Abstract
The hydrometallurgical recovery process of precious metals involves a great environmental load. This is because strong oxidant and complexing agents such as aqua regia are required to dissolve these metals which have high chemical stability. To enhance the dissolution, alloying with other metals may be effective as is conventionally used in production and refinement of some precious metals. When precious metal alloys are immersed in aqueous solution, the less noble metals in them dissolve preferentially and precious metals form transient particles. Thus, the Gibbs-Thomson effect, which explains the excess free energy of small particles, may contribute to the enhancement. Based on the assumption, an exposure to zinc vapor was proposed as a pretreatment for the leaching of precious metals. Precious metals form alloys or intermetallic compounds with zinc during the pretreatment, and if these products can be dissolved more easily than the pure metals, the environmental load involved in the recovery will be reduced. Dissolution rates of some precious metal-zinc compounds were evaluated quantitatively by channel flow double electrode method to discuss the effect of the pretreatment.
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