Effect of Sodium Chloride and pH on the Composition of the Equilibrium Phases and the Partition of Palladium(II) in the Aqueous Two-Phase System PEG1500–Na2SO4–Water

Binodal curves for aqueous two-phase systems (ATPS) polyethylene glycol 1500 (PEG1500)–sodium sulfate–water with additions of sodium chloride and hydrochloric or sulfuric acids were determined by turbidimetric titration and analysis of coexisting phases. The results are compared with published data for the ATPS PEG1500–sodium sulfate–water without additions, and the influence of additions on the width of the two-phase field, tie-lines length, and slopes was traced. The influence of initial concentration of palladium, time of phase contact, pH, concentration of sodium chloride and sodium sulfate on the extraction of palladium­(II) was studied. The coefficients of distribution of palladium­(II) between the phases of ATPS were measured as a function of the concentrations of sodium chloride (0.1, 1.0, and 2.0 mol·L–1) and pH values. At lower concentrations of Cl– ions Pd­(II) is extracted as a mixture of ions [Pd­(H2O)­Cl3]− and [PdCl4]2–, whereas the growth of C(Cl–) leads to prevalence of the latter, which has poorer extraction properties. Maximal values of the distribution coefficient D Pd of about 9.5 ± 0.75 were achieved in the ATPS PEG1500–Na2SO4–0.1 M HCl and PEG1500–Na2SO4–(0.05 M H2SO4 + 0.1 M NaCl).