A Comprehensive Comparison of Various Technologies for Regenerating Platinum Group Metals from Automotive Catalysts: The regeneration of platinum group metals from automotive catalysts is a global challenge. While various technologies can achieve the goal of recycling platinum group metals, a comparison is made of comprehensive indicators such as recovery rate, consumption, environmental impact, efficiency (processing cycle), equipment investment, and ease of industrialization. Pressure cyanidation in hydrometallurgical processes has no practical application, and chlorination leaching will eventually be phased out. Pyrometallurgical smelting has greater applicability and adaptability, and the secondary waste generated meets environmental protection requirements. Currently, almost all precious metal recycling plants worldwide use pyrometallurgical smelting for enrichment. Among pyrometallurgical enrichment processes, phase reconstruction smelting, plasma smelting, copper smelting, and lead smelting each have their own advantages and disadvantages in terms of comprehensive utilization and technical indicators.
Characteristics of Waste Catalysts:
Early catalysts used γ-Al₂O₃ as a support and were in the form of small spheres; these are no longer used. Currently, the primary materials used are high-melting-point silicon and aluminates (ferrous cordierite 2FeO·2Al₂O₃·0.5SiO₂ and magnesian cordierite 2MgO·2Al₂O₃·0.5SiO₂) and metals, forming cylindrical honeycomb or multi-layered cylindrical supports. The supports are first impregnated with a γ-Al₂O₃ active coating, dried, and then impregnated with a noble metal solution. The catalyst is then produced through reduction sintering. The cordierite binary catalyst contains 0.04% Pt and 0.015% Pd, totaling 550 g/t. The ternary catalyst contains 0.08~0.12% Pt, 0.017~0.04% Pd, and 0.007~0.014% Rh, totaling 1000~1500 g/t. Platinum metal is attached to the surface of the active coating of the support as <1 μm fine particles.
Due to the high melting point and chemical inertness of the carrier, which is poorly soluble in acids, and the low purity of precious metals, some precious metal particles may penetrate into the carrier during high-temperature use, or be partially encapsulated by sintering or localized glazing of the carrier, or transform into chemically inert oxides and sulfides. Therefore, the technology for recovering platinum group metals from spent automotive catalysts is correspondingly complex and difficult. These characteristics make the research and development of recovery process principles and overall technology representative in the field of secondary resource recycling.
Process Characteristics:
The complete process for treating spent catalysts still consists of three stages: enrichment, separation, and refining. The primary step and key technology of the entire process is the efficient enrichment of precious metals, i.e., using techniques such as pyrometallurgical smelting or wet leaching to separate the carrier from the precious metals, extracting the intermediate product enriched with precious metals, and obtaining a platinum-palladium-rhodium concentrate. Subsequent processing is small-scale; further separation and refining into products can be achieved using traditional selective precipitation, solvent extraction, or solid-liquid extraction methods, which are relatively mature technologies.
The enrichment technologies that have been studied or applied locally can be divided into two main categories: pyrometallurgical smelting and hydrometallurgical leaching. Large-scale recycling plants mostly use pyrometallurgical smelting for enrichment.
