Co-treatment of spent automotive catalyst and copper-bearing electroplating sludge to alloy platinum group metals with base metal matrices

Abstract

Spent automotive catalyst (SAC) is an important secondary metal resource of platinum group metals (PGMs). However, the traditional smelting process for recovering valuable metals from SAC generally has the problems such as high reagents consumption and increased solid waste. Thus, a novel co-treatment process of SAC and copper-bearing electroplating sludge (CBES) was proposed in this study, where CBES was first used as the capture agent and fluxing material in the pyro-capture process of PGMs. The effects of separation behaviors of PGMs and copper under different smelting conditions were studied systematically. The optimum conditions for this process are as follows: m(CBES)/m(SAC) of 2.0, m(SiO2)/m(Al2O3) of 3.00, basicity of 0.80, 5.0 wt% Na2B4O7, oxidative temperature of 1460 ℃, oxidative time of 30 min, NC/Cu of 1.250, reductive temperature of 1300 ℃, and reductive time of 90 min. Under these conditions, the sulfur removal rate exceeds 99% while the recoveries of Pt, Pd, Rh and Cu are 99.26%, 98.53%, 99.96% and 97.60%, respectively. The addition of pure reagents is only about 47% of the total waste mass. Furthermore, the capture process of Cu-Fe alloy for PGMs was discussed, which can consist of three steps: reduction of copper and iron, mutual migration and collision of the reduced metal atoms, and alloying. Finally, the produced slag was synthesized into non-hazardous glass-ceramics material successfully. To sum up, this study achieved the efficient recycling of two hazardous wastes simultaneously.