Aluminum interactions with iron oxides in the absence and presence of silicic acid

铝是一种没有已知生物功能的金属，是覆盖世界上约40%可耕地的酸性土壤中的常见溶液成分。这些土壤中高浓度的溶解单体铝对植物具有高风险，从而危及农业食品生产。因此，了解控制酸性土壤中铝的形态、流动性和生物有效性的因素具有全球经济意义。铝与矿物表面的相互作用对铝在土壤环境中的地球化学循环起着特别重要的作用。虽然铁氧化物被认为是无处不在的铝吸附剂，吸附反应的铁氧化物和他们的控制已经收到了令人惊讶的关注在过去，阻碍了我们的能力，准确地预测铝吸附重要的土壤铁氧化物。此外，光谱学衍生的分子水平上的信息形成的铁氧化物上的铝物种目前还没有。这同样适用于重要的无机土壤溶质，如草酸对铝吸附反应的影响的信息。硅酸是一种无所不在的土壤溶液成分，对氧化铁表面表现出高亲和力。土壤铁氧化物，因此，经常富含硅，迄今未知的后果铝动员和固定化反应。通过拟议的研究，我们试图更好地了解铝和铁氧化物之间的相互作用，在存在和不存在吸附的柠檬酸。我们的研究重点是铝表面形态以及铝吸附反应的程度，动力学和可预测性。为了解决这些方面，我们使用间歇和流通反应器实验、平衡和动力学建模以及本体和表面敏感光谱（例如，X射线吸收和X射线光电子能谱）。在这个项目中获得的知识将提高我们对影响土壤中铝的流动性和生物有效性的过程和机制的理解。

Aluminum is a metal without known biological function and a common solution constituent in acidic soils covering approximately 40% of the world's arable land. High concentrations of dissolved monomeric aluminum in these soils represent a high risk for plants and thus endanger agricultural food production. Understanding factors that control the speciation, mobility, and bioavailability of aluminum in acidic soils is thus of global economic importance. Aluminum interactions with mineral surfaces play a particularly important role for the geochemical cycling of aluminum in soil environments. Although iron oxides are recognized as ubiquitous aluminum sorbents, sorption reactions of aluminum on iron oxides and their controls have received surprisingly little attention in the past, hampering our ability to accurately predict aluminum sorption to important soil iron oxides. Furthermore, spectroscopy-derived molecular-level information on aluminum species formed on iron oxides is not currently available. The same holds for information on the effect of important inorganic soil solutes such as silicic acid on aluminum sorption reactions. Silicic acid is an omnipresent soil solution constituent exhibiting a high affinity for iron-oxide surfaces. Soil iron oxides are therefore frequently enriched in silicon, with hitherto unknown consequences for aluminum mobilization and immobilization reactions. With the proposed research we seek to better understand the interactions between aluminum and iron oxides in the absence and presence of sorbed silicic acid. Our research focuses on aluminum surface speciation as well as on the extent, kinetics, and predictability of aluminum sorption reactions. To address these aspects, we use a combination of batch and flow-through reactor experiments, equilibrium and kinetic modeling, as well as bulk and surface-sensitive spectroscopies (e.g., X-ray absorption and X-ray photoelectron spectroscopy). The knowledge gained in this project will improve our understanding of processes and mechanisms affecting the mobility and bioavailability of aluminum in soils.