Platinum Recovery Using Calcium Vapor Treatment

Abstract

To develop an effective process for the recovery of precious metals from scrap, a new platinum (Pt) extraction process using alloy formation by calcium (Ca) vapor and successive leaching with an aqueous solution were investigated. Pure Pt samples were reacted with Ca vapor at constant temperatures ranging between 1073 and 1173 K for three to twelve hours, and Ca–Pt alloy samples were synthesized. The obtained Ca–Pt alloy was then dissolved in aqua regia or in an aqueous HCl solution at room temperature. Platinum was recovered from the leaching solution by conventional (NH4)2PtCl6 precipitation method, and the amount of Pt obtained by each process was analyzed. It was found that more than 90% of the Pt was recovered by this process. After Ca vapor treatment, 100% of the Pt was dissolved when kept in aqua regia for one hour, whereas only 14% of untreated pure platinum was dissolved when kept in aqua regia for four hours. In some experiments, the obtained Ca–Pt alloy samples were oxidized in air for reducing the amount of acid needed for dissolution. Although Pt hardly dissolves in aqueous HCl solution at room temperature, it was found that Ca vapor treatment followed by oxidation is effective in increasing the rate of dissolution in aqueous HCl solution.