Solvent extraction of Pb(II) and Zn(II) from a Nigerian galena ore leach liquor by tributylphosphate and bis(2,4,4-trimethylpentyl)phosphinic acid

Physico-chemical conditions for the optimal separation of Pb(II) and Zn(II) from a galena ore leachate using a combination of tributylphosphate (TBP) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex®272) have been investigated. The results of fundamental studies using synthetic solution of Pb(II) showed that the extraction efficiency increased with increasing pH, extractant concentration and temperature. An extraction yield of 92.1 ± 0.2% for Pb(II) at pH 5.0 by 1 mol/L TBP in 100% MIBK and 94.6 ± 0.2% for Zn(II) at pH 3.0 by 0.032 mol/L Cyanex®272 in kerosene was obtained from an initial galena leach liquor containing 1705.1 mg/L Pb, 98.7 mg/L Zn and 130.2 mg/L total iron as major constituents at 25 ± 2 °C at a stirring time of 30 and 25 min, respectively. Iron was also effectively removed by precipitation using 1 mol/L ammoniacal solution at pH 3.5. The stoichiometry of the lead-extractable species was found to be HPbCl3·TBP. Values of 52.7 ± 0.01 kJ mol−1, −5.05 kJ mol−1, 159.6 ± 0.01 J K−1 mol−1 and 0.127 ± 0.003 M−2 were calculated for the apparent standard molar enthalpy (ΔH°), Gibb’s free energy (ΔG°), molar entropy (ΔS°) and extraction constant, respectively. About 94.5 ± 0.2% Pb(II) and 94.6 ± 0.2% Zn(II) were stripped from the TBP and Cyanex®272, respectively using 0.1 mol/L HCl solution. Finally, a compact extraction scheme has been provided.