Coupled transport of Tl3+ through triethanolamine–xylene–polypropylene supported liquid membranes

This study has been carried out for the uphill transport of Tl3+ across triethanolamine (TEA)–xylene based supported liquid membrane. The mechanism of transport of Tl3+ has been found to be based on the association of Tl3+ with six chloride ions to form anions, which associate with three protonated triethanolamine molecular cations (HOH4C2)3N+H at the feed side of the membrane face and form a complex. The complex is extracted into the liquid membrane organic phase, from where it diffuses towards the stripping side of membrane due to the concentration gradient and is dissociated due to alkaline conditions present in the stripping phase. It is also confirmed that proton addition to triethanolamine takes place at the N site and not at the –OH sites. 5.26 mol/dm3 of TEA in xylene in membrane phase, 1.0 mol/dm3 of HCl in feed and 1.0 mol/dm3 of NaOH in stripping phase have been found to be the optimum concentrations for the extraction of Tl3+. The method developed for transport of Tl3+ has been successfully applied to remove Tl3+ from coal ash acid leach liquors along with nickel, chromium and zinc ions.