Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5 to 8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and "bioavailable" metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 - 13 g kg(-1)) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4 - 6 g kg(-1)) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.

中文翻译：

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沙漠尾矿风化引起的酸化过程中铅和锌不稳定性的变化：耦合化学和微观分析

由于低水通量率，沙漠矿山尾矿可能会在近地表厘米处积聚有毒金属。与其他限制一起，金属毒性阻止了自然植物的定植，即使在十年的时间尺度上也是如此。由于未固结的颗粒可能会受到风和水的侵蚀，从而可能导致人类和生态系统的直接暴露，因此需要了解尾矿风化环境中金属的不稳定性和形态是如何变化的。结合化学萃取、X 射线衍射、微 X 射线荧光光谱和微拉曼光谱，研究了来自亚利桑那州克朗代克州立超级基金场地的表层干旱尾矿中的铅和锌污染。初始场地特征表明表层尾矿堆的 pH 值范围很广（2.5 到 8.0）。用于评估植物可利用金属池的配体促进 (DTPA) 提取表明，随着尾矿的逐渐酸化，可利用的锌和锰减少。铝表现出相反的趋势，而 Pb 和 Fe 表现出更复杂的 pH 依赖性。由于尾矿来自共同的来源和母体矿物学，因此推测 pH 值和“生物可利用”金属浓度的变化是由颗粒尺度地球化学的相关变化引起的。对 pH 范围为 2.6 至 5.4 的四个子样品进行进一步表征，以阐明对金属迁移率的微观控制。随着酸化，总铅（从 5-13 g kg(-1) 不等）越来越多地与铅黄铁矿聚集体中的 Fe 和 S 相关联。对于 Zn，总 (0.4-6 g kg(-1)) 和不稳定部分都随着 pH 值的降低而减少。发现锌主要与次生锰相锰锌矿和黄铜矿有关。结果表明，逐步尾矿酸化降低了总铅和锌池的整体不稳定性。