Recovery of valuable metals and regeneration of acid from the leaching solution of spent HDS catalysts by solvent extraction

Leaching and solvent extraction experiments have been performed to recover Mo and Co from spent HDS catalysts. The dissolution behavior of metals in spent catalysts was investigated with respect to HCl concentration, time and S/L ratio. Particle size had negligible effect, whereas reaction temperature had created a great effect. Under the optimum leaching condition viz: 3 mol/L HCl, 90 °C, 250 μm particle size, 5% (w/v) solid to liquid ratio and 60 min reaction time, it was possible to dissolve 97% and 94% of Mo and Co, respectively. Solvent extraction was conducted for recovery of Mo using TBP and Mo was stripped from the loaded TBP with dilute HCl solution. The Mo free raffinate was processed for the recovery of Co by Alamine 308 in three counter current extraction stages and Co was quantitatively stripped with acidified distilled water. Furthermore, a complete extraction and stripping of HCl was achieved with TEHA in counter current extraction and stripping experiments. Using the process developed in this study, it was possible to recover 99% of Mo and Co and 90% of HCl with their purity higher than 99%. Finally, a conceptual process flow sheet was presented.