The Use of Oxalic Acid as a Chelating Agent in the Dissolution Reaction of Calcium Molybdate
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MOLYBDENUM is widely used in steel, aviation, electronic, nuclear and chemistry industries. Industrially important molybdenum minerals are molybdenite (MoS2), powellite (CaMoO4) and wulfenite (PbMoO4), which are considered as primary molybdenum resources. Secondary molybdenum resources are spent catalyst and scrap. In general, molybdenum minerals co-existed with copper and tungsten minerals and they are obtained as secondary mineral during ore enrichment processes. MoO3 is produced commercially by roasting of primary molybdenum ores at elevated temperatures and processing of resultant calcine either by pyrometallurgical or hydrometallurgical routes. Commercial grade molybdenum is obtained by reduction of MoO3 with H2 in two or more stages.[1–4] Rapid development of the technology has increased the demand on molybdenum, resulting in the decrease of the amount of easy-handling molybdenum ores. Additionally, the conventional production methods have been limited because of the increased environmental restrictions. In order to meet the increasing demands, SEDAT ILHAN and AHMET ORKUN KALPAKLI, Research Assistants, CEM KAHRUMAN, Assistant Professor, and IBRAHIM YUSUFOGLU, Professor, are with the Department of Metallurgical and Materials Engineering, Faculty of Engineering, Istanbul University, 34320, Avcilar, Istanbul, Turkey. Contact e-mail: ilhans@ istanbul.edu.tr Manuscript submitted February 21, 2012. Article published online February 14, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
the new production methods should be developed to utilize low grade ores or secondary resources.[4] It is possible to process low grade molybdenum ores and secondary resources by hydrometallurgical processes which are more environmentally friendly than pyrometallurgical processes. Thus, the importance of the use of hydrometallurgical processes has been increasing in the molybdenum production industry. Wang et al.[5] investigated the recovery of molybdenum from low grade Ni-Mo ore by alkaline leaching and determined the optimum roasting conditions in which all molybdenum bearing compounds were converted to CaMoO4. Medvedev et al.[6] obtained monophase CaMoO4 by leaching of low grade molybdenum concentrate in nitric acid. Gupta[2] reported that CaMoO4 was obtained by roasting of low grade MoS2 with limestone and it was leached in 1 kmol m3 H2SO4 solution at 353 K to 363 K (80 °C to 90 °C) for 2 hours. Molybdenum was extracted from molybdenum concentrates with pressure oxidation leaching and solvent extraction.[7–9] Zhao et al.[8] reported a direct hydrometallurgical process, which included the leaching of molybdenum by air oxidation in alkaline solution and the extraction and recovery from Ni-Mo ore. Kholmogorov and Kononova[9] investigated the oxidative leaching of MoS2 in alkaline solution and the sulphur content of the final product was lowered to less than 0.1 pct. Padilla et al.[10] investigated the carbothermic reduction of MoS2 in the presence of CaO and studied the thermodynamics of the MoS2-C-CaO system to explain the proce
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