THE SEPARATION OF COLUMBXUM AND TANTALUM FROM FER- GUSONITE BY EMIL CHARLES NEMITZ THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CHEMICAL ENGINEERING COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1922 \ N 34 UNIVERSITY OF ILLINOIS Ma£_25j i 92 J3^_ THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Emil 0. Nemitz ENTITLED— _SEPARAT 1 ON _ 0F_ _0 OLUMBIUM _ MD_ TAN TALUM FERGUS ONI TE . IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE degree of _ _of _ jsnianoe _ Instructor in Charge Approved Jl __ HEAD OF DEPARTMENT OF Digitized by the Internet Archive in 2015 https://archive.org/details/separationofcoluOOnemi TABLE OF CONTENTS Page . I, Introduction 1 II. Chemical Characteristics of the Rare Elements in the Ore 2 III. Methods for Opening the Ore 6 IV. Experimental Part 10 V. Data 14 VI. Discussion of Results 16 VII. References 17 ACKNOWLEDGMENT . The author wishes to thank Dr. Rosalie M. Parr, under whose direction this work was carried out, for her helpful suggestions and encouragement. E. C. N. 1 . THE SEPARATION OF COLUMBIUM AND TANTALUM FROM FERGUSONITE. I . INTRODUCTION . Columbium and tantalum are always associated with each other in nature. They usually occur as oxides. In ferguson- ite, the columbium and tantalum oxides are found in combina- tion with various rare earth oxides. The general formula Is usually written H** (Cb,Ta)0 4 , in which R stands for a metal of the rare earth series, yttrium, erbium, and cerium are the ones generally found. Fergusonite is found in various parts of the globe. There are deposits in South Norway, Australia, Ceylon, Mada- gascar, and several parts of the United States. It is al- most always found on or between large flakes of biotite. The freshly mined mineral has a velvet black color, and is very shiny. After heating the color changes to olive green. The mineral used in connection with this work came from Norway. The first work done on the mineral was the removal of the rare earths. The ground ore was treated with concen- trated hydrochloric acid, and heated on a steam bath for 24 hours. From time to time concentrated nitric acid was added. At the end of 24 hours, the mass was evaporated, and then heated to 150°C to decompose the silicic acid. The rare earths were extracted with water, and the residuum was used for the following work. , ■ • 2 . II. CHEMICAL CHARACTERISTICS OF THE RARE ELEMENTS IN THE ORE. COLUMBIUM . Metallic columbium has a light gray color and a bril- liant luster. It is as hard as wrought iron, and is mallea- ble and ductile. When heated in the air, it slowly oxidizes to Cb^O^ • The metal is insoluble in hydrochloric, nitric, or sulphuric acid, but is attacked by hydrofluoric acid and by fused alkalies at a red heat. Columbium forms three oxides, CbgCX, , GbgO^ , and CbgOg, the latter being an acid anhydride. CbgOg is a white amor- phous powder which is infusible, and becomes cryatalline when strongly heated. It is insoluble in the mineral acids, ex- cept concentrated sulphuric acid, in which it is very slight- ly soluble, and hydrofluoric acid in which it very readily dissolves. If treated with concentrated hydrochloric acid, it does not dissolve, but the residue is soluble in water. By fusion with an excess of potassium hydroxide or potassium carbonate, the potassium hexacolumbate (K^Cb^O^) ls obtained. This compound is soluble in water. If a mineral acid is add- ed to the solution of potassium hexacolumbate, and it is boiled, columbic acid (HgCb^O^g) is precipitated. Tartaric acid prevents this precipitation. Columbic acid is a white amorphous powder, slightly soluble in hot concentrated sul- phuric acid, and very easily soluble in hydrofluoric acid. ' 3 . If potassium fluoride is added to the hydrofluoric acid solu- tion, potassium f luocolumbate (KgCbF^ ) is formed which is sol- uble in 12.5 partB of water. If a little free hydrofluoric acid is present, the oxyfluoride (K GbOF ) is formed, which is & O still more soluble. Zinc added to a solution of the hexacol- * umbate produces a fine blue color. The