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Oil sands tailings have a limited ability to dewater and can also release toxic water, so finding a cost-effective tailings reclamation strategy has been challenging. End pit lakes (EPLs) are being examined as one potential approach to reduce fluid fine tailings (FFT) inventories for the oil sands industry. This study investigated the effect of adding lime (650 to 4000 ppm) on FFT dewatering and improving cap water quality under the simulated EPL scenario. The results illustrated that a high lime dose of 3500 ppm achieved the highest FFT water recovery, decreased the cap water alkalinity at the end of the experiment (after 90 d), and increased the possibility of cation exchange (at day 0). In contrast, the degradation of petroleum hydrocarbons was slightly enhanced at low lime dose of 650 ppm in comparison to high doses. In addition, the 650 ppm dose resulted in minimal change in the microbial cell counts at day 90, compared with high lime doses that resulted in a large reduction in the cell counts. Comparisons of toxicity of the FFT pore water after lime addition exhibited higher toxic effects for lime dosages >1600 ppm. Nevertheless, at all lime doses, low cap water toxicity (i.e.

Over 80% of Athabasca, Alberta, Canada oil sands deposits are suitable for in-situ bitumen recovery processes. Steam assisted gravity drainage and cyclic steam stimulation processes are commercially implemented with current bitumen production capacity of about 850,000 bbl/d, which is projected to exceed 5000,000 bbl/d in the next two decades. Efficiency of these processes would be improved by reducing the steam-to-bitumen ratio. For this purpose addition of light hydrocarbons into steam as a solvent to reduce bitumen viscosity has been studied for decades with a limited commercial success. As an alternate strategy to solvent co-injection with steam, reduction of bitumen–water interfacial tension by co-injection of a surfactant, such as biodiesel (fatty acid methyl esters), with steam was proposed ( Babadagli et al., 2009 . Use of biodiesel as an additive in thermal recovery of heavy-oil and bitumen. In: Paper 049 Presented at the Canadian International Petroleum Conference (CIPC), 16–18 June, Calgary, Alberta, Canada; Babadagli and Ozum, 2012 . Oil Gas Sci. Technol.: Rev. IFP Energies Nouvelles 67 (3), 413–421). The present study focuses on three issues: (i) viscosity of bitumen in the neighborhood of the edge of the steam chamber using heat conduction models, where bitumen mobility should be controlled by viscosity and bitumen–water interfacial tension; (ii) generate bitumen recovery data, operating the steam chamber as a pressure cooker; where bitumen mobility should be controlled mainly by viscosity rather than bitumen–water interfacial tension, since the influence of the creeping flow of water-condensed steam is marginally small; and, (iii) measure bitumen content at different heights of the pressure cooker test spent core samples to predict bitumen mobility and permeability. Pressure cooker tests were performed using steam, steam and pentane as a solvent at 5%, 10% and 15% of bitumen by mass, and steam and biodiesel as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosages. Our test results showed that solvent, such as pentane, addition reduced bitumen recovery as the dosage of solvent addition increased from 5% to 15% of bitumen. This observation is interpreted that while solvent addition reduces bitumen viscosity it also increases bitumen–water interfacial tension; the overall effect of which results in reduction of bitumen recovery efficiency. When biodiesel was used as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosage, a slightly increase in bitumen recovery efficiency was observed. Bitumen mobility and bitumen permeability values predicted in this study were one order of magnitude smaller than that of the values reported in the literature; probably resulting from reduced bitumen–water interfacial tension, by the activation of natural surfactants contained in bitumen, promoting bitumen mobility in the field operations. Result of the present study suggests that further tests and modeling studies are needed to understand effects of bitumen viscosity reduction by solvent co-injection and bitumen–water interfacial tension reduction by surfactant co-injection with steam on the efficiency of steam assisted bitumen recovery processes.

In Alberta, Canada, bitumen production by surface mining followed by ore-water slurry based extraction processes is approaching 2,000,000 bbl/d capacity. The Clark Hot Water Extraction process developed in the 1930s is used at all commercial plants which use caustic NaOH as an additive to boost bitumen recovery efficiency. Use of NaOH as an extraction process additive increases process water salinity, specifically Na+ concentration, promotes dispersion of silt and clay size particles which results in greater production of toxic mature fine tailings. Increase in process water Na+ concentration detrimentally affects the performance of both bitumen extraction and tailings disposal processes. Existing mature fine tailings inventory stored in tailings ponds is exceeding 900x106 m3 and is predicted to grow alarmingly faster by the completion of new plants and by an increase in the production capacity of the existing plants. The Energy Resources Conservation Board of Alberta issued Directive 074 in February, 2009 urging oil sands plants to comply with a 50% reduction in mature fine tailings production. Proposed policies by the oil industry in response to Directive 074 have shown short fallings; which suggests that development of novel bitumen extraction and tailings management processes are needed. To reduce the mature fine tailings inventory, we studied production of nonsegregating tailings by treating a blend of cyclone underflow and thickened cyclone overflow with CaO additive. These tests were made using Albian Sands Muskeg River Mine tailings when the plant was operating at nonadditive and sodium citrate additive extraction modes and using Syncrude Canada Ltd.'s Aurora Mine tailings. Also, we studied the use of CaO as a bitumen extraction process additive replacing NaOH in the Clark Hot Water Extraction process; by which silt-clay size particles dispersion in the extraction process slurry is reduced and accumulation of Na+ in the process water is eliminated. Use of CaO as an extraction additive is considered as a fundamental and a new process alteration by the oil sands operators. Recently, to evaluate this new process the Canadian Oil Sands Innovation Alliance (COSIA) has requested NAIT-NARCOSS, an independent academic and industrial research laboratory, to perform a third party verification study for the use of CaO as a bitumen extraction process additive. The NAIT-NARCOSS test results are completed and are highly encouraging, confirming that use of CaO as an extraction process additive reduces dispersion of silt and clay size particles in the extraction process slurry without harming bitumen recovery efficiency. It also improves process water chemistry by eliminating accumulation of Na+ in the process water. It is concluded that a paradigm change is offered to the oil sands industry to reduce the adverse environmental impacts of oil sands plants in simple, cost effective and environmentally friendly manners; which is the simultaneous implementation of the use of CaO as additives in bitumen extraction and nonsegregating tailings production processes.