Application of hydrophobic extractant in aqueous two-phase systems for selective extraction of cobalt, nickel and cadmium.

This work developed a new and efficient method of extracting and separating Co(II), Ni(II) and Cd(II) in aqueous two-phase systems (ATPS) composed of triblock copolymer (L64)+Na(2)C(4)H(4)O(6)+water and L64+Li(2)SO(4)+water using the hydrophobic extractant 1-nitroso-2-naphtol, which complexes the metal ions and partitions in the triblock copolymer micelles in the ATPS top phase. Metal extraction from the salt-rich phase to the copolymer - rich phase is strongly affected by the fine-tuning of the following parameters: amount of added extractant, type of electrolyte, pH, and tie-line length. Excellent separation factors (S(i,j)) between the metals were obtained at pH=3.00 (S(Co,Cd)=1550 and S(Ni,Cd)=16,700) and pH=1.00 (S(Co,Ni)=826). In the interference study, Co(II) was selectivity extracted in the top phase in the presence of Ni(II) and Cd(II) in a concentration of up to 20 times the cobalt level in the system.