Enhanced dissolution of alkali metal platinates in dilute hydrochloric acid by addition of calcium chloride

• The addition of CaCl2 in 3 M HCl drastically enhanced the solubility of platinates.
• Platinates were prepared by calcinations of Pt(0) with alkali metal salts in air.
• Our new process is much safer than current methods using toxic oxidizing agents.

To decrease the environmental load from current Pt recovery processes that use strong acids in combination with oxidizing agents, the dissolution of Pt in hydrochloric acid (HCl) by way of alkali metal platinates was examined. The alkali metal platinates, Li2PtO3, Na2PtO3, and a (Na,Li)2PtO3 solid solution, were prepared by calcining mixtures of Pt black and the alkali metal carbonates (Li,Na) at 600−800 °C in air. The dissolution of the resulting alkali metal platinates in HCl solutions was monitored by inductively coupled plasma–optical emission spectrometry. The results showed that Pt solubility approached 100% after choosing the appropriate calcination conditions. It was also found that by adding calcium chloride, the rate of Pt dissolution in dilute HCl significantly increased. The dissolution behavior of the alkali metal platinates was discussed based on the dissolution rates of the alkali metals and Pt ions, together with the crystal structures of the platinates.