China Nonferrous Metallurgy

The iron collector product of spent three-way catalysts (PGMs-iron alloy) is a typical intermediate product from precious metal smelting tailings and scrapped catalyst treatment. The large amount of iron present not only severely interferes with the purification accuracy of precious metals but also reduces the processing efficiency of subsequent refining processes while increasing energy consumption and costs. This study takes PGMs-iron alloy as the research object, focusing on the efficiency and controllability of electrolytic separation technology. Anodic dissolution rate (reflecting the stability and sustainability of alloy dissolution) and cathodic current efficiency (characterizing the selectivity of target ion reduction and energy utilization efficiency) were selected as key evaluation indicators. The synergistic effects of process parameters such as electrolysis temperature, electrolyte pH, Fe²⁺ concentration, and current density, as well as the composite electrolyte system composed of sodium citrate (15 g/L), ascorbic acid (2 g/L) and ammonium sulfate (10 g/L) on separation efficiency, were systematically investigated. Key operating conditions were optimized through single-factor variable experiments and mechanism analysis. Experimental results show that under the optimal conditions of temperature 50℃ , pH=5.0, Fe²⁺ concentration 120 g/L, current density 350 A/m², the enrichment factor of platinum, palladium and rhodium in anode slime is 20 times, and the recovery rate exceeds 99 %; The peak position of cathode iron is consistent with the standard card ( PDF 01-087-0721 ), and no other single phase is detected; The waste electrolyte produced in the process can be used to prepare ferrous sulfate by dissolution crystallization; Under the optimum operating conditions, there is no obvious passivation phenomenon in the anode, and there is no obvious side reaction of hydrogen evolution in the cathode. The purity and current efficiency of the product are at a high level. This study not only provides a solid theoretical basis and a direct reference technical scheme for the industrial efficient separation of PGMs-iron alloy, but also provides a new idea for the utilization of PGMs containing waste.