presence of a little hydrofluoric acid prevents this reaction. With potassium fer- rocyanide a green precipitate is obtained. TANTALUM. Metallic tantalum is silver white in color, and as hard as the best steels. It can be rolled, hammered, and drawn in- to fine wire. Its melting point is about 2250°C. It is not attacked by aqua regia nor by any single acid except hydro- fluoric acid. It is also attacked by fused alkalies. The properties of the compounds of tantalum are very much the same as those of columbium. Tantalum forms the two oxides TagO^ and TagO^, which react the same as Cbg 04 and CbgOg. The tantalates are also similar to the columbates, except that alkali tantalates are precipitated by a current of COg^ - while the columbates are not. Tantalic acid is sol- uble in hydrofluoric acid. If however potassium fluoride is added, colorless crystals of potassium f luotantalate (KgTaFr, ) are precipitated, whion are soluble in about 200 parts of wa- ter. If the solution of the double fluoride is boiled, a very insoluble oxyfluoride is precipitated as a white powder. Zinc added to a solution of the hexatantalate produces no col- . ■ > 4. or. With potassium ferrocyanide a yellow precipitate is formed. TITANIUM. The metal has a brilliant white color, and is very brit- tle and hard. When heated in the air, it unites with oxygen to form TiOg. Metallic titanium is soluble in hydrochloric, nitric, sulphuric, hydrofluoric, and acetic acids. Its melting point is 1794°C. The dioxide is a white amorphous powder, insoluble in insoluble in water, hydrochloric or nitric acid, and is dif- ficultly soluble in sulphuric acid. It is rendered soluble by fusion with a bisulphate. If an alkali is added to a hydrochloric acid solution of a titanium salt, orthotitanic acid is precipitated, which is readily soluble in dilute acids. On long standing, it gradually changes to the metatitanic acid (ELTiO„), which up- on ignition is converted to the dioxide. Fusion of the dioxide with sodium carbonate produces the three soluble titanates, Na 2 Ti 2 0 5 , Na 2 Ti 3 0 7 , and Na^TigOg. Hydrogen peroxide reacts with the sulphuric acid solution of the dioxide to form the trioxide (Ti0 3 ), which gives an in- tense orange-brown color to the solution. When metatitanic acid is treated with hydrofluoric a- cid, the f luotitanate (H 0 TiF. ) is formed, which is not vol- <3 o atilized like SiOg by evaporation of the hydrofluoric acid solution in the presence of sulphuric acid. It is volatile however if the sulphuric acid is omitted. By the addition ■ 5 of potassium fluoride to HgTiFg, KgTiFg is formed which is soluble in 96 parts of water. GERMANIUM . Germanium is a grayish-white metal with a fine luster. It is soluble in sulphuric acid, nitric acid, and aqua regia, but not in hydrochloric acid. The compounds are found in two forms of oxidation, the higher form being the more stable. Germanium resembles tin in the formation of two sulphides, GeS, and GeSg, both of which are soluble in yellow ammonium sulphide. GeSg is a whits powder slightly soluble in water, but insoluble in concentrated hydrochloric acid. GeS is red- dish-brown and is slightly soluble in water. The tetra-chloride is a liquid which fumes in damp air. Its boiling point is 86°C. It decomposes in water, and forms the dioxide, a white difficultly fusible powder, which is sol uble in both acids and alkalies. If the dioxide is dissolved in hydrofluoric acid, and potassium ohloride added, gelati- nous K 0 GeF is precipitated. d 6 . . 6 . III. METHODS FOR OPENING THE ORE. In the literature the following methods for opening the ore are mentioned. 1. Fusion with potassium acid fluoride. 2. Fusion with potassium hydroxide. 3. Fusion with fused potassium acid sulphate. 4. Fusion with potassium carbonate. 5. Fusion with potassium carbonate and borax. 6 . Fusion with sodium carbonate . 7. Fusion with sodium peroxide. 8. Treat mineral with finely ground carbon in an elec- tric furnace. 9. Treat mineral with dry chlorine at a red heat. POTASSIUM ACID FLUORIDE FUSION.'