A bulk liquid membrane formed by dissolving 2-thenoyltrifluoroacetone (HTTA) in carbon tetrachloride is used to transfer, efficiently and selectively, thorium ions from the low pH nitrate medium into the hydrochloric acid solution. The effect of parameters influencing the transport efficiency such as the pH of the feed phase, the concentration of HTTA and the organic diluent used in the membrane, type and concentration of the acid used as the receiving phase, temperature and time has been investigated and discussed. Four replicate experiments show that a value of 95.4 (+/- 1.2)% of the initial concentration of thorium in the first aqueous phase (10(-4) M Th4+, I M NaNO3, pH 2.4, 10 ml) is extracted into the receiving phase (HCI 0.5 M, 10 ml) through the bulk liquid membrane (HTTA 0.02 M in CCl4, 20 ml) after 8 h. The selectivity of the method was assessed Eu3+, Fe3+,Ni2+, Pb2+, and Cd ions. The method by performing the single, as well as the competitive transport experiments of Th-4+,Th-Eu3+, Fe3+, Ni-2+,Ni- Pb2+, Mn2+, Co2+ and Cd2+ was applied successfully for the recovery of thorium ions injected in the tap and well water samples. (c) 2005 Elsevier B.V. All rights reserved.