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Extraction of Chromium from Domestic Chromites by Alkali Fusion

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II 7 7' RI89n PLEASE DO NOT REMOVE FROM LIBRARY Bureau of Mines Report of Investigations/1985 Extraction of Chromium From Domestic Chromites by Alkali Fusion By Gary L Hundley, D. N. Nilsen, and R. E. Siemens UNITED STATES DEPARTMENT OF THE INTERIOR i~~1 O~.~~ MINES 75TH A ~ ------------.~---.---- Report of Investigations 89n Extraction of Chromium From Domestic Chromites by Alkali Fusion By Gary L Hundley, D. N. Nilsen, and R. E. Siemens UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Hundley, Gary L Extraction of chromium from domestic chl'omites by alkali fusion. (Report of investigations / United States Department of the Interior, Bureau of Mines; 8977) Bibliography: p. :14. Supt. of Docs. no.: r 28.23: 8977. 1. 'Chromium-Metallurgy. 2. Sodium hydroxide. 3. Chromite-United States. I. Nilsen, D. N. lLSiemens, R. E. (Richard' E.). 1lI. Title. IV. Series: Report of investigations (United States. Bureau of Mines) ; 8977. TN23.U43 [TN799.C5] 6228 [669'.734] 85·600121 CONTENTS Abstract ••••••••••••••••••••••••••.•••.•••.••••••••••••••••.•••••••••• 41........ 1 Introduction. .•••••• •••. •. •. ... .•.. .. .•• .•• .•.•. .• .•• ...... .•.••.••••• • 2 Raw materials.................................................................. 3 Equipment and experimental procedures.......................................... 5 Experimental results and discussion............................................ 6 Chrotnium extraction.......................................................... 6 Viscosity of reaction mixture................................................ 10 Impu ri ty ext rae t ion. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • . • . • . • • . • • • • • • • • • • • • • • • • • • 13 Additives to reaction mixture. •••••••••• •••••••••••••• ••• •• •• ••• •• •• ••• • • •• •• 13 Summary and conclusions........................................................ 14 References..................................................................... 14 ILLUSTRATIONS 1. Flowsheet for chemical processing of chromite •••••••••••••••••••••••••••••• 3 2. Effect of sodium hydroxide-to-chromite weight ratio on metal extraction, Moua t chromi te ..•••••.••••••••••••••••••••...•..••••••••••••••.•••...•••.• 7 3. Effect of reaction time on metal extraction, Mouat chromite •••••••••••••••• 7 4. Effect of sodium hydroxide-to-chromite weight ratio on metal extraction, Eight Dollar Mountain laterite •••••••••••••••••••••••••••••••••••••••••••• 8 5. Effect of reaction time on metal extraction, .Eight Dollar Mountain laterite 8 6. Effect of sodium hydroxide-to-chromite weight ratio on metal extraction, Red Bluff Bay chromite ••••••••••••••••••••••••••••••••••••.••••••••••••••• 9 7. Effect of reaction time on metal extraction, Red Bluff Bay chromite •••••••• 9 TABLES 1. Head analyses of chrolute concentrates ••••••••••••••••••••••••••••••••••••• 4 2. Results of chromite fusion tests, Mouat concentrate •••••••••••••••••••••••• 6 3. Results of chromite fusion tests, Eight Dollar Mountain laterite ......... .. 8 4. Results of chrOlute fusion tests, Red Bluff Bay concentrate •••••••••••••••• 9 5. Results of chromite fusion tests on 10 other materials •••••••••••••••• ~ •••• 11 6. Best chromium extractions obtained for each concentrate •••••••••••••••••••• 12 . ' : I UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT degree Celsius mIn millimeter cm centimeter pct percent g gram ppm part per million h hour EXTRACTION OF CHROMIUM FROM DOMESTIC CHROMITES BY ALKALI FUSION By Gary L. Hundley, 1 D. N. Nilsen, I and R. E. Siemens 2 ABSTRACT The Bureau of Mines has devised a procedure to recover chromium chemi­ cals from low-grade domestic chromites, which contain silicon and alumi­ num impurity levels that are too high to permit processing by present industrial processes. The Bureau procedure consists of reacting chro­ mite with molten sodium hydroxide (NaOH) under oxidizing conditions to form sodium chromate (Na2Cr04). The reaction product is leached with methanol to remove the majority of the unreacted sodium hydroxide, then with water to remove the sodium chromate and the remainder of the sodium hydroxide. The sodium chromate product is recovered by evaporative crystallization from the aqueous solution. This report presents results of laboratory tests to determine the op­ timum fusion conditions and the chromium extractions obtained from sev­ eral domestic chrotdte concentrates. These concentrates are from a va­ riety of sources, including the Stillwater Complex in Montana, Kanuti River-Caribou Mountain, Red Bluff Bay, Kenai Peninsula, and Kodiak Is­ land areas in Alaska, deposits in northern California, and a nickel­ cobalt laterite from southern Oregon. All of these concentrates were successfully treated by the Bureau procedure. The best chromium extrac­ tions obtained for each of these materials ranged from 69.5 to 98.9 pet. 1Chemical engineer. 