The Influence of the Composition of Lead Cakes on the Extraction of Osmium and Rhenium During Their Hydrometallurgical Processing

The processing of lead cakes containing osmium and rhenium is complicated by the significant variability in their elemental and phase compositions. The aim of this study was to determine the effects of lead cake composition on acid consumption and the recovery of Os and Re during oxidative leaching in a continuous-flow reactor. The leaching of 15 industrial cakes derived from copper production—containing 440–4260 g/t Re and 23–63 g/t Os—was investigated in a sulfuric acid medium, using sodium hypochlorite as the oxidizing agent. The experimental results showed that increasing contents of PbCO3, PbO, and metallic Pb in the cake reduce Os and Re recovery at a fixed reagent dosage. It is established that variations in H2SO4 consumption are primarily driven by the cake’s phase composition; in particular, the acid is consumed through reactions with acid-neutralizing matrix components (PbCO3 and PbO), thereby altering the effective pulp acidity and oxidative leaching conditions. Thermodynamic modeling indicated that pH changes primarily affect the chemical state of matrix components, whereas Os and Re remain predominantly in the forms OsO4(aq) and ReO4−, respectively. Under near-optimal conditions, recoveries of up to 95–96% for Os and 99–100% for Re were achieved. The kinetic study results demonstrated a faster extraction rate for Re compared with Os. In summary, the results show that the phase composition of the cake is a key parameter influencing acid and oxidant consumption; furthermore, adjusting the reagent regime based on the composition of industrial lead cakes enhances the stability and efficiency of Os and Re recovery.