Equilibrium ion exchange isotherms in aqueous medium of H+/Cu2+, H+/Zn2+ and H+/Cd2+ on a weak acid resin Lewatit TP-207, at different pH values and at 298 K have been determined in order to assess the possibility of using ion exchange to eliminate heavy metal ions from industrial aqueous liquid streams. The experimental equilibrium data have been satisfactorily correlated using a Langmuir-type empirical equation. It was found that the operating resin capacity with respect to each metal ion increased with increase in solution pH, in accordance with a second-degree polynomial equation. Taking into account the variation of operating capacity with pH, each system exhibited a unique separation factor, namely all the experimental points can be described by a unique isotherm in a dimensionless form. Resin Lewatit TP-207 exhibited the following selectivity order: Cu2+ > Zn2+ > Cd2+ at 298 K. (C) 2004 Society of Chemical Industry.