Abstract:A novel process for the recovery of platinum group metals from spent automotive catalysts, of which Bi was used as the capturing agent with the properties of environment-friendly, non-toxic, and low melting temperature, was proposed, and the slag system of Na₂O-SiO₂-Al₂O₃-Bi₂O₃ was applied to the pyrometallurgical smelting process. The effects of slag basicity, capturing agent mass, smelting temperature, smelting capturing time, and mass ratio of Si to B on the recovery rates of Pd, Pt and Rh were systematically investigated. The results show that the platinum group metals containing bismuth alloy with smooth surface and simplicity in two-phase separation can be obtained under the optimal experimental conditions of slag basicity of 0.71, Bi mass of 1.9 g, smelting temperature of 1100 ℃, smelting capturing time of 10 min, and Si to B mass ratio of 0.94:1. The recovery rates of Pd Pt and Rh are 98.90%, 95.02% and 97.00%, respectively, and the overall Pd, Pt and Rh recovery reach as high as 99% by secondary smelting. The trace platinum group metals are preferentially reduced to atomic state or atomic clusters, which can bind with the newly generated metallic Bi, form the binary intermetallic compound of α-Bi₂Pd, Bi₂Pt and Bi₄Rh. The similar lattice structures can reduce system free energy, and further achieve excellent capturing effects of Pd, Pt and Rh. The successful development of this process provides a new route for the comprehensive utilization of platinum group metals in waste automotive catalysts.

Key words: bismuth; spent automotive catalyst; pyrometallurgical capture; palladium; platinum; rhodium