Heavy metal species in solid waste leachates.

The complexation of heavy metals by dissolved organic carbon from a leachate plume has been measured by means of ion exchange resin techniques. The dissolved organic carbon was studied in its original matrix in order to avoid artifacts by purification and loss of non-purifyable carbon (in some cases up to 30% is lost). Conditional stability constants have been estimated showing much higher complexation for Cu and Pb than for Cd, Ni and Zn. Experiments using aquifer material instead of resin gave comparable results but showed that even in the precence of dissolved organic carbon, the distribution coefficients for the metal sorption onto the aquifer material still was high indicating limited mobility also in the presence of dissolved organic carbon. Traditional purification of the dissolved organic carbon showed that 60% was fulvic-acid-like, 10% was humic-æacid-like and 30% belonged to a hydrophilic group somewhat related to fulvic acids. The characteristics of the separated fractions are eing studied and complexation modeled by Model V/WHAM and NICA-Donnan/Ecosat.