Effect of different leaching agents on the recycling of valuable metals in spent molybdenum-based catalyst.

Conventional hydrometallurgical recycling of spent molybdenum-based catalysts is often constrained by a trade-off between selectivity and total metal recovery when using single-step alkaline or acidic leaching. To overcome this limitation, this work presents a novel two-stage leaching process designed for the sequential and selective extraction of valuable metals. The approach leverages an initial alkaline leach (NaOH) to selectively dissolve molybdenum and silicon, achieving extraction efficiencies of 95.8% for Mo and 58.1% for Si while minimizing co-dissolution of other metals. The resulting residue is subsequently subjected to an acidic leach (HNO3) for the comprehensive dissolution of residual Fe, Mg, Mo, and Ni. A solvent extraction step employing P507 then enables highly efficient separation, extracting 96.0% Fe and 98.4% Mo from the mixed acidic leachate. The final step uses hydrochloric acid as a stripping agent to separate Fe from Mo. This integrated methodology demonstrates a significant advancement by synergistically combining the high selectivity of alkaline media with the broad dissolution capability of acids, offering a targeted and efficient route for the valorization of complex spent catalyst streams.