends on the conditions of the system, such as its pH, which further complicates the theoretical analysis of the system 2 6o2o Adsorption of Organic Compounds on Clay Minerals and Its Effects on Ion-Exchange Properties of These Clay Minerals 2 6 2olo Organic Adsorption on Clay Surfaces Interactions of organic compounds with clay minerals are surface reactions and are generally regarded as adsorption reactions o Interactions between clay surfaces and organic compounds may 30 be divided into two general types of adsorption , physical and chemical adsorption,, Physical adsorption, or Van der Waals adsorption as it is often called, is due to dipole-dipole or ion-dipole interactions „ Chem- ical adsorption is due to coulombic forces and results from bond formation between the adsorbent and adsorbate A hydrogen bond (-C-H O0 clay surface) may be classified under either physical or chemical adsorption Organic molecules having a positive charge can be readily (27) adsorbed on clay surfaces through an ion-exchange reaction „ Hendricks has indicated that when organic cations are adsorbed on clay surfaces 9 they are held on the surface by coulombic force, in addition to a Van der Waals force associated with the organic chain and the clay surface „ Since the clay-mineral surfaces are polar, when they are in contact with a solution containing polar organic compounds, the negative centers on the clay minerals attract the positive centers of the polar ( 28 ) ( 29 ) organic compounds „ MacEwan and Bradley both reported that a large number of polar organic compounds can be adsorbed on the clay- mineral surfaces „ From their X=ray diffraction data, it was concluded that these polar organic molecules lie flat between the sheets of ex- panding clay minerals (montmorillonite) , and that there may be hydrogen bonding 9 =C~H oo 0, between the chains of organic molecules and the oxygen atoms at the surface of the clay minerals „ 2„6o2o2„ Effects of Adsorbed Organic Compounds on Properties of Clay Minerals When an organic molecule is adsorbed on a clay surface, it is expected that the surface properties of the clay mineral will be 31 changed. Such change in the surface characteristics may affect the ion- exchange properties of these clay minerals. The clay mineral properties that may be altered by organic adsorption are (a) the negative charge of the clay surface, (b) the active surface area of the clay mineral, (c) the blinding at the edge of the basal plane surface, (d) the bridging of the basal planes of the expanding clay minerals, and (e) the water sorp- tion properties of the clay mineral surface. In terms of ion-exchange parameters, these effects may be (a) the reduction of the exchange capacity due to the permanent occupation of the exchange sites by strongly adsorbed organic cations or due to covering up of available exchange sites by a large, adsorbed organic molecule, and (b) the change in the selective properties of the clay mineral for hydrated metal ions resulting from the hydrophobic nature of the organic-adsorbed surfaces or the cross-linkage of the facing surfaces of the expanding clay min- eral. In addition, a large organic molecule adsorbed at the edge of the basal plane surface of a clay mineral may form some type of physical barrier, which may interfere with inorganic ions entering the basal plane of the clay mineral. (a) Effects of adsorbed organic molecules on the negative charge of clay surfaces Certain organic cations are so strongly held on the clay surfaces that once adsorbed, inorganic cations of the same molar concen- tration may not replace these adsorbed organic cations. This results in the net reduction of total negative charge on the clay surface, and hence may result in the reduction of exchangeable sites. In general 8 the larger organic cations are more strongly adsorbed because in addition to 32 the coulombic forces, the Van der Waals forces are greater, (b) Effects of adsorbed organic compounds on active surface area of clay minerals (27) Hendricks has shown when large organic cations are adsorbed on a clay surface s even though they are more strongly adsorbed than smaller ones, they occupy fewer exchange sites, indicating cover-up effects o A large organic cation, when it is adsorbed on a clay surface, may physically cover up more than one exchange site. On the average, the effective area of each exchange site on montmorillonite is about 80 to 100 A o If an organic cation which has an effective area larger than 100 A is adsorbed on a montmorillonite surface, this organic cation may cover up more than one exchange site, thereby reducing the active surface area of the clay mineral,, (c) Effects of adsorbed organic compounds on expanding character- istics of clay minerals (27) (30) (31) Hendricks , Bradley and Grim , Jordan , and many other investigators have found that when organic compounds are adsorbed on the interlayer surfaces of expanding clay minerals, a definite pattern of interlayer spacing exists, which depends on the size and concentration of the organic compound , When an organic molecule with more than one cat- ionic group is adsorbed on the interlayer surface of the expanding clay minerals such as montmorillonite, this organic molecule may act to tie two facing surfaces together by adsorbing on both surfaces. In montmorillonite, in the early stages of swelling 9 the inter- layer spacing increases stepwise (Crystalline swelling). Stable interlayer 33 distances of about 9„5, 12 „ 4, 15 „4„ 19„0 9 and 22.5 A have been found by ( 32 ) X-ray diffraction analysis „ These spacings are common to almost all ionic forms „ However , with strongly hydrated counter ions such as Li 9 the stages of crystalline swelling are finally overcome as more solvent (water) molecules are adsorbed,, Beyond 40 A s the interlayer spacing increases continuously 4 and the material behaved like a gel Montmoril- (29) lonite whose interlayer surfaces were covered with methylamine and glycerol showed the interlayer spacing of 12 „ 7 and 17 „ 7 A , respectively „ This indicated that when an organic cation about 10 A in size having more than one cationic group is adsorbed on two facing surfaces of inter- layer , the adsorbed organic may possibly limit the expanding of the interlayer planes „ The change in the interlayer spacing of expanding clay minerals may affect the mobility of other cations on the interlayer surface, and thus affect the selectivity of this clay mineral for certain inorganic cations „ (d) Effects of adsorbed organic compounds on water- sorption proper- ties of clay minerals In general 9 when organic molecules are adsorbed on a clay mineral surface 9 adsorbed water on the surface will be displaced „ The displacement of water molecules from the surface and the covering up of the oxygen layer with the chain of the organic molecules will have tend- ency to alter the clay surface from its hydrophilic to hydrophobic character o The water-adsorbing properties of montmorillonite are grad- ually reduced as the basal surfaces of the mineral are coated with (33) organic molecules., Geiseking'' reported that when montmorillonite clay minerals were saturated with a variety of organic cations 9 they lost 34 their tendency to swell by water sorption,, The degree of alteration in water -sorption properties of clay minerals due to organic adsorption will depend on the degree of saturation and the nature of the organic mole- cules on the clay mineral surface „ The change of the clay surface from hydrophilic to hydrophobic may affect the selective properties of the clay exchange medium for hydrated inorganic cations „ 35 3 MATERIALS AND EXPERIMENTAL PROCEDURE 3olo Materials Used Since the purpose of this investigation was to study various interactions of natural and pure organic compounds with soil constituents and the effects of these interactions on ion-exchange reactions between cationic radionuclides and soil exchange media, chemicals and soil materials were so selected that they would be closely related to the actual soil environmental conditions and yet still be able to demonstrate various interactions involved in the system,, Due to difficulties of selecting uniform and homogeneous soil materials which would give reproducible experimental results, relatively pure clay minerals were selected instead of soil materials for this in- vestigation o Because the major fraction of the ion-exchange properties of natural soil materials is probably embodied in the clay fraction^ it is common practice to use clay minerals in the study of the ion-exchange properties of soils „ Because of the unknown complexity of naturally-occurring organic compounds 9 it is virtually impossible to study individual inter- actions of natural organic compounds „ The probable interactions were studied using several groups of carefully selected pure organic compounds which are known to be present or similar to that present in the natural environment 3„lol Properties of Clay Minerals For the materials representing soils, montmorillonite and 36 illite were chosen because they represent the large fraction of clay minerals in natural soil It was hoped that using two clay minerals with different mineralogical characteristics, the individual physical forces and parameters that govern the ion-exchange properties of soils would be investigated. Montmorillonite (Mississippi) and illite (Fithian, Illi- nois) used in this investigation were obtained from the Illinois State Geological Survey. The X-ray diffraction analysis of these clay minerals showed considerable amounts of impurity. The approximate estimate of the purity from the X-ray data are summarized on Table 1, TABLE 1 APPROXIMATE PURITY OF CLAY MINERALS USED Contents Mississippi Fithian Montmorillonite Illite Montmorillonite 80-90% 10% Illite 55% Chlorite 12% Kaolinite 5-10% 0% Quartz and other impurit y 5-10 % 23% 3.1.1.1. Montmorillonite Montmorillonite constitutes one of the most widely occurring clay minerals. The structure of the montmorillonite unit con- sists of two silica tetrahedral sheets and a central alumina octahedral (13) sheet. Montmorillonite "s theoretical formula is (OH).Si Al =nH„0j 4 o 4 20 2. 4+ however, some fraction of the Si ions in the lattice are replaced by 3+ 2+ Al and Mg . Furthermore, the lattice is always unbalanced as a result of these substitutions, and has a net positive charge deficiency, depending 37 on the ionic substitutions within the lattice, which results in a large capacity for the ion -exchange adsorption of cations between unit layers and around their edges One characteristic of the montmorillonite structure is the tendency of the lattice to expand in the c-axis direction when polar molecules (water or polar organic molecules) penetrate between the unit layers „ The major fraction of exchangeable cations in montmoril- lonite are found between the silicate layers of adjacent units 9 and the c-spacing depends on the size of the interlayer cations and the nature of their hydration „ In the case of organic adsorption between the silicate layers 9 the c=spacing dimension also varies with the size and geometry of the adsorbed organic molecules „ Figure 1 shows a diagramatic sketch of the montmorillonite structure O o -L o -L o ■<- o I. ill l6 The basic illite structural unit was described by (13) Grim as consisting of a layer composed of two silica tetrahedral sheets separated by a central octahedral sheet „ The structure of illite is similar to that of montmorillonite j however 9 it has a great difference 4+ in physical properties Some of the silicon atoms (Si ) are always 3+ replaced by aluminum atoms (Al ) and the charge deficiency is balanced + by potassium (K ) 9 which occurs between unit layers where they just fit into perforations in the surface of tetrahedral layers „ The character- istics of the illite structural unit layer that differ from that of the montmorillonite structure are that it does not allow polar molecules to enter between its sheets and cause expansion of the lattice 9 and also that the interlayer balancing cations are not exchangeable „ In the illite 38 Q Oxygens (Q) Hydroxyls ^ Aluminum, Iron, Magnesium h Silicon, occasionally Aluminum FIG. I DIAGRAMATIC SKETCH OF THE STRUCTURE OF MONTMORILLONITE. 39 minerals, most of the exchangeable sites are at the edges which are caused by broken bonds around the edges „ Figure 2 shows a diagramatic sketch of illite 3 „ 1.1. 