Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg-1 (3080, 2200, and 2570 mg kg-1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.

中文翻译：

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半干旱气候下硫化铁尾矿风化过程中有毒金属（类）物质的形成

有毒金属尾矿对生态系统和邻近社区构成重大健康风险，原因是含有高浓度有毒金属（类物质）（例如铅、砷、锌）的颗粒随风和水扩散。在植被恢复之前，尾矿特别容易受到侵蚀，即在没有干预的半干旱环境中需要几十年或更长时间。与生物可及性和不稳定性直接相关的金属（类）形态受矿物风化控制，是评估与矿区相关的人类和环境健康风险时的关键考虑因素。在亚利桑那州中部半干旱的 Iron King 矿和 Humboldt Smelter Superfund 矿场，之前已经对尾矿顶部 2 m 的矿物组合进行了表征。在顶部 0 中观察到明显的氧化还原梯度。5 m 的尾矿和矿物组合表明亚铁硫化物逐渐转变为水铁矿和石膏，然后风化形成施韦特曼铁矿，然后是黄钾铁矾，伴随着 pH 值的逐渐降低（7.3 至 2.3）。在该反应前沿的地球化学背景下，我们检测了表面浓度分别为 41.1、10.7、39.3 mM kg-1（3080、2200 和 2570 mg kg-1）的富集有毒金属（类）As、Pb 和 Zn . As 和 Zn 的最高体积浓度出现在氧化还原边界，分别代表相对于表面浓度的 1.7 和 4.2 倍富集，表明有毒元素从铁皮区转移到下面的氧化还原边界或地壳。还使用 X 射线吸收光谱 (XAS) 将金属形态作为深度的函数进行了检查。最深的样品（180 厘米）含有硫化物（如黄铁矿、毒砂、方铅矿和闪锌矿）。来自氧化还原过渡区（25-54 cm）的样品含有硫化物、碳酸盐（菱铁矿、铁橄榄石、铜铁矿和菱锌矿）和吸附在新形成的次生铁相（主要是水铁矿）上的金属（铁矿）的混合物。在表面样品 (0-35 cm) 中，发现金属 (loid) 作为吸附物质或结合到次级 Fe 羟基硫酸盐相中，例如施威特曼铁矿和黄钾铁矾。在表面样品中检测到含金属的风化盐（例如，ZnSO4·nH2O）。综上所述，这些数据表明金属（类）的生物可及性和不稳定性因矿物风化而改变，