Facilitated transport of gold from cyanide or chloride media by Cyanex 923

The commercially available extractant Cyanex 923 (phosphine oxides mixture) was studied to be applied in the carrier-facilitated transport of gold, from either cyanide or chloride aqueous media, across a polymer-immobilized liquid membrane (PILM). Au(CN)(2)(-) is transported from alkaline pH values. The presence of lithium salts (and the respective counter anion) in the media improves the transport, whereas the organic diluent seems not to influence the metal permeability. Water can be used effectively, as receiving phase, for the present system. In chloride media, the carrier is able to transport gold(III), increasing the permeability as the initial HCl concentration is increased (up to 5x10(-1) M HCl). This permeability is dependent on the respective organic diluent, being the metal flux independent at higher initial gold concentrations but metal dependent at lower gold concentrations in the feed phase. Sodium thiocyanate solutions can be used effectively as receiving phase in this media. From the experimental data, the mass-transfer coefficient in the aqueous feed phase and the thickness of the aqueous boundary layer were calculated for both, cyanide and chloride, aqueous media.