i IM.J.S STATE OF ILLINOIS HENRY HORNER. Governor DEPARTMENT OF REGISTRATION AND EDUCATION JOHN J. HALLIHAN, Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA REPORT OF INVESTIGATIONS— NO. 48 WASHABILITY CHARACTERISTICS OF ILLINOIS COAL SCREENINGS BY D. R. MITCHELL AND L. C. McCABE IN Cooperation with the Engineering Experiment Station, UNIVERSITY OF ILLINOIS PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1937 ILUffJl. ^ ATE GtOLUGICAL SUaVEY LlBRAaY STATE OF ILLINOIS Hon. Henry Horner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Hon. John J. Hallihan, Director Springfield BOARD OF NATURAL RESOURCES AND CONSERVATION Hon. John J. Hallihan, Chairman Edson S. Bastin, Ph.D., Geology William A. Noyes, Ph.D., LL.D., Chem.D., D.Sc, Chemistry Louis R. Howson, C.E., Engineering William Trelease, D.Sc, LL.D., Biology Henry C. Cowles, Ph.D., D.Sc, Forestry Arthur Cutts Willard, D.Engr., LL.D., President of the University of Illinois STATE GEOLOGICAL SUEVEY DIVISION Urdana M. M. Leighton, Ph.D., Chief Enid Townley, M.S., Assistant to the Chief Jane Titcomb, M.A., Geological Assistant GEOLOGICAL RESOURCES Coal G. H. Cady, Ph.D., Senior Geologist L. C. McCaue, Ph.D. James M. Schopf, Ph.D. Earle F. Taylor, M.S. Charles C. Boley, B.S. Non-Fuels J. E. Lamar, B.S. H. B. Willman, Ph.D. Robert M. Grogan, M.S. H. C. Heilbronner, B.S. Oil and Gas A. H. Bell, Ph.D. Chalmer L. Cooper, M.S. G. V. CoHEE, Ph.D. Frederick Squires, B.S. Charles W. Carter, M.S. James L. Carlton, B.S. Areal and E7igineering Geology George E. Ekblavv, Ph.D. Richard F. Fisher, B.A. Subsurface Geology L. E. Workman, M.S. J. Norman Payne, Ph.D. Elwood Atherton, Ph.D. Gordon Prescott, B.S. Stratigraphy and Paleontology J. Marvin Weller, Ph.D. {on leave) Petrography Ralph E. Grim, Ph.D. Physics R. J. PlERSOL, Ph.D. M. C. Watson, Ph.D. Donald O. Holland, M.S. GEOCHEMISTRY Frank H. Reed, Ph.D., Chief Chemist W. F. Bradley, Ph.D. G. C. Finger, M.S. Mary C. Neill, M.S. Fuels G. R. YoHE, Ph.D. Carl Harman, B.S. Non-Fuels J. S. Machin, Ph.D. F. V. TooLEY, M.S. Analytical 0. W. Rees, Ph.D. Norman H. Nachtrieij, B.S. George W. Land, B.Ed. P. W. Henline, B.S. Mathew Kalinowski, B.S. MINERAL ECONOMICS W. H. Voskuil, Ph.D., Mineral Economist Grace N. Oliver, A.B. EDUCATIONAL EXTENSION Don L. Carroll, B.S. PUBLICATIONS AND RECORDS George E. Ekblaw, Ph.D. Chalmer L. Cooper, M.S. Dorothy Rose, B.S. {on leave) Alma R. Sweeny, A.B. Meredith M. Calkins Consultants: Ceramics, Cullen Warner Parmelee, M.S., D.Sc, University of Illinois; Pleistocene Invertel)rate Paleontology, Frank Collins Baker, B.S., University of Illinois. Topographic Mapping in Cooperation with the United States Geological Survey. December 1, 1937 (46998) ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00005 6592 C .^ CONTENTS PAGE Introduction 5 Foreword 5 Purpose of investigation 7 Acknowledgements 7 Laboratory procedure 8 Zinc chloride solutions 8 Organic solutions 9 Sizing and chemical analyses 11 Interpretation of washability curves 11 Specific gravity distribution curve 12 Mine B washability curves 15 1^-inch to 48-mesh coal 15 Coal recovery and specific gravity curves 15 Sulfur curve 16 Refuse reject-ash curve 16 Ash distribution curve 16 Sized coal '. 16 The use of curves in evaluating washability 16 Coal recovery and ash 17 Ash distribution curves 17 Comparison of dust and larger coal 17 General interpretation of data from all mines 18 Summary and conclusions 19 ILLUSTRATIONS FIGUEE PAGE 1. Map of Illinois showing location of mines where screenings were sampled 6 2. Float-and-sink apparatus for large sizes 9 3. Float-and-sink apparatus for small sizes 10 4. Aspirating arrangement for float-and-sink testing 11 5. Washability curves, Mine A 64-65 6. Washability curves, Mine B 66-67 7. Washability curves, Mine C 68-69 8. Washability curves, Mine D 70-71 9. Washability curves, Mine E 72-73 10. Washability curves, Mine F 74-75 11. Washability curves. Mine G 76-77 12. Washability curves. Mine H 78-79 13. Washability curves. Mine 1 80-82 14. Washability curves. Mine J 83-84 TABLES PAGE 1. Description of mines sampled 7 2. Sizing tests of screenings 12-13 3. Proximate analyses of screenings 14 4. Difficulty of washing as affected by concentration of material 14 5. Ash and recoveries in sized coal from Mine B 17 6. Comparison of recovery, ash, and sulfur percentages at 1.50 specific gravity in 13^ -inch to 48-mesh coal 18 7. Comparison of difficulty of cleaning 1 3^-inch to 48-mesh coal at 1.50 specific gravity . 19 8. Mine B. Calculations for ±0.10 specific gravity distribution curves 20-21 9. Washability data and calculations. Mine A 22-25 10. Washability data and calculations, Mine B 26-29 11. Washability data and calculations, Mine C 30-33 12. Washability data and calculations, Mine D 34-37 13. Washability data and calculations, Mine E 38-41 14. Washability data and calculations. Mine F 42-45 15. Washability data and calculations, Mine G 46-49 16. Washability data and calculations, Mine H 50-53 17. Washability data and calculations, Mine 1 54-59 18. Washability data and calculations. Mine J 60-63 WASHABILITY CHARACTERISTICS OF ILLINOIS COAL SCREENINGS D. R. Mitchell^ and L. C. McCabe'' INTRODUCTION Foreword. — The washability characteristics, size-range, and chemical analyses of screenings from Illinois mines are matters of growing interest. Screenings that are mechanically cleaned, carefully sized, mixed, dedusted, or made dustless by treatment with oil or chemicals have an advantage over screenings receiving no special preparation. The producers of raw screenings are accordingly interested in the possibilities of improvement