In order to develop a chemical technique for the recovery of gold (Au) and platinum (Pt) in the metallic state from spent catalysts, e.g., catalysts for environmental protection and automobile and petroleum catalysts, the coprecipitation behaviors of Au(III) and Pt(IV) complex ions with Fe(OH)2 as a scavenging and reducing agent were investigated. The Au(III) complex ions were found to be stoichiometrically and rapidly reduced to metallic Au due to electron transfer in acidic aqueous solution prior to coprecipitation with Fe(OH)2. Conversely, Pt(IV) complex ions were reduced only after coprecipitation with Fe(OH)2 due to electron transfer through a Pt(IV)-O-Fe(II) bond on the solid Fe(OH)2. Using this chemical technique, Au and Pt can be selectively and effectively recovered in the metallic state.
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