Liquid-liquid extraction of Cd(Ⅱ) from pure and Ni/Cd acidic chloride media using Cyanex 921: A selective treatment of hazardous leachate of spent Ni-Cd batteries

摘要

The present paper is focused on solvent extraction of hazardous Cd(Ⅱ) from acidic chloride media by Cyanex 921, a new extractant mixed with 10% (v/v) TBP in xylene. The optimum conditions for extraction and stripping of Cd(Ⅱ) were investigated with an aqueous feed of 0.1 mol/L Cd(Ⅱ) in 2.0 mol/L HCl. McCabe-Thiele diagram was in good agreement with the simulation studies, showing the quantitative extraction (99.9%) of Cd(Ⅱ) within two counter-current stages utilizing 0.30 mol/L Cyanex 921 at O/A ratio of 3/2 in 10min. Stoichiometry of the complexes extracted was determined and confirmed by numerical treatment and graphical method, revealing the formation of HCdCl_3·2L and HCdCl_3·4L for Cyanex 921(L) concentration in the range 0.03-0.1 mol/L and 0.1-1.0mol/L, respectively. The thermodynamic parameters for the extraction of cadmium were also determined. The stripping efficiency of cadmium from the loaded organic with 0.10 mol/L HCl was 99.6% in a three-stage counter-current process at an O/A ratio of 2/3. Cyanex 921 was successfully applied for the separation of Cd(Ⅱ) from Ni(Ⅱ) in the simulated leach liquor of spent Ni-Cd batteries. The study demonstrates the applicability of the present hydrometallurgical approach for the treatment of hazardous waste, the spent Ni-Cd batteries.