revealed by analytical data and the results of experimental tests on coals from the districts in which they operate. A number of reports have been published on the general subject of the washability of Illinois coal,^ none of which has treated screenings as a specific problem. In order to obtain the technical information necessary to answer the many requests received, an investigation of the screenings problem was started in 1934. This investigation was conducted as a cooperative project between the Coal Division of the Illinois State Geological Survey and the Department of Mining and Metallurgical Engineering of the University of Illinois. Ten mines distributed among the different mining districts, were sampled so that each of the commercially important coal beds as well as the different districts would be represented (table 1 and figure 1). They were all underground mines, and the data presented should be representative of screenings similarly produced from other underground mines for the particular district in which each of the samples was taken. ^ Associate Professor, Mining and Metallurgical Engineering, University of Illinois, Urbana. 2 Associate Geologist, Coal Division, Illinois State Geological Survey, Urbana. 3 Lincoln, F. C, Coal washing in Illinois: U. of I. Eng. Expt. Sta. Bull. 69, 1913. Holbrook, E. A., Dry preparation of bituminous coal at Illinois Mines : U. of I. Eng. Expt. Sta. Bull. 88, 1916. Eraser, T., and Yancey, H. F., Cleaning tests of Illinois coals : U. S. Bur. of Mines, T. P. 361, 1925. Callen, A. C, and Mitchell, D. R., Washability tests of Illinois coals: U. of I. Eng. Expt. Sta. Bull. 217, 1930. Mitchell, D. R., The possible production of low ash and sulphur coal in Illinois as shown by float-and-sink tests: U. of I. Eng. Expt. Sta. Bull. 258, 1933. McCabe, L. C, Mitchell, D. R., and Cady, G. H., Banded ingredients of No. 6 coal and their heating values as related to washability characteristics : 111. Geol. Survey, Rept. of Inv. No. 34, 1934. r5] WASHABILITY OF COAL SCREENINGS Fi&uRE 1.— Map of Illinois Showing Location of Mines Where Screenings Were Sampled. INTRODUCTION A preliminary report, "Proximate analyses and screen tests of coal mine screenings," was published by the Illinois State Geological Survey in 1935 as Eeport of Investigations No. 38. Other reports to be issued in the series will be concerned with the effect of washing and sizing on the ash fusion temperatures and the effect of sizing and washing on the distribution of the coal components. Purpose of the investigation. — This report is concerned with: (1) Float-and-sink tests made in the laboratory; (2) chemical analyses of the float-and-sink fractions; and (3) their significance in the preparation of screenings for the market. The methods used in sampling, sizing, and chemical analysis of the screenings from the ten mines are described in Eeport of Investigations No. 38 and are not repeated herein. Details of float-and-sink procedure are given. Acknowledgments. — The writers gratefully acknowledge the cooperation and assistance of the management of the mines in collecting the samples. Float-and-sink tests of sizes above % inch were made in the laboratory of the Department of Mining and Metallurgical Engineering. Table 1. — Location, Coal Beds Worked, Thickness of Beds, Mining Methods and Tonnages of Mines Sampled Mine County Coal bed number Average thickness Mining methods Daily average (Feet) (Inches) (Tons) A Henry 1 4 1 Room-and-pillar, coal shot from solid, hand loading. 450 B Woodford. . . 2 2 9 Longwall, hand mining, hand loading 425 C Peoria 5 4 2 Room-and-pillar, machine mining, hand loading. . . 3,000 D Vermilion. . . . (Grape Creek) 5 Room-and-pillar, m.achine mining, hand loading . . . 3,000 E Sangamon. . . 5 5 9 Room-and-pillar, coal shot (Springfield) from solid, hand loading. 1,500 F Christian .... 6 7 6 Room.-and-pillar, coal shot from solid, hand loading. 700 G...... St. Clair 6 7 Room-and-pillar, machine mining, machine loading 1,300 H Marion 6 6 4 Room-and-pillar, machine mining, hand loading . . . 1,700 I Williamson. . 6 10 Room-and-pillar, machine mining, mechanical load- ing 4,000 J Saline 5 5 3 Room-and-pillar, machine (Harrisburg) mining, hand loading. . . 2,000 8 WASHABILITY OF COAL SCREENINGS The project was carried on under the general supervision of Dr. G. H. Cadjj Head of the Coal Division of the Survey. L. G. Hazen and C. C. Boley^ Technical Assistants in the Coal Division, assisted in the laboratory preparation of samples and in assembling the data. Ash and sulfur de- terminations were made in the analytical laboratory of the Survey, under the supervision of Dr. F. H. Eeed, Head of the Geochemical Section, under the direction of Dr. 0. W. Eees, and with the assistance of J. W. Eobinson and C. S. Westerberg. LABORATORY PROCEDURE One-quarter of the gross sample of screenings of 1000 to 1500 pounds from each mine was sized as follows: 2 to 11/4-inch (one instance) 11/4 to %-inch (all mines) % to %-incli (all mines) % inch to 10-mesh (all mines) 10 to 48-mesh (all mines) Minus 48-mesh (all mines) (Round-hole screens were used in sizing at %-inch and above and Tyler standard sieves for sizing below %-inch). Each size was separated by heavy liquids of 1.30, 1.35, 1.40, 1.50, and 1.70 specific gravity into the following fractions: 1.30 Specific gravity float 1.30 to 1.35 1.35 to 1.40 1.40 to 1.50 1.50 to 1.70 1.70 " " sink Zinc chloride solutions. — Water solutions of zinc chloride were used in making float-and-sink tests of % to %-inch and larger coal. Galvanized iron cans for holding the solutions, a wire basket for holding the coal, dippers