| Soils contaminated with trace elements can pose an environmental risk because trace elements can leach and contaminate groundwater. To reduce trace element mobility, cement or Ca(OH)2 can be mixed with the soil being landfilled or re-used on site. The objectives of this thesis are to determine 1) how effective those products are at reducing trace element mobility in soils and 2) by what mechanisms they alter trace element mobility.;Using the toxicity characteristic leaching procedure (TCLP), it was shown that increasing the cement-to-soil ratio (c/s) generally reduced metal solubility in the alkaline soils, but not in the organic soil. In contrast, an increase in c/s increased the solubility of Sb. The magnitude of the reduction in solubility was also dependant on the water-to-soil ratio (w/s). It was shown that the acid neutralisation capacity of the treated soil could be used as a tool to evaluate the potential risk of contaminated soils disposed of in landfills or re-used. Using a sequential extraction procedure, it was shown that cement and Ca(OH)2 were good at reducing the amount of metal in the mobile fractions of the alkaline soil, but not in the organic soil. Extracting the soil over the pH range of 4-12.5 revealed that the addition of cement or Ca(OH) 2 reduced the solubility of every element at high pH, but enhanced the metallic cations' solubility at low pH. At low pH, Sb solubility was only reduced in cement-treated soils.;In general, the addition of cement or Ca(OH)2 to soils reduced trace element mobility, but in a way that is reversible as the pH decreases. Results also suggest that the precipitation of metals in soils generally occurs as metal carbonates and not as metal hydroxides, and that precipitation/dissolution reactions are not the main mechanisms controlling trace element solubility. Finally, the initial chemical form of the trace element has a significant impact on its subsequent immobilisation by alkaline products.;In order to attain these objectives, soils containing a mixture of trace elements from anthropogenic as well as geogenic origin were treated with cement or Ca(OH)2. Trace element mobility was assessed through leaching tests. |