3. Treatment of Clay Minerals Powdered clay minerals obtained from the Illinois Geological Survey contained exchangeable cations in many different forms, as they would be in natural conditions „ In order to make these clay minerals monoionic form (Ca , Mg , Na , and Sr ), the clay minerals (montmorillonite and illite) were first repeatedly saturated with 1„0 N solutions of CaCl~, MgCl_ 9 NaCl, and SrCl 9 in separate containers 9 fol- lowed by washing with demineralized water until the conductivity measure- ments of the centrifuged supernatants indicate no free electrolytes present in the clay suspensions. The particle sizes less than 2 u were fractionated from these (34) monoionic clay suspensions by a centrifuge separation method „ In order to make sure these clay mineral suspensions were in monoionic forms 9 these clay mineral suspensions were passed through ion-exchange columns packed with Amberlite-120 in the corresponding ionic forms. The aging effects on the stability of these monoionic clay mineral suspensions were determined by the periodic measurements of their pH and conductivity. Whenever the suspension showed high conductivity 9 indicating eluted free electrolytes in the suspension , the clay suspension was retreated to the monoionic form. 40 O Oxygens © Hydroxyls £ Aluminum (■) Potasium hSilicons (One fourth replaced by aluminum) FIG. 2 DIAGRAMATIC SKETCH OF THE STRUCTURE OF MUSCOVITE TYPE ILLITE. 41 3olo2 c Organic Compounds Used 3olo2 lo Pure Organic Compounds In the selection of pure organic compounds for this investigations, an effort was made to select those organic compounds which were known to be present in the natural environment and also to represent a variety of organic compounds with different chemical and physical properties 9 so that the various interactions with both clay minerals and metal ions would be adequately represented „ The groups of pure organic compounds used in this investigation are sequestering agents, organic cations , and polar organic compounds Sequestering agents such as citrate 9 tartrate, and EDTA were used to study the interaction of these organic compounds with metal ions and the effects of the interactions on the ion-exchange equilibrium be- tween the metal ions and clay minerals Cationic and polar compounds (methylaminej dodecylamine 9 methylene blue 9 arginine, and sucrose) were used to investigate the adsorption of these organic compounds on clay mineral surfaces and their effects on the ion-exchange properties of the clay minerals „ The chemical and physical properties of these pure organic compounds are summarized on Tables 2 and 3„ 3olo2 2 Mixture of Organic Compounds in Natural Environments The naturally occurring organic compounds used in this investigation include organics extracted from ground water and sur- face soil materials o The organic compounds extracted from ground water in ro to Z O H H < « o a. o CO W H & a. o H 00 0< CJ + +c N vw f (0 *H 4J CO C Id CO -P CD 0) -M C ft) + 4= S >iU ■p •H rH rH fTj H 4J X! CU + rd S +rd +j CO r J CO 4J - c i ■P W c o u rH I c c — ♦ o + •h a: ■p «— N -H C O H aj « fd rH 3 O C fd c O Q* e o u ^ «* rH CT> O O CN CT> 00 vO • CN o rH in vO rH o CO o o ^ 1 <3 ^^ s w >< *■-» fO f0 + u u + fd a V— « + + O O in 13 •H U fd u •H M fd U fd •p CM X X CM o o I O-o o-o X X I o CM o X CO o m CM O 00 o •H CN CN CO o rH J* ^ 33 *-s ^ I CN s # _ ( § i >* fd + "* fd u + o rd u w + 4- fd u CO o ro * v£) • I o rH I! CN 0> • in l o rH II rH CN CN en rH •H O fd a -H M ■P •H U fO X . X* CJ O a j -*■ o o-o-o CM X o I o i VO 1 rH o rH ro r> vO • • CN CO O o rH rH CO CM VO • • CN 00 O o ■H rH CT» rH in in • • o ro rH o o rH r-\ — ■ i *— "» | 1 <* a CN »-». >* ^-* fd -f fd + a 4 o + td •>-> rd u u CN I O rH II r> vo • CN I O rH II ro vO I O rH rH II II CN r- ^ in CN • CN CT» CN 63 X o _l_ o o o o o I 6- z— - o .N 1 CM X CM X o 1 tM X X CM o CM X 1 X O- -2- -o 1 o 1 o o o o o X X 42 c & VO CO CN "* • • O CN rH ■H 1 1 o c rH CN CD G •H C •H Cn fd 43 a* u M 2 O r? 10 4J C «J 4J m c o u rH r-l « I c c LT) c - *■"" ■H + 4J : CO | ret - 2 N O -H H 3 c frj < 1 M O O H 2 < o OS o fa o CO 1 w fl H E-. H PS »J W M CD fa fd < o rH +J ^ OS p x: & 0) H ^ rH CD < 2: u s. H CO + 33 C7> I cm i o i O rH rH !l II « (13 iH 3 £ o fa •d a f0 en c o a, s o « CM X o CO CO rH co in CO rH H r- rH © c H g rH >< ■p © 8 OJ X 'to X o c rH u CD O T3 OJ X -z. no AJ X OJ O 44 were a portion of those used in the experiments conducted by L Robin- ( ^fi ^ son at the University of Illinois in 1962 „ The water soluble organic compounds in surface soil materials were extracted from soil materials obtained from a woody area Approxi- mately 2 5,000 grams of soil material which contained 5% vegetable decaying matter were placed in a 4-liter bottle containing 3 liters of demineral- ized water o After being shaken in the bottle for two days s the samples were centrifuged 9 followed by filtration through a o 45 u membrane filter The dark brown filtered solution was evaporated at 50°C under vacuum until only 100 ml of the solution were left„ The soil organic extracts probably contained metal ions either as free electrolytes or as metal ions chemi- cally bound to the natural organic compounds „ To remove the free metal ions the organic extracts were dialized against running demineralized water o The metal ions of higher valence that might have been chemically o o + bound to the natural organic compounds were exchanged into Na form by passing the extracts through an ion-exchange column previously saturated with Na ionso Before the extracts were passed through the ion-exchange column j, NaOH was added to the extracts to raise the pH value to 8<,0 9 so that the organic cations would not be adsorbed on the column a The chemical properties of these two extracts may have been somewhat different 9 for the ground water had passed through soil media for some distance 9 which may have caused this extract to be high in those organic constituents that do not readily interact with soil minerals „ On the other hand s the organics extracted from the woody surface soils may have contained the organic compounds that do readily interact with soil minerals o 45 It should be noted , however, that as a result of the inefficient extraction method used in this investigation these organic extracts repre- sented only a fraction of the probable constituents of the natural organic compounds o 3„2o Experimental Procedure 3 2olo Analytical Methods and Equipment In all experiments reactions were carried out in 6-ounce (180 ml), Armstrong prescription bottles The bottles containing 50 ml of solution were agitated for 7 to 18 hours, which was found experimen- tally to be sufficient for equilibrium to be reached, by tumbling end- over-end on a mixing wheel at a speed of 5-10 rpm After equilibrium was reached, 30 ml of the solution were transferred into a plastic centrifuge tube for phase separation and chemical analysis „ The remaining volume was used for the measurement of the final pH of the solution,, Because the concentrations of samples involved in the experi- ments were too low for conventional chemical analyses, whenever possible radiotracer techniques were employed 9 in which one or more of constituents were labelled with radiotracers of the very same chemical compounds „ By the combination of the radioassay analysis of the solution phase and an overall material balance, the distributions of various constituents of the system were analyzed „ For all the experiments involving strontium ion, the solutions 85 were labelled with the gamma-emitting radioisotope, Sr „ The strontium ion concentrations in the solution phase were determined by counting 10 -ml 46 samples in plastic counting tubes with a gamma scintillation counter. Whenever possible pure organic chemicals used for reaction 14 studies were also labelled with C radiotracer of the very same compounds. The organic concentration in the solution phase was determined by counting 14 the C activity of the solution with a liquid scintillation counter. The samples to be counted by the liquid scintillation counter were prepared by dissolving 3 ml of aqueous samples into 15 ml of the scintillation liquid „ The scintillation liquid was prepared by dissolving 7 grams of PPO (2,5 s -Diphenyloxazole), 0,28 grams of P0P0P (p-bis(2-(5-phenylox- azolyl)) -benzene) , and 75 grams of napthalene in the mixture of 875 ml dioxane and 125 ml Cellosolve (ethylene glycol monoethyl ether )„ This composition of the scintillation liquid was experimentally determined to give the best efficiency (46%) for 3 ml of aqueous sample in 15 ml of the liquid o 3 2o2o Ion=Exchange Reactions 3 2o2olo Exchange Capacity Ion-exchange capacity is one of the most important parameters governing the ion-exchange equilibria of clay minerals „ The knowledge of the exchange capacity is indispensable for the evaluation of the ion=exchange equilibrium between clay minerals and various counter ionSo In general , reported ion-exchange capacities are known to vary according to the laboratory procedure employed to determine them 9 and therefore a method should be chosen duplicating as nearly as possible the actual conditions of the system to which the results are to have applica- tion,, 47 A method of actual exchange of counter ions with the radio- isotope of concern was employed in this investigation „ However, for comparative purposes, other methods such as the ammonium acetate (37 38) (39) method v and the methylene blue method were also used,, The method for the determination of ion-exchange capacity used in this inves- tigation is primarily based on the exchange of Sr ion on Sr-clay 85 minerals by the radioisotope, Sr „ When Sr-clay minerals are added to a solution containing Sr (m ) and Sr (cpm ), isotopic replacement will 85 ++ occur until the isotopic ratio (Sr /Sr ) is the same in both the ex- 85 o changer and the solution phases. Knowing the total Sr (cpm ) added into the system, the amounts of Sr in the exchanger phase are determined from the following relationship, (cpm s ) m Sr (cpm°) m Sr + m Sr Equation (3-1) may also be written in the form, (3-1) 1,0 'Sr " m. loO = m „ x iii, (3-2) Sr o 85 where (cpm ) and (cpm ) refer to the Sr activities of the total and s solution phase, respectively. If the ratio of the radioactivity in the exchange phase to that in the solution phase (cpm /cpm - 1,0) is to be plotted as a function of the value of 1,0/m 9 the form of Equation (3-2) is a straight line whose slope is m , From the known value of m and radioassay data, the U8 exchange capacities are determined,, In the determination of exchange capacities, 0„05 to 2 grams of monoionic Sr-clay minerals (montmorillonite and illite) were equili- 85 brated with 50 ml of Sr(N0 ) solution labelled with Sr . The exchange capacities were determined as a function of Sr concentration varying -4- -2 ++ from 1x10 to 1x10 N At the higher concentration, Sr in the ex- changer phase becomes insignificant compared to the solution concentration, and hence the accuracy of the determination is reduced , 3 2o2„2o Equilibrium Constants For the prediction of the distribution and trans- port of radionuclides disposed to an environment, knowledge of equilibrium reactions between these radionuclides and soil materials is essential,, In this investigation, an effort was made to apply the various ion-exchange theories for evaluating the most reliable equilibrium constants „ The ion-exchange reactions performed for the evaluation of the ++ equilibrium constants included the reaction in which (1) Sr ions are ++ ++ ++ ++ replacing Ca ions, (2) Sr ions are replacing Mg ions 9 and (3) Sr + . . . ions are replacing Na ions on both montmorillonite and illite minerals „ In order to examine the reversibility of the exchange reactions, all the equilibria were approached from both directions „ For the deter- ++ mmation of the equilibrium constant for the reaction where Sr ions ++ were competing with Ca ion for exchange sites on the clay mineral, both Ca-clays and Sr-clays were used Similarly, Mg-clays and Sr-clays, and Na-clays and Sr-clays were used for the determination of the equilibrium ++ ++ constants for the reactions where Sr ions were competing with Mg ions 49 and where Sr Ions were competing with Na ions for the exchange sites on clay minerals The equilibrium constants were determined as a function of the counter ion concentrations at room temperature „ For the determination of ++ . the equilibrium constants for the reaction where Sr ions were replacing ++ Ca on Ca-clay minerals, the initial concentrations of strontium and calcium ions (m and m_ ) were varied from 10 to 10 N The maximum Sr Ca concentration was limited by the fact that at higher concentrations, the radioassay analysis became difficult „ The concentration distribution of the counter ions In the liquid phase was determined by counting 10 ml of