Centre for Environmental Radioactivity (CERAD CoE), Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Elizabeth Stephansens vei 29, 1433 Aas, Norway; Norwegian Geotechnical Institute, P. O. Box 3930, Ullevål Stadion, 0806 Oslo, Norway.
Centre for Environmental Radioactivity (CERAD CoE), Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Elizabeth Stephansens vei 29, 1433 Aas, Norway.
Sci Total Environ. 2023 Jul 1;880:163035. doi: 10.1016/j.scitotenv.2023.163035. Epub 2023 Mar 24.
Construction and mining activities in acid-producing alum shale regions often produce large volumes of crushed rock. Disposal under groundwater level (e.g., a bog) may minimize oxygen access. In this study, the effect of varying oxygen access on the leaching potential of alum shale was investigated by submerging tunnel construction rock debris in synthetic rainwater under atmospheric (AOC) and low oxygen conditions (LOC) for 52 weeks. The sulphate increase and nitrate decrease in the leachates suggested that pyrite (FeS) in the alum shale was oxidized, but carbonates originating from calcite dissolution provided sufficient buffering capacity (leachate pH ~7.7 over 52 weeks), resulting in neutral rock drainage. Less available oxygen led to significantly lower production of sulphate and acid from pyrite oxidation, reducing the release of harmful elements. Under LOC, the leaching of Mo, Co, Ni, Zn and Cd was 2-4 times lower than under AOC and the lower buffering requirement diminished the release of Ca as well as divalent cations (Mg, Sr, Mn) likely present as impurities in calcite. Contrastingly, limited pyrite oxidation led to less oversaturation with respect to BaSO and lower release of Fe in the LOC leachates. Thus, co-precipitation of Ra was inhibited and scavenging of leached V, As and Sb by newly formed Fe(OH) was not as dominant as in the AOC systems. Leaching of U was ~20 % higher under LOC likely due to enhanced complexation by dissolved carbonate. In general, element leaching rates were slower under low O levels. Characterization of water collected at the disposal site after ~1.2 years of discarding tunnel materials showed that the weathering of debris submerged in the open, water-filled pond occurred similarly to leaching under low oxygen conditions. Overall, these results highlight the importance of minimal oxygen access or anaerobic conditions when acid-producing rock waste is stored under water.
在产酸铝页岩地区，建筑和采矿活动通常会产生大量的碎岩。将其置于地下水位以下（例如沼泽地）处置可以最大程度减少氧气的进入。在这项研究中，通过将隧道施工岩屑浸入模拟雨水下，在大气（AOC）和低氧（LOC）条件下分别进行为期 52 周的实验，研究了不同氧气供应条件对铝页岩淋滤潜力的影响。淋出液中硫酸盐的增加和硝酸盐的减少表明，铝页岩中的黄铁矿（FeS）被氧化，但方解石溶解产生的碳酸盐提供了足够的缓冲能力（52 周内淋出液的 pH 值约为 7.7），导致中性岩石排水。较少的可用氧气导致黄铁矿氧化产生的硫酸盐和酸的产量显著降低，从而减少有害元素的释放。在 LOC 条件下，Mo、Co、Ni、Zn 和 Cd 的浸出量比 AOC 条件下低 2-4 倍，较低的缓冲要求减少了 Ca 以及二价阳离子（Mg、Sr、Mn）的释放，这些元素可能作为方解石中的杂质存在。相反，有限的黄铁矿氧化导致在 LOC 淋出液中对 BaSO 的过饱和度较低，并且 Fe 的释放量较低。因此，镭的共沉淀受到抑制，并且新形成的 Fe(OH)对淋出的 V、As 和 Sb 的捕获作用不如 AOC 体系那样占主导地位。LOC 条件下 U 的浸出率约高 20%，可能是由于溶解的碳酸盐增强了络合作用。一般来说，低氧水平下元素的浸出率较慢。在将隧道材料丢弃约 1.2 年后收集到的处置场水样的特征表明，在开放的、充满水的池塘中，碎屑的风化与低氧条件下的淋滤相似。总的来说，这些结果强调了当产酸岩石废物在水下储存时，最小化氧气进入或无氧条件的重要性。
