The Kinetics of Oxidation of Molybdenite Concentrate by Water Vapor
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I.
INTRODUCTION
MOLYBDENITE (MoS2) is the major mineral for molybdenum. In the conventional pyrometallurgical process, oxidation roasting is applied to produce MoO3, one of the commercial products containing Mo. However, there are several serious problems in processing molybdenite by this method: Valuable elements in the concentrate such as rhenium and selenium cannot be recovered easily to high degrees and air pollution may occur due to the emission of SO2 gas.[1,2] The rhenium-bearing off-gas is scrubbed and the scrubbing solution is subjected to ion exchange to recover part of the rhenium contained in the concentrate. However, this process is expensive and has poor recovery efficiency. Sohn[3–6] and Hakobyan[7] investigated a water-vapor oxidation process as an alternative to the conventional roasting process. This new process offers the possibility of lower emission of sulfur containing pollutants by recovering the sulfur in MoS2 in an elemental form. It also makes it easier to extract valuable minor elements from the ore. The major objective of this research was to study the feasibility of this new process and to determine the kinetics of oxidation of MoS2 by water vapor.
EDGAR BLANCO, Graduate Student, HONG YONG SOHN, Professor, and GILSOO HAN, Postdoctoral Fellow, are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112. Contact e-mail: [email protected] KLIMENT Y. HAKOBYAN, Head and Principal Investigator, is with the, Navro Ltd., Kapan, Armenia 377810, and the Kapan Metallurgy and Enrichment Laboratory, Academy of Science of Armenia, Kapan Town, Armenia, 377810. Manuscript submitted April 19, 2006. Article published online July 10, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
II.
EXPERIMENTAL
The experimental setup used in this study is shown in Figure 1. It consisted of a water-vapor feeding system with an evaporator, a movable vertical tube furnace with vertical trail, a reactor, and an off-gas system with a NaOH-solution scrubber. The reactor had a double wall: the outer wall was a stainless steel tube and the inner wall was a mullite tube with 45-mm inner diameter, which prevented hydrogen generation from the reaction between water vapor and stainless steel at high temperatures. The sample used in this study was a molybdenite concentrate containing 80 pct MoS2 screened to – 60 mesh size. Figure 2 shows the size distribution of the sample measured using a Beckman Coulter laser diffraction analyzer model LS230 (Beckman Coulter, Inc., Fullerton, CA). This figure also shows the size distribution of the oxidation products to be discussed subsequently. The chemical composition of the concentrate is summarized in Table I. The sample was homogenized and kept in a desiccator after being dried to remove moisture and a small amount of oil used for flotation. A layer of sample powder with a thickness of 1 mm was placed in an alumina tray and put into the vertical reactor. The reactor, purged with Ar gas, was positioned in the furnace by pulling up the furnace after
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