Separation of Co(II), Ni(II), Al(III), Fe(III), V(V), and Mo(VI) by Solvent Extraction and Precipitation from Sulfuric Acid Leaching Solution of Spent HDS Catalysts and Recovery of High Purity VOSO ₄ Crystals

In the petroleum refining sector, hydrodesulfurization (HDS) plays a critical role by eliminating sulfur contaminants from crude oil feedstocks. Spent HDS catalysts serve as significant secondary resources, containing valuable metals such as cobalt, molybdenum, nickel, and vanadium, along with some impurities. Given the demand for these elements, developing an effective procedure for processing discarded HDS catalysts is highly necessary. Therefore, separation experiments were performed to recover the targeted metals from a synthetic sulfuric acid leachate, which simulated the multi-element composition of spent HDS catalysts consisting of Co(II), Ni(II), Al(III), Fe(III), V(V), and Mo(VI). Regulating the leachate to pH 4.5 by NaOH induced Al(III) and Fe(III) to simultaneously precipitate as metal hydroxides. Subsequently, Ni(II) was selectively precipitated over other metal ions by using dimethylglyoxime (DMG). Then, a pure Co(II) solution was isolated through extraction utilizing saponified Cyanex 272, with subsequent stripping performed using a sulfuric acid solution. Next, LIX 63 was employed in a three-stage counter-current extraction to separate V(V) from Mo(VI). Following this, the loaded organic phase was subjected to stripping with a NaOH solution, allowing for the recovery of a pure V(V) solution. Subsequently, pure crystalline VOSO4 solids were obtained from the recovered V(V) solution by chemical reduction followed by precipitation, dissolution, and crystallization. To ensure the purity of both the solutions and precipitates, ICP-OES analysis was performed. Ultimately, an integrated procedure was developed to recover pure Co(II) and Mo(VI) solutions, Ni(II) precipitates, and solid VOSO4 from the synthetic solution through precipitation and solvent extraction under ambient conditions.