Assessing the feasibility of using lime to mitigate chemical flux in oil sands end pit lakes

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In northeastern Alberta, large volumes of fluid fine tailings (FFT) are produced during bitumen extraction fromsurface-mined oil sands ore. FFT is comprised of water, fine clays, naphthenic acids (NAs), residual bitumenand other unrecovered hydrocarbons. FFT takes decades to dewater in tailings ponds. Hence, the growinginventory compels operators to seek alternative tailings management strategies. End pit lakes (EPLs) with FFTbelow a water cap in mined out pits are one of the potential options. The expectation is that EPLs will slowlydevelop into self-sustaining aquatic ecosystems. Potential issues with EPLs may include movement ofconstituents of potential concern (COPCs) from the FFT into the overlying cap water contributing to on-goingsources of possible toxicity. Thus, research has been undertaken to resolve these issues and determine thefeasibility of EPLs as a reclamation strategy.Graymont Western Canada Inc. is an emerging global leader in the supply of lime and limestone products.Graymont has conducted preliminary tests showing that 1) lime addition to FFT in the range of 750 to 1500mg-CaO/kg-FFT improves FFT dewatering and facilitates the release of residual bitumen, and 2) lime additionto oil sands process-affected water (OSPW) induces calcium naphthenate precipitate formation at pH 12. Thesepreliminary findings can be leveraged by further investigating how lime treatment can mitigate COPC fluxacross the FFT-water cap interface in EPLs. Both of these issues are of relevance for the timely development ofEPLs in the oil sands industry.In this study, lime will be tested for its ability to enhance FFT dewatering and NA removal in lab-scale batchexperiments representative of an EPL. The purpose of this study to assess the feasibility of using lime as apre-treatment step in EPLs for efficient and economical oil sands tailings reclamation.