Recovery of platinum from spent catalyst

During the manufacture of nitric acid from ammonia there is a slow loss of catalytic platinum gauze. This fine dust, which contains 13.7% Pt, 1.3% Rh and other impurities such as iron oxide and silica, is deposited on the internal reactor walls and cooling coils. The dust was refluxed with aqua regia at a liquid/solid ratio of 7.5 for 1.5 h to solubilise platinum for subsequent recovery. Platinum was separated from the leach liquor by direct precipitation and by solvent extraction using trioctylamine in kerosine. In both cases the platinum was recovered as diammonium hexachloroplatinate by precipitation using ammonium chloride. The precipitate was decomposed by ignition to produce platinum powder with purity of 97.9% and 99.9% for direct and SX routes, respectively. A platinum recovery of 97.5% was achieved by both routes.