Method for refining precious metals

摘要

A method for economically removing base metal impurities, other oxidizable impurities, and volatile impurities from precious-metal-bearing metallic materials, consisting of silver and gold, to obtain, with high recovery, a resultant precious metal of high purity (more than 99.9%) that greatly reduces refining time and precious metal loss in recovery. The method includes the steps of (1) controlled heating to maintain a temperature slightly above the melting temperature of the molten metallic mass, (2) maintaining contact between an oxidizing agent and the metallic mass to provide a concentration of dissolved oxygen within the molten metal throughout the refining process, (3) maintaining a flux medium on the surface of the molten material that absorbs base metal and other impurity oxides, and (4) controlling the concentration of base metal and other impurity oxides in the flux to a level that ensures continued transfer of the base metal oxides into the flux medium. The oxidizing agent, which is continuously absorbed into solution in the molten precious metal, combines with base metal impurities such as copper, zinc, iron or lead, and other oxidizable impurities to form oxides which are absorbed in the molten flux floating on the metallic surface. The concentration of base metal oxides is controlled in one embodiment in the flux medium through sequential treatments in which flux is applied and then removed after an appropriate amount of time. The amount of precious metal, and its purity recovered is greatly enhanced. Each flux increment is reused in a subsequent batch at a prior sequential stage of refinement.