Cossey, HL, Kaminsky, H & Ulrich, AC 2022, 'Evaluating the long-term behaviour and viability of an oil sands tailings management and reclamation strategy', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 307-320, https://doi.org/10.36487/ACG_repo/2215_19
(https://papers.acg.uwa.edu.au/p/2215_19_Cossey/)
Abstract: Surface mining of oil sands ore in Alberta, Canada, has generated over a billion cubic metres of waste, known as fluid fine tailings (FFT). FFT are a mixture of fine-grained solids (silt and clay), water, dissolved salts, and organic compounds. Eventually, FFT must be reclaimed and integrated into mine closure landscapes. One proposed method of FFT management and reclamation is through end pit lakes (EPLs), which are engineered water bodies that consist of a thick layer of FFT capped with water. FFT deposited in EPLs may also be treated with a coagulant (alum) and polymer flocculant (polyacrylamide, PAM) to improve tailings dewatering and cap water quality. Theoretically, EPLs are a suitable reclamation strategy because the water cap develops into habitat for an aquatic ecosystem while the FFT slowly dewaters over time. However, successful use of EPLs in the oil sands has not been demonstrated, and knowledge gaps exist surrounding the long-term behaviour of EPLs and their viability as an FFT management and reclamation strategy. Uncertainties surrounding EPL behaviour include the flux of salts and organics into the water cap, biogeochemical cycling processes, which can generate sulfide species and greenhouse gases, and the environmental fate of PAM. To address these knowledge gaps, aging experiments are being performed in 1 L and 19 L EPL columns containing untreated or treated (with alum and PAM) FFT and a water cap. Aging is simulated in the columns through higher temperature and carbon amendments. Results to date show that fluxes of salts into the water caps are generally consistent with consolidation trends and are similar in columns containing either untreated or treated FFT. Compared to untreated FFT, treated FFT has undergone more extensive sulfur cycling, as evidenced by higher sulfate reduction rates and higher sulfide species concentrations.

Keywords: mine waste management, end pit lakes, biogeochemistry, sulfur cycling, consolidation, salt fluxes, polyacrylamide