The role of carbonate mineral dissolution in turbidity reduction in an oil sands end pit lake.

Surface water turbidity from dispersed clay particles can hinder the development of aquatic ecosystems. One of the primary objectives for proposed oil sands end pit lakes is that they support ecological functions and lake-specific wildlife habitat. However, high surface water turbidity has been observed in the Base Mine Lake cap water, the first full-scale demonstration oil sands end pit lake. Our previous study showed that adjusting the solution pH through carbon dioxide (CO) addition reduced surface water turbidity in oil sands tailings. Carbonate minerals such as calcite and dolomite were also previously identified in tailings, and thus the goal of this study was to determine the effect of calcite and dolomite dissolution through CO-mediated pH reduction on turbidity and the stability of suspended clay particles. Calcite dissolution resulted in ∼99% reduction of turbidity. The suspended clay particle stability was analyzed using DLVO (Derjaguin-Landau-Verwey-Overbeek) theory with water chemistry data from this column study. An inverse correlation was observed between the amount of dolomite and the energy barrier values on day 42 of the experiment. These results suggest CO-mediated calcite dissolution changes the water chemistry and is the most promising treatment condition for the settlement of suspended tailings particles.