PLEASE DO Nar REMOVE FROVI LIBRARY Recovery of Sulfur From Phosphogypsum: Conversion of Calcium Sulfide to Sulfur By David A. Rice, Olice C. Carter, Jr., Alexander May, Margaret M. Ragin, and Robert G. Swanton 1910 * 80 * 1990 YEARS AU OF MI UNITED STATES DEPARTMENT OF THE INTERI U.S. Bureau of Mine~ ··"1 Spo!(;:ifle Research Center E. :;! 5 Montgomery twe. Sn':1:~:na, INA 99207 i F? [il Lb!G:w"hnP h'Y Mission: As the Nation's principal conservation agency, the Department of the Interior has respon­ sibility for most of our nationally-owned public lands and natural and cultural resources. This includes fostering wise use of our land and water resources, protecting our fish and wildlife, pre­ serving the environmental and cultural values of our national parks and historical places, and pro­ viding for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also promotes the goals of the Take Pride in America campaign by encouraging stewardship and citizen responsibil­ ity for the public lands and promoting citizen par­ ticipation in their care. The Department also has a major responsibility for American Indian reser­ vation communities and for people who live in Island Territories under U.S. Administration. 1 i I ! Report of Investigations 9297 Recovery of Sulfur From Phosphogypsum: Conversion of Calcium Sulfide to Sulfur By David A. Rice, Olice C. Carter, Jr., Alexander May, Margaret M. Ragin, and Robert G. Swanton UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary BUREAU OF MINES TS Ary, Director This report is based upon research conducted under an agreement between the University of Alabama and the Bureau of Mines. Library of Congress Cataloging in Publication Data: Recovery of sulful' f!'Om phosphogypsum convel'Slon of calcium sulfide to sulful' / by David A. Rice ... ret aLl. p. cm. - (RepOl't of investigations; 9297) Includes bibliogmphical l'efel'ences. Sup!. of Docs. no.: I 28.23:9297. 1. Sulphul'. 2. Phosphogypsum. 3. Calcium sulphide-Metallll1'gy. I. Rice, David A. (David Al'thur) II. Series: RepOl't of investigation (United States. BUl'eau of Mines); 9297. TN23.U43 [TN890] 622 s-dc20 [661'.1] 89-600337 CIP CONTENTS Page Abstract. .......................................................................... 1 Introduction ........................................................................ 2 Initial considerations 2 Overall potential process 2 Acknowledgments .................................................................... 3 Materials used 3 Analytical methods ................................................................... 4 Experimental methods 4 Conversion of calcium sulfide to ammonium bisulfide 4 Conversion of ammonium bisulfide to sulfur ........................................•..... 5 Tests using laboratory-grade carbon 5 Tests on commercial-grade activated carbons 5 Removal of sulfur from carbon ................................. .. ..................... 6 Thermal methods ........................................................... .. 6 Sulfur extraction with liquid anhydrous ammonia ......................................... 6 Carbon recyclability 6 Results and discussion 7 Preparation of ammonium bisulfide from calcium sulfide ..................................... 7 Preparation of ammonium bisulfide from calcium sulfide made from phosphogypsum ............. 8 Conversion of ammonium bisulfide to sulfur 8 Tests using laboratory-grade carbon 8 Tests on commercial-grade activated carbons 10 Removal of sulfur from carbon ........................................................ 11 Thermal nlethods ................................................................ 11 Sulfur extraction with liquid anhydrous ammonia ......................................... 13 Carbon recyclability .•............................................................ 14 Conclusions 15 References ......................................................... .. .............. 15 ILLUSTRATIONS 1. Laboratory test apparatus for converting ammonium bisulfide to sulfur 5 2. Continuous flowthrough system for ammonia leaching ...................................... 7 3. Recovery of sulfur from SLC-l as function of temperature using vacuum distillation. ............... 12 4. Recovery of sulfur from SLC-l as function of temperature 12 5. Recovery of sulfur from SLC-2 as function of heating time 12 6. Recovery of sulfur from SLC-2 as function of total nitrogen volume at constant temperature ...•..... 13 7. Cumulative recovery of sulfur from SLC-2 as function of total leaching time using liquid anhydrous ammonia. .............. .. ..................................................... 13 8. Flowsheet for recovery of sulfur from phosphogypsum, incorporating ammonia leaching. ............ 