Leaching Velocity of Precious Metalswith Various Leaching Agents

Abstract

Leaching velocity of Au, Ag, Pt and Pd was investigtated using four leaching agents : aqua regia, I₂/KI, bleaching powder and thiourea.
In the aqua regia leaching, Pd and Au are rapidly leached, while Ag and Pt are little leached. In the 12/KI leaching, Au and Pd are rapidly leached, whereas Ag and Pt are not leached enough. In the bleaching powder leaching, Au and Pd are rapidly leached compared with a small leached velocity of Ag and Pt. On the other hand, Au and Ag are rapidly leached by the thiourea leaching method, but then Pd and Pt are not leached at all. These leaching phenomena can be explained by the ability to form stable complexes with precious metal ions and the oxidation power of the leaching agents.