Leaching Kinetics of Platinum and Palladium from Spent Automotive Catalysts

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Abstract
Empirical rate expressions for both platinum and palladium were obtained from mass balances and concentration-time data in a packed bed reactor using different (HCl):(HNO3) leaching solution concentration ratios. The spent catalysts used in this study (-60+70 mesh to -120+140 mesh) were analyzed to be 3791 ppm platinum and 1306 ppm palladium. High initial rates for both platinum and palladium were obtained for the early stages of leaching and were followed by rapid decay up to about 110 minutes and 50 minutes respectively. Typical concentrations in the leached solution were about 40 ppm Pt and 20 ppm Pd after about 5 hours for the experimental conditions used. The extent of reaction for platinum was in the 90 percent range while that of the palladium was in the 70 percent range.