for removing the float, and a drainage and washing table were used as shown in figure 2. Fifty per cent zinc chloride solution (sp. gr., 1.568) is available from chemical manufacturers. From this solution the 1.70 specific gravity solution was prepared by adding granular zinc chloride; the solutions of 1.50 specific gravity and lower were made by diluting the commercial solution with water. Dry coal is not easily wet by zinc chloride solutions and pieces of slightly greater specific gravity than the solutions tend to float. Soaking the coal over night prior to float-and-sink testing restores the moisture to the ^^as mined" condition and makes wetting by zinc chloride less difficult. However, this procedure causes disintegration and loss of refuse in samples containing clay. To reduce this loss, all samples to be soaked in water were flrst quickly passed through the solution of 1.70 specific gravity and separated into a LABORATORY PROCEDURE float and a sink fraction. The float was then soaked in water overnight, drained, and then tested in the 1.30, 1.35, 1.40, 1.50 and 1.70 specific gravity zinc chloride solutions. The sink material from the 1.70 specific gravity separation of the dry coal was composed largely of shale and pyrite or mix- tures of the two. The sink from the separation of the soaked coal at the same specific gravity was largely "bony" coal and slate which do not readily disintegrate in water or heavy solutions. The two sink fractions were com- bined to make the complete sample of 1.70 sink. All other fractions separated in zinc chloride solution were washed in a water spray to remove the solution adhering to the coal, drained, and then surface dried. A small grab sample was taken of all fractions for moisture determinations and the remaining coal was ground to % inch and reduced to two pounds by riffling. This sample was sent to the laboratory for moisture, ash, and sulfur determinations. Figure 2. — Float-and-Sink Apparatus for Large Sizes Organic solutions. — Carbontetrachloride, benzene, and bromoform mix- tures were used in preparing the solutions for the specific gravity separation of sizes smaller than % inch. Bromoform (sp. gr. 2.890) was used with carbontetrachloride (sp. gr. 1.595) in preparing the solution of 1.70 specific gravity. Carbontetrachloride and benzene (sp. gr. 0.878) mixtures were used in preparing solutions of 1.30, 1.35, 1.40, and 1.50 specific gravity. 10 WASHABILITY OF COAL SCREENINGS Organic solutions will wet dry coal readily and do not cause disintegration of shale and clay. All samples were air-dried to remove surface moisture before making float-and-sink separations in organic solutions. Battery jars were convenient containers for the solutions (fig. 3). A metal can with a 60-mesh screen bottom and having a slightly smaller diameter than the battery jars, was used to hold the coal larger than 48-mesh while it was in the solutions. The float-coal was skimmed ofl with a wire- bottom dipper and the can containing the sink-coal was lifted and drained. The contents of the can were then surface dried with an electric fan before the procedure was repeated in the solution of next higher specific gravity. Fic I RE 3. — Float-and-Sink Apparatus for Small Sizes As the minus 48-mesh dust may stay in suspension for several hours the apparatus and procedure for float-and-sink testing differed from that described above. The sample was placed in the separating medium in a battery jar and allowed to stand until the solution was clear between the float and the sink fractions. The float particles w^ere then collected by means of an aspirating apparatus (fig. 4), filtered from the heavy liquid and dried. The sink was collected on filter paper, dried, and the procedure was repeated in the next higher gravity solution. Organic solutions must be kept covered to prevent a change in specific gravity because of diflerential evaporation. Frequent checking of the specific gravity of solutions with a good hydrometer or Westphal balance is necessary. INTERPRETATlOiS^ OF CURVES 11 SIZING AND CHEMICAL ANALYSES A brief summary of the size characteristics and chemical properties of the samples follows. Those interested in the detailed chemical analyses of the various sizes in the screenings are referred to Eeport of Investigations No. 38. The distribution of the various sizes in the samples is given in table 2. At all mines except 1 and ./ the impurity content of the dust^ or minus 48-mesh size^ is so high that the dust has little value. Such dust removed by dedusting methods would be very difficult to market. Figure 4. — Aspirating Arrangement for Float-and-Sink Testing Most of the samples showed an increase in ash content from the coarse to the smallest sizes. Five samples show the same trend for sulphur distri- bution. Four samples ((7, F, G, H) showed an opposite trend in that the amount of sulphur actually decreased in the small sizes. Screenings from mine E contained about the same amount of sulphur in all sizes. The as received and moisture free proximate analysis of the screenings produced at the ten mines are given in table 3. INTERPRETATION OF WASHABILITY CURVES Because of variation in moisture from one float-and-sink fraction to another, the as received ash and sulfur percentages of the different sizes are not directly comparable with each other or with the as received data of the screenings in table 3. For this reason all washability data are calculated 12 WASHABILITY OF COAL SCREENINGS to the moisture-free basis and the curves constructed therefrom. Yields and chemical analyses can easily be changed from the dry basis upon