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Abstract
During bitumen separation from the mined oil sands ore, ultra‐fine, aluminosilicate clays, having a particle size of < 0.3 μm, are mobilized and become dispersed in the process water. In the presence of certain electrolytes these clays flocculate, ultimately forming thixotropic gels and producing tailings with a poor dewatering and consolidation characteristics.
The effect of sodium chloride and sodium bicarbonate (the major electrolytes present in tailings water) on the aggregation and settling behavior of suspensions of an ultra‐fine clays was investigated. The rate of ultra‐fines flocculation and gelation was significantly lower in the presence of bicarbonate ions. However, regardless of electrolyte type, increasing amounts of salt ultimately produced increased particle settling rates by increasing the degree of flocculation.
Ultra‐fines flocs, formed in the presence of either sodium chloride or sodium bicarbonate, settle freely to a 0.8 to 1.4 volume percentage solids. At this concentration steric interference between particle clusters produces a voluminous gel that immobilizes large amounts of water. For systems with ultra‐fines concentrations above the gelation point, final sediment volumes and their solid's content, are virtually independent of salt type, concentration and amount of ultra‐fines in the original suspension.
These results offer an insight into the effect of amount and type of electrolyte on the water holding capacity of tailings produced under existing and predicted conditions in the tailings pond. This is of a significant importance providing that oil sands tailings disposal and site reclamation is a major environmental issue.