Pyrometallurgical processing of spent automotive catalysts by collector metal smelting

This review consolidates current knowledge on the influence of flux addition on the structural and rheological properties of the slag phase during the pyrometallurgical smelting of spent automotive catalysts using a collector metal. The analysis draws on Russian and international studies that examine the processing of automotive catalysts containing platinum-group metals. The study evaluates the mechanisms by which flux additives, including calcium, sodium, and boron oxides, as well as calcium fluoride, modify the melt microstructure. It focuses on the degree of polymerization in silicate and aluminosilicate networks resulting from variations in the distribution of chemically bound oxygen. The findings show that effective control of the pyrometallurgical smelting process depends on maintaining an appropriate balance between polymerized and depolymerized structural units in the slag. Basic oxides reduce melt viscosity by breaking bridging bonds; however, they also increase oxygen activity, which promotes oxidation and loss of platinum, palladium, and rhodium. These results underscore the need for composite flux formulations that adjust melt properties while minimizing the oxidation potential of the slag. A central challenge in improving the recovery of platinum-group metals from this secondary raw material is the development of quantitative models that link flux composition, slag structure, and oxidation potential. These conclusions support predictive evaluation of multicomponent systems and provide a basis for optimizing smelting parameters to increase metal recovery to the collector while reducing energy use and operating costs. The development of predictive models using modern thermodynamic software packages represents a key direction for further research.