the centrifuged aqueous sample with a gamma-scintillation counter,, When a Ca-clay was used for the determination of the equilibrium ++ ++ constant for the reaction m which the counter ions Ca and Sr were in equilibrium with the clay minerals 9 the concentration distributions of the counter ions were determined from the following relationships 9 m Sr = m Sr + m Sr (3 ~ 3a) m° + C„E„Co = m_ + m„ (3-3b) Ca Ca Ca CoEoCo = m + m (3=3c) cpm m —|=-§£ (3~3d) cpm m gr> where m q 9 m 9 and C„E C are the concentrations of strontium , calcium 8 and Ca-clay initially added to the system 9 and m , m 9 m 9 and m are 50 85 the final concentration distributions „ cpm refers to the Sr ' activity of the final solution phase, while cpm is the total Sr ' activity of the system. By rewriting Equation (3-3) in terms of the radioassay data 9 the following relationships were obtained, cpm OS y ^ m = m c — (3-4a) Sr Sr o cpm com ™Sr = • (3 " 4d) cpm which give the complete concentration distribution of the counter ions,, ++ ++ Sr and Ca , in both the exchanger and solution phases. The equilibrium constant for the system containing other pairs of counter ions were determined in a similar manner,, 3„2„2o3o Equilibrium Reactions of Heterogeneous Clay Mixtures As mentioned in Section 2„4 09 when the soil ex- change medium is a mixture of clay minerals or a mixture of different types of exchange sites 9 the equilibrium constants depend on the experi- mental conditions o Experiments were performed with a mixture of montmorillonite 51 and illite to examine the effects of nonhomogeneity of the exchange media,, For the ion-exchange reaction in which Sr ions were replacing Mg ions on the mixture of Mg-montmorillonite and Mg-illite, the equilibrium con- stants were determined as a function of the counter ion concentration „ The effective equilibrium constants, K , were experimentally determined using Equation (2-22) „ These values were compared with the effective equilibrium constant computed from Equation (2-23) The equilibrium con- ++ + . stants for the exchange between Sr and Na were also investigated with various compositions of the mixture. The experimental procedure was similar to that described in Section 3,2o2„2„ 3„2o2 4o Ion-Exchange Equilibrium in a Multicomponent System When a trace quantity of radioactive strontium ion comes in contact with soil materials, strontium ions will compete for the exchange sites on the soils with a number of other gross cations present in the system Various ion-exchange theories have been found satisfactory for describing ion-exchange reactions involving a pair of counter ions However 9 a theory will have little practical value if its application is limited to a system having only one pair of cations „ Use of the mass- action expression (without activity corrections) for describing the equi- librium conditions of a multicomponent system was previously discussed in Section 2 5„ The application of the mass-action expressions for a multi- component system was next subjected to experimental testo Experiments were performed to examine the ion-exchange reactions . . ++ ++ + ++ m a multicomponent system containing Ca , Mg , Na 9 and Sr „ Applying the simultaneous equations (2-=24) described in Section 2„5 9 the strontium 52 concentration in the solution phase can be shown to be, o o o o o Na m„ = nu + m.. + m„ + m Sr Ca Mg Na Sr o ._ 1 m Sr~ m Sr 1/2 1 + (~^ ~~ )) K °SrNa m Sr (3-5) m.. + CEoCo m,. Ca Mg 1 m Sr™ m Sr 1 m Sr~ m Sr K °SrCa m Sr K °SrMg m S r where m 9 m,. . m. T , and m n are the total concentrations of these cations Ca' Mg 9 Na' Sr added to the system, and C„E C o is the amount of Ca-clay added to the system, ++ The experimental data for Sr distribution m the system were compared with the value computed from Equation (3-5)„ 3o2,,2o5o pH Effects on Ion-Exchange Equilibria In general, the expressions for the mass-action law have been found satisfactory for the exchange between a large number of ion pairs over wide variation in ion concentration and in various amounts of exchange media; however, a notable exception was encountered + (24) in ion pairs involving hydrogen, H , Krishnamoorthy and Overstreet found that the equilibrium conditions involving hydrogen ions can not be predicted by any theory proposed thus far A possible reason for the behavior of hydrogen may be found in the fundamental assumptions necessary for formulation of any ion-exchange equation „ Most important of these is 53 the assumption that either the specific interaction energies of the ion in question with the charged surface (clay surface) are constant over a wide variety of conditions, or their differences for a chosen pair of ions is constant o Unless this condition is fulfilled no ion-exchange formulation based on concentration terms is possible. For pairs of ions which interact with the surface by purely electrostatic forces, this assumption appears reasonable (as will be discussed in a later section). On the other hand s for ions that may be held to the surface by other chemical bonds as well as by electrostatic forces, it seems that the interaction will depend on their amounts in the solid exchanger phase , For the purpose of examining the effects of hydrogen ion on the ion-exchange parameters of clay minerals used in this investigation, the ++ ++ ++ ++ ion-exchange reactions of the counter ion pairs Sr -Ca and Sr -Mg in the presence of hydrogen ions were investigated. Possible interactions of hydrogen ion other than an ion exchange reaction were examined by testing the equivalence of adsorbed hydrogen and eluted strontium ion in ++ + the reaction where the pair of ions, Sr and H , were m equilibrium with Sr-clay minerals. The strontium ions removed from the Sr-clay minerals by hydrogen ions were computed from the following relationships , -4.4. Q Eluted Sr = m_ - m n (3=6a) Sr Sr cpm s m Sr cpm m + C,E,C, (3-6b) Disappeared H ions, AH = m - m (3-6c) 54 pH = - log m H (3-6d) - io" 14 Disappeared OH ions. AOH = ■■ « - (3-6e) m H Here m and m represent the final concentrations of strontium and hydrogen ions in the solution phase, and m , m„, and m represent the br H On initial amounts of strontium, hydrogen, and hydroxyl ions added to the system. 3o2o2 6„ Effects of Sequestering Agents on Ion-Exchange Reactions of Clay Minerals Many organic anions which commonly occur in natural water , as well as in soils, form stable chelates with metal ionso Among these reagents may be listed citrate, tartrate, malate, high-molecular-weight organic anions with polycarboxyl groups, and various amino acid anions „ The exact nature of these natural sequestering agents is not always known „ These organic ligands (sequestering agents) are believed to be either the synthesis products of microorganisms or bac- terial decay products of vegetable matter in soils „ As a result of the unknown complexity of their composition, it is impossible to examine individual interactions involved with sequester- ing agents in organic mixture obtained from natural environment „ The specific interactions of the various sequestering agents with metal ions and their effects on the ion-exchange reactions between metal ions and soil materials were studied using chemically pure sequestering agents. These sequestering agents include citrate, tartrate and EDTA 55 (ethylenediaminetetraacetic acid)„ The effects of these sequestering agents on the equilibrium distribution of the various counter ion pairs (Sr -Ca , Sr -Mg , Sr -Zn 9 and Sr -Na ) in equilibrium with clay minerals were investi- gated at concentrations of these reagents varying from a trace quantity to that approximately equivalent to twice the total metal ions in the system, 14 The sequestering agents were labelled with carbon tracers to determine their concentration distribution by a radioassay analysis „ The adsorption of the ligands on clay surface was computed from the radioassay data 3o2o2 7o Effects of Adsorbed Organic Compounds on Ion- Exchange Reactions of Clay Minerals The probable effects of adsorbed organic compounds on the ion-exchange properties of clay minerals were discussed in Section 2o6 2o A variety of organic compounds with different physical and chemi- cal properties were used for the investigation of their effects on the ion-exchange properties of clay minerals „ These organic compounds may be further divided into four groups, each having its typical properties? (a) monocationic amine compounds (methylamine and dodecylamine) , (b) a strong cat ionic compound (methylene blue), (c) a polycat ionic compound (arginine) s and (d) a polar organic compound (sucrose),, The probable effects of these organic compounds on the ion- exchange properties of clay minerals were studied by the comparison of ++ ++ ++ ++ the equilibrium distribution of counter ion pairs (Sr -Ca , Sr -Mg , 56 ++ + . ... and Sr -Na in two systems, one in which the counter ions were in equi- librium with clay minerals only and the other in which the counter ions were in equilibrium with clay minerals in the presence of these organic compounds „ (a) Methylamine and Dodecylamine Monocationic amine compounds, methylamine and dodecylamine, were used to study the effects of these organic compounds as a function of the organic chain sizes and concentrations „ From the reactions in which Sr ions on Sr=-clay minerals were being replaced by these organic cations, the relative selectivities of the clay minerals for these organic cations with respect to Sr ions were investigated „ The effects of these organic compounds on the ion-exchange reactions of various counter ion pairs were examined as a function of the organic concentration =5 -3 varying from 10 to 10 N, which in terms of milligrams per liter is 0o31 to 31 mg/1 for methylamine „ The concentration distribution of Sr ions and organic compounds were determined by the tracer technique using Sr and C labelled compounds. (b) Methylene Blue Because of their strong cationic characteristics, methylene blue ions are irreversibly adsorbed on clay minerals and cannot be eluted from the clay surface by any inorganic cation in reasonable concentration,, Methylene blue ions were used to blanket various portions of the exchange sites on clay minerals and to study the effects of this covering up on the ion-exchange reactions of these clay minerals with various cation pairs „ The monoionic clay minerals whose surfaces were covered with 57 methylene blue Ions (20% s 40% 9 60%, and up to 80%) were subjected to reactions with various counter ion pairs, and the equilibrium constants were calculated based on the uncovered exchange sites , The effects of the presence of the large organic molecules, that is, methylene blue ions adsorbed on the basal plane surfaces of the clay minerals, on the ion- exchange properties of these clay minerals were investigated „ The change in the selectivity of the clay minerals for various counter ions due to the adsorption of methylene blue ions was investigated as a function of the portion of the covered up surfaces, (c) Arginine The arginine molecule has two cationic groups which may be adsorbed on the two facing surfaces of the basal planes, and thereby, limit the c-spacing of expanding clay minerals (montmorillonite) by a bridging effect „ The fixation of the c-spacing of expanding clay minerals may affect the mobility of the inorganic counter ions between the facing layer surfaces „ The Ion-exchange reactions of clay minerals with various counter ions in the presence of arginine molecules were studied to inves- tigate the effects of c-spacing fixation of expanding clay minerals,, The equilibrium distribution of the counter ion pairs, Sr -Mg and Sr -Na , in equilibrium with clay minerals whose surfaces were partially covered with arginine molecules were examined as a function of the arginine con- centration „ (d) Polar compound, Sucrose The adsorption of polar organic compounds on clay surface may 58 not affect the charge distribution of the surface; however, it may affect other properties governing the ion exchange reaction of these clay minerals „ The effects of polar compounds on the ion-exchange equilibrium between clay minerals and the counter ion pairs, Sr -Mg and Sr -Ca 9 were investigated with sucrose as the polar compound „ The adsorption of sucrose molecules on clay surfaces was determined by radioassay analysis 14 of the C activity of the solution phase „ The amounts of adsorbed 14 sucrose molecules were calculated from the difference of C activities in the total system and the solution phase The experiments were per- formed to examine the effects of sucrose on changes in inorganic counter ion distribution