Development of New Dissolution Process of Platinum via Double Oxides

To decrease the environmental load due to current Pt dissolution processes that use strong acids in combination with oxidizing agents, dissolution of Pt in hydrochloric acid (HCl) by way of alkali metal platinates was examined. Synthesis of Pt containing double oxides was examined by calcining mixtures of Pt black and the alkali metal carbonates (Li, Na, K) at 600-800 degrees C in air. As a result, it was found that Li2PtO3 powder was obtained through the calcination of Pt black and Li2CO3 at 600 degrees C. The formation of NaPt3O4 and Na2PtO3 was also confirmed upon the calcination of Pt black and Na2CO3 at 600-800 degrees C, whereas a part of Pt remained unreacted in the calcined samples. In contrast, the calcination of Pt black and K2CO3 did not yield any Pt containing oxides, even at 800 degrees C. These results indicate that Li2CO3 has the highest reactivity among the examined alkali metal carbonates for the formation of the platinates. The time dependence of the concentrations of Pt and Li ions leached out of the resulted Li2PtO3 in HCl was monitored by inductively coupled plasma optical emission spectrometry. The results showed that Li+ leached into HCl solution prior to Pt4+, and the solubility of the double oxides increased with decreasing calcination temperature. The dissolution behavior of Li2PtO3 was discussed based on its particle properties such as crystallite size, surface areas and anisotropy of the crystal.