Arsenic (As) is a potent carcinogen and the most common metal(loid) contaminant in drinking water sources globally. In acidic, Fe-rich systems, nanocrystalline Fe(III) precipitates (Fe(III)_NP) are the main scavengers of As. However, the redox cycling of Fe(III)_NP highly enhances As mobility and bioavailability. Notably, the irreversible release of As in runoff resulting from reductive dissolution of Fe(III)_NP makes the effective remediation of As an ongoing environmental challenge. Here, we show for the first time that detrital clay minerals originating from the partial weathering of coal mining waste substantially increased total As uptake by acid mine drainage (AMD) sediments. The As immobilization mechanisms by the AMD sediments were investigated by the combined use of microbial community structure characterization (16S rRNA), chemical extractions, and synchrotron-based X-ray fluorescence (XRF), diffraction (XRD), and absorption (XANES). The use of an X-ray spot size as small as one micrometer allowed a detailed examination of the heterogeneous AMD sediments. Our results suggest that during sustained redox cycling of iron in Fe(III)_NP-clay mixed-mineral systems, the clays controlled As mobility by (1) enhancing heterogeneous precipitation of Fe(III)_NP under oxic conditions, which then adsorbed or incorporated As; and (2) facilitating the transfer of As from Fe(III)_NP to clay during microbially mediated reduction of Fe(III)_NP coatings under anoxic conditions. Designing remediation strategies that incorporate clay could become a promising low-cost strategy for As remediation in mining-impacted areas.

中文翻译：

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碎屑粘土矿物增强酸性矿山排水中砷的固定化

砷（As）是一种强力的致癌物质，是全球饮用水水源中最常见的金属（胶体）污染物。在酸性，富铁系统中，纳米晶Fe（III）沉淀物（Fe（III）_NP）是As的主要清除剂。但是，Fe（III）_NP的氧化还原循环_大大提高了As的迁移率和生物利用度。值得注意的是，由于Fe（III）_NP的还原溶解而导致径流中As的不可逆释放进行有效的补救是一项持续不断的环境挑战。在这里，我们首次表明，源自煤矿废弃物局部风化的碎屑粘土矿物大大增加了酸性矿山排水（AMD）沉积物对总砷的吸收。通过结合使用微生物群落结构表征（16S rRNA），化学提取和基于同步加速器的X射线荧光（XRF），衍射（XRD）和吸收（XANES），研究了AMD沉积物对As的固定机理。使用小至1微米的X射线光斑可以对异质AMD沉积物进行详细检查。我们的结果表明在Fe（III）_NP中铁的持续氧化还原循环过程中-粘土混合矿物系统，通过以下步骤控制粘土的迁移率：（1）在有氧条件下增强Fe（III）_NP的非均相沉淀，然后吸附或掺入As；（2）在缺氧条件下，在微生物介导的Fe（III）_NP涂层的还原过程中，促进了As从Fe（III）_NP向粘土的转移。设计结合粘土的修复策略可能会成为受采矿影响地区砷修复的一种有前途的低成本策略。