in the presence of sucrose „ 3o2o2 8 Effects of Natural Organic Compounds on Ion- Exchange Reactions of Clay Minerals The natural organic compounds used in this investi- gation included water-soluble organic compounds extracted from both ground water and woody surface soils The experiments with these organic extracts were performed in a similar manner as those with pure organic compounds; however 9 due to the unknown compositions and difficulties with the chemical analyses of these extracts 9 the distribution of the extracts in the system was not analyzed „ The effects of the extracts on ion-exchange reactions of clay minerals were investigated on the basis of the total organic added into the system „ The ion-exchange reactions of the counter ion pairs , Sr -Ca , Sr -Mg , and ++ + . Sr -Na 9 in equilibrium with clay minerals were studied in the presence of these extracts „ The effects of the extracts were examined in terms of the change in the counter ion distributions „ 59 l+o ION- EXCHANGE EQUILIBRIUM IN ABSENCE OF ORGANICS', RESULTS AND DISCUSSION <4 lo Treatment of Clay Minerals Clay suspensions (Mississippi montmorillonite and Fithian Illite) converted into various monoionic forms were stored in polyethyl- ene bottles o To determine the aging effects on their stabilities, pH and conductivity of the supernatant of the centrifuged clay suspension were periodically measured „ The values of the measurements are summarized in Table 4„ The measurements of the conductivity indicated that after one month of aging, the illite suspension contained considerable amounts of free electrolyte „ The instability of the illite suspension suggested that the impurity contained in Fithian illite might have been dissolved „ The measurements of pH indicated that hydrogen ions were not involved in the instability of the clay suspension „ Because of the unstable nature of the treated clay suspensions, all clay suspensions were periodically reprocessed to eliminate free electrolytes and to keep the clay suspensions in monoionic forms, 4 2o Determination of the Cation Exchange Capacities A method based on an actual exchange of the counter ion Sr and the radioisotope Sr was employed to determine the exchange capacities,, The exchange capacities were determined as a function of ++ -4 -2 Sr concentration varying from 1 x 10 to 1 x 10 N The experimental results are presented in Fig„ 3„ It is shown in Equation (3-2) that the slopes of the curves in Fig u 3 represent the exchange capacities „ 60 w pq < CO O l— I co CO CO < < o Q < >- O Q O O o £: w CO < CM CD rH CM CM 3C -1 tfl c, ID m to CD C"> _2^ p c E >, CM II p °rl > E •H ">s CD O IT) O bfl P CO e C O , H CD CO cn O ■H 3 r- H lO CM CO bO T) e <-\ o >H \ P W O £ CO CO LD to CD (O (O CO in o o CO o en o CO CO o o to o > -H •H •H N aj fn fc k °H H a> O a) O cu rH O B p e p e p ra u P •H p •rl p »H fc cu C H c rH c rH 0) ro o U CM CD 4J •H H » ^8 o h- Q O >;2 OJ i_ ** £ oS to C7 CD E Y OF CONC ► tz +- + ^ o ^1 4_ < — (/) E CAP NTER CO e> 3 o ^ ° < o X <3- o S£ o ro 6 paqjospv ( ++ J s) 62 It is apparent from the curves shown in Fig, 3 that the values of the exchange capacities do not change in the range of Sr concentra- tion used„ In the case of the illite minerals,, two batchs prepared separately showed different values for the capacities . This probably resulted from the fact that the illite minerals which had been subjected to more steps of the centrifuge -resuspens ion cycles during the treatment process might have been broken down to finer particles by the high speed rotary blade of the suspension equipment . The dependence of illite ex- (13) change capacity on its particle size was also reported by Grim For comparison s the exchange capacities were also determined by the ammonium acetate method and the methylene blue method discussed in Section 3.2.2.1. The results are summarized in Table 5. TABLE 5 EXCHANGE CAPACITIES OF CLAY MINERALS Method Montmoriflonite Illite v_- o l-> o ^ o ' o o *■— L Sample L o tj o ^ o SgUo Sample m o eq o /100 g number m.eq./lOO g number Sr exchange 69 o * 1.9 20 17.7 4 0.64 20 Ammonium acetate 71 o * 2 5 12 18.1 * 1.1 12 Methylene blue 75.2 ± 2„3 12 22.5 * 1.3 12 A fair agreement was observed between the ammonium acetate ++ method and the Sr exchange method. However, the exchange capacity determined by methylene blue adsorption was generally 10 to 20% greater than those of the other methods. This probably is due to the monoionic adsorption of methylene blue in addition to the ionic adsorption. There was also uncertainty in the ionic purity of methylene blue used (Fisher 63 Scientific Company ) u Higher results with the methylene blue method were (39) also reported by Ludwig and his co-workers U 3o Behavior of Hydrogen Ions in Clay Ion-Exchange Reactions The study of the behavior of hydrogen ions was conducted because of necessity for determining whether hydrogen ions can be treated as an independent competing counter ion or whether the hydrogen ion seriously influences the exchange parameters by some mechanism other than itself competing for the exchange site,, The effects of hydrogen ions on soil ion-exchange reactions were examined in terms of? (1) the equivalence of the exchange of strontium by hydrogen , (2) the soil selectivity of hydro- gen ions in reference to strontium ions, and (3) the effects of adsorbed hydrogen ions on the selectivities of soil exchangers for other counter ++ ++ ++ ++ ion pairs Sr -Mg and Sr -Ca The equivalence of the hydrogen exchange was investigated by + adding known amounts of H ions into the system m which Sr-clay minerals were in equilibrium with known amounts of Sr ions„ Increases in the ++ „ ++ + amounts of Sr ions in the solution phase (eluted Sr ) as H ions were added were computed from Equation (3-6)„ In order to investigate the behavior of hydrogen ions on the clay exchanger phase, in another batch ++ = containing the same amounts of Sr-clay and Sr s OH ions were added 9 and the change in Sr concentration in the solution phase was measured as a function of disappeared hydroxide (AOH ) in the solution phase „ The ++ experimental results are presented in Fig„ 4 S m which the eluted Sr from Sr-clay minerals were plotted as a function of disappeared hydrogen (AH + ) 64 ++ Sr added H + added OH"added Clay added PH a b -4 4x10 -4 2x10 * 0-4xl0"" 4 0-4xl0~ 4 0-1.6xl0~ 4 0-1.6xl0~" 4 Sr-Mont.=1.0xl0~ 3 Sr-Ill. ^4.4xl0~ 4 3.73-7.45 4.10-7.30 I o a O i CO E o L±J CO 4 j 1 1 1 1 3 2 ^ i y *jr o ^^ + -?*** i A OH", I0 _4 N 2 3 4 in-4 AH + , I0~ 4 N FIG. 4 EFFECTS OF H + AND OH* IONS ON EXCHANGE CAPACITY OF CLAY MINERALS. 65 A line with the slope of unity and passing through the origin in Figo 4 would represent the equivalence of the exchange of strontium by hydrogen o The curves in Fig 4 are further extended to represent the eluted Sr as a function of AOH (dotted lines) „ The negative quantities of the eluted Sr correspond to the increased amounts of Sr adsorbed on the clay minerals „ The origin in Fig 4 represents the system con- ++ + taming Sr-clay and Sr ions before either H or OH are added to the system o The pH values before either H or OH were added were 6.5 and 6 7 for the systems containing Sr-montmorillonite and Sr-illite, respec- tively o On the basis of the experimental data, it is apparent that the reaction of hydrogen ions does not always involve ion exchange,, That hydrogen ions may involve a reaction other than ion exchange is shown by the fact that the equivalence of the disappeared hydrogen ions and eluted Sr was not observed at the pH higher than 6„5 for montmorillonite and not at all for illite The equivalence of the disappeared hydrogen and eluted Sr from Sr-clay minerals was only observed m montmorillonite at a pH value lower than 6 5 In the case of illite minerals , the disap- + ++ peared hydrogen ions (AH ) were more than equivalent amounts of Sr eluted o The excess amounts of hydrogen may have been involved in attack- ++ mg the clay structure or its impurity „ Increase in the amounts of Sr adsorption s that is the amounts disappeared from the solution phase, by addition of OH ions was observed in both montmorillonite and illite, which indicates that either creation of new exchange sites or the precip- itation of Sr may have occurred „ The solubility of Sr(OH) at the highest pH (7 M-) indicates precipitation is not expected „ It was more 66 probable that the addition of OH created new exchange sites on which Sr could be adsorbed „ The creation of new exchange sites perhaps resulted from the fact that OH ions might have neutralized hydrogens on the clay minerals, and hence created new exchange sites for the adsorp- tion of Sr o The hydrogen neutralized by OH ions might be either the hydrogen of exposed hydroxyl parts of the clay structure or the hydrogens adsorbed on the clay minerals during their treatment process „ The pos- sible creation of exchange sites by removing the hydrogen of exposed (13) hydroxyl groups of clay minerals was reported by Grim „ The selectivity of hydrogen with respect to strontium ion was examined by determining the equilibrium constant (Ko ) for the ion- exchange reaction between hydrogen and strontium „ The results are summarized in Table 6 The selectivity of montmorillonite for hydrogen TABLE 6 EQUILIBRIUM CONSTANT OF MONTMORILLONITE FOR THE EXCHANGE BETWEEN Sr ++ AND H + pH K °SrH ™H ™H + ™Sr '4 9 3 7 0„085 OollO o 800 0.065 0ol30 0„220 decreased as more hydrogen adsorbed on montmorillonite , indicating the + + decrease in the affinity for H as more H occupied the exchange sites „ The change in the selectivity probably resulted from the fact that the exchange sites are not uniform in their properties „ Initially, the 67 hydrogen ions might be adsorbed on more favorable sites resulting in its high affinity. As more hydrogen occupied the favorable sites 9 further adsorption of hydrogen may have involved unfavorable sites 9 resulting in the low value of the selectivity , The determination of equilibrium constants for the counter ion ++ ++ ++ ++ pairs Sr -Ca and Sr =Mg in the presence of hydrogen ions in the exchanger phase are summarized in Table 7 As shown in Table 7, the ++ ++ ++ ++ equilibrium constants for the ion pairs Sr -Ca and Sr -Mg are inde- pendent of the presence of hydrogen ions in the exchanger phase, even TABLE 7 INFLUENCE OF HYDROGEN ON THE EXCHANGE EQUILIBRIUM CONSTANTS OF MONTMORILLONITE % exchange sites -b exchange sites Ko ., ,\ TT+ Final pH Ko _ , 6 , u+ Final pH Sr~Mg__ covered by H T ** Sr~Ca covered by H 1.31 lo30 1,22 lo31 3.35 6,23 12o2 I8o9 bo «0 1,09 4,79 1.07 4,40 1 03 3,70 1,10 3,25 6,25 12,2 21,0 5,14 4,76 4,42 3,76 though the equilibrium constants for the reaction between hydrogen and others depended on the hydrogen concentration, Thus 9 it can be concluded that regardless of the types of exchange sites on a clay mineral or the presence of other cations 9 the selectivity coefficient of a clay mineral is constant for most of the counter ion pairs except that involving hydrogen ions. 68 Ho 1 *. Determination of Equilibrium Constants A number of ion-exchange expressions discussed in Section 2 3„1 were subjected to experimental tests The experiments were performed to determine the equilibrium constants for various counter ion pairs, Sr -Ca j Sr -Mg s and Sr -Na , over a wide range of concentrations. The equilibrium constants were computed from expressions described in Section 2,3.1a Rearranging the terms of Equation (2-16) and taking logarithms leads to the equation, U A ) b (a,) b log = log + log K (4-la) <* B > ( V or ,= ,b ,— x b , ,b , .b (m ) (Y A ) (m ) (Y A ) log =— — _^-= — , = log- — ■ - — — + log K s (4-lb) (- B ) 3 a , ,b, , s a , , , , v b , , x a /(a E ) = (m A ) /(m B ) , (b) (a A< used; (a) (a A )/(a n r = (m A ) /(iO , (b) (a„)7(aj 69 (m ) (y a ) /( m B ) a (Y B ^ a with ^ A ) /(Y B ) computed using the individual ionic concentration, and (c) (a ) /(a R ) = (m ) (y ) /( m B ) (Yg) with (y a ) /(Ytj) computed using the total ionic concentration,, In the case of A B the ion pair of the same valence, (a) and (c) reduce to the same value „ The reliability of each expression was tested by examining the ability of each expression to produce a constant value of the equilibrium constant over the range of concentrations used„ Each equilibrium reaction was carried out over a wide range of the counter ion concentrations as shown in Tables 8 and 9„ The equilib- rium constants at each concentration were computed from the expressions discussed in Section 2 3olo The average values for each reaction and the experimental conditions are summarized in Tables 8 and 9. Using the average value of the equilibrium constants, a straight line satisfying the equilibrium condition is drawn on a log-log plot (Fig„ 5 through Fig„ 12 ) On each of the same figures 9 the experimental data in terms of the exchanger activity ratio (m ) (y ) /(m ) (y d ) are A A B B plotted as a function of the solution activity ratio (m )" (y )b/(m ) a (yf-„ A A B B By comparing the experimental points with the line representing the average value of the experimental points 9 one can examine qualitatively the degree and nature of the deviation of each experimental result „ In FigSo 5 and 6 9 the experimental results of the exchange ++ ++ reaction between Sr and Ca with montmorillonite and illite are shown „ Because both cations have the same valence 9 the activity coefficient ratio in the exchanger phase is unity,, In both Figs„ 5 and 6 9 the curve (a) on the left represents the value without the solution phase activity correc- tion „ The results are present similarly in Figs 7 and 8 for the reaction between Sr and Mg 70 TABLE 8 THE VALUE OF EQUILIBRIUM CONSTANTS FOR THE EXCHANGE BETWEEN Sr ++ -Ca ++ AND Sr ++ -Mg ++ Clay Concentrations, N Ko A a+ ,b+ AB s.d, Ko AB * s.d, Coefficient of Coefficient of Variation. C Variation. C » y ' v Sr-Mont , 5-10xl0" Ca-Mont, 5=10x10° Sr ++ Ca ++ CO 1 1 o 5x10 -2xl0~ 1x10" -2xl0~ Sr ++ Ca ++ 5x10" =2x10 lxl0~ -2x10 1.065*0.085 8.0 1.086*0.045 4.2 1.026*0.143 14.0 0.8853*0,110 12.5 Sr-Illite 5-20xl0~ 4 Sr ++ 5xl0~ 6 -lxl0" 3 Ca ++ 1x10 -1x10 1.110*0.080 7.2 1.067*0.105 9„8 Ca-Illite 5~20xl0~ 4 Sr-Mont . 