which they are given to the as received or as mined condition by making the necessary correction for the total moisture in the coal. The normal coal bed moisture as determined by averaging total moisture from several face samples is usually used for this calculation. If the coal is to be cleaned by a wet washery^ it may be necessary to make further adjustments for moisture added during washing. The tables of float-and-sink data (tables 9 to 18) contain the calculations necessary for the construction of washability curves. Methods of calculating washability data from chemical analyses and of constructing and interpreting washability curves are given by Callen and Mitchell* so that it is not necessary to present a general discussion of them here. However^ to illustrate the washability characteristics of the screenings studied in this investigation^ the curves constructed from the data obtained from the mine B screenings are discussed in some detail. Only the most significant washability characteristics of the screenings from the other mines sampled are discussed. SPECIFIC GRAVITY DISTRIBUTION CURVE^ The dzO.lO specific gravity distribution curve shows the weight per cent of material present within the range of 0.10 of a unit of specific gravity above and 0.10 of a unit of specific gravity below a stated specific gravity. Thus at 1.5 specific gravity the specific gravity distribution cur\^e, reading on the coal recovery ordinate coal, per cent, gives the weight per cent of material present betM^een 1.40 and 1.60 specific gravity. 4 Callen, A. C, and Mitchell, D. R., Washability tests of Illinois coals: Univ. Illinois Eng-. Expt. Sta., Bull. 217, 1930. 5 Bird, B. M., Interpretation of float-and-sink data, Proceedings Second International Conference on Bituminous Coal, A^ol. 2, p. 82, 1928. Proceedings of the Third Interna- tional Conference on Bituminous Coal, vol. 2, p. 722, 1931. Table 2. — Sizing (Comparison of weight per cent, and per Mine m to H in. Ash S. HtoVs in. Ash S. 3/8 in. to 10 mesh A B C D 25.0 20.3 34.7 18.8 29.5 28.3 29.0 33.0 28.6 30.7 17.2 11.0 14.3 12.6 12.8 14.2 15.5 15.4 9.8 9.7 6.1 1.7 3.5 1.9 5.2 4.7 4.7 4.7 1.7 2.8 25.5 29.4 28.8 24.1 28.6 28.7 26.5 23.5 25.6 26.0 17.7 14.3 14.6 13.6 14.1 17.0 16.9 15.5 9.9 10.2 6.2 1.8 3.3 2.0 5.5 4.8 4.7 4.9 1.9 2.7 31.8 31.0 23.5 32.2 E F G H 26.6 27.3 26.0 26.7 P J 27.0 25.4 At this mine 2-inch screenings were sampled. The 2 to li^-inch size was 22.6 per INTERPRETATION OF CURVES 13 The curve was developed to show the relative difficulty of separating coal from refuse at any selected specific gravity and is constructed to show the proportion of coal present within a narrow range both sides of any selected specific gravity. The point to be made is that separation is relatively difficult at those gravities at which relatively large percentages of material are present and relatively easy at other places. The authority cited above writes as follows in explanation : "Suppose that a raw coal could be found, three-fourths of which was composed of particles between 1.45 and 1.55 specific gravities. Obvi- ously a very sharp separation at 1.50 specific gravity would be more difficult to obtain with such a coal than in a coal of which three- fourths was less than 1.30 and more than 1.70 specific gravities." The difficulty or ease of separation is determined by the extent of con- centration of the coal material at any one narrow range of specific gravity. Table 4^ indicates the nature of the washing problem as determined by this concentration as revealed by the specific gravity distribution curve. The use of specific gravity distribution curves makes it possible to select a gravity at which washing can be done most efficiently. Furthermore, they clearly show that the possibility of efficient separation at one gravity does not assure similar efficiency at another. Elaborate discussion of the fundamentals involved in the specific gravity distribution curves and their methods of construction may be found in the publications cited to which the reader who is in search of a complete dis- cussion of this item of the washability diagram should refer. 6 Bird, B. p. 722, 1931. M., Proc. 3rd International Conference on Bituminous Coal, Vol. 2, Tests of Screenings cent of ash and sulfur on a dry basis) Ash S. 10 to 48 mesh Ash S. 48 mesh Ash S. 19.5 6.2 12.5 25.5 6.2 5.2 29.9 7.1 19.7 2.0 13.6 30.5 2.9 5.7 36.5 4.0 16.3 3.2 9.3 18.9 2.9 3.7 22.9 2.7 14.7 2.1 16.1 17.5 2.5 8.8 21.4 3.8 13.8 5.3 10.7 17.3 5.4 4.6 20.2 5.0 18.7 4.7 10.2 25.3 4.7 5.5 21.1 3.5 19.3 4.5 12.5 25.8 4.2 6.0 25.2 3.4 15.0 4.7 11.8 17.3 4.2 5.0 20.4 3.7 10.8 2.2 12.9 14.4 2.3 5.9 14.6 2.2 11.7 2.9 12.3 18.5 3.3 5.6 16.8 3.7 cent of the sample and analyzed 9.2 per cent ash and 1.5 per cent sulfur on the dry basis. 14 washability of coal screenings Table 3. — Proximate Analyses of Screenings^ Mine Condi- tion^ Moisture Ash Volatile matter Fixed carbon Sulfur B. t. u. per pound A, B C D E F, G H I. J. 14.1 11.8 13.5 13.6 13.1 12.5 9.5 9.7 8.4 5.7 16.8 19.6 17.1 19.4 14.2 16.5 12.7 14.6 12.0 13.8 15.5 17.8 16.3 18.1 14.7 16.3 9.5 10.4 11.2 11.8 35.0 40.7 30.1 34.2 34.3 39.7 32.0 37.0 35.1 40.4 33.6 38.4 35.7 39.6 35.0 38.7 32.1 35.0 32.7 34.7 34.1 39.7 41.0 46.4 38.0 43.8 41.7 48.4 39.8 45.8 38.4 43.8 38.1 42.3 40.6 45.0 50.0 54.6 50.4 53.5 5.21 6.06 1.98 2.24 2.81 3.25 1.97 2.28 4.58 5.27 15 74 14 59 12 56 1.73 1.89 2.79 2.96 9,811 11,422 10,195 11,557 10,322 11,939 10,506 12,157 10,608 12,202 10,441 11,585 10,402 11,544 10,707 11,856 11,847 12,928 12,116 12,852 2 All analyses are of l^/i- to O-inch coal 0-inch coal. 2 The form of analysis is denoted by