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

Abstract

The extraction of Zn 2+ by mixtures of tri-butyl-phosphate (TBP, B) and trialkyl amine (N235, R 3N, R = C 8–C 10) has been carried out. The mixtures have evident synergistic effects on Zn 2+ 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 (R 3N) 1.5·ZnCl 2·B. The extraction reaction is as the following: ZnCl 2 ( a ) + 1.5 R 2 N ( 0 ) + B ( 0 ) ⇌ ( R 3 N ) 1.5 ⋅ ZnCl 2 ⋅ B ( 0 ) The equilibrium constant and thermodynamic functions, Δ H, Δ G, and Δ S have been calculated, indicating that the reaction is exothermically driven. The extraction of Zn 2+ and Cd 2+ 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 Cd 2+, while TBP-N503 mixing systems have similar effects on neither Zn 2+ nor Cd 2+. Moreover, the separation factors of Zn 2+ and Cd 2+ by TBP-N235 system was studied. It is feasible and advantageous to separate Zn 2+ from bulk cadmium solutions.