5-10xl0 =l4 Mg=Mont. 5-10xl0~ 4 Sr ++ -6 -3 5x10 =1x10 Sr ++ Ixl0~ 4 =lxl0 =3 Sr ++ Ixl0~ 5 -lxl0~ 3 Ca ++ Ixl0" 4 -lxl0~ 3 Mg Ixl0 _l+ =5xl0" 3 Mg -4 -3 1x10 -5x10 1.116*0.068 5.8 1.262*0.094 7.5 1.293*0.083 6.4 0.9449*0.091 9.6 1.220*0.120 9.8 0.920*0.168 18.4 Sr-Illite 5=20xl0~ 4 Sr ++ Ixl0™ 5 -lxl0 =3 ++ Mg lxlO^-lxlO™ 3 1.493*0.067 4.5 1.358*0.129 9.5 Mg-Illite -4 5-2-xlO Sr Ixl0" 5 -lxl0" 3 Mg Ixl0~ 4 -lxl0~ 3 1.619*0.099 6.1 1.348*0.087 6.5 71 o rH CN P» CO CD CD CD in cn cn CD r- rH r> rH zt rH in O x) CN o CM o CM □ H o o o o o o o o a o CO o +1 O -H o +1 O +1 ■H oo -H CD ■H co +) CN 1-1 CO =r rH in CO CO CD r> LO H ID CO in o r- d- p o CD CN CD o r> rH in CO o o o o o o o o rd rH o rH o rH o rH o .^N V II II II II II n II ii >> H CM H CN H CM ■H CM H X X X X X X X X CD + > + •H CD CD =f en CD CN p P CN in 00 in CO d- CN CD CO O a in rH rH o o o H O CO X! CM o o o o ■ a o Q (X o o O o o o o o O S3 CO CO o -H ■H ■M ■H +1 -H ■H < d- m tD r- CO p ■M J- in CO d- in d- CM in + en 00 rH CT! J rH CO CM ft) - O CO rH < CO "H 55 -a o c 4- J- m in o «H 11 o II o ii o 8 O s -C H H rH rH o ■H o X X X X j-H °H X) CO E-* CO o « 5 in CN CO CM m CO o o o o M 13 rH rH CM J- j CO -in ■H ■H ■» +1 M P 4 J" =t- J- ID 3 p. 11 I o ft CA o O o o w O rd rH X rH X rH X £m O o CO o rH J- o CO x CM 00 CO o CM O w u o o o o < rd 00 CO CM CO CM > x 3" =t w T) S3 3- d- 1 t X c 1) II O o E-i a) 04 o o rH rH CO rH m rH X in X H C X i X 3- o 8 o zf X O o CO o o 11 CM CO o CM co 6 ^^ »H rH H rH CM o 8 rH 8 8 O P o X 11 (1 rH in o X m O rH ro IT) rH o in O X ii H o ii rH X P II X o ii H o a) X o CO X O P o o CM o X CM p o rH p O H C P in II p in 11 •H CN B •H CM 8 © a a rH C 8 rH rH in rH 8 H o o rH || O rH II rH in ii rH in n c s II + s II + M n -t- M n + o ii +- 4- 11 + +■ 9 + + 8 + + o p. cd P. rd rrj P. P rd P. It) ft) P CO 53 C/3 53 S3 CO CO S3 CO S3 S3 tt) 72 average value o a experimental data a: pSt = i.o; Ko SrCa = 1.0855 IO I O to o O sr 'ca 1000 500 200 100 50 20 = computed with individual ionic strength; Ko' c = 0.8853 10 - jT - a — v - b— x _ y/i - Jj/a - /£/*■ _ ~ ' 1 A 1 1 1 1 1 1 1 i i i i i i i i i 1 1 1 1 10 20 m Sr r, Sr 50 100 200 -3 500 1000 m Ca ?Cc , io FIG. 5 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE, Ca ++ , AND Sr ++ . average value o A experimental data r 73 a: b: P^= ^ Ko SrCa= X - 1162 ™ ■ computed with individual ionic strength; Ko c rCa Ca CM I O CO IE o o IE m Sl X, £r m Ca Xcc , 10 -2 0.9449 1 50 60 FIG. 6 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Sr ++ , AND Ca ++ . 74 O A average value experimental data a: ?£ = X - ' K °SrMg = l-»3 Sr b: = computed with individual ionic strength; Ko' .. >Mg SrMg - 0.92 CM b co 500 200 100 50 20 IE - - a — .. Ok/ - - b ^\>4 - 6$/ rk X ( Kyj^ - /Oy ^A - /D - ^ ~ <&/G 1 r A 1 1 1 1 1 1 1 1 1 I i l l I 1 1 5 10 m Sr 20 m. r* , io 50 -2 100 200 500 FIG. 7 'Mg 'Mg EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE, Mg ++ , AND Sr ++ . average value 75 o A experimental data a: b: ' Sr = computed with individual ionic strength; Ko' ^Mg g 100 1.348 b IE o> 50 20 - 0/ - a — v \ ° 9t jt - /o \-b cP 1 1 1 1 1 1 1 1 1 1 1 i i m Sl io .3c 20 m Mg ^Mg 10 -2 50 60 FIG. 8 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Sr ++ , AND Mg ++ . average value oiD experimental data 76 a: ~& < 1.0; Ko NaSr = 8.3803xl0~" Y Sr Na in b - b ^v - A AyOyj a - A / 7/ - X A : - a/o a on/ l/l 1 1 1 1 1 MM 1 l 1 i i i i i 1 I 20 50 (m M J Na 100 200 2 500 1000 2000 5000 (m Sr ) (r Sr ) 10 -2 FIG. 9 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH MONTMORILLONITE, Na + , AND Sr ++ . average value 77 oAD experimental data a: -r^ = l-0> *£- — = 8.000x10" r Sr ~Na NaSr b: — =^ = computed with individual ionic strength; K NaSr = 1.261 Sr Na • = computed with total ionic strength; K N s = 6.356x10 ^Sr 5000 2000 -1 CVJ l o (VI o Z IX < 7k 'ty roru - - A a/o - s°s 1 — A/y "~ S^j/V - - /a/ - A^ a on y i in /J 1 1 1 MM 1 1 1 i i i i i 1 1 10 20 50 100 <%<■> (r Na ) 200 2 500 1000 2000 5000 (m Sr ) (y Sr ) 10 -2 FIG. 10 CORRECTED EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH M0NTM0RILL0NITE, Na + , AND Sr ++ . 78 average value a: - — = 1.0; Ko Nagr -4 o A experimental data r Na Sr Na —4 b: = computed with individual ionic strength; Ko • _ =3.8826x10 ^Sr Na —4 c: = computed with total ionic strength; Ko' _ = 2.192x10 Yc r NaSr m i O 1000 500 200 100 CM IE IE° » 20 - - a — \ - C ~^C \y/ J5 D - /o n ■ - l/o/l - 'o/ri I 1 1 1 1 1 1 i i i l l l i 1 1 1 1 1 1 10 20 v2 50 100 200 500 1000 ( m Na) (X Na ) H m Sr ^Sr FIG. II EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Na + , AND Sr ++ . 79 average value o A Q experimental data a: J* -1.0, K^ asr = 7.000X10" 1 'Sr Na b: — — = computed with individual ionic strength; K N _ = 1.179 ^Sr c: - — = computed with total ionic strength; K— _ = 5.472x10 ^ r (SI i O CM IX IE CO IX CO IE 1000 500 200 100 50 20 - A / rf □ - *sQ°s - — a - \— b - ^^c — Jra ■ S A, nyn ...I i i i i i i i 1 1 i i i i i l I tin 10 20 (%a) 2 50 100 200 500 1000 m Sr 10 -I FIG. 12 CORRECTED EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH ILLITE, Na + , AND Sr ++ . 80 ++ + In FigSo 9 and 10 9 the experimental results for the Sr -Na exchange reaction with montmorillonite are presented „ In Fig 9, the concentration ratios in the exchanger phase are plotted as a function of the activity ratios in the solution phase „ In Fig„ 10 9 the activity ratios of the exchanger phase computed from Krishnamoorthy and Over- street's expression (Equation 2-21) are plotted as a function of the activity ratios in the solution phase „ Similarly , in Figs 11 and 12 , the experimental results with illite are presented „ It is apparent from the curves shown in Fig„ 5 through Fig„ 12 that regardless of the form of the expressions used for the computation of the equilibrium constants, they all show the same degree of reliability for producing a constant value of the equilibrium constant. There is no clear evidence of one expression being better than the others in describ- ing the equilibrium conditions „ No improvement on the constancy of the equilibrium constants by including the solution phase activity correction is observed o The coefficients of variation 9 C = (s d„ )/( average value) x 100 (Table 8) s show that the variation of the equilibrium constant with the solution phase activity correction is even greater than that without the correction o The greater variation of the equilibrium constant with the solution activity correction may be a result of the approximation made in the computation of the activity coefficients „ ++ + In the case of the exchange reaction between Sr and Na , the values of the equilibrium constants with and without the solid phase activity correction differed by a factor of about 1000 „ The constancy of the equilibrium constants computed from the two. expressions , that is one with the exchanger phase activity correction and the other without the correction 9 is about the same over a wide range of counter ion concentrations „ The ratio of the two constants remained the same at about 1000 o On the basis of the findings in this section, it is concluded that s (1) the ion-exchange equilibrium of the counter ion pairs , Sr - ++ ++ ++ ++ + . Ca 9 Sr -Mg 9 and Sr =Na wxth either montmorillonite or lllite can be described satisfactorily with the simple mass-action equation without the activity correction; (2) regardless of the direction of the approach, that is whether A is replacing B or B replacing A , a constant value of the equilibrium constant is obtained; and (3) the direct rela- tionship between the expanding properties of an exchange medium and its selectivity does not apply for the exchange reactions of montmoril- lonite and illite 4o5 Ion-Exchange Equilibria of Heterogeneous Clay Mixtures On the basis of the theoretical considerations discussed in Section 2 i + 9 it was shown that in the case of exchange media that are mixtures of two or more pure exchangers 9 the equilibrium constant would not be a constant but would depend on the mixture and the concentration of reactantSo With the mixture of montmorillonite (8 9 x 10 ) and illite (3 8 x 10 ' N) 9 the exchange reaction between Sr and Mg was studied ++ ++ with varying concentrations of Sr and Mg „ The results are presented in Figo 1H The experimental values of the effective equilibrium con- stant of the mixture (Equation 2-22) were compared with the value estimated from the theoretical equation (Equation 2-23 )„ The exchange reactions between Na and Sr were also studied with a mixture of 82 montmorillonite and illite with varying illite contents from zero to 100% , The results are presented in Fig„ 13 „ From the results, it is evident that equilibrium constants of the clay mixtures depended on both clay composition and ion concentration, However 9 the effect of ion concentration was insignificant compared to that of the clay composition „ On the basis of the experimental results 9 it is shown that an approximate estimate can be made of the equilibrium constant of a montmorillonite and illite mixture by a simple linear interpolation between the equilibrium constants of the two pure compo- nents and their relative amounts in the mixture. That is 9 the effective equilibrium constant Ko can be approximated by, Ko, R = x (Ko, R ) + (1 - x)(Ko AT J. (4-2) AB m AB m m AB l where x and 1 - x are the fractions (expressed in equivalents) of mont- mm c ^ morillonite and illite 9 and (Ko ATJ ) and (Ko. D ). are the equilibrium Ad m Ad 1 constants of pure montmorillonite and illite „ 4o6o Ion-Exchange Equilibrium in a Multicomponent System The mass-action expression s without the activity corrections, which has been found satisfactory for describing the exchange reactions involving most pairs of counter ions 9 was subjected to experimental tests + ++ for its applicability in the multicomponent system containing Na 9 Mg , ++ ++ Ca 8 and Sr With the known amount of each cation added into the system (m_ 9 m. T 9 m., » and m n ) and the equilibrium constants determined in the Ca* Na 9 Mg 9 Sr ^ 83 i „ o o Ill ite Illite + Montmorillonite FIG. 13 EFFECTS OF IMPURITY OF CLAY ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ ,AND Na + . 84 ▲ experimental values computed from Eq. 2-23 CO o l.b 1.4 - T 1.3 1.2 1 1 A A A ., 20 30 m Mg m 40 50 Sr FIG. 14 EQUILIBRIUM CONSTANTS OF A CLAY MIXTURE AS A FUNCTION OF THE COUNTER ION CONCENTRATIONS. 85 previous sect ion , the final Sr distributions were estimated using Equation (3-5) 9 which was derived from a set of simultaneous mass-action expressions representing the reactions in the system. The estimated Sr distributions were compared with the experimental results , The results are presented in Figs, 15, 16, and 17, The experimental conditions are summarized in Table 10, In FigSo 15 9 16 , and 17 8 the estimated values are presented as lines 9 while the points represent the experimental data It is apparent from the curves and points shown in Figs, 15, 16, and 17 that the mass- action expression was quite satisfactory for describing the equilibrium conditions even in a multicomponent system. 