Soil Manganese: Speciation, Transformation, and Reactivity

尽管锰是植物必需的微量营养素，在溶液浓度升高时可能引起植物毒性作用，而且锰（III，IV）-（氧）氧化物是土壤中微量金属（样金属）的重要清除剂和氧化剂，但人们对土壤中锰的固相形态和转化知之甚少。因此，对土壤锰的形态、转化和反应性的研究将探索土壤中不同锰库的相对丰度和可变性，验证现有的针对土壤锰的顺序提取方法，并探索亚/缺氧土壤环境中锰氧化物的还原转化及其对重金属溶解度的影响。为了达到这些目标，我们将使用基于同步加速器的x射线吸收光谱来研究欧洲主要土壤类型中锰的形态，并验证顺序提取程序作为简单且经济有效的方法来研究土壤锰循环。此外，我们将进行批量实验，结合详细的x射线衍射，红外光谱和拉曼光谱分析，以探索溶解锰（II）在水铁（II）存在下对重金属负载锰氧化物还原转化的影响，这一过程被假设强烈影响重金属在经受周期性水淹的土壤中的迁移。总之，计划中的项目将为土壤锰的形态提供基本的见解，通过顺序提取对土壤锰库进行可靠的量化，以及对土壤锰循环进行重要的地球化学控制。

Despite that manganese is an essential micronutrient for plants which may cause phytotoxic effects at elevated solution concentrations and manganese(III,IV)-(oxyhydr)oxides are important scavengers and oxidants for trace metal(loid)s in soils, the solid-phase speciation and transformation of manganese in soils are poorly understood. Therefore, the proposed research on the speciation, transformation, and reactivity of soil manganese will explore the relative abundance and variability of different manganese pools in soils, validate existing sequential extraction procedures used to target soil manganese, and explore the reductive transformation of manganese oxides in sub-/anoxic soil environments and its effect on heavy metal solubility. To reach these objectives, we will use synchrotron-based X-ray absorption spectroscopy to study the speciation of manganese in major soil types of Europe and validate sequential extraction procedures as simple and cost-effective means to investigate the soil manganese cycle. Additionally, we will conduct batch experiments in combination with detailed X-ray diffraction, IR-, and Raman spectroscopy analyses to explore the effect of dissolved manganese(II) on the reductive transformation of heavy metal-loaded manganese oxides in the presence of aqueous iron(II), a process which is hypothesized to strongly impact the mobility of heavy metals in soils subjected to periodic water logging. In summary, the planned project will provide fundamental insights into the speciation of soil manganese, the reliable quantification of soil manganese pools using sequential extractions, and important geochemical controls of the soil manganese cycle.