For the purpose of developing the extraction of tellurium, we have investigated the extraction using the chloride salt of tri-iso-octylamine (TIOA) in xylene. Experimental data have been analyzed graphically and numerically to determine the stoichiometry of the extraction species. It is found that the extraction reaction is exothermic (DeltaH = -51.49 KJ/mol). Tellurium was extracted according to the following the reaction: 2[R3N+HCl-](org) + [TeCl62-](aq) [(R3N+H)(2)TeCl62-](org) + 2[Cl-](aq). The extraction of tellurium proceeds through an ion-association mechanism and the extracted species is [(R3N+H)(2)TeCl62-]. The distribution constants and thermodynamic functions; enthalpy (DeltaH), entropy (DeltaS), and free energy (DeltaG) in the extraction of tellurium with TIOA have been evaluated. (C) 2004 Elsevier B.V. All rights reserved.