86 V) X) computed from Eq. 3-5 o , a experimental values 2.4 2.0 1.6 0.8 0.4 \° S* ° A \ Ay V y, b A A^ A 10 20 30 m r „, ICT 4 N 40 50 FIG. 15 'Ca ION EXCHANGE EQUILIBRIUM OF MONTMORILLONITE WITH THREE COMPETING COUNTER IONS. 87 XL 2.4 2.0 1.6 1.2 0.8 0.4 computed from Eq. 3-5 experimental values Q 20 40 60 s 80 100 m CQ , I0-«N FIG. 16 ION EXCHANGE EQUILIBRIUM OF MONTMORILLONITE WITH FOUR COMPETING COUNTER IONS. 88 computed from Eq. 3-5 a,o experimental values 1.4 1.2 1.0 0.8 CO 0.6 0.4 0.2 °\ \ /" — Q X (\j^— 8 12 16 20 , 24 28 m Ca , lO" 4 N FIG. 17 ION EXCHANGE EQUILIBRIUM OF ILLITE WITH THREE COMPETING COUNTER IONS. 89 w PQ < CO >h CO E-" w 2; o Ph s o o IH E- J 3 m H M c/ w w S3 < o X w PS o CO o a § o < W Pi w PL, x: M CO 11 CO co 1 CO 1 o a o 1 o 1 o rH rH H H X X CM X X tt3 o o 1 o o c_> o o o o a CO CO rH CO CO 1 o H o 1 o o o 3- I o H X CN rH CO X CN H CO co o H X en o ID I X cn o cr> co co IT) II o ■H X CO CO X to ID (D O H o X rH ID Zt X zt O 1 CD I o o IT) H o o X cn J- in t CO I 1 o o H H X X CO CN CO CO CO S3 g o j 8 o o H o O A H H X H rH C X X m X X O CN CM cn CO CO °H 3- 3" r- a o >i +J o o o CT> en to nj rH H rH II ii H fc ill II 11 a> +J +J °H •H " a A "" (1 + m y x K Ay ) (2-27) m, 1/a BA m A J Kc\ - ■■,. ■ * a B (1 + m y x K fiY ) (2-28) K °AB = K °AB (1 + m y K BY )' J (1 + m y K Ay ) (2-29) 91 Equations (2-27) , (2-28) 9 and (2-29) show the dependency of the counter ion distribution on the sequestering agent concentration (m Y ) Equations (2=27) and (2-28) indicate that the formation of stable sequestered com- pound prevents the cation from adsorbing on the exchanger , that is the value of Kd becomes small „ When both cations A and B form sequestered compounds with Y 9 the effective equilibrium constant Ko depends on the iigand concentration and the stability constants of both sequestered com- pounds o If cation B forms a more stable sequestered compound (K >K \ then the effective equilibrium constant Ko is greater than Ko , and Ad Ad a+ hence cation A is more favorably adsorbed on the exchanger phase when the Iigand Y is present „ It should be well understood that these equa- tions only describe the system with the conditions imposed by the assump- tions that (1) the sequestering agent (H Y) is in one ionic form (Y ), (2) the sequestering agents form only one type of chelated compound with a+ b+ A and B and (3) neither the sequestering agents nor the sequestered metal ions interact with the ion exchanger „ The effects of sequestering agents ( citrate 9 tartrate , and EDTA) on the ion-exchange reactions of soil minerals were investigated by batch equilibrium-type experiments „ All the reactions were carried out in 6-ounce Armstrong prescription bottles containing 50 ml of the total solution The effects of the sequestering agents were examined in terms ++ of changes in equilibrium distributions of the counter ion pairs (Sr - f. -f-j. ++ ^.j. .j..}. .J..J. +4, Na 9 Sr -Ca 9 Sr -Mg 9 and Sr -Zn ) in the presence of these agents „ In all the experiments in this section 9 the concentrations of the inor- ganic counter ion pairs were kept constant , while the sequestering agents were varied from zero to about twice the concentration of the total 92 cat ions „ The results of the experiments are summarized in Fig„ 18 through Fig 24 „ In Fig„ 18 and Fig 21 (curves a and c), the effects of citrate ++ + on the ion-exchange reactions of the various counter ion pairs (Sr -Na 9 ++ ++ ++ ++ Sr -Ca 9 and Sr -Zn ) are shown The experimental conditions are summarized in Table 11 Theoretically, Equation (2-27) should satisfy the experimental data if all assumptions were valid Rewriting Equation (2-27) in terms of m 9 m 9 and the experimental conditions, the follow- ing equations are obtained, Ko c KT (~— ) SrNa m Kd„ = r ~— ^H.^ - (5-la) Sr X + m Cit K SrCit (m SrCit } K a b ^ ir , (5-lb) SrCit (m )(m ) m Sr S ™Sr + m Sr + m SrCit (5 ~ lc) t m_, = m„. + m„ _„ (5»ld) Cit Cit SrCit with Ko grNa - 1.19 x 10 3 9 K SrCit = 0„333 x 10 2o7 9 where all the concentrations are in normal concentrations 9 and m and m . represent the total amounts of Sr and citrate added to the system „ 3 The value of the equilibrium constant (Ko_ „ = 1 19 x 10 ) is SrNa the average value determined in Section 4o4 The stability constant 9 7 / qc \ (K . = o 333 x 10 ) of strontium citrate ' is corrected to be used 93 Na + Sr Clay Minerals, N a b 6xlO~ 3 2xlO" 3 5xlO~ 5 lxl 0" 4 Na-Mont . =8 . 3x1 0"~ 4 Sr-Mont . =7 . 8x10 CO IS 100 50 20 ' Eq,5-2 /—q x-Eq.5-1 10 20 50 100 Concentration Of Citrate, I0~*N FIG. 18 EFFECTS OF CITRATE ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. 94 Na + Sr Clay Minerals, N a, b, 8xl0~ 3 8xl0~ 3 -4 1x10 -4 1x10 -4 Na-Mont.=8.3xl0 -4 Sr-Mont.=19.0xl0 en P 100 Concentration Of Tartrate, 10 4 N FIG. I 9 EFFECTS OF TARTRATE ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. 95 Na + o + + Sr Others Clay Minerals, N a 5xlO~ 3 -4 1x10 -4 Na -Mont. =7. 4x10 b 2xl0" 3 -4 1x10 -4 Sr-Mont.=8.2xl0 c 4xl0" 3 -4 1x10 ++ -3 Ca =10 J Na-Mont.=7.4xl0" d 2xlO~ 3 -4 8x10 ++ -3 Mg =10 J Na-Mont.=7.4xl0~ 4 en 12 500 2 5 10 20 Concentration Of EDTA, I0" 4 N 50 FI6.2C EFFECTS OF EDTA ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. 96 Na + r, + + Sr, Others Clay Minerals, N Agents a 4xl0" 3 -4 2x10 zn ++ =10- 3 -4 Sr-Mont.=8.2xl0 Citrate b 4xl0~ 3 -4 2x10 * zn ++ =10- 3 Sr-Mont . =8 . 2x1 EDTA c 4xl0" 3 5x1 0~ 5 Ca ++ =10- 3 Na-Mont . =8 . 3x10 Citrate d 4xl0~ 3 5xl0" 5 Ca ++ =10- 3 -4 Na-Mont. =7. 4x10 Tartrate 1"° FIG. 2 uu " 50 - — s-C ?o 1 J — C /* .... .... ( L/^ S 10 y-Q ( c 5 3 ' ^-b 2 1 i i i 1 1 1 1 i i i i i i i 12 5 10 20 50 100 Concentration Of Chelating Agents, I0~ 4 N EFFECTS OF CHELATING AGENTS ON DISTRIBUTION OF Sr ++ IN EQUILIBRIUM WITH CLAY AND COMPETING COUNTER IONS. 97 with normal concentrations, m In the case of Fig„ 18 (curve a), in which m n << m. T , & ' Sr Na' << m^ 9 and m << m . s it can be approximated that m = C E o C , m i>T - m „T 9 an d m_,„, s m „_,o With an additional assumption that all Na Na 9 Cit Cit r 3- citrate ions are ionized as tertiary citrate (Y ), Equation (5-la) becomes,, Kd K °SrNa ( m7" ) Na Sr " t 1 + m Cit K SrCit (5-2) TABLE 11 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF CITRATE ON CLAY ION-EXCHANGE REACTIONS Cations 8 N Clay minerals N PH Figure Na + Sr others Number 6xl(T 3 5xl0^ 5 »4 Na-Monto=8„3xl0 7.0-7.1 18-a 2xlcT 3 =14. 1x10 Sr-Mont„=7, ) 8xl0 = ' l+ 7.1-7.3 18-b 4xl(T 3 =4 2x10 ++ Zn =10 -3 Sr~Mont„=8,,2xlO 7,1-7,3 21-a 4x10 5xl0° 5 Ca ++ =10 = =3 _4 Na-Mont .=8.3x10 6,8-7.0 21-c The effective distribution coefficient Kd_ computed from Equation (5-2) is shown as a dotted line on the same figure 9 Fig 18 „ When Sr ions are presented as gross concentration (Fig 18 9 curve b) 9 the above approximations are not valido m and m „ can no longer be treated as constant values The system must satisfy the set of simultaneous equa- tions B Equation (5-1). The solutions of the simultaneous equations are 98 presented as a dotted line In Fig„ 18 (curve b). In Figo 21 (curve c), the effects of citrate on the ion- ++ ++ exchange reactions of the counter ion pair Sr -Ca are shown. Because the citrate added to the system was in the form of sodium citrate, the presence of Na ions in the system was unavoidable. To make the influence of Na ions in the system more or less constant , the concentrations of Na -3 ions in the system were kept at a constant value (4 x 10 N) by adding NaCl„ The effects of tartrate on soil ion-exchange reactions were studied in a similar manner as that with citrate. The experimental re- sults are shown in Fig, 19 and Fig, 21 (curve d). The effects of EDTA were studied for the counter ion pairs Sr -Na , Sr -Ca s Sr -Mg , ++ ++ . and Sr -Zn „ The experimental results with EDTA are shown in Fig, 20 and Fig, 21 (curve b). The experimental conditions for the study of the effects of tartrate and EDTA are summarized in Tables 12 and 13, In general^ the experimental results are In good agreement with the qualitative rules for the selectivity of ion exchangers (clay min- erals) and the stability of metal chelates. The effects of a sequester- ing agent on the distribution of Sr ions in equilibrium with a soil exchange system depend on the nature of the other counter ion present. In the presence of the counter ions that form less stable chelates with the sequestering agent , the Sr ion concentrations in the solution were increased as sequestering agents were added. These effects were observed ++ . + in all exchange reactions where Sr ions were competing with Na ions. The same effects , but less in their intensities, were noticed in the ++ ++ reactions involving the pair, Sr -Mg „ On the other hand s when the 99 TABLE 12 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF TARTRATE ON CLAY ION-EXCHANGE REACTIONS Cations, N Clay minerals N pH Figure Na + Sr ++ others Number 8xl0~ 3 lxio" 4 ~4 Na-Mont .=8.3x10 6.2-6.8 19-a 8xl0 =3 lxio" 4 Sr-Mont .=19. 0x10 " 4 6.2-6.5 19-b 4xl0~ 3 5xl0~ 5 Ca ++ =10" =3 Na-Mont. =7. 4xlO~ U 6.0=6.5 21-d TABLE 13 EXPERIMENTAL CONDITIONS FOR THE STUDY OF EFFECTS OF EDTA ON CLAY ION-EXCHANGE REACTIONS Cations s N Clay minerals N pH Figure Na + Sr others Number =3 5x10 =4 1x10 Na-Mont „ =7. 4xl0~ 4 7.2=7.4 20-a 2xl0 =3 _4 1x10 Sr=Mont =8.2xlO~ 6.0-7.0 20-b 4xl0' 3 1x10 ++ Ca =10 -3 -4 Na-Mont. =7 .4x10 6.0=6.4 20-c =3 2x10 ~4 8x10 ++ Mg =10 =3 Na-Mont „ =7. 4xl0~ 4 5.8-6.5 20-d 4xl0~" =4 2x10 ++ Zn =10 -3 Sr-Mont. =8. 2x10° 5. 5-6. 5 21-b 100 -t-t ++ counter ions (. Ca g Zn ) that form more stable chelated compounds were ++ present s the Sr ion concentrations in the solution phase were decreased as the agents were added „ As shown in Fig 18 s the experimental results indicate that the effects of citrate are even greater than theoretically predicted. It is not clear what factors cause the experimental values to show the greater effects than theoretically predicted,, Possible reasons may be found in the assumptions made to evaluate the theoretical predictions „ The assumption that all citrate ions are ionized as tertiary citrate (Y ) seems to be accurate „ The percentage of an ionized acid may be computed from the expression , % Ionized = 7— ^^ Q ° ; - (5-3) For the value of pKa = 5„49 (Table 2) and pH 7 (experimental condition), 3- the percentage of tertiary citrate (Y ) is 98%, which indicates that at pH 7 the ionization of citrate ion is practically complete,, (35) It has been shown that citrate ions are involved in three f + - + different chelate formations with Ca ions (CaY , CaHY, CaH_Y ); however s their stability constants differ by factors of more than 10, and hence the assumption that citrate ions form only one chelated compounds, that is, the most stable compounds, seems quite reasonable „ At present,, the sta- bility constant of Sr=citrate is reported for only one compound (SrY )„ There are some discrepancies in the reported values of metal chelate stability constants,, For instance, in the case of Ca-citrate (CaY ), values' 9 of K = 10 ° to K = 10 ' have been reported „ Using the 101 experimental data (Fig. 21 , curve a) and Equation (5-2), the stability constants of Sr-citrate are calculated for citrate concentrations of 4 x icf 4 and ICT" N. The values are 10 ° and 10 ° . There is no clear 2 7 evidence that using a value of K. . = 10 in the evaluation of the theoretical prediction was wrong; however, it is of interest to note that 3.4 the prediction is in good agreement if a K . value of 10 ° is used. To determine if sequestering agents or the sequestered compounds interacted with clay minerals, experiments were performed in which citrate 14 adsorption was determined with C -labelled tracers. The experimental results are summarized in Figs. 22 , 23 , and 24 „ It is shown that all the sequestering agents were adsorbed on the clay minerals; however, in the case of EDTA, the adsorption was much lower than with either citrate or tartrate . The adsorption of the sequestering agents on clay minerals was found to depend on the concentration of electrolyte in the solution and exchanger phases . It is not known what physical mechanisms were involved in this adsorption,, Increase in the adsorption of the organic anion (Fig. 24) at higher electrolyte concentrations (NaCl) suggests that anion exchange was not involved,, The adsorption of sequestering agents on clay minerals further complicates the quantitative analysis of the exchange reactions in the presence of these agents . The effects of citrate are in general greater than those of tartrate. This is expected, since with most metal ions, citrate forms more stable sequestered compounds than does tartrate „ The chelate forma- tion of EDTA is pH dependent . For example, at pH 7, EDTA (H^Y) ionizes into three different ions Y 4 " (0 o 055%), HY 3 " (87.5%), and H 2 Y 2 ~ (12.5%). 