Interaction of oil sands tailings particles with polymers and microbial cells: First steps toward reclamation to soil

Production of bitumen by surface mining of Alberta's oil sands has given rise to tailings ponds, containing large volumes of finely dispersed clays (10(8) m(3)), which settle only slowly. The mature fine tailings (MFT) in these ponds are operationally defined as consisting of particles smaller than 44 μm with a solids content in excess of 30% (w/w). Increasing the rate of densification of MFT is a rate-limiting step in tailings pond reclamation. Accelerated densification has been achieved through mixing of MFT with sand in the presence of calcium sulfate as a binding agent to generate consolidated tailings. Addition of negatively charged polymer, together with either calcium or magnesium ions, is similarly effective. Although toxic to higher aquatic life, tailings ponds harbour a wide variety of mainly anaerobic microbes. These convert residual hydrocarbon, causing methane emissions of up to 10(4) m(3) day(-1). Interestingly, anaerobic microbial activity also accelerates tailings pond densification. Hence, many technologies designed to accelerate densification move tailings, at least conceptually, towards soil in which sand and clay particles are linked by large amounts of humic and fulvic acid polymers supporting large numbers of microbes in a mechanically stable structure.