Kinetics of manganese reduction leaching from weathered rare-earth mud with sodium sulfite
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I. INTRODUCTION
THE Panxi rare-earth (RE) deposit in the western Sichuang province (Sinchuang, China) is the second-largest RE deposit in China. The main RE mineral in this deposit is bastnasite (Ce (La, Nd, . . .) FCO3). Geological study showed that the deposit has been severely weathered, and about 20 pct of RE deposits are in the form of weathered mud. The RE mud weathered as such contains about 3 to 10 pct RE oxides in the enriched form[1] and is referred to as weathered RE mud (WREM). About 20 pct of the total RE elements in the deposit are contained in the WREM. The partition of medium (Eu) and heavy (Y) RE elements is higher in the WREM than in bastnasite,[2,3] as a result of the enrichment by geological weathering.[4,5] The RE content at this level in the WREM is of sufficient economic value to be recovered. However, the RE in the WREM coexists as a colloidal sediment phase highly disseminated in amorphous manganese and/or iron oxides.[6,7,8] Conventional physical processing methods, such as flotation, magnetic, gravity, and electrostatic separation were found to be ineffective in recovering RE minerals from such sources. Recent studies on chemical leaching or leaching after roasting to break manganese and iron oxide bonds[9,10] showed some promise for RE recovery from the WREM. The WREM from the Panxi RE deposit contains up to 14 pct manganese, mainly as MnO2, MnO(OH), and Mn2O3. These manganese oxides are highly soluble and dissolve readily during chemical leaching, releasing manganese along with RE elements in the leachates. The presence of manganese will interfere with the subsequent recovery of RE elements from corresponding leachates. To improve RE recovery and reduce chemical and purification costs, there is an incentive to selectively remove manganese before RE R. CHI, G. ZHU, and S. XU, Associate Professors, are with the Institute of Nuclear Energy Technology, Beijing, 100084, People’s Republic of China. J. TIAN, Research Associate, is with the Jiangxi Institute of Science, Nanchang, People’s Republic of China. J. LIU, Postgraduate Student, and Z. XU, Professor, are with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada T6G 2GB. Manuscript submitted March 13, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
leaching. To maximize the utilization of natural resources, manganese recovery should be considered as an integral part of the process. It is well documented that MnO2, MnO(OH), and Mn2O3 are highly soluble in an acidic reducing environment. Ferrous sulfate (FeSO4)[11–14] and pyrite (FeS2)[15] have been tested as reducing agents of tetravalent and trivalent manganese to a divalent state, which is recovered as manganese sulfate. A recognized concern of using FeSO4 and FeS2 as reductants is the release of a significant amount of iron, which interferes with the manganese recovery. It is clear that there is a need to search for an alternative reductant that does not affect the manganese recovery. In this communication, sodium sulfite (Na2SO3) is cons
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