14 9. Carbon recycle testing: material weight as function of test cycle number. ....................... 14 TABLES 1. Typical properties of commercial-grade activated carbons 3 2. Chemical analysis of reaction solutions prepared from commercial-grade chemicals 7 3. Sulfur species in ammonium bisulfide solution 7 4. Quantitative analysis of calcium sulfide prepared from phosphogypsum 8 5. Analyses of ammonium bisulfide solutions 9 6. Sulfur and ammonia distribution in products ............................................. 9 7. Sulfur loading on carbon-coated mullite beads 10 8. Results of loading tests on commercial-grade activated carbons ............................... 11 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT °C degree Celsius mL milliliter g gram mL/min milliliter per minute g/mL gram per milliliter mm millimeter h hour jJ-mHg micrometer of mercury in inch mmHg millimeter of mercury L liter pct percent m2 square meter ppm part per million m2/g square meter per gram psi pound per square inch meq millequivalent wt pct weight percent mm minute RECOVERY OF SULFUR FROM PHOSPHOGYPSUM: CONVERSION OF CALCIUM SULFIDE TO SULFUR By David A. Rice, 1 Olice C. Carter, Jr} Alexander May,3 Margaret M. Ragin,4 and Robert G. Swanton5 ABSTRACT As part of a cooperative effort between the Bureau of Mines and the Florida Institute of Phosphate Research (FIPR), with input from the phosphate industry, the conversion of phosphogypsum to sulfur is being investigated. The proposed process incorporates the thermal reduction of phosphogypsum to calcium sulfide (CaS) and a hydrometallurgical treatment to convert calcium sulfide to sulfur (SO). The research described herein is focused on the latter half of the process. It was demonstrated that calcium sulfide could be converted to ammonium bisulfide (NH4SH), and that ammonium bisulfide could be oxidized by air in the presence of a catalyst, to elemental sulfur, which was adsorbed on the catalyst. Two methods for recovering sulfur from the catalyst were developed: (1) thermal treatment to volatilize sulfur, and (2) leaching the sulfur from the catalyst with liquid anhydrous ammonia. Over 90 pct of the sulfur adsorbed on activated carbon (the catalyst) was recovered by both methods. Based upon the encouraging laboratory investigations, a hydrometallurgical scheme was proposed for the overall conversion of calcium sulfide to elemental sulfur. lChemical engineer (now with Salt Lake City Research Center, Bureau of Mines, Salt Lake City, Uf). 2Envil'onmental engineer. 3Reseal'ch chemist. 4Physical scientist. 5Chemcial engineer. Tuscaloosa Research Center, Bureau of Mines, Tuscaloosa, AL. 2 INTRODUCTION As part of its mission to ensure that the Nation has an method for converting calcium sulfide to sulfur, which adequate supply of minerals at acceptable economic, en­ involved converting calcium sulfide, which is only slightly vironmental, and social costs, the Bureau of Mines is de­ water soluble, to the very soluble sodium bisulfide (NaSH), veloping a process to convert phosphogypsum to elemental by ion exchange, and then releasing hydrogen sulfide by sulfur. This investigation was cofunded by the Bureau and treating the sodium bisulfide with water and carbon diox­ FIPR, Bartow, FL. ide in a reaction analogous to reaction A. The hydrogen The voluntary cooperation of the following Florida sulfide was then converted to sulfur by the Claus process phosphate companies in offering valuable advice and sug­ (9-10). gestions on the research efforts is gratefully acknowledged: Gardinier, Inc.; Agrico Chemcial Co.; Farmland Industries Inc.; Royster Co.; W. R. Grace & Co.; Occidental Chem­ ical Corp.; Conserve; International Minerals & Chemical However, applying the Claus process to the larger ton­ Corp.; USS Agri-Chemicals Inc.; and C. F. Industries Inc. nages of stockpiled phosphogypsum would create many Forecasts of sulfur supply between 1990 and 2000 pre­ additional problems, and experts in the phosphate industry dict a depletion in primary sulfur reserves and an increase advised against this approach. Therefore, direct oxidation in sulfur demands and prices on a worldwide scale (1).6 of aqueous sulfide by air was considered. Tests were The fertilizer industry in the United States annually con­ performed on direct oxidation of aqueous slurries of pure sumes about 65 pet of the Nation's sulfur (2). This sulfur calcium sulfide by air and/or oxygen with and without is used to make sulfuric acid, which is mixed with phos­ catalysts. The sulfur recoveries were low when the direct phate rock to make phosphoric acid, the major ingredient oxidation techniques were used. Rosenwald, Hamblin,