Soil contamination is an important issue that poses a real threat to human health. The stabilization/solidification (S/S) technique consists in adding a hydraulic binder, usually Portland cement, to the contaminated soil. This technique transforms mobile contaminants in more stable phases. Even if its efficiency has been demonstrated, this technique is seldom used in Quebec, among others because the potential long term behaviour of S/S soils remains uncertain. This project is centered on carbonation of S/S soils, the reaction of cement phases with atmospheric CO2, one of the phenomena that can influence the long term performances of S/S soils. We are particularly interested in the impact of carbonation on the release of arsenic and lead from cementitious matrix and the evolution of the mineralogy and chemical characteristics of these materials due to carbonation.
Batch leaching tests, based on thermodynamic equilibrium, were used to evaluate the solubility of these heavy metals as a function of pH and at the natural pH of the noncarbonated and carbonated matrices. The thermogravimetric analysis (TGA), phenolphthalein and X-ray diffraction analysis (XRD) were used to follow the progress of carbonation with time and its effect on the monoliths’ chemical and mineralogical properties. The obtained results showed that the carbonation caused the decrease of pH of the S/S materials and the complete and partial transformation of the portlandite and C-S-H respectively to calcium carbonate. Following carbonation, the dissolution of these cement hydrates, which played an important role in the retention of heavy metals, led to the release of the arsenic immobilized by the S/S treatment over the entire pH range. Lead, on the contrary, was less mobile after
carbonation.
El Bedoui, S. (Author),
Duhaime (Supervisor) &
Dubé (Co-supervisor),
30 Sept 2016Student thesis: Master's thesis › Master in Engineering: Environmental Engineering