Surface properties and elasticity of oil-sands-derived clays found in a sludge pond☆

Abstract Bitumenous sands of the province of Alberta in Canada constitute a major reserve of energy in the form of hydrocarbons. The processing of these sands to recover the crude oil results in the production of vast amounts of tailings which eventually settle into unconsolidated but stable masses of structured clays (sludge), which hold large amounts of inaccessible water in the ponds. The causes of this lack of consolidation are not well understood. Problems in transportation via pumping, water recovery, trapped crude oil recovery and water treatment are strongly influenced by the nature of the clay structures. This paper is aimed at understanding of the causes lack of consolidation of these sludges. Clays found in an oil sands tailings sludge pond were separated into three distinct populations (layers) by ultracentrifugation. The characteristics of each layer were studied under indigenous conditions to understand sludge stability. The three separated layers were found to be distinctly different in appearance, density and surface functionalities. The electrokinetic properties of each layer were similar, but the particle-particle interactions in concentrated suspensions showed different elastic moduli indicating varied structures. Interparticle interactions of the layer clays either depressed or enhanced the elasticity depending on the ratio of the mixtures and the history of shearing. The elasticity of one layer was found to be closest to that of the whole sludge and may be related to the organics present.