Leaching velocity of precious metals with various leaching agents

Leaching velocity of Au, Ag, Pt and Pd was investigtated using four leachin g agents: aqua regia, I-2/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 I-2/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 l eaching method, but then Pd and Pt are not leached at all. These leaching p henomena can be explained by the ability to form stable complexes with prec ious metal ions and the oxidation power of the leaching agents.