A new synthesis of ion exchange resins containing thiol groups directly bonded on the aromatic ring is described, These resins are used to remove the small quantities of mercury (10 ppm) contained in waste water from chloralkali industries which use a mercury cathode (solvay cell). Optimum conditions have been developed to obtain resins with maximum thiol content groups. Elemental analysis, NMR, and FTIR spectroscopies data have been used to confirm the chemical structure of all products. When used in decontamination of water containing 10 ppm of Hg, we obtained a final Hg concentration of 1 ppb. (C) 2000 Elsevier Science B.V. All rights reserved.