Abstract

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.

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