The effect of the elemental sulfur reaction product on the leaching of galena in ferric chloride media
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I.
INTRODUCTION
MOST of
the world's lead production originates from the sinter plant-blast furnace treatment of lead sulfide concentrates containing galena as the predominant lead mineral. Although such technology effectively recovers both lead and associated precious metals, it faces considerable difficulties with respect to environmental and in-plant hygiene regulations. Lead-rich dusts and fumes are a persistent problem, and dilute SO2 gases from the sinter strand are difficult and costly to process. Although the recently developed Queneau-Schuhmann-Lurgi (QSL) m and Kivcet r21 processes overcome many of the traditional difficulties associated with lead smelting, the problems of dealing with dry dusty lead concentrates and dilute SO: tail gases remain. Hence, the hydrometallurgical treatment of lead concentrates is attractive from the perspective of SO2 avoidance, in-plant hygiene, and selectivity with respect to other base metals3 3] Most hydrometallurgical activity has focused on the FeC13-HC1 system, although a lesser amount of work also has been carried out using CuC12-HC1 lixiviants, t4'5~ All the chloride leaching options offer the advantages of wet processing to minimize dust formation and elemental sulfur production to avoid SO: emissions. I6'7] The kinetics of galena dissolution in ferric chloride media are of considerable interest to any ferric chloride leaching process for lead concentrates. The kinetics define the conditions for the rapid and complete dissolution of lead and identify opportunities for the selective removal of lead from associated base metal impurities. A number of kinetic studies have been carried out on the reaction of galena with FeC13, and these investigations were recently the subject of a critical review, t8] For dilute ferric chloride solutions, linear kinetics and chemical control seem to prevail. For example, Rath e t al. [91 examined the leaching of a sized galena concen-
J.E. DUTRIZAC and T.T. CHEN, Research Scientists, are with the Mineral Sciences Laboratories, CANMET, Energy, Mines, and Resources Canada, Ottawa, ON K1A OG1, Canada. Manuscript submitted February 7, 1990. METALLURGICAL TRANSACTIONS B
trate containing 86.3 pct Pb ha 0.1 M Fe3+-0.5 M NaC1 solution over the temperature range of 14 ~ to 80 ~ The simple shrinking core model was obeyed and the rate constant increased according to the 0.76 power of the Fe 3+ concentration. It was concluded that the reaction was electrochemically controlled. Arai e t al. tl~ studied the dissolution of two sized galena concentrates in 0.025 to 0.075 M FeC13 media. The shrinking core model was consistently followed, and the rate increased as the 0.9 to 1.0 power of the FeC13 concentration. It was concluded that the rate-controlling step was the reduction of the ferric ion to the ferrous state on the surface of the PbS. Fuerstenau e t a l . [111 examined the leaching of sized galena concentrates in both dilute and concentrated F e C l 3 media. In dilute solutions containing < 0 . 1 M FeC13, the rate increased as the 2.25 power o
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