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This work presents the results concerning the first use of activated composite membranes (ACMs) for the removal of Hg(II) ions from aqueous solution, using as the ligand di-(2-ethylhexyl)dithiophosphoric acid (DTPA). The effects on the removal percentage of Hg(ll) of variables such as pH, the nature of the acid, the concentration of mercury (in the feed solutions), and the ligand content (in the membrane) as well as the total surface membrane area exposed to the Hg(II) aqueous solution were studied. During the course of the removal experiments, the membrane was immersed in the Hg(II) aqueous solution in acid media and samples of the solution were taken at different times to enable monitoring of the mercury concentration changes. Itwasfound that when the ACM was prepared with a 1.0 M DTPA casting solution and the feed solution contained 2.49 x 10(-4) M Hg(II) in HCI 0.1 M the amount of mercury extracted was higher than 93%. Straight forwardly, additional experiments were carried out with the free-DTPA composite membranes to make up a set of control reference points to verify that removal of the investigated heavy metal was a consequence of the presence of the organic ligand; otherwise there was no Hg(II) concentration variation at all.