^ * The mineral Is fused with three parts of potassium fluo- ride, and the melt pulverized and dissolved in hot water. Dil- ute hydrochloric acid is added to precipitate the columbic and tantalic acids. The acids are thoroughly washed with water, dissolved in hydrofluoric acid, and potassium carbonate add- ed until a precipitate is formed. The tantalum precipitates as the potassium f luotantalate, and the coiumbium as the oxy- f luoride . POTASSIUM HYDROXIDE FUSION. This fusion is recommended by Simpson 3 for high-grade > . ■ . 7 coiumbiura and tantalum minerals that are substantially free from titanium. The finely ground mineral is fused with six times its weight of potassium hydroxide in a nickel or sil- ver crucible. The crucible snould be supported in a perfor- ated piece of asbestos board, so that only the lower part of the crucible is heated. In this way creeping is prevented. The heat is applied slowly at first, and gradually increased to a dull red heat. It is kept at this temperature for one half hour or more. The soluble part of the fused mass is then dissolved in water, and filtered from the insoluble part. A mineral acid is then added, and the solution boiled for 20 minutes to precipitate the earth acids. The probable impu- rities are tin, tungsten, silica, and titanium. The tin ana tungsten are removed by digesting the precipitate with yellow ammonium sulphide. The silica is volatilized with hydrofluoric acid and sulphuric acid. The titanium may be removed by either fusing with potassium acid sulphate, or by treating the mixed acids with ammonium sali- 4 cyiate. The bisulphate fusion for the removal of titanium is in all respects the same as the bisulphate fusion for the opening of an ore. The best separation is with ammonium sa- licylate. The mixed acids are treated witn an excess of am- monium salicylate, refluxed for three or four hours, and fil- tered hot. The titanium salicylate is soluble and is there- fore found in the filtrate, while the columbium and tantalum salicylates are insoluble. POTASSIUM ACID SULPHATE FUSION. 5 * The finely powdered mineral is mixed with 6-10 times its 8 . weight of fused potassium acid sulphate. It is gently heated at first, and then submitted to a strong heat until no dark particles of undecomposed mineral are visible. The melt is then extracted with a large quantity of boiling water con- taining a little dilute hydrochloric acid. The impurities are removed by the same method as in the potassium hydroxide fusion. The bisulphate method is usually used on the lower grade ores or those high in titanium. The results obtained by this method are a little low, because it is impossible to precipitate the earth acids completely. The decomposition also is very slow, often taking more than five hours, while many finely powdered minerals are decomposed by fusing one half hour with potassium hydroxide. FUSION WITH POTASSIUM CARBONATE AND FUSION WITH POTASSIUM CARBONATE AND BORAX. These fusions are in ail respects the same as the po- tassium hydroxide, but they are not as convenient, because the carbonate is much less fusible than the hydroxide. FUSIONS WITH SODIUM CARBONATE AND SODIUM PEROXIDE. Fusion with sodium carbonate is not as satisfactory as with potassium carbonate, because of the greater solubility of the potassium salts of the earth acids. The fusion witn sodium peroxide is a very rapid method. ■ . 9 . SPECIAL TREATMENT FOR IMPURITIES. On account of the difficulties encountered in purifying the earth acids, Schoeller and Powell 6 recommend the removal of as many impurities as possible before precipitating the earth acids. Therefore instead of leaching the fused mass with wa- ter, they suggest using a concentrated solution of tartaric acid in water. Tartaric acid prevents the precipitation of the earth acids by the addition of ammonia, ammonium sulphide, or by boiling. After the fused mass has been leached, the filtrate is saturated with hydrogen sulphide which removes tin, antimony, and any other second group metals that may be present. The precipitate is filtered off, and the filtrate digested with ammonia and ammonium sulphide. This removes the iron, uranium, and some of the manganese, if manganese is present. The operation so far eliminates such troublesome impu- rities as iron, silica, tin, and antimony, while the oolumbiura and tantalum are still in solution. A method for removing the titanium before preoipitation has not yet been found. . 