Selective up-hill transport of gold to iodide stripping solution through a solvent modified liquid membrane containing a polysulphide podand as carrier

The polydentate neutral sulphide podand 1,12-di-2-thienyl-2,5,8,11- tetrathiadodecane, (TTD), C4H3S-(CH2-S-CH2)4-C4H3S, which shows high affinity towards 'soft metal ions' has been used as a carrier for gold transport through a supported liquid membrane (SLM). Transport of gold (5 x 10-5 M) from hydrochloric acid solution to the stripping solution was facilitated by TTD in m-chlorotoluene(MCT)/kerosene solution immobilized in the pores of a polyvinylidene fluoride Millipore membrane. A study of the influence of different chemical and physical parameters on Au transport has been carried out. This includes the presence of kerosene in TTD-MCT solutions, the concentration of the carrier in the liquid membrane, the concentration of the stripping agent NaI (or NaSCN) and the stirring rate of both aqueous solutions. The highest value obtained for the permeability coefficient P was 0.34 cm min-1, and for the Au flux 1.5 x 10-6 mol m-2 s-1. A high selectivity in the separation of Au from its bi-cation mixtures with an excess of Zn, Cu(II), Fe(III), or Cd was achieved.