Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, T6G-2W2, Canada.
J Contam Hydrol. 2011 Jan 25;119(1-4):55-68. doi: 10.1016/j.jconhyd.2010.09.008. Epub 2010 Sep 29.
In Northern Alberta, the placement of out-of-pit oil sands tailings ponds atop natural buried sand channels is becoming increasingly common. Preliminary modeling of such a site suggests that process-affected (PA) pond water will infiltrate through the underlying clay till aquitard, reaching the sand channel. However, the impact of seepage upon native sediments and groundwater resources is not known. The goal of this study is to investigate the role of adsorption and ion exchange reactions in the clay till and their effect on the attenuation or release of inorganic species. This was evaluated using batch sorption experiments (traditional and a recent modification using less disturbed sediment samples) and geochemical modeling with PHREEQC. The results show that clay till sediments have the capacity to mitigate the high concentrations of ingressing sodium (600 mg L(-1)), with linear sorption partitioning coefficients (K(d)) of 0.45 L kg(-1). Ion exchange theory was required to account for all other cation behaviour, precluding the calculation of such coefficients for other species. Qualitative evidence suggests that chloride will behave conservatively, with high concentrations remaining in solution (375 mg L(-1)). As a whole, system behaviour was found to be controlled by a combination of competitive ion exchange, dissolution and precipitation reactions. Observations, supported by PHREEQC simulations, suggest that the influx of PA water will induce the dissolution of pre-existing sulphate salts. Sodium present in the process-affected water will exchange with sediment-bound calcium and magnesium, increasing the divalent ions' pore fluid concentrations, and leading to the precipitation of a calcium-magnesium carbonate mineral phase. Thus, in similar tailings pond settings, particularly if the glacial till coverage is thin or altogether absent, it is reasonable to expect that high concentrations of sodium and chloride will remain in solution, while sulphate concentrations will exceed those of the ingressing plume (150 mg L(-1)).
在加拿大北部，将露天油砂尾矿池放置在天然埋藏的砂质河道之上的做法越来越普遍。对这样一个地点的初步建模表明，受处理过程影响的（PA）池塘水将渗透过下面的粘土层隔水层，到达砂质河道。然而，渗漏对当地沉积物和地下水资源的影响尚不清楚。本研究的目的是研究粘土中吸附和离子交换反应的作用及其对无机物质的衰减或释放的影响。这是通过使用批量吸附实验（传统方法和最近使用较少受干扰的沉积物样本的改进方法）和使用 PHREEQC 的地球化学建模来评估的。结果表明，粘土具有减轻高浓度钠（600mg/L）进入的能力，线性吸附分配系数（Kd）为 0.45L/kg。需要离子交换理论来解释所有其他阳离子的行为，从而无法为其他物质计算这些系数。定性证据表明，氯将表现为保守行为，大部分仍保留在溶液中（375mg/L）。总的来说，系统行为是由竞争性离子交换、溶解和沉淀反应的组合控制的。由 PHREEQC 模拟支持的观察结果表明，PA 水的流入将诱导先前存在的硫酸盐盐的溶解。受处理过程影响的水中存在的钠将与沉积物结合的钙和镁交换，增加二价离子的孔隙流体浓度，并导致钙镁碳酸盐矿物相的沉淀。因此，在类似的尾矿池环境中，特别是如果冰川粘土层覆盖较薄或根本不存在，有理由预计高浓度的钠和氯将保持在溶液中，而硫酸盐浓度将超过进入羽流的浓度（150mg/L）。
