Reduction of Environmental Impacts of Oil Sands Plants by Implementing Bitumen Extraction and Tailings Disposal Processes using Lime (CaO) Additive

ABSTRACT: In Alberta, Canada, bitumen is produced by surface mining of Athabasca oil sands ore followed by ore-water slurry-based extraction processes, at a capacity exceeding 1.3x106 barrels/day. Clark Hot Water Extraction (CHWE) process developed in 1930s is used at all oil sands plants, which uses caustic NaOH as an additive to keep the pH of the extraction process slurry at about 8.2 to 9.0. Increase in slurry pH activates naphthenic acids in bitumen, which act as surfactant species reducing water surface and bitumen-water interfacial tensions. Reduction in surface and interfacial tensions promotes clay-water and bitumen-water wettability. As a result, NaOH additive promotes liberation of bitumen from oil sands matrix; however, it promotes silt-clay size particles dispersion and slows down coalescence and aeration of bitumen droplets, which harms overall efficiency of oil sands plants. Also, CHWE process causes accumulation of Na+ in recycle process water, which detrimentally effects bitumen extraction and promotes production of toxic mature fine tailings. Existing mature fine tailings inventory is exceeding 109 m3 and its production rate is exponentially increasing as bitumen production capacity increases. At our laboratory, bitumen extraction process is being studied by using lime (CaO) as additive replacing NaOH of the CHWE process. Use of CaO as an extraction process additive eliminates Na+ accumulation in recycle water, reduces surfactant activities of water soluble naphthenic acids, suppresses silt-clay size particles dispersion in the extraction process slurry, reduces mature fine tailings production, promotes bitumen extraction efficiency and increases the kinetics of bitumen droplets coalescence and aeration processes. Furthermore, tailings disposal processes, such as production of nonsegregating tailings, whole tailings treatment, and mature fine tailings dewatering processes were studied, also using CaO additive at different dosages. Experimental data will be presented by focusing on practicality, integration to the existing plants, capital and operating cost reduction perspectives.