number, as follows laboratory ; 2, moisture-free or dry coal. except that of Mine I which is of 2- to 1, sample as received at Before leaving the explanation, however, it is desirable to indicate the reason for and the method of making adjustments of percentages of recovery as shown in table 8 and as used in the construction of the specific gravity distribution curves. In any series of float-and-sink tests a certain amount of high gravity material is likely to be present Mng considerably beyond the range of specific gravity agents employed. This material consists mainly of rock and shale from the roof and floor which would be eliminated in the most crude separation processes. The cleaning problems obviously concerns that part of the product of the mines that is not so obviously non-coal material. If this rock material is not eliminated from consideration, inter- Table 4. — Difficulty of Washing as Affected by Concentration of Material Per cent of coal present (±0.10 curve) Degree of difficulty 0—7 7—10 10 — 15 15 — 20 Above 25 Simple Moderately difficult Difficult Very difficult Formidable INTERPRETATION OF CURVES 15 pretation of the float-aiid-sink data becomes unreliable, as Bird^ has pointed out. The selection of a specific gravity of 2.00 as the point of separation of the mineral and rock materials is more or less arbitrary but is determined mainly ^^because it is as high as existing specific gravity curves can be extrapo- lated with any degree of accuracy.^^^ Calculations for the specific gravity distribution curves of coal B are given in table 8. MINE B WASHABILITY CURVES The washability curves for the mine B screenings (fig. 6) may be used, with some additional discussion of characteristics peculiar to individual mines, to illustrate the washability of the screenings selected for this investigation. In the study of the washability characteristics of screenings, the minus 48-mesh dust was excluded from consideration because in practice it is recog- nized that removal of dust before washing facilitates water clarification and permits more rapid dewatering of the larger coal. The dusts are little improved by washing and they may interfere with the effective washing of larger sizes. When the dust is not removed by screening or dedusting before washing, it is commonly lost in the sludge. 114-INCH TO 48-MESH COAL Coal Recovery and Specific Gravity Curves. — The ash content (moisture- free basis) of mine B 114-inch to 48-mesh screenings is 16.26 per cent (table 10). It is to the advantage of both producer and consumer to reduce the ash content of this coal before it reaches the market if it is economically feasible to do so. Assuming that it is desired to reduce the ash in the screen- ings to 5 per cent (moisture-free basis) the use of washability curves in determining the practicability of such an improvement in the coal may be examined. On the first set of curves (li/4-inch to 48-mesh) of figure 6 a vertical line extending from 5 per cent ash would intersect the coal recovery-ash (A) curve at 81.6 per cent coal recovery as read on the left ordinate. A horizontal line at this level would intersect the specific gravity (S.G.) curve at 1.50 specific gravity. A third line extending vertically at this point would intersect the specific gravity distribution (±0.10 sp. gr.) curve at 4.4 per cent, this being the amount of material in the coal being tested having a specific gravity between 1.40 and 1.60. Table 4 shows this to be a simple washing problem. The intersections of two of the remaining washability curves with a horizontal line at 81.6 per cent recovery are also significant. ^Op. cit., Vol. 2, 1928, p. 95. 8 Op. cit. 16 WASH ABILITY OF COAL SCREENINGS Sulfur curve. — The sulfur {S) curve would cross such a horizontal line at 1.2 per cent^ indicating a sulfur content of that percentage when the coal is washed to 5 per cent ash. The termination of the sulfur curve on the 100 per cent recovery line shows that the unwashed coal contained 2.0 per cent sulfur. Refuse Reject-Ash Curve. — The horizontal line would cross the refuse reject-ash {R) curve at 73.8 indicating this percentage of ash in the refuse from the washed coal. Eefuse having this much ash contains little or no coal. Ash Distribution Curve. — The ash distribution {D) curve shows the percentage of ash in each float-and-sink fraction involved in the calculation. Its primary function is to indicate the degree or admixture of refuse and coal, hence a sharp change in-direr^tion to the right in this curve is indicative of a rapid increase of high ash material. SIZED COAL Close sizing of screenings before cleaning is rarely practicable but the washability characteristics of the individual sizes are important in an evalua- tion of the cleaning problem for the whole coal. A study of the individual sizes may indicate the desirability of diverting one or more sizes of the feed to be pneumatically cleaned while other sizes are cleaned by a wet process; or it may be found advisable to by-pass certain of the smaller sizes without cleaning and to remix them with the larger sizes after the latter have been cleaned. Each coal and every size making up the screenings has its own characteristics and an understanding of these is imperative to the successful selection and operation of the units to be used in preparing the coal for the market. Use of Curves in Evaluatiiig Washahility. — The basis for the construction of the ±0.10 specific gravity distribution curves for the various sizes of coal B above minus 48-niesh is presented in table 8. The method of adjustment of the percentages has already been explained. The