Recovery of platinum from spent catalysts by liquid-liquid extraction in chloride medium

This work examines a hydrometallurgical route for processing spent commercial catalysts (Pt and PtSnIn/A2O3) used in Brazilian refineries for recovery of the noble metal with less final wastes generation. Samples were initially pre-oxidized (500 °C, 5 h) in order to eliminate coke. The basis of the present route is the partial dissolution of the pre-oxidized catalyst in aqua-regia. Temperature and time necessary to dissolve all platinum were optimized in order to reduce the operation severity and aluminum solubilization. All platinum and 16-18 wt.% of aluminum were dissolved at 75 °C in 20-25 min. Separation of platinum from the acidic solution was accomplished by solvent extraction. The best extractant (>99 wt.%) was Aliquat 336 (a quaternary ammonium salt) in one stage (A/O phase ratio = 1, v/v). Platinum was stripped (>99.9 wt.%) in one stage (A/O phase ratio = 1, v/v) with aqueous sodium thiosulfate (≥0.75 mol L−1). Black platinum was obtained from this solution via reduction with magnesium or ascorbic acid.