Synergistic Extraction of Zn(II) by Mixtures of Tri-Butyl-Phosphate and Trialkyl Amine Extractant

The extraction of Zn2+ by mixtures of tri-butyl-phosphate (TBP, B) and trialkyl amine (N235, R3N, R = C8–C10) has been carried out. The mixtures have evident synergistic effects on Zn2+ with a synergistic enhancement factor of 12.34. The extraction mechanism was studied using the methods of slope analysis and constant mole. The extracted complex is determined as (R3N)1.5·ZnCl2·B. The extraction reaction is as the following: ZnCl2(a)+1.5R2N(0)+B(0)⇌(R3N)1.5⋅ZnCl2⋅B(0)ZnCl2(a)+1.5R2N(0)+B(0)⇌(R3N)1.5⋅ZnCl2⋅B(0)The equilibrium constant and thermodynamic functions, ΔH, ΔG, and ΔS have been calculated, indicating that the reaction is exothermically driven. The extraction of Zn2+ and Cd2+ by the mixtures of TBP and N235 or N,N-di(1-methyl-heptyl) acetamide (N503) was also conducted. The results show that the mixtures of TBP and N235 do not have evident synergistic effects on Cd2+, while TBP-N503 mixing systems have similar effects on neither Zn2+ nor Cd2+. Moreover, the separation factors of Zn2+ and Cd2+ by TBP-N235 system was studied. It is feasible and advantageous to separate Zn2+ from bulk cadmium solutions.