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，也是酸性土壤中常见的溶液成分，覆盖了全球约40%的耕地。这些土壤中高浓度的溶解单体铝对植物具有很高的风险，从而危及农业粮食生产。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土壤环境中铝的地球化学循环起着特别重要的作用。尽管铁氧化物被认为是普遍存在的铝吸附物质，但铝在铁氧化物上的吸附反应及其控制在过去很少受到关注，这阻碍了我们准确预测铝对重要土壤铁氧化物的吸附。此外，光谱学衍生的关于铁氧化物上形成的铝物种的分子水平信息目前还不可用。有关硅酸等重要无机土壤溶质对铝吸附反应的影响的信息也是如此。硅酸是一种无处不在的土壤溶液成分，对氧化铁表面具有很高的亲和力。因此，土壤中的氧化铁经常富含硅，对铝的活化和固定反应的影响迄今尚不清楚。通过拟议的研究，我们试图更好地理解铝和铁氧化物在没有吸附硅酸和存在吸附硅酸的情况下的相互作用。我们的研究集中在铝表面的形态以及铝吸附反应的程度、动力学和可预测性。为了解决这些方面的问题，我们结合使用了间歇和流动反应器实验、平衡和动力学建模以及体相和表面敏感光谱(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移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.