amount of material having a specific gravity of 2.00 and above was not determined experimentally but by extrapolation of the specific gravity curve to the 2.00 specific gravity point using an appropriately shaped curve. Examination of the adjusted percentages of mine B sized coal as given in table 8 or as obtained from inspection of the specific gravity distribution curves, shows, when taken in connection with the data given in table 4, that for any size coal the washing problem is more difficult at 1.45 or 1.4 than at 1.50, 1.60, or 1.70 specific gravity. On the other hand washing at 1.50 where but relatively small percentages of the coal are present would accom- plish good separation. It may be noted that a similar conclusion was reached in regard to the effectiveness of washing at 1.50 specific gravity in the pre- ceding consideration of the l^^-inch to 48-mesh coal. At this specific gravity INTERPRETATION OF CURVES 17 the washing problem could be classified as a simple one (table 4) for each of the sizes since in no case do the adjusted percentages (table 8) exceed 6.7 per cent. Although it would be still easier to wash at 1.60 and 1.70 specific gravity the washed coal would undoubtedly have a higher ash content. Coal Recovery and Ash. — Table 5 shows ash percentages for the sized unwashed coal and the corresponding recovery and ash percentages of the washed coal floating at 1.50 specific gravity. This information is also shown by the A curves^ figure 6. Table 5. — Ash and Recoveries in Sized Coal From Mine B Raw coal ash (drv) (Per cent) Washed coal Size Recovery 1.50 sp. gr. (Per cent) Ash (dry) 1.50 sp. gr. (Per cent) V/i to ^/i inch ^ to ^ inch 11.0 14.3 19.7 30.5 36.5 91.8 86.1 77.8 65.0 48.0 5.5 5.3 ^ inch to 10 mesh 10 to 48 mesh 4.6 4.2 Minus 48 mesh 7.0 The low recoveries in the small sizes at 1.50 specific gravity are accounted for by the high ash content of these sizes. This is due to the association with the screenings of relatively friable mineral matter consisting of soft clay from the roof and floor of the mine which concentrates in these small sizes. Ash Distritution Curves. — As stated in the discussion of the 114-iiich to 48-mesh coal, the ash distribution curve indicates the ash content of the coal of each float-and-sink fraction. Where this curve shows a sharp change in direction, as is true of all D curves for coal B except that of the minus 48-mesh, sharp changes in ash content are indicated, pointing to good differentiation of coal and mineral matter. Comparison of Bust and Larger Coal. — Generally when two different sizes of coal from the same mine are separated into several specific gravity fractions by heavy liquids, as previously described, the increments of the smaller coal have lower ash than the corresponding increments of the larger coal. The 10- to 48-mesh and minus 48-mesh sizes invite comparisons bearing on this generalization. Comparison of the ash content of the float-and-sink fractions of the two sizes (table 10, col. 4) shows uniformly, lower ash in the minus 48-mesh size. Examination of the amounts of coal at each specific gravity (col. 3) shows thai 46.9 per cent of the 10- to 48-mesh coal floats at 1.30 specific gravity while only 4 per cent of the minus 48-mesh size floats at the same specific gravity. The fractions of intermediate specific gravity 18 WASHABILITY OF COAL SCREENINGS (1.35 to 1.50) are large in the minus 48-mesh dnst and small in the 10- to 48-niesh size. As a result at 1.50 specific gravity, the cumulative ash (col. 8) shows 4.2 per cent in the 10- to 48-mesh size and 7.0 per cent ash in the minus 48-mesh dust. GENERAL INTERPRETATION OF DATA FROM ALL MINES Most cleaning plants in Illinois are so operated that the cleaned coal compares closely with that obtained by float-and-sink tests made at or near to 1.50 specific gravity. Table 6 shows the character of the cleaned coal and refuse of all ten mines at this specific gravity. The highest recoveries were from coals C, E, I, and -/. The ash content of the float from coals A, C and E is high; the ash content of the sink is low. This relationship indicates the necessity of clean- ing at a lower specific gravity in order to secure an acceptable low ash product. However, cleaning at a lower specific gravity would result in a still lower ash in the refuse which is undesirable since considerable fuel would be lost in the refuse. Table 6. — Comparison of Recovery, Ash and Sulfur Percentages (1.50 Specific Gravity in li/4-inch to 48-mesh coal, dry basis) Mine Recovery Float ash (Cumulative) Float sulfur (Cumulative) Sink ash (Cumulative) Sink sulfur (Cumulative) A B C D E F G H I J 80.6 81.6 89.1 86.0 90.0 82.2 83.5 85.1 92.6 91.4 9.5 5.0 11.8 7.9 10.0 8.5 9.1 8.8 6.5 7.1 4.4 1.2 2.9 1.6 4.2 3.9 3.6 3.2 1.4 1.9 53.5 73.8 54.7 56.5 46.1 60.6 61.1 55.1 58.8 59.2 11.4 5.4 6.7 5.4 14.6 9.1 9.0 13.2 6.4 12.2 The lowest ash and sulfur were obtained from coal B at this specific gravity. The refuse, containing 73.8 per cent ash, was free of coal but the recovery is only 81.6 per cent. However, the greater part of the refuse was introduced in mining and can hardly be considered coal recovery. Con- sidering recovery, ash and sulfur percentages, coals I and ./ shows the best response to cleaning at 1.50 specific gravity. Coal A is very difficult to clean at 1.50 specific gravity as 15 per cent of the coal is within ±0.10 per cent of this specific gravity. Cleaning at 1.55 specific gravity would increase recovery and place the cleaning problem in the difficult classification with a 0.5 per cent increase in ash in the washed coal. SUMMARY AND CONCLUSIONS 19 Table 7 gives