China Nonferrous Metallurgy

Spent automotive catalysts are an important secondary resource of platinum group metals (PGMs). Conventional iron-collection pyrometallurgical processes require the addition of extra iron collectors and large amounts of slag-forming fluxes, resulting in high processing costs. To reduce costs and promote the synergistic utilization of solid wastes, this study proposes a co-smelting process using iron tailings rich in SiO₂, CaO, and Fe₂O₃ together with spent automotive catalysts. In this process, iron tailings serve simultaneously as both a collector for pyrometallurgical recovery of PGMs and a fluxing agent. Thermodynamic analyses and single-factor experiments were conducted to investigate the effects of key process parameters on the recovery of PGMs, followed by validation experiments and characterization analyses. Thermodynamic calculations indicated that at 1 500℃, platinum group metal oxides could be reduced to their metallic states by carbon, iron, and iron oxides, with Gibbs free energy changes (ΔG) below zero. When the temperature exceeded 1 550℃, SiO₂ was readily reduced to elemental silicon, which subsequently reacted with iron to form Fe-Si alloys, thereby hindering the subsequent separation process. Furthermore, at 1 500℃, the SiO₂-CaO-Al₂O₃-MgO (5%) quaternary slag system exhibited a broad liquid-phase region, ensuring complete melting, favorable fluidity, and good stability. The experimental results showed that under the optimal conditions of a smelting temperature of 1 500℃, binary basicity (CaO/SiO₂) of 0.7, iron tailings addition of 30%, and reductant addition of 1.2%, the recovery rates of Pt, Pd, and Rh reached 98.45%, 98.23%, and 96.7%, respectively. XRD and SEM-EDS analyses revealed that PGMs were highly and uniformly dispersed within the Fe-based alloy phase, forming stable solid solutions with metallic iron and achieving efficient enrichment of PGMs. The final slag exhibited a glassy structure, enabling the stable immobilization of hazardous components. This technology provides an efficient, low-cost, and environmentally friendly solution for the synergistic resource utilization and harmless treatment of spent automotive catalysts and iron tailings. It also demonstrates significant industrial application potential for promoting the recycling of secondary platinum group metal resources and the sustainable management of metallurgical solid wastes.