Comparison of sulphur and sulphur-oxygen ligands as ionophores for liquid-liquid extraction and facilitated transport of silver and palladium

The reactivity of new ligands described as S-1, S-5, S2O9 (in respect to character and amount of donors) towards metal ions was examined by extraction from HNO3 and HCl media. These ligands were next utilised as carriers for Ag and Pd transport through a supported liquid membrane (SLM). The effect of collecting a greater number of S donors in one molecule and the influence of type of donors (O-S versus S) on efficiency and selectivity of Ag and Pd(II) extraction and transport were examined. The extraction of Ag from HNO3 solutions increased with increasing amount of S-donors in one molecule (S-1 < S2O9 < S-5). For palladium the sequence was different (S-5 < S-1 < S2O9). The transport of Ag through SLM impregnated with m-chlorotoluene solution of ionophore increased in the same order as in the case of extraction, whereas for Pd the row was different: S-5 < S2O9 < S-1. The highest fluxes of Ag and Pd transported from HNO3 equalled to 5.25 x 10(-7) and 1.37 x 10(-7) mol/m(2) s, respectively. Palladium flux depended on stripping solution type (Na2S2O3 < NaSCN). Very high selectivity of Ag and Pd extraction and Pd transport over Cu(II), Pb, Cd, Zn, Ni ions was achieved. The value of separation factor in Pd transport ranged from 30 to 19,000. (C) 2002 Elsevier Science B.V. All rights reserved.