Analysis of the Oxidation of Chalcopyrite,Chalcocite, Galena
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PLEASE 00 Nor REMOVE FRCM LIBRARY Bureau of Mines Report of Investigations/1987 Analysis of the Oxidation of Chalcopyrite, Chalcocite, Galena, Pyrrhotite, Marcasite, and Arsenopyrite By G. W. Reimers and K. E. Hjelmstad UBRARY ""OKANERESEARC H CENTER .... RECEIVED OCT 021 1981 US BUREAU Of MINES t 315 MONTGOMBlY ",'IE. SPOICANl,. WI>. 99201 UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9118 Analysis of the Oxidation of Chalcopyrite, Chalcocite, Galena!' Pyrrhotite, Marcasite, and Arsenopyrite By G. W. Reimers and K. E. Hjelmstad UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES David S. Brown, Acting Director Library of Congress Cataloging in Publication Data : Reimers, G. W. (George W.) Analysis of the oxidation of chalcopyrite, chalcocite, galena, pyr rhotite, marcasite, and arsenopyrite. (Bureau of Mines report of investigations; 9118) Bibliography: p. 16 . Supt. of Docs. no.: 128.23: 9118. 1. Pyrites. 2. Oxidation. I. Hjelmstad, Kenneth E. II . Title. III. Series: Reportofinvestiga tions (United States. Bureau of Mines) ; 9118. TN23.U43 [QE389.2] 622 s [622'.8] 87-600136 CONTENTS Abst 1 Introduction ••••••••• 2 Equipment and test • .,.,.,.,.,.,., .•. .,., ..... .,.,.,.,., ... ., . ., ........ ., .... ., ..... ., .. ., . .,. 3 Samp Ie ., .. ., ., ., ., ., ., ., ., ., ., ., .. ., .• ., .. ., ..... ., •.••• ., . ., ., ..•. ., ., ., . ., ., ., ., • ., ., ., ., • 4 Results and discussion .. ., . .,.,.,. ........ .,., ...... ., ., .... " . ., . .,.,., . .,., . .,., ,.,.., ., . ., 5 Ore-type sulfides., . .,.,.,.,.,., ...... .,., .... ., ........... .,., ... .,., ........ .,.,.,.,.,.,.,.,.,., ... .,. 5 Thermal ric analyses., • ., ...... ., .... ., . .,.,.,., . .,.,., .. .,.,., . .,.,., . .,.,.,.,.,.,.,.,., ... .. 5 Chalcopyrite ... ., .. .,.,.,., . .,., .. ., . .,., It.,., • ., .. .,.,.,.,.,., •• .,.,.,.,.,.,.,., • .,., .. ., .. ., •• ., • .,., • .,.,.,., 5 Chalcoci tee ••• ., .•. ., .•. .,., ., .. ., ., ., •• ., ., ., .. ., ., ., • ., ., ., ., .,., ., ., ., ., .. ., ., .• ., ., . ., ., . ., . ., ., It •• ., .... 9 Galena .•.•••••...••.........••.•.•..••••...••..•.•...•.••.....•...•...... 9 Differential thermal 10 Di s cus s ion . ., • ., ., ., ., .. ., .. ., ................. II • II .......................................... 10 11 ric analyses ...................................... II •••• II • •• II 11 Pyrrhoti tea .................................................................... .,. .. 11 Marcasi tea ....................................... II ................................. 11 Arsenopyrite ••••••••••••• 12 Differential thermal analyses ..•.. " ............................. " ...... .,. 13 Di s cus s ion .................................................................. 14 Summa ry and conclusions .••••••..•...••••.•••••...•..........••.•............... 14 Re f e rences •......•......•••.•......•.....••.•...•.........•.................... 16 ILLUSTRATIONS L Thermal gravimetric is illustrating effect of milling time on oxi- dation of chalcopyrite A in air ........................................... .,. ... 7 2. Isothermal oxidation of chalcopyrite A at 290 0 C, with air and air contain- 40 pct water vapor and with oxygen and oxygen 40 pct water vapor. • • • ..... • • •• •• •• •• •••• •• ••• ••••• •••• •• •• ••• .... •••. •• •••• •• •••. .. 7 3. Thermal tric of B oxidized with oxygen con- taining pct water vapor, chalcopyrite C oxidized with air, chalcocite A oxidized with air, and oxidized with oxygen containing 40 water vapor ••••••• ., •• .,,,,, ..................... " • • •• .. • •• .. ... •• •• .. .... •• • .... • ••• •••• ••• 8 4. Isothermal oxidation cna~.copy'rlte B with air, chalcocite B with air, and with oxygen pet water vapor ••••••••••••••••••••••••.• 9 5. Differential thermal chalcopyrite B, chalcocite B, and milled for 120 min and oxidized with air •••••••••••••••••••••••••••••. 10 6. Thermal ric analyses of pyrrhotite A milled for 15 min, A milled for 120 ite B milled for 120 marcasite milled for 120 and milled for 120 min •••••••••••••••••••••••• 12 7. Isothermal test of marcasite milled for 120 min and oxidized with air 40 pct water vapor •••••••• 13 8. Differential thermal analyses of A, marcasite, and te milled for 120 min and oxidized with air 4.5 pct water vapor ••• 13 TABLES 1. Standard heats of reaction (8H~98) ••••••••••••••••••••••••••••••••••••••••• 3 7.. of s ulf ide ......... , ............... " ..... ., .. 