4_ Even though only 0.055% are in the form of Y , because of its high 102 Na + Sr Clay Minerals, N a, 2xl(T 3 lxl 0" 4 Sr-Mont. =7. 8x1 0~ b, 2xlO" 3 lxl 0~ 4 Sr-Xllite=2 . Oxl O -4 c, 6xlO~ 3 5xl0 -5 Na-Mont . =8 . 3x1 0" 4 a, Sr-Mont . =7 . 8x1 0~ 4 e, Na-Mont . =8 . 3x1 0~ 4 2 O ■♦— O a> o (0 < o 4- o 0) o c o o 500 200 100 50 20 10 5- i — '^irz: 10 20 50 100 200 500 Concentration Of Citrate Added, I0" 5 N FIG. 22 ADSORPTION OF CITRATE ON CLAY MINERALS. 103 + Na Sr ++ Clay Minerals, N Agents a, b. 8x1 O" 3 8xl0~ 3 2xl0" 3 -4 1x10 * 5xlO~ 5 -4 1x10 Sr-Mont . =7 . 8xl0~ 4 Na-Mont . =8 . 3x1 0*" 4 Sr-Mont . =7 ,4xl0~ 4 Tartrate Tartrate EDTA •o z t- (0 O 1 c D> o < •*- o o> •♦— c c •~ j=i t_ o CO ■D < c cu o c o o 500 200 100 100 200 500 Concentration Of Nad Added, I0' 4 N FIG. 24 ADSORPTION OF CITRATE ON CLAY MINERALS AS A FUNCTION OF NaCI ADDED. 105 2- stability, most of Sr-EDTA is in the form of SrY . At a higher pH, the effect of EDTA will be much greater than that of citrate or tartrate „ Summarizing the results of the study of the effects of seques- tering agents , it can be concluded that the results are in good agreement with the general rules for the selectivity of soil exchange media and the stability of metal chelates „ It can be shown that the velocity (R„ ) of Sr ion relative to the velocity of water (R ) containing Sr in a soil exchange medium is (5-4) ++ which shows that the rate of migration of Sr depends on the effective distribution coefficient , Kd q «, Assuming the concentration of a seques- tering agent in natural water in contact with soil exchange media to be about 10 mg/1 as citric acid (5,2 x 10 N) s which may be considered as a high organic content in natural water , it can be shown from Equation (5-1) that the change in the effective distribution of Sr is less than one percent o It is not probable that in a natural environment s the concen- tration of a sequestering agent is so high as to give significant effects on the movement of radionuclides disposed into the environment „ The presence of a noticeable concentration of sequestering agents , which may be found in certain nuclear wastes, may even be beneficial in terms of contaminating the water system; for in the presence of a sequestering 90 137 agent the hazardous radionuclides such as Sr and Cs will be more favorably adsorbed on soil if the system contains gross concentrations of 106 + + 3+ competing counter ions such as Ca and Al s because they are more strongly sequestered than Sr or Cs » 5 2 Adsorption of Organic Compounds and Effects on the Clay Ion- Exchange Properties Interactions of soil-sorptive organic compounds with clay minerals were briefly discussed in Section 2 6 2 There has been consid- erable work done in the field of organic adsorption on clay minerals, (13) Grim has presented a comprehensive survey of this subject „ The effects of organic adsorption on the ion-exchange properties of soil minerals is a problem deserving some attention „ The investigations in this area will not only aid the understanding of organic-clay reactions, but will also furnish information regarding the fundamental mechanisms involved in soil ion-exchange reactions In this sect ion , studies of organic-clay interactions were carried out to learn the effects of organic adsorption on the ion-exchange properties of soil minerals „ In general 9 the effects of the organic-clay interactions were examined in terms of changes in the soil ion-exchange parameters such as the exchange capacities and the selectivities of the soil minerals o 5 2olc Adsorption of Methylene Blue and Its Effect on the Clay Ion-Exchange Properties Methylene blue has a unique property in the sense that it can be irreversibly adsorbed on clay surfaces to block out any desired portion of the clay exchange sites without the presence of residual 107 methylene blue In the solution phase „ This allows study of the effects of its presence only in the exchanger phase „ In addition, its large size makes possible the study of the effects of methylene blue on covering-up of the exchange sites „ Comparing the effective area of the methylene (27) blue molecule with that of coedine which has about the same configu- ration as the methylene blue molecule, the effective area of the methylene blue ion may be approximated to be about 150 A „ The interactions of methylene blue ions (M B ) with clay minerals were carried out to study: (1) the selectivity of clay minerals for M„B , (2) the covering-up effects of MoB , and (3) the effects of adsorbed M B on the selective properties of the available exchange sites for various counter ions The attempt to determine the relative selectivity of clay + ++ minerals for M B ion with respect to Sr was unsuccessful, because the + + selectivity for M B was so strong that the exchange adsorption of M B was practically irreversible,, Regardless of the concentration of the ++ =2 + counter lon 9 Sr (up to 10 N), the adsorption of M B continued until all the exchange sites were occupied with M„B„ ions + The cover-up effects of the adsorbed M B ions were invest i- i"+ — 3 gated by examining the adsorption of Sr ions (2 x 10 N) on Na= montmorillonite whose exchange sites were previously covered (0-100%) + o + with MoBo ionso Similar experiments, with the exception that the M B ft ions were added after the Sr ions were equilibrated with Na-montmonllo- nite 9 were also carried outo The difference between the two experiments was that in the first experiment, the cover-up effects would be shown as ++ less Sr adsorption 9 whereas in the second experiment the cover-up ++ effects would be shown as trapping some of adsorbed Sr ions„ Similar 108 experiments were also performed with Na-illite As shown in Figs, 25 and 26, for both montmorillonite and illite, M„B„ ions were able to smother the exchange sites „ The degree of the cover-up effects depended on the amounts of the adsorbed M B ions The cover-up effects increased as the adsorbed amounts of M B o increased. Comparing the results for mont- morillonite and illite, it is evident that the degree of the cover-up effects were about the same for both clay minerals , even though the loca- tions of the exchange sites in the two minerals may have been quite different, illite minerals having most of the exchange sites at the edges of the basal planes , whereas in montmorillonite most of the exchange sites are on the basal planes „ The effects of the adsorbed M„B on the selective properties of the available exchange sites were investigated for the counter ion pairs Sr -Ca and Sr -Na „ The ion-exchange reactions between Sr ++ . and Ca were carried out with Ca-clay minerals whose exchange sites were partially covered with M B„ ions (0 8 15 , 30 9 and 50% )„ Similar experi- ++ + ments were also conducted for Sr ~Na with Na-clay minerals „ The experimental results are summarized in Figs 27 through 30 „ The effects + ++ ++ of Mo B on the ion-exchange reactions between Sr and Ca with mont- morillonite and illite are shown in Figs 27 and 28, in which the ratio mg r of the counter ion concentrations in the exchanger phase Csp— ) is plotted Ca as a function of the ratio in the solution phase „ The ratio of the values of the ordinate to the abscissa is a mass-action equilibrium constant + without the activity corrections „ The effects of M,B„ on the exchange ++ + . . reactions between Sr and Na with montmorillonite and illite are shown in FigSo 29 and 30 In Fig„ 29, the mass-action equilibrium constants 109 i O CO IE o O c O E 3 O ■4— -dr + + + M.B. added before Sr M.B. added after Sr >sP o\ 20 40 60 80 100 Percent Of Exchange Site Covered By Methylene Blue FIG. 25 ADSORPTION OF METHYLENE BLUE ON M0NTM0RILL0NITE AND EFFECTS ON EXCHANGEABLE CATIONS, Sr ++ . 110 in l O CO IE o O E '+— C o ■t- + ++ M.B. added before Sr + ++ M.B. added after Sr O^S. 20 40 60 80 100 Percent Of Exchange Sites Covered By Methylene Blue FIG. 26 ADSORPTION OF METHYLENE BLUE ON ILLITE AND EFFECTS ON EXCHANGEABLE CATION, Sr ++ Ill m° -1x1 Cf 4 - lxlC"" 3 ; rn° =lxlO" 3 ; Ga-Mont. =8.7x1 0~ 4 a b c d % covered by M.B. + 15 30 50 0.6 0.5 0.4 CO IE o o 0.3 0.2 a — v 0.1 0.2 0.3 0.4 0.5 0.6 m Sr m Ca FIG. 27 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ AND Ca ++ , FOR Ca-MONTMORILLONITE. 112 m° =5x10 5 - 2xl0" 4 ; in° =5xl0"" 4 ; Ca-Illite=4.95xlO~ 4 N Sr Ca a b c % covered by M.B. + 18 36 28 24 20 CM b CO o o a — v^ _ a 12 m Sr m , 10 -2 20 24 28 Ca FIG. 2 8 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ AND Ca ++ , FOR Ca-ILLITE. 113 m„ =1x10 r Na ra° =1x1 (T 4 Sr Na-Mont.=8.82xl0 1.8 o 1.7 1.6 1.5 1.4 1.3 ( ) ^s^ { 5 10 20 30 40 50 60 Percent Exchange Sites Covered By Methylene Blue FIG. 2 9 EFFECT OF METHYLENE BLUE ON ION EXCHANGE EQUILIBRIUM CONSTANTS. 11M m° a =lxl0~ 2 ; m° r =5xicf 5 - 2xl0" 4 ; Na-Illite=3 . 7xl0~ 4 a b c % covered by M.B. + 23 46 O CO CM IE a C V \ b — v ' ^ — a 0.2 0.4 0.6 0.8 1.0 1.4 m Sr ( m Na) 2 FIG. 3 EFFECT OF METHYLENE BLUE ON EQUILIBRIUM DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na+, FOR Na-ILLITE. 115 Ko are plotted as a function of M„B adsorption on montmorillonite. In Fig, 30, the values of the counter ion concentration ratio are plotted, ++ ++ As shown in Figs, 27 and 28, for the counter ion pair Sr -Ca , the presence of M,B, ions in the exchanger phase reduced the amounts of Sr adsorbed. On the other hand, for the Sr -Na pair, the selectivity ++ + . for Sr increased as more exchange sites were covered with M„B„ ions The explanation may be that the effects of M,B, result from two different mechanisms 9 one in which the cover-up effect is involved and the other in which the presence of organic molecules on clay mineral surfaces affect the selectivity of the available exchange sites. In the reaction between ++ ++ Sr and Ca , because of their similarity in chemical and physical properties, the effects of the latter mechanism may be insignificant com- pared to that of the covering-up. In this case, the covering-up and trapping of Ca ions on clay minerals by M„B, before Sr addition may result in a higher Ca concentration in the exchanger phase than its + equilibrium value in the absence of M„B, On the other hand, in the case of Sr -Na , the effect on the selectivity of clay minerals due to + the presence of M,B ions may have been the dominating factor; therefore, the results show the increase in the selectivity of the clay mineral for ++ + Sr in the presence of M B„ „ As will be discussed in the next section, the presence of organic compounds on the exchanger generally increases the selectivity of the clay minerals. 5,2,2, Adsorption of Amine Compounds and Effects on the Clay Ion-Exchange Properties It has been shown that when certain organic compounds are adsorbed on clay mineral surfaces, it changes the swelling and dispersion 116 (31) properties of the clay minerals „ Jordan has investigated this matter in great detail „ His data show that when aliphatic amine compounds are adsorbed on montmorillonite, their surface properties changed from hydro- philic to hydrophobic,, The degree of the change depends on the size and concentration of the adsorbed amine compounds „ Jordan, for example, found that when dodecylamine covers all the exchange sites of bentonite its gel volume in water changed from 15 ml per gram to 1 ml per gram. In the discussion of ion-exchange theory in Section 2.3, it was mentioned that the selective properties of a clay mineral for an inor- ganic counter ion are closely related to the hydration nature of the cation o Thus, it is evident that when a hydrated inorganic cation comes in contact with the clay surfaces which have been changed to hydrophobic by the organic adsorption, the selectivity of the clay mineral will be (i+2) different from that of the hydrophilic clay minerals , Glueckauf has shown that the sequence of decreasing hydration number of the divalent ++ ++ ++ ++ ++ cations is Be (7„0) > Mg (7„0) > Ca (5.2) > Sr (4.7) > Ba (2.0), which is in the same sequence as that of the increasing selectivity of the clay exchange media. It is reasonable to assume that the differences in the selectivities of various divalent cations will be increased if the clay exchanger surfaces are to be coated with hydrophobic organic com- pounds o Investigations of aliphatic amine adsorption and its effects on the clay ion-exchange properties were conducted using methylamine and dodecylamine. The various experiments with these amines included the reactions carried out to determine (1) the