10 IV. EXPERIMENTAL PART. POTASSIUM HYDROXIDE FUSION. The raw material obtained by treating fergusonite with aqua regia, and leaohing out the rare earths with water, oon- tained a large amount of moisture, and had to be dried at 104° to 110°C for one hour before the fusion oould be made. The potassium hydroxide was first placed in a large fire-clay cru- cible and gently heated in a gas furnace . When it was in a state of quiet fusion, the finely ground residuum was added, and the temperature gradually increased until a dull red heat was obtained. It was kept at this temperature for one and one half hours, and then poured into an iron mold. The melt had a color very similar to the green ferrous salts, and was very hygroscopic. After remaining in contact with the air for a while, the color turned brown. This was probably due to the oxidation of the ferrous salts to ferric salts. The soluble part of the melt was extracted with a large quantity of water, and the insoluble portion filtered off. The earth acids were precipitated by the addition of sulphuric a- cid, and then boiling the solution for 20 minutes. Should the solution be made too acid, the precipitate would be very fine- ly divided, and very hard to filter. By neutralizing most of the excess acid with ammonia, and by boiling, this inconven- ience can be avoided. REMOVAL OF TITANIUM. After titanium was found to be present, it was decided ' . . - 11 . that the ammonium salicylate method be used to remove it. The mixed acids were treated with concentrated nitric acid, and a neutral solution of ammonium salicylate added. A large excess of this reagent should be used. A curdy mass, light yellow in color was formed. This was then refluxed with a large quanti- ty of water for four hours, and filtered hot. The titanium formed a compound which was soluble in hot water, while the columbium and tantalum compounds were not soluble in hot water. TREATMENT OF RESIDUUM FOR GERMANIUM. The original material (f ergusonite ) had germanium pre- sent, and because of the value of this element, it was deci- ded to attempt to extract it from the residuum before treat- ing it for columbium and tantalum, xhe simplest way of ob- taining the germanium seemed to be by the distillation of the tetra-chloride in an atmosphere of chlorine. At first a dry method was tried. The raw material was placed in a hard glass combustion tube, which was placed in a combustion furnace and heated to a temperature of 150°C. During the heating, a slow current of chlorine was passed thru the tube. The distillate was caught in water, where the germanium tetra-chloride would be hydrolized, and germanium dioxide would be precipitated. However no precipitate formed. It was then decided to try a wet method that was used in the extraction of germanium from zinc residues. The material was treated with concentrated hydrochloric acid, and the hydro- chloric acid distilled in an atmosphere of chlorine. The ger- manium would be converted to the tetra-chloride, which would 12 distill over with the hydrochloric acid. The apparatus consisted of a one liter round-bottom Py- rex distilling flask supported on an asbestos collar 10 cm. high, which rested on a piece of transits. A 2-hole rubber stopper was placed in the neck of the flask, the one opening for a separatory funnel to introduce the hydrochloric acid, the second opening for a glass tube extending nearly to the bottom of the flask, thru which the chlorine was introduced. A Liebig condenser was attached to the arm of the distilling flask. A bent glass tube was attached to the farther end of the condenser. This tube reached nearly to the bottom of a half liter bottle partly filled with