Molecular-scale mechanisms of antimony binding to soil organic matter

锑(Sb)是一种有毒的金属，由于其在广泛的工业和技术产品中的应用，它被越来越多地释放到环境中。因此，锑化合物被环境保护机构视为优先污染物。尽管土壤中的Sb投入量很高(约26,000吨/年)，但很少有研究研究土壤中Sb的形态及其控制其环境命运的因素。泥炭土壤中Sb的低移动性表明，土壤有机质(OM)对Sb的络合作用是土壤Sb循环中的关键元素。然而，关于Sb与固有的复杂的溶解和颗粒土壤OM之间的分子尺度相互作用的信息是缺失的。因此，本项目旨在研究Sb与土壤有机质结合的分子尺度机理。在项目的第一部分，我们利用同步加速器的Sb K边X射线吸收光谱(XAS)研究了在缺氧和缺氧条件下Sb与土壤有机质的结合机理，重点研究了羧基/羟基和硫醇基团与Sb的结合以及有机络合的Fe(三元Sb络合物)。我们还用稳定的Sb同位素示踪方法阐明了Sb-OM络合物的动力学稳定性。在本项目的第二部分中，我们研究了英国山顶地区泥炭土壤中Sb的形态和分布。这些有机土壤受到了长期大气Sb沉积的影响，因此受到了广泛的Sb污染。在XAS的帮助下，我们探索了在这些土壤中运行的主要的Sb固定机制。与这些测量相补充的是扫描电子显微镜-能量色散X射线能谱(扫描电子显微镜-能谱)和X射线光电子能谱分析，以研究Sb的微观分布和形态及其与其他可能控制其形态的元素(如Fe和S)的联系。综上所述，该项目将提高我们对Sb-OM相互作用的机械理解，并阐明OM在受人类释放和大气沉积Sb影响的有机土壤中作为Sb的吸着剂的作用。

Antimony (Sb) is a toxic metalloid which is increasingly released into the environment owing to its use in a vast range of industrial and technological products. Antimony compounds are therefore considered as priority pollutants by environmental protection agencies. Despite high Sb inputs to soils (ca. 26,000 t/a) only few studies have examined the speciation of Sb in soils and factors controlling its environmental fate. The low mobility of Sb observed in peat soils suggests that Sb complexation by soil organic matter (OM) represents a key element in the soil Sb cycle. Yet, information on molecular-scale interactions of Sb with inherently complex dissolved and particulate soil OM is missing. Therefore, this project aims at the investigation of molecular-scale mechanisms of Sb binding to soil OM. In the first part of the project we use synchrotron-based Sb K-edge X-ray absorption spectroscopy (XAS) to explore the mechanisms of Sb binding to soil OM under both oxic and anoxic conditions, focusing on Sb binding by carboxyl/hydroxyl and thiol groups as well as organically complexed Fe (ternary Sb complexes). We also elucidate the kinetic stability of the Sb-OM complexes using an enriched stable Sb isotope tracer approach. In the second part of this project, we study the speciation and distribution of Sb in peat soils of the Peak District, U.K. These organic soils have been impacted by long-term atmospheric deposition of Sb and are thus extensively contaminated with Sb. With the help of XAS we explore major Sb sequestration mechanisms operating in these soils. These measurements are complemented by scanning electron microscopy – energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses to study the micro-scale distribution and speciation of Sb and its association with other elements potentially controlling its speciation (e.g., Fe and S). In summary, this project will improve our mechanistic understanding of Sb-OM interactions and clarify the role of OM as a sorbent for Sb in organic soils impacted by anthropogenically released and atmospherically deposited Sb.