Column study to evaluate the biogeochemical and geotechnical behavior of treated oil sands tailings in pit lakes

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4. Column study to evaluate the biogeochemical and geotechnical behavior of treated oil sands tailings in pit lakes

Pit lakes are a common feature of open pit mines across the globe and have been proposed as a reclamation strategy for Canadas oil sands tailings. Oil sands tailings are a waste stream made up of fine-grained solids, water, salts, and organics. A relatively new approach to oil sands pit lake technology is called Permanent Aquatic Storage Structure (PASS) in which tailings are first treated with alum (a hydrated aluminum sulfate salt) and polyacrylamide (a polymer flocculant) prior to being deposited in a pit lake and capped with water. There is limited information on the effects of alum, polyacrylamide, and pressure (from overlying tailings) on the biogeochemical and geotechnical behavior of pit lakes tailings. As such, 12 x 5.5 L columns have been designed to evaluate the biogeochemical and geotechnical behavior of PASS-treated tailings in pit lakes. Each column contains PASS-treated tailings and a freshwater cap, and tailings in six of the columns are subjected to pressures using a multi-step loading scheme. Results up to Day 180 highlight the importance of sulfur cycling in PASS-treated tailings, with 62 to 97% of the sulfate reduced within 60 days. Sulfate reduction has produced gaseous and aqueous hydrogen sulfide in the columns. The generation of biogenic methane and carbon dioxide gases, and aqueous ammonia/ammonium is occurring in all columns, though the columns under pressure (0.3 to 0.6 kPa) are generating higher volumes and concentrations of these compounds. This suggests that pressure may be increasing metabolite solubility and thereby, microbial activity in the tailings.

9th International Congress on Environmental Geotechnics (ICEG2023)

Resource Mining and Extraction