Separation and Recovery of Zinc(II) and Cobalt(II) from a Mixed Sulfate/Thiocyanate Solution using some Commercial Organophosphorus Extractants

The separation and recovery of divalent zinc and cobalt ions from mixed sulfate and thiocyanate solutions have been carried out using CYANEX 921 (trioctylphosphine oxide), CYANEX 923 (a mixture of straight chain alkylated phosphine oxides), and CYANEX 925 (a mixture of branched chain alkylated phosphine oxides) in kerosene. Different parameters affecting the extraction equilibrium of Zn(II) and Co (II) in addition to temperature, were studied and the stoichiometry of the extracted Zn (II) and Co(II) species were postulated based on the slope analysis method. The extraction percent of the metal ions was found to increase with increasing pH and zinc was preferentially extracted over cobalt with CYANEX 925. The respective loaded organic phases were stripped with different mineral acids. The highest separation factor was obtained when using 0.015 M CYANEX 925 as extractant. Based on the obtained results, the application of the method was tested to separate Zn( II) and Co( II) from Nickel Metal Hydride batteries (Ni-MH batteries) leached by 2.0 M H(2)SO(4) and good results were obtained.