| One major task facing the geoenvironmental engineering today is the development of methods to assess the long term changes, release and transport of contaminants from waste disposal sites, considering the hydrochemical interaction of the contaminants with the clay barrier.;Modelling of the leaching processes, which take place in a landfill, is an invaluable tool as it is often not possible to conduct experiments over sufficiently long timescales to observe the long term leaching behaviour of wastes. In this study the multi-component transport of heavy metals into a clay barrier has been investigated experimentally and theoretically by coupled solute transport and geo-chemical reaction. An experimental design for coupled solute transport and chemical reaction, based on the column leaching test in association with the batch equilibrium test for comparison, is proposed to examine the Cl and EDTA effects on the partitioning of Zn and Pb (dissolved, adsorbed, precipitated) into uncontaminated or; precontaminated kaolinite or; kaolinite mixtures with silica gel and calcium carbonate (K, KS, KC, KSC).;A COupled Solute Transport and CHemical Equilibrium SPeciation (COSTCHESP) model was developed to simulate the transport of multiple thermodynamically reacting chemical substances through clay barrier systems. It consists of two main modules; a finite difference transport module (COST), and an equilibrium geochemistry module (CHESP). This simplifies the coupling between the physical and chemical processes and leads to a simple and efficient model to simulate the simultaneous processes of advective-dispersive transport (advection; diffusion, osmotic and ion restriction effect) and geochemical reactions (complexation, exchange, precipitation, adsorption and desorption). The reliability of the model has been verified by laboratory experiments.;The proposed model accounts for most of the hydro-geochemical interactions of the multi-components with the clay liner. The model will lead to proper identification of the form of specific ions (i.e. adsorbed and precipitated on solid, and available in solution) and can be a useful tool for (i) assessing the importance of geochemical reactions on the transport of heavy metals in groundwater; (ii) predicting the forms by which the metals are partitioned in the clay barrier, and (iii) indicating the potential availability of the heavy metals from contaminated soil through the chemical processes, particularly, if one recognizes that the local equilibrium pH environment is neither stagnant nor uniform throughout the subsurface underlying the waste landfill. (Abstract shortened by UMI.). |
