Separation of V (V) and Mo (VI) in roasting-water leaching solution of spent hydrodesulfurization catalyst by co-extraction using P507-N235 extractant

P507 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) - N235 (trioctyl tertiary amine), diluted with kerosene, was used for separation of vanadium (V) and molybdenum (VI) from roasting-water leaching solution generated by spent hydrodesulfurization catalyst. Due to the leach solutions contain impurities like aluminum (Al) and magnesium (Mg), the effects of various conditions on the separation of V (V), Mo (VI), Al and Mg were investigated. Upon using 20% P507 - N235 (P507: N235 = 2:1) (v/v) as the extractant, kerosene as the diluent and 5% tributyl phosphate (v/v) as the phase modifier, 94.81% V (V) and 95.78% Mo (VI) were obtained in a phase ratio (O/A) of 2 (7 min at 298.15 K in a single-stage contract) and aqueous pH of 1.8. After a two-stage of countercurrent extraction, over 99% V (V) and Mo (VI) were extracted while less than 1% Al and Mg were co-extracted. Upon a three-stage countercurrent stripping with 2.5 mol/L sulfuric acid at a phase ratio (O/A) of 2, the complete removal of vanadium (V) from the loaded organic phase could be achieved. In the selective stripping of molybdenum (VI), almost all of the molybdenum (VI) was stripped after two-stage countercurrent stripping using 2.5 mol/L ammonia. Both oxide components of vanadium and molybdenum can be achieved by further processing of stripped solutions, respectively. In addition, thermodynamic calculations showed that vanadium (V) extraction from the roasting-water leaching solution using P507 - N235 is an irreversible, exothermic reaction at 298.15 - 338.15 K.