Effect of Redox Conditions on the Crystallinity of Fe Oxides in Soil
Effect of Redox Conditions on the Crystallinity of Fe Oxides in Soil
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发表时间：
2013
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通讯作者：
R. Balint;C. Orbeci;G. Nechifor;Marinela Plesca
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作者：
R. Balint;C. Orbeci;G. Nechifor;Marinela Plesca
重金属的毒性取决于其在土壤液固两相中的含量和形态。HM与Fe和Mn的氧化物可能在氧化还原条件下释放，因此了解还原性溶解、结晶度变化和在操作定义的馏分中的重新分配的机制非常重要。当含有大量HM的土壤被淹没时，由于污染物可能从土壤扩散到其他环境区隔，一个重要的问题就出现了。在气候变化的背景下，各种情景预测极端洪水的频率和强度都会增加，降雨模式和强度也会发生变化，因此土壤水分状况可能会受到重大影响。这可能导致通常不浸水的受污染土壤被淹没的可能性增加，就像全球许多含金属的矿区一样。缺氧条件可通过氧化相的还原性溶解导致微量元素的释放，如铁和锰（它们与之相结合）或通过有机物（OM）的氧化（金属与之络合）导致微量元素的释放。此外，在随后的氧化条件下，它们可能以不太稳定的形式结合（即，在无定形的铁（氢）氧化物上）。一些作者表明，土壤氧化还原振荡可能会增加热带地区土壤中铁氧化物的结晶度，从而增加胶体的稳定性，胶体是HM的潜在载体，Contin等人（2007）的工作得出结论，氧化还原循环增强了一些HM对铁氧化物的固定。然而，很少有研究涉及缺氧和缺氧交替条件对矿化土壤溶液中Fe和Mn离子的增溶和转运的影响，以及它们在固相组分之间的重新分布作为金属稳定性释放机制的研究。这使得评估铁和锰化学形态的变化变得非常必要，因为它们随后的溶解可能特别危险，因为它可能引发HM的释放，从而缩短人类接触的途径。
The toxicity of heavy metals (HM) depends on their content and speciation in the liquid and solid phases of the soil. HM associated with Fe and Mn oxides might be released under redox conditions, therefore it is important to understand the mechanisms of reductive dissolution, changes in crystallinity and redistribution in operationallydefined fractions. An important issue arises when soils containing high amounts of HM are flooded, due to the possibility of contaminant diffusion from soil to other environmental compartments. In the context of climate change for which scenarios predict an increase of the frequency and intensity of extreme floods, as well as variations in rainfall patterns and intensities [1], soil moisture status may be significantly influenced. This may result in an increasing probability of submergence of contaminated soils that are not normally waterlogged, as in numerous metalliferous mining areas around the globe. Anoxic conditions may cause the release of trace elements by reductive dissolution of oxide phases, i.e. Fe and Mn, to which they are associated [2] or through the oxidation of organic matter (OM) to which metals are complexed [3]. In addition, on the subsequent onset of oxic conditions they may be bound in a less stable form (i.e., on amorphous Fe (hydr)oxides). Some authors showed that soil redox oscillations may increase the crystallinity of Fe oxides in tropical area soils [4], thus increasing the stability of colloids which are potential carriers of HM, and the work of Contin et al. (2007) [5] concluded that redox cycles enhance fixation of some HM into Fe oxides. However, few studies have dealt with the influence of alternating oxic and anoxic conditions on the solubilization and translocation of Fe and Mn ions in solution from mineaffected soils, and their redistribution among solid-phase components as a release mechanism of metal lability. This makes it highly necessary to assess changes in Fe and Mn chemical forms as their consequent dissolution may be particularly dangerous since it could trigger the release of HM, therefore shortening the pathways for human exposure.