POLLUTANTS LEACHING BEHAVIOR FROM SOLIDIFIED WASTES - A SELECTION OF ADAPTED VARIOUS MODELS

Leaching tests are essential in the environmental assessment of stabil ized wastes. Research programmes were conducted on their interpretatio n in order to develop tools for the evaluation of long term release of pollutants contained in solidified wastes. Models for the leaching of porous materials are discussed in this paper according to the specifi city of the chemical species (i.e. transport model with total dissolut ion of species-diffusional model; transport model with progressive dis solution of species due to limitation of solubility-shrinking core mod el; and the model coupling transport and chemical phenomena). The leac hing behaviour of pollutants (i.e. lead) solidified in a cement matrix was studied under different chemical conditions. Results have shown t hat the release of species whose solubilities depend on the physico-ch emical conditions, and especially the pH (e.g. amphoteric metals), is governed by the solubility of the species in the pore water at local c onditions and by the pH evolution within the matrix. A coupled dissolu tion/diffusion model was developed to describe the release of chemical ly complex species contained in a porous medium in contact with water. Leaching tests of cement matrices and artificial porous matrices cont aining calcium hydroxide and pollutants were conducted in order to val idate the coupled dissolution/diffusion model. A good assessment of th e retention of some pollutants contained in cement matrices could then be obtained by the association of two tests: solubilization of the po llutants related to the chemical context (pH) under steady state condi tions and monolithic long term dynamic leaching tests in order to char acterize the evolution of the chemical context (pH) and consequently t he release of pollutants. The objective is to integrate this approach in the standardization process (CEN TC 292- WG 6, in progress). (C) 19 98 Elsevier Science B.V. All rights reserved.