ABSTRACT:

There are two forms of soil remediation methods, in-situ and ex-situ methods. This project is related to one group of in-situ methods, namely reactive wall technologies. This involves the placement of material in a trench downstream of the contaminant plume. The contaminant is swept along by the groundwater into the reactive wall where it is modified in some way. One type of reactive wall uses the interception-sorption/precipitation technology. The strategy is based upon the interception and sorption of the contaminant onto the immobile solid phase in the reactive wall. In this project the contaminant is fluoride and the reactive wall media is alumina. Several batch tests were done with these substances investigating variables such as pH, contaminant concentration, complexation, sorption and total dissolved aluminium. Relationships between sorption, complexation and free fluoride ion concentration under different pH were recorded so as to predict results in future column tests. A computer program was written to predict the amount of sorption and chemical speciation of the alumino-fluoride system.

INTRODUCTION

There are many ways in which groundwater may be polluted and this is contributing towards a significant degradation of the environment. It is desirable that strategies be implemented that will lead to an improvement in environmental conditions over time at a particular site. An approach to soil decontamination may be developed from a strategy based upon interception and sorption. This approach relies on the usual mechanisms of solute transport through porous materials, namely, diffusion and advection/dispersion to transport the pollutant through the soil to an interception point where the pollutant is sorbed. The diagram figure 1 illustrates this in-situ method. One practical way the interception and sorption strategy may be implemented is by simply constructing a trench and backfilling the trench with sorbant material.

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