1997 Volume 23 Issue 1 Pages 1-10
A new solvent extraction process using a single extractant, PC-88 A, was developed for efficient separation and recovery of rare metals such as molybdenum, vanadium, aluminum, cobalt and nickel from an aqueous solution, derived from total dissolution of spent hydrodesulfurization catalysts in sulfuric acid solution. In this process, preferential extraction and separation of molybdenum and vanadium over aluminum is achieved at low pH based on the differences in equilibria and kinetics of extraction between these metals. The co-extracted vanadium together with molybdenum is eliminated from the loaded organic phase by selective scrubbing with sulfuric acid solution. Molybdenum in the scrubbed organic phase is easily stripped and separated from small amouns of iron by employing an aqueous solution of NH4OH+NH4Cl and recovered as ammonium molybdate. Vanadium in the scrub solution is separated from small amounts of aluminum and recovered as vanadyl sulfate by extraction with PC-88 A after adjustment of pH to approx. 1.5 with ammonia solution, followed by stripping with sulfuric acid solution. The raffinate obtained after recovery of molybdenum and vanadium is contacted with an organic solution of PC-88 A neutralized by ammonia so as to quantitatively extract aluminum and separate from cobalt and nickel. Aluminum sulfate is obtained after stripping the organic phase with sulfuric acid solution. Cobalt in the raffinate is further recovered as cobalt sulfate with high purity by extraction with PC-88 A, followed by scrubbing with an aqueous solution of CoSO4+ H2SO4 and then, by stripping with dilute sulfuric acid. Nickel in the final raffinate is readily concentrated and recovered as high-purity nickel sulfate after direct extraction with PC-88 A, followed by stripping with dilute sulfuric acid. This process has the potential for incorporating a practical system on a commercial scale.
