Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
Chemosphere. 2019 Feb;217:715-723. doi: 10.1016/j.chemosphere.2018.11.064. Epub 2018 Nov 12.
Fluid petroleum coke generated at oil sands operations in the Athabasca Oil Sands Region of northern Alberta, Canada, contains elevated concentrations of molybdenum (Mo) and other metals including nickel (Ni) and vanadium (V). Solid-phase Mo concentrations in fluid petroleum coke are typically 10 to 100 times lower than V and Ni, yet dissolved Mo concentrations in associated pore waters are often comparable with these metals. We collected pore water and solids from fluid petroleum coke deposits in the AOSR to examine geochemical controls on Mo mobility. Dissolved Mo concentrations increased with depth below the water table, reaching maxima of 1.4-2.2 mg L, within a mixing zone between slightly acidic and oxic meteoric water and mildly alkaline and anoxic oil sands process-affected water (OSPW). Dissolved Mo concentrations decreased slightly with depth below the mixing zone. X-ray absorption spectroscopy revealed that Mo(VI) and Mo(IV) species were present in coke solids. The Mo(VI) occurred as tetrahedrally coordinated MoO adsorbed via inner- and outer-sphere complexation, and was coordinated in an environment similar to Fe-(hydr)oxide surface complexes. The OSPW likely promoted desorption of outer-sphere Mo(VI) complexes, resulting in higher dissolved Mo concentrations in the mixing zone. The principal Mo(IV) species was MoS, which originated as a catalyst added upstream of the fluid coking process. Although MoS is likely stable under anoxic conditions below the mixing zone, oxidative weathering in the presence of meteoric water may promote long-term Mo release.
从加拿大艾伯塔省北部阿萨巴斯卡油砂区油砂作业中产生的流体石油焦含有较高浓度的钼（Mo）和其他金属，包括镍（Ni）和钒（V）。流体石油焦中固相 Mo 的浓度通常比 V 和 Ni 低 10 到 100 倍，但与之相关的孔隙水中的溶解 Mo 浓度通常与这些金属相当。我们从 AOSR 中的流体石油焦沉积物中采集了孔隙水和固体样品，以研究 Mo 迁移的地球化学控制因素。溶解 Mo 的浓度随地下水位以下深度的增加而增加，在微酸性和有氧的大气水与微碱性和无氧的油砂加工影响水（OSPW）之间的混合区达到 1.4-2.2mg/L 的最大值。在混合区以下的深度，溶解 Mo 的浓度略有下降。X 射线吸收光谱表明，Mo(VI)和 Mo(IV)物种存在于焦固体中。Mo(VI)以通过内和外配位络合吸附的四面体配位 MoO 的形式存在，并且在类似于 Fe-(水合)氧化物表面络合物的环境中配位。OSPW 可能促进了外配位 Mo(VI)络合物的解吸，从而导致混合区中溶解 Mo 浓度升高。主要的 Mo(IV)物种是 MoS，它起源于流体焦化过程上游添加的催化剂。尽管 MoS 在混合区以下的缺氧条件下可能是稳定的，但在大气水存在的情况下氧化风化可能会促进长期 Mo 释放。
