Solvent Extraction of Zinc (II) Using Alamine 336 and TBP: Removal of Zinc from Gold Mining Waste

Abstract

In this work zinc was extracted with TBP and Alamine 336. A study of the kinetics showed that equilibrium was relatively rapid for both extractants. The best extraction percentages were achieved for a zinc concentration of 50 ppm at 91.35% and 84% for TBP and Alamine 336 respectively. The following zinc speciation’s \(Zn^{2+}, ZnCl_3^-, ZnCl_4^{2-}\) and \(ZnCl^+\) were obtained from pH, E-pH and speciation diagrams in high Cl- concentrated solutions. The nature of the extracted species was determined by the slope method, and the complexes formed in the organic phase were \((ZnCl_2(TBP)_2 )_{org}] \) and \([(Zn(Cl)_4 (R_3 NH)_2 )_{org}]\). These results were confirmed by the study of functional groups by FTIR. The effect of diluent on zinc extraction was as follows: Kerosene > Diisobutylketone > Heptane > Toluene. The addition of Na2CO3, Na2S2O3, NaCl, NaClO, Na2SO4 and NaHCO3 significantly enhanced Zn(II) extraction for both extractants. Zn(II) recovery by stripping follows the sequence HCl (82.33%) > H2O (75.09%) > H2SO4 (63.85%) > HNO3 (50.09%) > NaOH (30.33%) for Alamine 336 and HCl (74.02%) > H2SO4 (43.29%) > H2O (41.86%) > HNO3 (37.82%) > NaOH (36,19%) for TBP. The combination of TBP and Alamine 336 has an antagonistic effect on zinc extraction. The negative values of the thermodynamic parameters ΔG° and ΔH° indicate spontaneous, exothermic processes. The Pb(II)/Zn(II) separation is in favor of lead for synthetic solutions and from gold cementation on zinc chips.