Abstract
The rising demand for platinum-group metals (PGMs) along with the fast depletion of high-grade natural ores make necessity to search for the alternative resources. In this context, the recycling of spent automobile catalysts can play a vital role mainly due to a higher concentration of PGMs than in primary ores. In this study, the recycling of PGMs from spent automobile catalysts has been investigated using the pressure oxidative leaching while using the biogenic cyanide solution as the potential lixiviant to PGMs’ complexation. Notably, the bio-cyanide was produced by the oxidative decarboxylation of glycine during the late exponential growth phase of Chromobacterium violaceum. The pressure leaching parameters were optimized to be temperature = 150 °C, pO2 = 14 bar, and time = 2 h, yielding >95% PGMs’ leaching efficiency. The kinetic plots of {–ln(1–x)}2 vs. t for PGMs’ dissolution determined the values of apparent activation energy (i.e., Pt-leaching = 40.3 mol∙L−1 and Pd-leaching = 45.7 mol∙L−1), indicating that the pressure leaching process was controlled by the surface-chemical reaction and followed the empirical rate model. The obtained leach liquor was found suitable to undergo for the downstream separation and recovery process.