Column Size Impacts Chemical Fluxes and Consolidation of Untreated and Treated Oil Sands Tailings in a Pit Lake Column Study

This 40-column study investigated the effects of column size (19 and 1 L) on consolidation and contaminant transport in water capped oil sands tailings. Column size had a significant effect on consolidation, consolidation-induced advection, and diffusion. Tailings in 1 L columns achieved self-weight consolidation by Day 180, whereas tailings in 19 L columns did not achieve self-weight consolidation by the end of the study (Day 540), even though 19 L columns had greater water release and more tailings settlement due to the higher total stress and longer drainage pathway in these columns. As a result, advective fluxes continued to transport pore water constituents to water caps in the 19 L columns for the duration of the experiment. Diffusion became the dominant mass transport process in 1 L columns after Day 180, partly due to the higher concentration gradients in these columns. By Day 540, 1 L columns had higher water cap concentrations of pore water constituents than 19 L columns, despite the 19 L columns having a greater water release. This suggests that diffusion will continue to drive pore water constituents into pit lake water caps, even after self-weight consolidation and advection are complete.