2supervisory research metallurgist. Albany Research Center, Bureau of Mines, Albany, OR. 2 INTRODUCTION Chromium is a commodity that is essen­ with carbon dioxide (C02 ) to precipitate tial to the Nation's metallurgical, chem­ aluminum and silicon compounds, and then ical, and refractory industries. The is treated with lime to remove the car­ United States has no domestic production bonate compounds formed during the carbon or economic reserves of the only commer­ dioxide sparge. The final sodium chro­ cial ore of chromium, chromite, and must mate product is recovered from the aqeous rely on imports to meet national needs. solution by evaporative crystallization. The chemical industry uses approximately The sodium chromate product from this 25 pct of the chromite consumed in the procedure is a basic chemical used indus­ United States for the production of pig­ trially, and it can be used to produce ments, chromic acid for plating, and the other common chromium chemicals in other chemicals for leather tanning, wood commercial use. preservatives, catalysts, and corrosion This report describes the experimental inhibitors 0).3 results obtained in the first step of the Commercial-processes presently used to Bureau process--the fusion reaction of chemically treat chromite concentrates the chromite with the sodium hydroxide. include an oxidizing roast of the chro­ The general equation for the chemical re­ mite with sodium carbonate and lime in a action involved is shown below. rotary kiln at a temperature of 1,1000 to 0 1,150 C. The amount of reagents and a FeO°Cr203 + 4NaOH + 7/402 --+ 2Na2Cr04 diluent is controlled so that the reac­ tion mixture remains as a solid phase in + 1/ 2Fe2 03 + 2H20. the kiln (2). Concentrates that have been produced from domestic chromite de­ Previous work by Chandra (4) showed posits contain too much silicon to be that an excess of sodium hydroxide must processed by this method. The silicon be used to maintain a fluid reaction mix­ forms molten, sticky reaction products ture. A weight ratio of approximately with the sodium carbonate, which cause 4:1 (22.4:1 mole ratio) of sodium hydrox­ balls or rings of material to form in the ide to chromite is typically necessary to kiln, hindering its operation. The alum­ maintain fluidity and to obtain good con­ inum content in domestic resources is version of the chromium in the chromite also high, resulting in an excess con­ to sodium chromate. Reaction products sumption of reagents (3). build up on the surface of the chromite A simplified flowsheet for the Bureau particles, preventing further reaction, of Mines procedure to recover chromium so the mixture must be kept well agitated chemicals from low-grade domestic chro­ to remove these surface products. mites is shown in figure 1. Briefly, the Chandra used a small ball-mill-type re­ procedure consists of reacting the chro­ actor in his studies, but this type of mite at 550 0 to 650 0 C with an excess of reactor proved to be unworkable in larger molten sodium hydroxide under oxidizing sizes. A stirred-pot-type reactor was conditions to produce sodium chromate. used in the present work. Studies are The product from the fusion reaction is also being conducted in Japan on a simi­ solidified, crushed, and leached with lar procedure, 'using sodium nitrate methanol to remove the bulk of the unre­ (NaN03) as the oxidizing media rather acted sodium hydroxide. The residue from than air as used in the Bureau method (5- the methanol leach is leached with water ~. - to remove the remainder of the sodium hy­ The other major steps of the process droxide and the sodium chromate. The (methanol and water leaching, solution aqueous solution is purified by sparging purification, and evaporative crystalli­ zation) are currently being studied at 3Underlined numbers in parentheses re­ the Bureau, and the results will be pre­ fer to items in the list of references at sented in a future publication. the end of this report. 3 Makeup NaOH Oxidation and fusion 550°-650° C Recycle methanol Methanol leach Solid-liqUid Solution Recycle separation NaOH - ........ Water Recycle NaOH CO 2 sparge Solution Purification ~~~~,~~ I m~111111"111111 I Residue to AI and Si disposal compounds FIGURE 1. Flowsheet for chemical processing of chromite. RAW MATERIALS The chromite concentrates tested in 2. High-iron (chemical grade) chromite this study were obtained from a variety that contained 40 to 46 pct Cr203 with a of sources in Alaska, California, Mon­ Cr:Fe ratio of 1.5:1 to 2.0:1. tana, and Oregon. They were categorized
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