Clays contamination modelling

A chemo-elasto-plastic model for the behaviour of clays in contact with a single contaminant has been presented. The model has been implemented in the finite elements program LAGAMB JE providing an efficient tool for solving problems involving clay-contaminant interaction. Comparison of model predictions with available... 

Schofield RK, Samson HR (1954) Flocculation of kaolinite due to the attraction of opposite charged crystal faces. Discuss Faraday Soc 18 135-145 Schofield RK, Samson HR (1953) The defiocculation of kaolinite suspensions and the accompanying change-over from positive to negative chloride adsorption. Clay Miner BuU 2 45-51 Schulten HR (2001) Models of humic structures association of humic acids and organic matter in soils and water. In Qapp CE et al. Humic substances and chemical contaminants. Soil Science Society of America, Madison, Wl, pp 73-88... 

The cost of a vertical Lasagna system was evaluated by DuPont using a cost optimization model. For remediation of TCE to a depth of 40 to 50 ft (12 to 15 m) in clay on a 1-acre (4047-m ) site, costs were estimated to range from 40 to 90/yd ( 52 to 117/m ). Soil properties, depth of contamination, cost of emplacing electrodes and treatment zones, required purge water volume, cleanup time, and cost of electrical power were all included in the estimate (D12500Y, p. 10). 

A DUAL POROSITY MODEL FOR CONTAMINANT TRANSPORT IN EXPANSIVE CLAYS... 

A Dual Porosity Model for Contaminant Transport in Expansive Clays 175... 

Clays are generally considered to be effective barriers for flow of water and solutes due to their low permeability and high ion adsorption capacity. However, as environmental criteria for the emission of contaminants and water from clay barriers become increasingly stringent, it is crucial to be aware of all relevant driving forces and fluxes and to take them into account in model assessments. In this respect the processes of chemical and electro-osmosis may not be neglected in clayey materials of hydraulic conductivity < 10-9 m/s [7], At these low conductivities the surface charge of the clay particles and the counter-ion accumulation in diffuse double layers enable explanation and quantification of osmotic processes and semi-permeability in clays [1],... 

Hydrodynamic dispersion may however be significant in small, local hydrogeological problems, such as a point source contamination (Plummer et al., 1992). Another instance where diffusion may play an important role in water chemistry is the diffusion from permeable to less permeable parts of the aquifer, or matrix diffusion. This process appears to be important in fractured aquifers (Maloszewski and Zuber, 1991 Neretnieks, 1981), volcanic rock aquifers, aquifers adjacent to confining units (Sudicky and Frind, 1981), and sand layers inter-stratified with confining clay layers (Sanford, 1997). In systems in which a chemical steady state (see below) has not been reached, matrix diffusion effects may severely limit the applicability of inverse mass balance modeling to those systems. 

Figures 2.8 and 2.9 present the spatial distribution of the total lead and the pH for 1-day and 35-day runs of the Cao model. Superimposed on the numerical solutions are results from laboratory tests of Pb(N03)-contaminated kaolinite clay subjected to long-term electrokinetic treatments. Although the initial concentrations of the lead used in the numerical simulator and the experiments were different (0.05 M in the numerical and 0.15 M in the experiment), as well as the length of the...

We hypothesized that the above treatise of DDL interactions in the presence of an electrical field is a viable model for the explanation of enhanced oxidation-reduction in clay-electrolyte systems. Electrolytic transformations of selected chlorinated hydrocarbons (CHCs) and polyaromatic hydrocarbons (PAHs) have been demonstrated successfully in water and wastewater (Franz, Rucker, and Flora, 2002 Pulgarin et al., 1994). There has been field and laboratory evidence that these transformations can also take place in porous media (Banarjee et aL, 1987 Pamukcu, Weeks, and Wittle, 2004 Alshawabkeh and Sarahney, 2005 Pamucku, Hannum, and Wittle, 2008). As discussed previously, faradic reactions do take place on clay particle surfaces when current pass in the pathways of the DDLs (Grahame, 1951, 1952). Hence, external supply of electrical energy can help drive favorable oxidation-reduction reactions in contaminated clays not only in the bulk fluid but also on clay surfaces, as well as on where most of the contaminants tend to reside because of adsorption or exchange. 

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