Synthesis of sodium platinates and their dissolution behaviors in hydrochloric acid: Effects of lithium carbonate addition on platinate formation

• Pt dissolution from a Na–Pt complex oxide is studied.
• Addition of Li2CO3 significantly promoted the formation of Na2PtO3.
• Na2PtO3 easily dissolved in HCl, irrespective of the addition of Li salt.
• A safe and low-cost Pt recovery process realized by using Na2PtO3

The Pt-containing complex oxide Li2PtO3 easily dissolves in HCl in the absence of an oxidizing agent. A similar dissolution behavior is expected for Na2PtO3 that has a crystal structure similar to Li2PtO3; however, the preparation of Na2PtO3 requires high temperature and prolonged time. In the present study, we report our investigation on the effect of Li salts on the synthesis and dissolution properties of Na2PtO3, a cost-effective Pt-group metal complex oxide alternative to Li2PtO3. The addition of a small amount of Li2CO3 drastically accelerates the formation of Na2PtO3, allowing for synthesis of the complex oxide under milder conditions. Calcination of Pt black and Na2CO3 at 800 °C for more than 12 h was necessary for reaction completion; however, samples calcined with Li salt with the ratio Li/(Na + Li) = 0.20 showed complete reaction of Pt after calcination at 800 °C after only 1 h. The obtained samples were identified as a (Na,Li)2PtO3 solid solution having the structure of Na2PtO3 in which Na+ is substituted with Li+. Investigations of the effect of Li addition on complex oxide dissolution properties in conc. HCl were performed by examining the time dependence of Pt, Na, and Li concentrations using inductively coupled plasma-optical emission spectroscopy. The results showed that (Na,Li)2PtO3 solid solutions are easily dissolved in HCl as well as Na2PtO3. A Pt dissolution process using (Na,Li)2PtO3 solid solutions is facile and does not require a toxic oxidizing agent; therefore, this process is promising in terms of cost-efficiency and safety.