Geochemical enrichment, speciation and mobilization of arsenic and antimony in black shales (southern China): Evidence from sequential fractionation and XANES spectroscopy
Geochemical enrichment, speciation and mobilization of arsenic and antimony in black shales (southern China): Evidence from sequential fractionation and XANES spectroscopy
复制标题
DOI：
10.1016/j.chemgeo.2023.121647
复制
发表时间：
2023-08
期刊：
影响因子：
3.9
通讯作者：
J. Cui;Xingyu Zhou;Yuxiao Chen;Chengbo Zhang;T. Xiao;Qiugui Wang;Xiaoxia Zhou;Ting-Shan Chan-Ting-Shan-Cha
中科院分区：
文献类型：
--
作者：
J. Cui;Xingyu Zhou;Yuxiao Chen;Chengbo Zhang;T. Xiao;Qiugui Wang;Xiaoxia Zhou;Ting-Shan Chan-Ting-Shan-Cha
黑色页岩中高含量的痕量金属（类金属）在自然风化过程中会释放出来，引起了全球的关注。目前，砷（As）和锑（Sb）这两种高毒性金属在黑色页岩中的累积、形态和潜在迁移等问题尚未得到解决，这阻碍了其对周围环境潜在风险的评估。在这里，我们展示了地球化学富集，物种转换，并通过风化蚀变，连续提取和同步辐射X射线吸收近边光谱（XANES）的分析范围内的黑色页岩和风化样品收集的两个配置文件从典型的寒武纪沉积地层中，中国南方珠江三角洲，砷和锑的淋溶行为。结果表明，土壤中As等微量金属元素有明显的积累（43.8-458.0 mg/kg），Sb（7.2-34.5毫克/千克），铜（8.8-451.0 mg/kg）和Ni（22.2- 108.0mg/kg），富集系数高（22.0-266.8）和Sb（1.2-6.4），与非常高的风化程度（化学蚀变指数：83-91）一致。页岩中的砷主要是砷酸盐（46-85%），使用XANES鉴定，这是由于广泛的风化，促进了砷和毒砂物种的氧化。因此，在高度风化的产品中观察到硫化物相关的As和Sb的显着减少。因此，As和Sb主要是在与无定形和结晶良好的Fe/Mn氧化物，主要是由于次生Fe（oxyhydr）氧化物，包括针铁矿样矿物，这主要是来自于氧化风化的绿泥石类矿物的形成增加的固定馏分。然而，在18 h的模拟酸雨淋滤实验中，黑色页岩样品中As（<64 μg/L）、Sb（14-70 μg/L）和Ni（3-92 μg/L）的含量仍然很高。我们的综合表征结果表明，一小部分的高含量的地质砷和锑可能会被释放。然而，页岩渗滤液中的可溶性微量金属（类）仍然可能危害周围的生态系统，并在长期的自然风化过程中的持续监测是值得全球黑色页岩地区。
The high geogenic levels of trace metal(loid)s preserved within black shale can be released during natural weathering, causing global concern. Currently, the accumulation, speciation and potential mobilization of two highly toxic metal(loid)s, arsenic (As) and antimony (Sb), from black shale to soils remain unresolved, which hinders the evaluation of their potential risk to surrounding environments. Here, we demonstrate the geochemical enrichment, species transformation, and leaching behavior of As and Sb by applying weathering-induced alteration, sequential extraction and synchrotron-based X-ray absorption near edge spectroscopy (XANES) in the analysis of a range of black shale and weathered samples from two profiles collected from typical Cambrian sedimentary strata of the Pearl River Delta, southern China. The results showed significant accumulation of trace metal(loid)s, including As (43.8–458.0 mg/kg), Sb (7.2–34.5 mg/kg), Cu (8.8–451.0 mg/kg) and Ni (22.2–108.0 mg/kg), in the black shale and weathered products, and high enrichment factors for As (22.0–266.8) and Sb (1.2–6.4) were observed, consistent with the very high degrees of weathering (chemical index of alteration: 83–91). Arsenic in the shale was dominated by arsenate (46–85%), as identified using XANES, and this was resulted from extensive weathering, which facilitated the oxidation of arsenite and arsenopyrite species. Accordingly, significant decreases in sulfide-associated As and Sb were observed in highly weathered products. As a result, As and Sb were primarily in the immobilizable fractions associated with amorphous and well-crystallized Fe/Mn oxides, largely due to the increased formation of secondary Fe (oxyhydr)oxides, including goethite-like minerals, which mainly derived from the oxidative weathering of chlorite-like minerals. Nevertheless, high concentrations of As (<64 μg/L), Sb (14–70 μg/L), and Ni (3–92 μg/L) still leached from black shale samples exposed to synthetic acid rain in the 18-h batch leaching experiment. Our combined characterization results indicated that a small percentage of the high contents of geogenic As and Sb could potentially be released. However, soluble trace metal(loid)s in shale leachate could still endanger surrounding ecosystems, and continual monitoring during long-term natural weathering processes is merited for global black shale regions.