ROLE OF BICARBONATE IONS IN THE STABILITY OF ULTRA-FINES SUSPENSIONS

During bitumen separation from the mined oil sands ore, ultra-fine, al uminosilicate clays, having a particle size of less than or equal to 0 .3 mu m, are mobilized and become dispersed in the process water. In t he presence of certain electrolytes these clays flocculate, ultimately forming thixotropic gels and producing tailings with a poor dewaterin g 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-f ine clays was investigated. The rate of ultra-fines flocculation and g elation was significantly lower in the presence of bicarbonate ions. H owever, regardless of electrolyte type, increasing amounts of salt ult imately produced increased particle settling rates by increasing the d egree of flocculation. Ultra-fines flocs, formed in the presence of ei ther sodium chloride or sodium bicarbonate, settle freely to a 0.8 to 1.4 volume percentage solids. At this concentration steric interferenc e between particle clusters produces a voluminous gel that immobilizes large amounts of water. For systems with ultra-fines concentrations a bove the gelation point, final sediment volumes and their solid's cont ent, are virtually independent of salt type, concentration and amount of ultra-fines in the original suspension. These results offer an insi ght into the effect of amount and type of electrolyte on the water hol ding capacity of tailings produced under existing and predicted condit ions in the tailings pond. This is of a significant importance providi ng that oil sands tailings disposal and site reclamation is a major en vironmental issue.