Removal of gold as Au(Tu) 2+ complex with a supported liquid membrane containing macrocyclic polyethers ligands as carriers

Abstract

Facilitated transport of gold(I) ions in acidic thiourea medium, across a Supported Liquid Membrane (SLM) by using dibenzo-18-crown-6 (DB18C6), diaza-18-crown-6 (DA18C6), hexathia-18-crown-6 (HT18C6) and hexaaza-18-crown-6 (HA18C6) as carriers, dissolved in chloroform, has been investigated. The fundamental parameters influencing the transport have been determined, they are: thiourea concentration in the feed phase, pH of the feed solution, carrier concentration in the membrane phase, gold concentration in the feed phase and type of acid. Thiourea can form, with gold ions, only one type of complex which is less mobile than the free metal cation. In fact, the mass transport flux of gold ions decreases when thiourea is added to the feed solution. However, when thiourea concentration increases, mass flux remain constant. Transport fluxes of gold ions from feed solutions of different anionic composition followed the order: NO 3 −> Cl −> SO 4 2−> PO 4 3−. This means that preferentially nitric acid should be used in preparing leaching solutions of polymetallic ores that are then used as feed in the SLM system.