The leaching of galena in cupric chloride media
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I.
INTRODUCTION
THE
hydrometallurgical treatment of either conventional lead concentrates or lead-bearing pyritic bulk concentrates is promising from the points of view of SO2 avoidance, in-plant hygiene, and selectivity of lead extraction with respect to other base metals. The hydrometallurgical route can directly produce high purity lead, and preliminary cost estimates are encouraging, especially for small-scale operations. Problems sometimes are encountered with the recovery of the associated silver values, and such difficulties usually can be related to the presence of refractory silver minerals in the feed. Although many hydrometallurgical routes have been considered, ill most of the activity has focused on either FeC13-HC1 or CuClz-HC1 leaching systems. In fact, two major pilot-scale campaigns t2,31have been carried out on the ferric chloride leaching of lead concentrates, and a significant amount of fundamental research has been done on the relevant kinetics of reaction of galena with ferric chloride solutions. Ill Cupric chloride leaching processes offer some advantages over ferric chloride leaching in terms of the reaction rates, subsequent solution purification operations, and the ease of lixiviant regeneration. As a result, cupric chloride-hydrochloric acid leaching processes have been evaluated extensively for copper concentrates t4`Sj and also have been examined for the treatment of mercury concentrates to avoid the in-plant mercury hygiene problems associated with roasting, t6~ Although the cupric chloride processing of lead concentrates has not been examined exhaustively, a number of studies have been carried out. The Reynolds process m treats lead concentrates at 30 ~ to 60 ~ with 8 to 25 g / L CuClz and 100 to 250 g / L NaC1 solutions to form PbC12 and elemental sulfur. Even at the low temperatures employed, >97 pct overall Pb recovery is achieved during 1 to 14 hours of leaching. The PbC12
J.E. DUTRIZAC, Research Scientist, xs with the Mineral Sciences Laboratories, CANMET, Energy, Mines, and Resources Canada, 555 Booth Street, Ottawa, ON, K1A 0G1, Canada. Manuscript submitted August 1, 1988. METALLURGICAL TRANSACTIONS B
crystals are purified v/a a high temperature-high pressure brine leaching operation, and lead metal is formed by H 2 reduction of the PbC12. The HC1 formed during lead reduction is used in combination with O2 to regenerate the CuC12 lixiviant. Various CuC12-FeC13 and CuC]2-CI 2 media were evaluated for the treatment of McArthur River ores.t8~ In all cases, rapid lead leaching is realized, and total lead extractions invariably exceed those of Cu, Zn, or Ag. A pure PbC12 product is formed by cooling the CuC1-ZnC12PbC12-FeC12 pregnant solution. The Minemet cupric chloride leach process I91has been applied to lead-bearing complex sulfide ores and concentrates. Lead is leached rapidly and completely under the preferred conditions, and a residue consisting mostly of elemental sulfur and pyrite is formed. Although details of the lead recovery circuit are not given, it seems that PbC
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