a concise picture of the relative difficulty of cleaning the coals at 1.50 specific gravity. At this specific gravity the coals present the following order of increasing difficulty in cleaning F, H, E, and A, most difficult. B easiest; /, I, D, G, C, Table 7. — Comparison of Difficulty of Cleaning ( 114-inch to 48-mesh coal at 1.50 Specific Gravity) Mine Per cent of ±0.10 material Degree of difficulty of cleaning A 15.0 Very difficult B 4.3 Simple C 11.2 Difficult D 9.5 Difficult E 13.5 Difficult F 11.5 Difficult G 10.5 Difficult H 11.5 Difficult I 5.6 Simple J 4.5 Simple SUMMARY AND CONCLUSIONS Screenings were sampled at ten mines in the State representing five different producing horizons and a considerable variety of operating con- ditions. The ash and sulfur would be lowered in all these coals by a washing procedure based on specific gravity differences of coal and refuse. The specific gravity best suited for separating most of the coals, con- sidering ash and sulfur reduction^ recoveries, and ease of washing is 1.50, although for coal A washing at a slightly higher specific gravity might be desirable. The ash content (dry basis) of 114-inch screenings as they came from the mines varied between 10.8 and 19.7 per cent; the extremes of sulfur were 1.98 and 6.2 per cent. The range of ash in the 114-inch to 48-mesh screen- ings floating at 1.50 specific gravity was 5.0 to 11.8 per cent. Ash in the refuse ranged between 53.5 and 73.8 per cent. The lowest recovery of coal at this specific gravity was 80.6 per cent, the highest 92.6 per cent. At 1.50 specific gravity the washing problem varies from simple to very difficult but in no instance is the problem too difficult for available cleaning equipment operated with competent supervision. The data are applicable only to the coals sampled but no doubt have characteristics in common with screenings similarly produced from other mines in the respective districts. 20 WASHABILITY OF COAL SCREENINGS pq O I lO o T-H I 00 I 00 X 8 ^ O : o3 O I to O T-H 00 I 00 X ft ft OO + 1 CD oi > > o o p^p^ ^ 188 X -*-* o 00 (M CO CD 00 t^ CO lO t^ 1 00 7-1 c^' CO CiOO II ,-H CS ft 00 O CO ^ ft bC O "o ft c« o O -H i-H T-H I O O 1-^ '-' 2 00 CO 00 00 ft o 00 > > ft s ^ >-. bC bJO ."ti o o 03 cjn cd o o So QJ , >, fe ^ 1 > > o o 13 o o O) ; (N (N* 00 00 QJ bC 03 d O) ^^ fn > > ft bJD bD ^ > o o bC O) CD o ft ft ca t/3 02 OO 0) 1—1 T-H ft OO o T-H + 1 -(-^ -1^ o 03 03 -H >> >> TJ 0) -2 > > w 13 Q^ OJ TJ P^P^ > ft 2 1 >^ be M .|_i % 'o "o bi) o; q; u ft ft ^ 02 02 oo a- 1—1 1—1 S^ v\ O 1—1 o 03 03 ■tl ^b ■s > w o o 1=1 0) a; T3 P^P^ <1 bX) a CO (U 00^. •^ (M ~M o3 O ^ !>.' Ol I id O CO I fl ^ o o 00 >o '^ Cvi (M O O t^ iM CO COCO a; bC CS rt a; +3 -^^ a; > > ft t t >> faCbC .!_, o o ^ o o bJO m Qj ft ft cd OO O) ft OO + 1 1—1 -1-2 -1-2 O > 1 o o 13 (D S 59 Concluded 6 7 8 9 10 11 12 Cumulative float Cumulative sink Weight (Per cent) Products Ash or sulfur (Per cent) Weight (Per cent) Products Ash or sulfur (Per cent) Ordinate for Curve D Ash 69.33 76.54 80.34 84.94 88.10 00.00 242.66 315.48 369.06 452.32 548.07 1,394.16 3.5 4.1 4.6 5.3 6.2 13.9 100.00 30.67 23.46 19.66 15.06 11.90 1,394 16 1,151 50 1,078.68 1,025 10 941 84 846.09 1 13.9 37.5 46.0 52.1 62.5 71.1 34.66 72.93 78.44 82.64 86.52 94.05 Sulfur Same above 78.34 89.37 95.83 103.74 110.42 235.49 1.13 1.17 Same 1.19 as 1.22 1.25 above 2.35 235.49 2.35 Same 157.15 5.12 146.12 6.23 as 139.66 7.10 131.75 8.75 above 125.07 10.51 Ash 17.87 31.53 45.39 57.60 87.25 100.00 30.38 82.29 170.99 275.99 584.35 1,381.22 1.7 2.6 3.8 4.8 6.7 13.8 100.00 82.13 68.47 54.61 42.40 12.75 1,381.22 1,350.84 1.298.93 1,210.23 1,105.23 796.87 13.8 8.93 16.4 24.70 19.0 38.46 22.2 51.49 26.1 72.42 62.5 93.62 Same 15.90 0.89 Same 203.07 2.03 Same 30.65 0.97 187.17 2.28 as 45.76 1.01 as 172.42 2.52 as 56.75 0.99 157.31 2.88 above 85.13 0.98 above 146.32 3.45 above 203.07 2.03 117.94 9.25 60 washability of coal screenings Table 18. — ^Washability Data and 1 2 3 4 5 Size Specific gravity Weight (Grams) Weight (Per cent) Ash or sulfur (Per cent) Products (3X4) Ash l}i inch to 48 mesh. 114- inch to 48 mesh. IM to % inch. IM t'O ^ inch, ^ to ^ inch , 1.30 float 1.30-1.35 1.35-1.40 1.40-1.50 1.50-1.70 1.70 sink 30 float 30-1.35 1.35-1.40 40-1.50 50-1 . 70 70 sink 30 float 30-1.35 35-1.40 40-1.50 50-1 . 70 1.70 sink 1.30 float 1.30-1.35 1.35-1.40 1.40-1.50 1.50-1.70 1.70 sink 1.30 float 1.30-1.35 1.35-1.40 1.40-1.50 1.50-1.70 1.70 sink Sulfur Ash 16,413 11,603 1,887 937 508 1,126 Sulfur Same above Ash 13,608 9,574 1,533 763 362 1,308 Sulfur 52.64 30.05 5.48 3.23 1.79 6.81 Same as above 50.54 35.73 5.81 2.89 1.56 3.47 Same above 50.13 35.26 5.65 2.81 1.33 4.82 4.7 9.2 13.1 17.7 26.2 67.9 1.48 2.02 3.64 5.81 9.30 12.92 5.3 9.4 13.4 19.0 28.1 67.8 1.51 1.99 4.12 6.95 10.32 16.65 4.8 9.0 13.3 19.0 26.7 68.0 245.68 276.21 71.61 57.26 46.84 462.22 77.89 60.81 19.92 18.77 16.64 87.96 267.86 335.86 77.85 54.91 43.83 235.27 76.31 71.10 23.94 20.08 16.10 57.77 240.62 317.34 75.14 53.39 35.51 327.76 3^ to ^ inch 1.30 float Same Same 1.47 73.69 1.30-1.35 2.00 70.52 1.35-1.40 as as 3.77 21.30 1.40-1.50 7.09 19.92 1.50-1.70 above above 11.37 15.12 1.70 sink 15.25 73.50 DATA AND CALCULATIONS 61 Calculations for Screenings, Mine J 6 7 8 9 10 11 12 Cumulative float Cumulative sink Weight (Per cent) Products Ash or suKur (Per cent) Weight (Per cent) Products Ash or sulfur (Per cent) Ordmate for Curve D 52.64 245.68 4.7 82.69 521.89 6.3 88.17 593.50 6.7 91.40 650.76 7.1 93.19 697.60 7.5 00.00 1,159.82 11.6 Same above 50.54 86.27 92.08 94.97 96.53 100.00 Same above 50.13 85.39 91.04 93.85 95.18 100.00 77.89 138.70 158.62 177.39 