Effect of complexing agents (EDTA and ATMP) on the remobilization of heavy metals from a polluted river sediment

EDTA and ATMP are synthetic chelating agents used in many industrial applications. Because of their low biodegradability, they are present in many aquatic systems where their strong complexing capacities can modify the transfer of toxic heavy metals between solid and liquid phases. The remobilization of Cu, Pb and Cd from polluted superficial river sediments in the presence of two synthetic organic ligands (a polycarboxylate, EDTA, and a phosphonate, ATMP) is investigated as a function of reaction time to determine the time necessary to reach dissolutive equilibrium, and as a fonction of the complexing agent concentration. The dissolutive equilibrium times are similar (10 to 20 hours) and the solubilizing power of ATMP is slightly lower than that of EDTA. The curves of solubilization of metals in the presence of the complexing agents present a shape of a "chelate concentration" desorption edge, for a chelate range between 10(-5) to 10(-3) mol L-1, the solubilised metals increasing dramatically. This remobilization is the result of a competition between association with the solid phase and dissolved complexation. With EDTA, the desorption order of metals seems to be imposed by association with the solid. For ATMP is it the chelate complexing strength which determines this order.