Numerical Simulation of Volcanic Clay Microstructure Calculation of the Hydraulic Conductivity in Contaminated Soils.

Abstract:

Volcanic soils (allophanic) are interesting in terms of pollutant retention because they are known for accumulating the pollutant in the soil microstructure with a poor transfer to environment (fresh water and cultivated plant contaminations). Knowledge of the allophanic soil microstructure is required to understand the pesticide retention in soils. Allophane clay is a natural amorphous silicate and has physical features very close to those of synthetic gels. We introduce a numerical model to simulate the structure of this natural gel. The algorithm is based on Diffusion-Limited Cluster-Cluster Aggregation and the textural properties (specific surface area and pore size distribution) of the simulated structures are calculated. From the simulated data, we can derive the pore volume and the hydraulic conductivity in the micro porosity as a function of the allophane content. We show that at the scale of the allophanic aggregates the calculated transport properties are low. This confining effect in the microstructure is an important parameter to explain the poor soil to water (and plant) transfers.

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