194.03 281.99 267.86 603.72 681.57 736.48 780.31 1,015.58 76.31 147.41 171.35 191.43 207.53 265.30 240.62 557.96 633.10 686.49 722.00 1,049.76 1.48 1.68 1.80 1.94 2.08 2.82 5.3 7.0 7.4 7.8 8.1 10.2 51 71 86 01 15 65 4.8 6.5 6.9 7.3 7.6 10.5 Ash 100.00 47.36 17.31 11.83 8.60 6.81 Sulfur Same above Ash 100.00 49.46 13.73 7.92 5.03 3.47 Sulfur Same as above Ash 100.00 49.87 14.61 8.96 6.15 4.82 Sulfur 1,159.82 914.14 637.93 566.32 509.06 462.22 281.99 204.10 143.29 123.37 104.60 87.96 1,015.58 747.72 411.86 334.01 279.10 235.27 265.30 188.99 117.89 93.95 73.87 57.77 1,049.76 809.14 491.80 416.66 363.27 327.26 11.6 26.32 19.3 67.66 36.9 85.43 47.9 89.78 59.2 92.29 67.9 96.59 2.82 4.31 8.28 10.43 12.16 12.92 10.2 15.1 30.0 42.2 55.5 67.8 2.65 3.82 8.59 11.86 14.68 16.65 10.5 16.2 33.7 46.5 59.1 68.0 Same as above 25.27 68.40 89.17 93.52 95.75 98.26 Same above 25.06 67.76 88.21 92.44 94.51 97.59 Same 73.69 1.47 Same 274.05 2.74 Same 144.21 1.69 200.36 4.02 as 165.51 1.82 as 129.84 8.89 as 185.43 1.97 108.54 12.11 above 200.55 2.11 above 88.62 14.41 above 274.05 2.74 73.50 15.25 62 WASHABILITY OF COAL SCREENINGS Table 18— 1 2 3 4 5 Size Specific Weight Weight Ash or sulfur (Per cent) Products gravity (Gram.s) (Per cent) (3X4) Ash % inch to 10 mesh 1.30 float 4,009 58.96 4.5 265.32 1.30-1.35 1,606 23.62 9.4 222.03 1.35-1.40 331 4.87 13.0 63.31 1.40-1.50 199 2.93 16.8 49.22 1.50-1.70 127 1.87 25.7 48.06 1.70 sink 527 Sulfur 7.75 69.2 536.30 ^ inch to 10 mesh 1.30 float Same Same 1.49 87.85 1.30-1.35 2.16 51.02 1.35-1.40 as as 3.40 16.56 1.40-1.50 5.50 16.11 1.50-1.70 above above 9.51 17.78 1.70 sink Ash 13.04 101.06 10 to 48 mesh 1.30 float 1,236 50.12 3.2 160.38 1.30-1.35 449 18.21 8.4 152.96 1.35-1.40 136 5.52 11.9 65.69 1.40-1.50 137 5.55 15.7 87.13 1.50-1.70 77 3.12 23.8 74.26 1.70 sink 431 Sulfur 17.48 66.6 1,164.07 10 to 48 mesh 1.30 float Same Same 1.40 70.17 1.30-1.35 1.92 34.96 1.35-1.40 as as 2.53 13.96 1.40-1.50 3.26 18.09 1.50-1.70 above above 5.87 18.31 1.70 sink Ash 9.60 167.81 Minus 48 mesh 1.30 float 96.6 15.88 2.0 31.76 1.30-1.35 90.8 14.93 4.4 65.69 1.35-1.40 54.4 8.94 7.2 64.37 1.40-1.50 68.1 11.20 9.0 100.80 1.50-1.70 189.2 31.11 10.3 320.43 1.70 sink 109.1 Sulfur 17.94 60.3 1,081.78 Minus 48 mesh 1.30 float Same Same 1.19 18.90 1.30-1.35 1.44 21.50 1.35-1.40 as as 1.59 14.21 1.40-1.50 1.59 17.81 1.50-1.70 above above 1.86 57.86 1.70 sink 13.34 239.32 DATA AND CALCULATIONS 63 Concluded 6 7 8 9 10 11 12 Cumulative float Cumulative sink Weight (Per cent) Products Ash or sulfur (Per cent) Weight (Per cent) Products Ash or suKur (Per cent) Ordinate for Curve D 58.96 82.58 87.45 90.38 92.25 00.00 Same above 50.12 68.33 73.85 79.40 82.52 00.00 Same above 15.88 30.81 39.75 50.95 82.06 100.00 Ash 265.32 4.5 100.00 1,184.24 11.8 29.48 487.35 5.9 41.04 918.92 22.4 70.77 550.66 6.3 17.42 696.89 40.0 85.01 599.88 6.6 12.55 633.58 50.5 88.91 647.94 7.0 9.62 584.36 60.7 91.31 1,184.24 11.8 7.75 Sulfur 536.30 69.2 96.12 87.85 1.49 Same 290.38 2.90 Same 138.87 1.68 202.53 4.93 155.43 1.78 as 151.51 8.70 as 171.54 1.90 134.95 10.75 189.32 2.05 above 118.84 12.35 above 290.38 2.90 Ash 101.06 13.04 160.38 3.2 100.00 1,704.49 17.0 25.06 313.34 4.6 49.88 1,544.11 30.9 59.22 379.03 5.1 31.67 1,391.15 43.9 71.09 466.16 5.9 26.15 1,325.46 50.7 76.62 540.42 6.5 20.60 1,238.33 60.1 80.96 1,704.49 17.0 17.48 Sulfur 1,164.07 66.6 91.26 70.17 1.40 Same 323.30 3.23 Same 105.13 1.54 253.13 5.07 119.09 1.61 as 218.17 6.89 as 137.18 1.73 204.21 7.81 155.49 1.88 above 186.12 9.03 above 323.30 3.23 Ash 167.81 9.60 31.76 2.0 100.00 1,664.83 16.6 7.94 97.45 3.2 84.12 1,633.07 19.4 23.34 161.82 4.1 69.19 1,567.38 22.7 35.28 262.62 5.2 60.25 1,503.01 24.9 45.35 583.05 7.1 49.05 1,402.21 28.6 66.50 1,664.83 16.6 17.94 1,081.78 60.3 91.03 Sulfur Same 18.90 1.19 Same 369.60 3.70 Same 40.40 1.31 350.70 4.17 as 54.61 1.37 as 329.20 4.76 as 72.42 1.42 314.99 5.23 above 130.28 1.59 above 297.18 6.06 above 369.60 3.70 239.32 13.34 64 WASHABILITY OF COAL SCREENINGS Figure 5. — Washability Curves, Mine A WASHABILITY CURVES 65 Figure 5. — Continued 66 WASHABILITY OF COAL SCREENINGS Figure 6. — ^Washability Curves, Mine B WASHAIJILITY CURVES 67 Figure 6. — Continued 68 WASHABILITY OF COAL SCKEENINGS ASH % 10 SULFUR % 5 Figure 7. — ^Washability Curves, Mine C WASHABILITY CURVES 69 Figure 7. — Continued 70 WASHABILITY OF COAL SCREENINGS \ lO.IOS.G. 1^4 X ^A INCH 20 \ \ \ \ \ f" \ \ \ \ 0. 1 \\ \ R -1 geo \ 1 \ / \ v^ V / 80 \ \, ^\^ / \ \ V S^G^_^ l^ [\ A " ^ .IH;^ -J ) 100 -X s , SULFUR % 5 SP.GR. 1.70 1.60 1.50 Figure 8. — Washability Curves, Mine D WASHABILITY CURVES 71 ASH % 10 SULFUR % S Figure 8. — Continued 72 WASHABILITY OF COAL SCREENINGS Figure 9. — Wash ability Curves, Mine E WASHABILITY CURVES 73 Figure 9. — Continued 74 WASHABILITY OF COAL SCREENINGS A X % - INCH SP. CR. 1.70 1.60 Figure 10. — Washability Curves, Mine F 90 100 1.40 1.30 WASHABIUTY CURVES 75 SP. GR, 1.70 Figure 10. — Continued WASHABILITY OF COAL SCREENINGS 1.40 1.30 Figure 11. — ^Washability Curves, Mine G WASHABILITY CURVES 77 Figure 11. — Continued 78 WASHABILITY OF COAL SCREENINGS Figure 12. — Washabiuty Curves, Mine H WASHABILITY CURVES 79 Figure 12. — Continued 80 WASHABILITY OF COAL SCREENINGS "1 ! P ' xLc°-'° ^-^ 2 X I '/A - INCH \ 20 40 1 \ \ \ \ \ \ \ 60 w \ \ \ \ / ' \ V V / eo \ \ / 1 s ^ V V, ' S.G. / 6 — --A>J U 1 ASH % 10 SyLFUR% 5 Figure 13. — Washability Curves, Mine I WASHABIUTY CURVES 81 Figure 13. — Continued 82 WASHABILITY OF COAL SCREENINGS Figure 13. — Concluded WASHABILITY CURVES 83 Figure 14. — Washahility Curves, Mine J 84 WASHABILITY OF COAL SCREENINGS ASH% 10 SULFUR % 5 Figure 14. — Continued