The Effect of Freezing and Thawing on the Dewatering of Oil Sands Sludges

Oil sands processing operations in northeastern Alberta generate 25 x 106 m3 of water-fines mixtures (sludge) per year. The fines settle in several weeks but will not consolidate to more than 35% solids, even over centuries. Freezing and thawing the
oil sands sludge led to rapid dewatering. One cycle of freezing and thawing caused 15, 25, 35, and 45% solids sludge to reach 35, 39, 48, and 51% solids content, respectively. Subsequent freeze-thaw cycles, up to a total of three, caused less rapid increases in solids content. The maximum concentration of solids by freezing and thawing, even after repeated cycles, was 60%. The amount of dewatering due to freeze-thaw can be confidently predicted by knowing only the initial solids content. The freezing time for each sludge concentration was monitored to compute proportionality coefficients required
to predict freezing depths under field conditions.