Synthesis of alkali metal platinates and their dissolution behavior in hydrochloric acid

To decrease the environmental load due to current Pt dissolution processes that use strong acids in combination with oxidizing agents, the synthesis and dissolution of alkali metal platinates in hydrochloric acid (HCl) were examined. The alkali metal platinates were prepared by calcinating mixtures of Pt black and the alkali metal carbonates (Li, Na, K) at 600-800 degrees C in air. Li2PtO3 powder was obtained through the calcination of a Pt black and Li2CO3 mixture at 600 degrees C. The formation of NaPt3O4 and Na2PtO3 was confirmed upon the calcination of Pt black and Na2CO3 at 600-800 degrees C; however, unreacted Pt also remained in the calcined samples. The calcination of Pt black and K2CO3 did not yield any Pt-containing oxides, even at 800 degrees C. These results indicated that Li2CO3 was the most active reagent among the examined alkali metal carbonates for the formation of alkali metal platinates. The dissolution of the resulting Li2PtO3 in conc. HCl was monitored by inductively coupled plasma-optical emission spectrometry. The results showed that Li ions leached into HCl prior to the Pt, and the solubilities of the metals increased with decreasing calcination temperature. The dissolution behavior of Li2PtO3 was discussed based on the crystallite size and anisotropy of the crystal. A Pt dissolution process by way of these platinates is expected to benefit the establishment of recovery processes for PGMs with low environmental loads. (C) 2013 The Ceramic Society of Japan. All rights reserved.