water, which served as a receiver. The receiver was surrounded with cracked ice. The heat was applied with a large Meker burner. The distil- lation was continued until nearly all of the hydrochloric a- oid was distilled over, but no preoipitate formed in the re- ceiver. Failure to find any germanium seemed to indicate that the germanium was lost when the fergusonite was treated with aqua regia and then heated to 150°C to decompose the silicic acid. EXTRACTION OF COLUMBIUM AND TANTALUM. After the material had been treated with concentrated hydrochloric acid, it was possible to dissolve out the oolum- bium and tantalum with water, and a fusion of the residue was not necessary. To precipitate the columbium and tantalum, it was only necessary to boil the solution. When obtained by this ■ ' 13 . method, the columbium and tantalum are free from silica, but contain a great deal of iron and titanium. It was attempted to remove the iron by washing with dilute hydrochloric acid, but it was not possible to get rid of the traces by this meth- od. PYROSULPHATE FUSION. The residuum was fused with six times its weight of fused sodium acid sulphate in a large fire-clay crucible. The heat was applied gently at first, and gradually increased to a dull red heat, and kept at that temperature for two hours. The melt had a light yellow color. At this point however, instead of extracting the columbium and tantalum with water, a tartaric acid solution was used, and the procedure outlined by Schoeller and Powell was followed. In this way all of the impurities except titanium were removed. ' " 14 V. DATA. MOISTURE CONTENT. Weight of moist residuum Weight of residuum after drying Weight of moisture driven off POTASSIUM HYDROXIDE FUSION. Weight of dried residuum Weight of potassium hydroxide Weight of impure mixed acids REMOVAL OF TITANIUM WITH AMMONIUM SALICYLATE. Weight of mixed acids Weight of salioylio acid Weight of mixed acids remaining Apparent weight of TiOg PYROSULPHATE FUSION. Weight of mineral used Weight of sodium pyrosulphate used Weight of mixed acids obtained 110 gr. 95 gr. 15 gr. 95 gr. 550 gr. 80 gr. 42 gr. 25 gr. 38.5 gr. 1.5 gr. 100 gr, 600 gr. 12 gr. ■ 15 TREATMENT OF MINERAL WITH HOI AND Clg. I II Weight of mineral used 250.0 gr. 250.0 gr. volume of HC1 added 300.0 cc. 300.0 cc. Weight of GeOg obtained — _ Weight of impure mixed aside. 75.1 gr. 83.7 gr. . ■_ 16 DISCUSSION OF RESULTS. In the potassium hydroxide fusion, the weight of the mixed oxides was high due to the silica present. This fu- sion was made in a fire-clay crucible, so the amount of si- lica dissolved by the potassium hydroxide was very high. By using a graphite crucible, however, this oould be avoided. By this method no iron was present in the mixed acids. By using concentrated hydrochloric acid, the mixed a- cids obtained were free from silica, but contained a great deal of iron which could not be completely washed out with dilute hydrochloric acid. This method is a very good one, if the mineral contains germanium, and by using tartaric a- oid to dissolve the columbium and tantalum instead of water, and removing the impurities according to Schoeller and Po- well’s method, this difficulty of removing the iron could be overcome. In the pyrosulphate fusion, all of the impurities, ex- cept titanium, were removed according to Schoeller and Powell’s method before the acids were precipitated. The weight of the mixed acids, however, was low, because it was impossible to precipitate the acids completely after tartaric acid was used. The solution in this case would have to be evaporated and the tartaric acid ignited. ■ . 17 . VII. REFERENCES . 1*. Weiss and Landecker. Zeit. Anorg. Chem. 64, 65. (1909). 2. Browning’s Introduction to the Rarer Elements. Page 119. 3. Simpson. Chem. News. 99 , 243. (1909). 4. Dittrich and jfreund. Zeit. Anorg. Chem. 56 , 344. (1908). 5. Schoeller and Powell’s Analysis of Minerals and Ores of the Rare Elements. Page 139. 6. Schoeller and Powell. J.C.S. 119 , 1927. (1921). 7. Dennish and Papish. J.A.C.S. 43, 2131. (1921).