Chemistry and Mechanism of Interaction Between Molybdenite Concentrate and Sodium Chloride When Heated in the Presence o
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INTRODUCTION
MOLYBDENITE concentrate is the principal source from which molybdenum is extracted. The commercial route for the extraction of molybdenum involves roasting of its concentrate, purification of the resultant calcine by hydrometallurgical way to MoO3, and hydrogen reduction of the trioxide to the metal. Although this method is the main way for the production of molybdenum and has long been used in industry, studies on its application to different concentrates,[1] as well as kinetics[2,3] and mechanism[4] of roasting, are still scarce. However, as a result of the well-known disadvantages of molybdenum pyrometallurgical extraction, hydrometallurgical processes have become more and more attractive. Among them, nitric acid leaching,[5,6] oxygen pressure leaching,[7,8] electric-oxidation extraction,[9] sodium chlorate[10,11] and hypochlorite leaching,[12] and bio-leaching[13–15] are more popular.
PAVEL V. ALEKSANDROV, ALEXANDER S. MEDVEDEV, and VITALIY A. IMIDEEV are with the Department of Non-Ferrous Metals and Gold, National University of Science and Technology MISiS, Moscow, Russia 119049. DMITRY O. MOSKOVSKIKH is with the Center of Functional Nano-Ceramics, National University of Science and Technology MISiS, Moscow, Russia 119049. Contact e-mail: [email protected] Manuscript submitted June 4, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
Another way to extract molybdenum from molybdenite concentrate is through the use of combined methods where the concentrate is roasted with various additives in order to convert Mo to a soluble form and to bind sulfur to form sulfates, thus enabling the elimination or significant reduction of SO2 emissions. Lime[16] or sodium chloride could be used as additives.[17–19] In this paper, roasting of molybdenite concentrate with sodium chloride was studied. Special aspects of the interaction between molybdenite concentrates and sodium chloride when heated in the presence of oxygen are not very well known, although their applied significance may be large. As it was shown,[17] replacement of conventional oxidizing roasting of molybdenite concentrates with low-temperature roasting with sodium chloride makes it possible to significantly reduce the formation of SO2 due to the capture of sulfur in sodium sulfate. When this occurs, about 30 to 50 pct of molybdenum is present in the roast residue in the form of water-soluble sodium molybdates, and the roasting temperature thus may be reduced from the conventional 853 K to 873 K (580 C to 600 C) to 698 K to 748 K (425 C to 475 C), thereby reducing the costs of the heating of the furnace charge and the hydrometallurgical processing of the roast residue. The first paper on the interaction between molybdenite and sodium chloride in an oxygen flow was published in 1988, and is not very informative.[18] Therefore, the authors concluded about the existence of chemical reactions in the MoS2-NaCl-O2 system when heated at
temperatures 473 K to 903 K (200 C to 630 C); however, sodium sulfate, chlorides, or oxychlorides were not identified in th
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