Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada.
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada.
Sci Total Environ. 2017 Feb 1;579:396-408. doi: 10.1016/j.scitotenv.2016.11.084. Epub 2016 Nov 24.
This study investigated the geochemistry of arsenic (As) in low sulfide-high carbonate coal waste rock of the Elk Valley, British Columbia, Canada. Its abundance and mineralogical associations in waste rock of different placement periods were determined in addition to its mobilization into porewater and rock-drain effluent. The mean (5.34mg/kg; 95% confidence interval: 4.95-5.73mg/kg) As concentration in the waste rock was typical of sedimentary rock. Electron microprobe and As K-edge X-ray absorption near-edge spectroscopic analyses showed the As is predominantly associated with primary pyrites in both source and freshly blasted waste rock. However, in aged waste rock the As is associated with both primary pyrites and secondary Fe oxyhydroxides. Oxidation of pyrite in waste rock dumps was reflected by the presence of high concentrations of SO in porewater and oxidation rims of Fe oxyhydroxides around pyrite grains. Acid released from pyrite oxidation to Fe oxyhydroxides is neutralized by carbonate mineral dissolution that buffers the pH in the waste rock to circumneutral values. Adsorption of As onto secondary Fe oxyhydroxides provides an internal geochemical control on As release during pyrite oxidation and porewater flushing from the dump, resulting in the low As concentrations observed in porewater (median: 9.91μg/L) and rock-drain effluent (median: 0.31μg/L). Secondary Fe oxyhydroxides act as a long-term sink for As under present day hydrologic settings in waste rock dumps in the Elk Valley.
本研究调查了加拿大不列颠哥伦比亚省埃尔克谷低硫化物-高碳酸盐煤矸石中砷（As）的地球化学性质。除了研究其在孔隙水中的迁移和岩石排水中的迁移外，还确定了不同放置时间矸石中的 As 含量及其矿物组合。矸石中的 As 浓度平均值（5.34mg/kg；95%置信区间：4.95-5.73mg/kg）与沉积岩相似。电子探针和 As K 边 X 射线吸收近边光谱分析表明，As 主要与原生黄铁矿相关，无论是在源矸石还是新爆破的矸石中都是如此。然而，在老化的矸石中，As 与原生黄铁矿和次生 Fe 氢氧化物都有关联。矸石堆中黄铁矿的氧化反映在孔隙水中 SO 浓度高和黄铁矿颗粒周围 Fe 氢氧化物的氧化边。黄铁矿氧化为 Fe 氢氧化物释放的酸被碳酸盐矿物溶解中和，使矸石的 pH 值缓冲至近中性值。As 吸附到次生 Fe 氢氧化物上，为黄铁矿氧化和孔隙水从矸石堆中冲洗过程中 As 的释放提供了内部地球化学控制，导致孔隙水中 As 浓度较低（中位数：9.91μg/L）和岩石排水中的 As 浓度较低（中位数：0.31μg/L）。在埃尔克谷矸石堆现今水文条件下，次生 Fe 氢氧化物是 As 的长期汇。