equivalence of the exchange ++ between the amines and Sr , (2) the relative selectivities of clay min- ++ erals for these amines with respect to Sr ions, and (3) the effects of 117 the adsorbed amines on the selectivities of clay minerals for the inor- ganic counter ions, Sr , Ca , and Na . The results are summarized in Fig„ 31 through Fig. 36 . ++ The equivalence of the exchange between the amines and the Sr ++ ions was examined by the reactions in which Sr ions of Sr-clay minerals were leached out by the adsorption of these amines . The experimental ++ . results are summarized in Fig„ 31, in which the Sr ions leached out are plotted as a function of the amine adsorption. As shown in Fig. 31, for methylamine, a strict equivalence between the adsorbed amine and the Sr ions leached out was observed; however, in the case of dodecylamme Sr leached out was slightly less than the amine adsorption, indicating the adsorption of dodecylamine may involve non-ionic type adsorption in addi- tion to the cat ionic adsorption. The nature of the equivalence of the ++ exchange between the amine and Sr was independent of the type of clay mineral. The same results were observed for both montmorillonite and illite. The equivalence of the amine adsorption and the counter ion elution indicates that the adsorption of these amines was primarily ex- change adsorption. In order to determine the relative selectivity of the clay minerals for these amines with respect to Sr ions, the exchange ++ reactions between Sr and the amines were studied with both montmoril- lonite and illite. The results are summarized in Figs. 32 through 36. In Figs. 32 and 33 the exchange adsorption of methylamine and dodecyl- amine on montmorillonite and illite are presented. The amounts of the adsorbed amines are plotted as a function of total amine concentration in the presence of various counter ions. In Fig. 32, line "a" represents 118 (a) Methylamine, (b) Dodecylamine , (c) Arginine i o 3 o x: o o + + J — I.I— H I . I —^ — — — — — ^— — ^ ^ —■■■ ■ ■— . .M b— x i a v ^^ /^ \ — c Adsorbed Organic Cations, I0~ 4 N FIG. 31 Sr ++ LEACHING FROM Sr-CLAY BY ORGANIC CATIONS. 119 Organic Cations „ ++ Sr Other Clay Minerals, N a, Dodecylaroine lxlO~ 3 Sr-Mont . =7 . 9x10 b, Methyl amine c, Methylamine lxl0~ 4 d. Methylaroine lxlO" 3 e, Arginine 2xl0~ 4 f, Arginine 2xl0" 4 ++ —4 Mg =4x10 g, Arginine -4 4x10 Na + =lxl0~ 2 Na-Mont . =5 . 0x1 o" 4 I O o o d> -Q >_ o to < 500 200 100 Concentration Of Organic Cation Added, I0" 4 N FIG. 32 ADSORPTION OF ORGANIC CATION ON MONTMORILLONITE. 120 Organic Cations Sr Other Clay Minerals a, b, c, Arginine Arginine Methylamine Methylamine 2xl0~ 4 lxio" -4 5xl0" 5 -4 5x10 Na + =lxl0~ 2 ++ -4 M g^ =4x10 * -4 Na-Illite=8.5xl0 Sr-Illite=3 . 5xl0 -4 Sr-Illite=2 . 0x1 o" 4 Sr-Illite-2 . Oxio" 4 I O c o •o -Q k- O v - ^-b -^nr >C - ^S^ ^ — c - ^x""^ \- d 1 i i i i i i i i i 20 50 Concentration Of Organic Cation Added, I0" 4 N FIG. 33 ADSORPTION OF ORGANIC CATION ON ILLITE. 121 -& — Na-Illite -o— Na-Montmorillonite 20 10 to X 2 ro I O - - t - k/L A 1 1 1 1 1 1 \ 1 20 50 m No m , 10' CH 3 NH 3 FIG. 34 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Na + , METHYLAMINE , AND CLAY MINERALS. 122 a b c Organic Cation methylaroine methyl amine arginine Clay Minerals Sr-Mont. Sr-Illite Sr-Mont . o to CM IE 300 200 100 50 20 10 - a — \ n/ A - > ^^b - c — . i 1 1 1 I II " 1 1 1 1 1 1 1 10 20 50 100 200 m Sr 2 ' (m R t) FIG. 35 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Sr t+ , ORGANIC CATIONS, AND CLAY MINERALS. 123 O CO IE CJ 1000 500 200 100 50 X 2 if) CM X 10 20 50 100 200 500 1000 m Sr ( m C l2 H 25 NH+) 2 10' FIG. 36 EQUILIBRIUM DISTRIBUTION OF COUNTER IONS IN A SYSTEM WITH Sr ++ , DODECYLAMINE , AND MONTMORILLONITE. 124 complete adsorption of dodecylamine. All others represent about 10 to 50% of the organic adsorptions. Complete adsorption was not attained for arginine or methylamine on either the montmorillonite or the illite. The adsorption data of methylamine and dodecylamine were also analyzed in terms of ion-exchange equilibrium reactions between the organic cations and the inorganic cations The results of the exchange reactions between methylamine and Na are shown in Fig.. 34, in which the ratios of the counter ion concentrations in the exchanger phase are plotted as a func- tion of the ratios in the solution phase. Similarly the results of the exchange reactions between Sr and the organic cations are shown in Figs. 35 and 36 „ The ratio of the ordinate to abscissa values is the mass-action equilibrium constant without the activity corrections. Comparing Figs. 34, 35, and 36, with those of Section 4,4 (Fig. 5 through Fig. 12), it is evident that for the counter ion pairs involving the organic cations , the mass-action equilibrium expression is not satisfactory for describing the ion-exchange reactions. The value of the mass-action equilibrium constants depended on the experimental con- ditions. The equilibrium constants computed from the data shown in Figs. 34s, 35 9 and 36 are summarized in Table 14. As shown in Table 14, for both methylamine and dodecylamine, the selectivity of clay minerals for the organic cations decreased as more of the organic cations were adsorbed on the clay minerals, which indicates that the affinity for organic cations decreases as more of the organic cations occupy the ex- change sites. A similar phenomenon has been observed in the exchange reactions involving hydrogen ions (Section 4.3). As shown in Table 14, the selectivity of clay minerals was much higher for a large organic 125 0) fc ^ CD rt rQ O 2 XI j- zf in in in UD bO E co CO CO CO CO CO •H 3 tM iS CO is o t—i 6-1 < H C_> 1 1 1 H O 1 CM O CM CM CM CD J- 1 1 o Pi O O H O H O O O O O l-H < H rH X H X H rH rH H H is O X X in x 3- X X X in X X < i*i m co in CO rH Zt" CD O c CN Pi cm in cm in CO 00 H J" r-- h r> in o Q is < CN H o H H in 10 m in d- m d- ! M rt) H H S y— N y— V X X cm 53 M s w M CD .3- <0 Ds d" ■p I 3- -P d" " d- j- J- H ■P 1 •H O ■P 1 •H 1 ■p 1 ■p 1 rH H >, c H H C O H O c c m f0 O H H X O H rH rH O H O H W H s X M C- S X M X S X S X iJ w O 1 1 O 1 in 1 1 a> 1 CT> m CD rd • (ti fc u ^ ^ < is < SG O w w is is m !S rH co c-» CO CN co r> CO C^ 1 K A J=-~S. m co CO CO O H CD + 1 1 I 1 CO H bD Pi 0) m 0) 0) a> C X Pi C °H w C 1 C H C H G H rH •H J" O to C °H O •H X •H X •H X X e i Cn fc «o a £ H e * 6 co 6 rH CO iH rrj J- bO O cd X rd ! a) 1 ffl i C 1 H i CO c fc »H H in H ID rH J" H zi- •H J" >-. O H O 4-> >> 1 >> 1 >1 1 >> 1 C 1 O H is •H rC & m x: X! x: •H O O X < ■P O -P 8 -P H ■P rH +J H W) rH t3 O H (0 CD O CD X CD X j- M a *~ \ 1 « +• 1 PQ (0 ; rH 1 i-l •H < CO co X 1 ■J a w 1 l in 1 M rd 1 1 ns bO C H rH J- O" fc O X X 1 w O *H £ -P CN 1 3- l CM 1 rH 1 co 1 M (T) CO +■ CO + X -J- O 4- O O +- i +- rH +- 1 4- O + rH + -H rd rd x U O U U X U X 53 H g; m c/> H CO H CO CN CO .H 126 cation, which probably resulted from the fact that in the case of a large organic cation the Van der Waals forces are also involved in addition to the coulombic force. The selectivity of clay minerals for dodecylamine is so strong that the adsorption is practically irreversible, as it was also in the case of methylene blue. In order to examine the effects of the adsorbed organic cations on the selective properties of the available exchange sites, ion-exchange ++ ++ ++ + reactions between the counter ion pairs Sr -Ca and Sr -Na were per- formed with clay minerals whose exchange sites were partially covered with organic cations „ The results are shown in Figs. 37, 38, 39, and 40 „ In Figo 37, the results of the exchange reactions between Sr and Ca with montmorillonite whose exchange sites are partially covered with methyl- amine (0-22%) are presented. In Figs, 38, 39, and 40, the results of the exchange reactions between the counter ion pairs Sr -Ca , Sr -Mg , and Sr -Na in equilibrium with montmorillonite, whose exchange sites are partially covered with dodecylamine, are presented,, As shown in Figo 37, for methylamine adsorption , no significant effects on the equi- librium constants were observed „ On the other hand, in the case of dodecylamine adsorption, the equilibrium constants increased as more of the exchange sites were covered by dodecylamine. The effects of dodecyl- amine are greater for the counter ion pair whose equilibrium constant is further from unity ; that is the effects are much higher for Sr -Na than ++ ++ for Sr -Ca „ This is probably due to the fact that in the case of the ++ ++ counter ion pair Sr -Ca , the chemical and physical properties of these ions are so similar that the effects of the organic may have been about the same. In the case of Sr -Na pair, however, the effects are much higher due to the differences in their properties. (a) Kd sr ; (b) Kd Ca ; (c) Ko^ nig r =6xl0" ; m£ a =5xlcT 4 ; Ca-Mont .=8. 0xl0~ 4 N 127 o o C D CO o o CO o Percent Exchange Sites Covered By Methylamine FIG. 37 EFFECTS OF ADSORBED METHYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Ca ++ . 128 ■»- XL (a) Kd sr ; (b) Kd ca ; (o) Ko SrCa ro° r =lxl0 -4 ; ro° =lxlO -3 ; Sr-Mont.=7.9xlO _4 N I.O 1.4 /— c 1.2 ( / >— — o- — — " . -0 .1 /____ . — _ 1.0 0.8 0.6 0.4 0.2 1.4 1.2 1.0 / — Q 10 20 30 40 50 60 Percent Exchange Sites Covered By Dodecylamine o O k. C/> o FIG. 38 EFFECTS OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr* + AND Ca ++ . 129 +■ ■o (a) ko = Kdsr = 1*=±1 . ( b ) ko = t. b -l) {a) K °SrMg Kd Mg (a-2) ' (b) K °SrMg (b-2) 1.6 Mg ++ ++ Sr Sr-Mont., N a b lxlO" 3 lxlO" 3 -4 2x10 4x1 0~ 4 7.3xl0" 4 7.3xl0" 4 1.4 bt*' . -o— J± -0 0.8 0.6 0.4 0.2 1.6 1.2 1.0 : " f " — '*'" X~ (a " -1) > r ^-(b-i ) s- (a- -2) • ^-(b -2) CO o 10 20 30 40 50 60 Percent Exchange Sites Covered By Dodecylamine FIG. 39 EFFECTS OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Mg ++ 130 (1) Ko_ ._ for a; * SrNa (2) Ko KT for b * SrNa Na + Sr Na-Mont . , N a, b, lxl(T 2 lxl0~ 2 -4 2x10 * 4x1 0" 4 Na-Mont . =7 . 4x1 O -4 Na-Mont . =7 . 4x1 0~ 4 1000 CM b CV) b CM ■o 20 10 0,000 5000 2000 o O 1000 N. ^s. s — a 200 100 50 20 10 20 40 60 80 100 Percent Exchange Sites Covered By Dodecylamine FIG. 40 EFFECT OF ADSORBED DODECYLAMINE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na 1 " 131 5 2o3o Adsorption of Arglnine and Effects on the Clay Ion-Exchange Properties The adsorption of polycationic organic compounds and its probable effects on soil ion-exchange properties were discussed in Sec- tion 2o6o2o2 Arginine, which is accepted as a naturally occurring amino (43) acid s was used to study adsorption on clay minerals and its effects on the ion-exchange properties of clay minerals „ The experiments were performed in a similar manner to those for the amine compounds,, The equivalence of the arginine adsorption and Sr elution from Sr-clay minerals are shown in Fig„ 31, and the adsorption of arginine on montmorillonite and illite is shown in Fig 32 and Fig„ 33, respectively c The selectivities of montmorillonite for arginine with respect to Sr ions are shown in Fig 35 (curve c) and in Table 14, The effects of the adsorbed arginine on the soil ion-exchange properties were ++ ++ examined from the exchange reactions between the cation pairs Sr -Ca , ++ ++ ++ + . . . _ „ . Sr -Mg 9 and Sr ~Na in equilibrium with the clay minerals whose ex- change sites were partially covered with arginine „ The results are summarized in Figs 41, 42, and 43 „ As shown in Figs 41 and 42, the effects were similar to those of methyiamine and dodecylamine<> The degree of the effects was much lower than with dodecylamine and slightly higher than with methyiamine „ The effect of arginine was about the same for both montmorillonite (Figo 42) and illite (Fig 43), which indicates that the change in the expanding properties of the clay minerals are not involved in these effects o The effect of arginine was probably due to the same mechanism involved in the effect of the amine compounds „ It is uncertain whether (a) Kd SR ; (b) Kd Mg ; (c) Ko SrMg m° =2x1 0~ 4 ; m° =4x1 0~ 4 ; Sr-Mont.=7 .9xlO" 4 N Sr Mg 132 1.6 r c f— o _ — — - -0 1 2f k^^ ° A a 1.0 / "v^O *: o.8 ^— b O^v 0.6 0.4 0.2 1.4 .2 CO o 12 16 20 24 28 Percent Exchange Sites Covered By Arginine FIG. 41 EFFECTS OF ADSORBED ARGININE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Mg ++ . (a) K<3 Sr; (b) (Kd Na )< ; (c) Ko SrNa m° =4x1 0" 4 ; m° =1x1 0" 2 ; Na-Mont .=5 . 0xl0" 4 N sr Na 133 CO ■o ■o c o I O ro O CO o Percent Exchange Covered By Arginine FIG. 42 EFFECTS OF ADSORBED ARGININE ON DISTRIBUTION OF COUNTER IONS, Sr ++ AND Na + WITH MONTMORILLONITE. (a) Kd sr ; (b) (Kd Na )'; (c) Ko^ nig r =2xl0" 4 ; ro° a =10~ 2 ; Na-Illite=5 .7xl0~ 4 134 T3 C o 10 l O CM ro O o Z L_