4 3. Particle size and 6 ----- UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cm centimeter kcal/mol kilocalorie per mol cm ~ cubic centimeter ).lm micrometer cm 3 /min cubic centimeter per minute mg milligram °c degree Celsius min minute °C/min degree Celsius per minute mm millimeter g gram pct percent h hour wt pct weight percent AN ALYSIS OF THE OXIDATION OF CHALCOPYRIT E, CHALCOCITE, GALENA, PYRRHOTITE, MARCASITE, AND ARSENOPYRITE By G. W. Reimers 1 and K. E. Hjelmstad2 ABSTRACT Conditions in the underground mine environment can cause self-heating of sulfide ores as a result of exothermic oxidation reactions, which may result in mine fires. This Bureau of Mines report describes thermal analyses of finely ground chalcopyrite, chalcocite, galena, pyrrhotite, marcasite, and arsenopyrite, to characterize their responses under oxidizing conditions. Thermal gravimetric analysis (TGA) and differ ential thermal analysis (DTA) were used, in the temperature range 100 0 to 500 0 C. Chalcopyrite showed an initial weight gain, due to formation of sul fates, a weight loss, caused by ignition of iron sulfide to iron oxide, and a final weight gain, indicating the conversion of copper sulfide to sulfate. Chalcocite did not ignite in the temperature range studied but exhibited a rapid weight gain, because of the rapid conversion of copper sulfide to sulfate. Likewise, g a lena failed to ignite but underwent a steady weight gain when oxidized in a moist atmosphere, showing conver sion of lead sulfide to sulfate below the ignition point. Marcasite underwent a rapid weight loss, indicating ignition, at 200 0 C. Moisture in the oxidizing atmosphere lowered the ignition point of marcasite and arsenopyrite but not that of pyrrhotite. All the sulfides exhibited exothermic behavior at temperatures below the ignition point. l p hysical scientist. 2Geophysicist. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. INTRODUCTION This report describes the results of spontaneous combustion in sulfide depos laboratory thermal analysis experiments its are not well understood. Thus, cur conducted to follow the oxidation of rent efforts by mine personnel to control chalcopyrite, chalcocite, galena, pyr spontaneous combustion problems, regard rhotite, marcasite, and arsenopyrite. less of how well intended, are not always These tests are part of a broader Bureau based on sound engineering and technical of Mines research program to develop principles. The intent of this research methods of controlling the oxidation of is to delineate the thermal behavior of sulfide ores in underground mines, thus sulfide minerals exposed to oxidizing preventing spontaneous combustion mine conditions, thereby providing a back fires. ground of data that will enable mine per Previously, Ninteman (~)3 completed an sonnel to undertake fire prevention extensive literature review of the nature efforts with maximum effectiveness. and problems associated with the oxida In his monograph on chalcopyrite, tion and combustion of sulfide minerals Habashi (2) refers to work by Tafel and in underground metal mines. Sulfide oxi Greulich, who followed the oxidation of dation is an exothermic process that pro powdered chalcocite in air. They found duces heat, which, if not dissipated, that both cupric sulfate and ferrous sul causes a temperature rise within the min fate were formed slowly at about 350 0 C. eral mass. If the temperature begins to Ferrous sulfate reached its maximum form rise, a thermal runaway situation may ation at 400 0 C; at 500 0 C, its rate of develop that will cause the sulfide and formation equaled its rate of decomposi other combustibles to burn. tion. Cupric sulfate reached its maximum Reactions similar to those that cause formation at 550 0 C. Above 550 0 C, it spontaneous combustion in underground gradually decomposed to copper oxysul mines can also be responsible for the fate. Habashl also ci ted the work of self-heating of sulfides during shipment. Meunier and Vanderpoorten in studying the Kirshenbaum (~) described many such inci oxidation of chalcopyrite cubes (2 to 3 dents, involving both rail and ship car cm 3 ) in the temperature range of 300 0 to riers of sulfide concentrates. His 900 0 C. At 330 0 C, they noted oxidation teview provided details of the conditions on the surface of the cube. At 500 0 C, that led to the oxidation and self the surface film was thick enough that heating of sulfide cargoes and, ultimate when the cube was sectioned the red outer ly, to combustion. Mention was also made layer could be identified as ferric of the high levels of toxic S02 generated oxide. Work by Razouk and others to during such events, which impeded fire study the oxidation of chalcopyrite by control efforts. TGA was also reviewed (2). Razouk pro The spontaneity and prolonged incipient posed a mechanism for the temperature stage (weeks or months) of these fires range of 350 0 to 400 0 C, suggesting that make their occurrence difficult to pre chalcopyrite oxidized to form ferric sul dict and to detect. Furthermore, these fate and cuprous