Synergistic extraction of zinc from ammoniacal ammonia sulfate solution by a mixture of a sterically hindered beta-diketone and tri-n-octylphosphine oxide (TOPO)

The solvent extraction of zinc from ammoniacal ammonium sulfate solution is studied using a mixture of a sterically hindered β-diketone, 1-(4′-dodecyl)-phenyl-3-t-butyl-1,3-octadione (HR), and tri-n-octylphosphine oxide (TOPO) in sulphonated kerosene. TOPO and HR show evident synergistic effects on the solvent extraction of zinc and the optimum composition of TOPO and HR is 50% v/v (molar ratio TOPO: HR = 2). Zinc extraction, as Zn2+ ion decreases with an increase of initial pH value and total ammonia concentration and increases with an increase of phase ratio, has no relationship with the zinc concentration of the aqueous phase. Based on batch scale equilibrium results, a continuous extraction of zinc from simulated leaching solution and zinc oxide ore ammoniacal leaching solution was carried out in a mixer-settler unit containing two extraction stages and one stripping stage. The two-stage extraction efficiencies of zinc are 86% and 85% for the simulated and ore leaching solutions, respectively, whereas the stripping efficiency is 85% for both cases. By applying an “ammonia leaching–solvent extraction–electrowinning” process, extra-pure zinc metal (Zn > 99.995%) was obtained.