Abstract
Solvent extraction with organophosphorus extractants has potential as a low-cost method for efficient Mo recovery for acidic leaching solutions. However, improved selectivity is required to obtain high-purity Mo products. In this study, various acidic organophosphorus extractants were compared, and 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P507) was found to be optimal for efficient Mo extraction and Fe separation from acidic leaching solutions. Under the optimized conditions (40 vol% P507, 3:1 organic/aqueous, 20 °C, 5 min), the Mo and Fe extraction efficiencies reached 98.1 % and 35.2 %, respectively, with a separation factor of 90.1. The Mo/Fe separation efficiency was further improved using a two-stage countercurrent extraction method. The Mo extraction efficiency was attributed to coordination bonds (P = O → Mo) formed between Mo(VI) oxycations and P507 dimers, as well as covalent bonds (POMo) formed by substituting the hydrogen ions in P507. Increasing the H2SO4 concentration in the leaching solution gradually transformed MoO22+ into Mo2O52+ dimers, which formed MoO2(HA2)2 and Mo2O5(HA2)2 metal complexes during the extraction process. HCl scrubbing of the loaded organic phase effectively removed Fe. For subsequent ammonia stripping of the HCl-scrubbed organic phase, the optimal ammonia concentration was 1.25 mol/L. Further increasing the ammonia concentration promoted the saponification reaction of ammonia with P507, thereby reducing the Mo stripping efficiency. In summary, using multistage countercurrent extraction, increasing the H2SO4 concentration in the leaching solution, and scrubbing the loaded organic phase with HCl facilitate efficient Mo/Fe separation, providing a feasible approach for the preparation of high-purity ammonium molybdate with broad application prospects.
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