FACILITATED TRANSPORT OF GOLD THROUGH A MEMBRANE VIA COMPLEXATION TO THIOUREA-BASED REAGENTS

The facilitated transport of Au(III) from hydrochloric acid solutions through double solid supported liquid membranes (SSLMs) is reported. T he organic phase consisted of a chloroform solution of thiourea-based extraction reagents, dodecylthiourea (DTH) or nonylthiourea (NTH), phy sically absorbed onto microporous polypropylene films, Celgard 2500 or Celgard 2400 (Celanese Plastic Inc.). A cell composed of three compar tments, including a reservoir of organic solution, with double SSLM wa s used in this study. Aqueous solutions of thiourea, KSCN, or Na2S2O3 were used for removing Au(III) from the membrane phase. The permeabili ty coefficient, P, of the SSLM was determined from the slope of log[Au ]/[Au](0) or log A/A(0) vs time plot. The influences of the stirring r ate in aqueous feed and organic solutions, of the stripping reagents a nd their concentration, of the carrier concentration, and of the conce ntration of HCI in the aqueous feed on the permeability coefficient we re determined. A model describing the transport mechanism consisting o f diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion through the membranes is reported. T he study also demonstrates the suitability of the liquid membrane tech nique to use reagents with low solubility in organic solutions for the permeation of Au3+ without problem of solid-phase formation.