A harmless slagging treatment to separate key impurities from Fe-PGMs alloys for improving the recovery ratio of PGMs from spent auto-catalysts

Abstract

Spent auto-catalysts are main secondary resources for platinum group metals (PGMs) Pt, Pd, and Rh. Considering their scarcity and excessive prices, recycling PGMs from spent auto-catalysts is important for sustainability of PGMs. The dissolution of Fe-PGMs alloys in acids is an important step that significantly influences the recovery ratio of PGMs from spent auto-catalysts by smelting using Fe as a PGMs collector. However, the presence of impurities, such as Si, in Fe-PGMs alloys makes them difficult to completely dissolve in acids, resulting in low PGMs recovery ratios. Few studies have been reported on solutions for eliminating these impurities from the Fe-PGMs without loss of PGMs. In this study, a green slag refining process was proposed to remove key impurities from Fe-PGMs alloys. Different compositions of CaO-SiO2-Al2O3-FeOx and CaO-Al2O3-FeOx slags were investigated to improve the removal of impurities such as Si, Ca, Mg, Ti, and Al in Fe-PGMs to increase the total recovery ratios of PGMs; the removal rates of Si, Ca, Al, Mg, and Ti were 99.2 %, 99.8 %, 99.8 %, 99.7 %, and 99.9 %, respectively, when a CaO-Al2O3-35Fe2O3 (C/A = 1.5; S/A = 1.2) slag was used at 1843 K. After slagging treatment, Fe-PGMs alloy could be easily dissolved in aqua regia, which is conducive to subsequent ion exchange or supramolecular recognition process to obtain high PGMs recovery ratios. This slagging treatment is considered a green and economic approach as the residual slag exhibits no hazardous elements and can be recycled or reused to prepare other products.