Comparative Study of Lead/Zinc Extraction Using Aliquat 336 and Trioctylphosphine Oxide (TOPO)

Abstract

In this study, lead extraction was performed using TOPO and Aliquat 336 in toluene. The respective contact times required to reach extraction equilibrium were determined to be five minutes (E = 99.29%) and 10 minutes (E = 90.46%) for TOPO and Aliquat 336, respectively. The optimal extraction percentages were obtained at a lead concentration of 500 ppm, with E > 90% for all extractants. Lead speciation, defined as the occurrence of different forms of lead compounds, was investigated through the analysis of the E-pH diagram and the speciation diagram at elevated chloride concentrations. The obtained results, which included lead ions such as Pb²⁺, PbCl₃⁻, PbCl₄²⁻, and PbCl⁺, provided valuable insights into the behavior and interactions of lead compounds under these conditions. The extracted species were identified using the slope method, with complexes formed in the organic phase identified as either [(PbCl2(TOPO)2)org] or [(PbCl3(R3CH3N)org]. The confirmation of these complexes was achieved through the analysis of functional groups utilizing Fourier-transform infrared spectroscopy (FTIR). The extraction percentages obtained with kerosene were the most optimal, with values greater than 80%. The addition of Na₂CO₃, Na₂S₂O₃, NaCl, NaClO, Na₂SO₄, and NaHCO₃ resulted in enhanced Pb²⁺ extraction percentages for both extractants, thereby producing a salting-in effect at a concentration of 5.10⁻² M. The lead stripping process was found to be significant with Na₂S₂O₃ (E = 99.70%) for Aliquat 336, Na₂CO₃ (E = 92.89%), and Na₂S₂O₃ (E = 42.2%) for TOPO. The mixture of TOPO and Alamine 336 exhibited an antagonistic effect on lead extraction. The determination of negative ΔG° values for Pb²⁺ ion extraction indicated that Pb²⁺ reacts spontaneously with Aliquat 336 and TOPO. Lead is extracted more readily from synthetic solutions than zinc.