The modelling of ZnCl2 extraction and HCl co-extraction by TBP diluted in ShellSol 2046

Zinc chloride and hydrochloric acid extraction from solutions of high zinc concentration by tri-n-butyl phosphate (TBP) diluted in ShellSol 2046 (an aliphatic solvent) has been studied with a combination of experiments and mathematical modelling. Above 0.4 mol/L aqueous zinc chloride, zinc is extracted predominantly as ZnCl2 accompanied by small amounts of an acido–metal complex, most likely to be HZnCl3. The Pitzer and Hildebrand–Scott models are used to estimate the activity coefficient of ions in the aqueous and organic phase respectively. Both the thermodynamic equilibrium constants and Hildebrand–Scott solubility parameters are fitted for the extracted species: ZnCl2(H2O)3 ∙ 3TBP and HZnCl3(H2O)3 ∙ 3TBP. The modelling was able to predict both the extraction and stripping processes for aqueous zinc and acid concentration up to 1.6 and 1 mol/L respectively.