Understanding the competition for adsorption between arsenate and other common oxyanions at mineral-water interfaces is critical for enhancing arsenate retention in the subsurface environment and mitigating exposure risks. This study investigated the competitive adsorption between arsenate and phosphate on hematite facets using batch experiments, together with in-situ infrared spectroscopy, two-dimensional correlation spectroscopy (2D-COS), and ab initio molecular dynamic (AIMD) simulations. This study's findings revealed that hematite exhibited notable selectivity for arsenate over phosphate in both adsorption capacity and rate, with selectivity significantly influenced by the exposed facets of the hematite and reaction concentrations. To wit, the (001) facet exhibited stronger selectivity for arsenate than the (110) facet, and increasing reaction concentration further enhances this selectivity. This selectivity was driven by surface hydroxy structure-mediated complexation, where both surfaces primarily formed stable inner-sphere monodentate complexes with an affinity for arsenate. On the (001) surface, the available Fe₂OH featured two close-spaced iron sites (Fe - Fe ≈ 2.86Å), enabling arsenate to interact with both sites simultaneously, significantly boosting arsenate selectivity. At higher surface loadings, the (110) surface formed partially more selective bidentate binuclear complexes, further enhancing arsenate retention. These findings emphasize the critical role of interfacial complexation, particularly the formation of inner-sphere bidentate complexes and the availability of iron sites, in controlling arsenate retention. By tailoring mineral facets and optimizing reaction conditions to improve iron site availability and promote bidentate complexation, arsenate retention can be significantly enhanced in phosphate-rich aquatic environments, such as rivers and groundwater in agricultural areas.

中文翻译：

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砷酸盐和磷酸盐在赤铁矿面上的竞争性吸附：增强砷保留的分子见解


了解砷酸盐与其他常见含氧阴离子在矿水界面处的吸附竞争对于增强砷酸盐在地下环境中的保留和降低暴露风险至关重要。本研究使用批量实验以及原位红外光谱、二维相关光谱 （2D-COS） 和从头分子动力学 （AIMD） 模拟研究了砷酸盐和磷酸盐在赤铁矿刻面上的竞争吸附。本研究结果表明，赤铁矿在吸附能力和速率方面对砷酸盐的选择性优于磷酸盐，选择性受赤铁矿暴露面和反应浓度的显着影响。也就是说，（001） 分面对砷酸盐的选择性强于 （110） 分面，增加反应浓度进一步增强了这种选择性。这种选择性是由表面羟基结构介导的络合驱动的，其中两个表面主要形成稳定的球内单齿复合物，对砷酸盐具有亲和力。在 （001） 表面，可用的 Fe₂OH 具有两个紧密间隔的铁位点 （Fe - Fe ≈ 2.86Å），使砷酸盐能够同时与两个位点相互作用，显着提高砷酸盐选择性。在较高的表面负载下，（110） 表面形成部分选择性更高的双齿双核复合物，进一步增强了砷酸盐的保留。这些发现强调了界面络合的关键作用，特别是球内双齿络合物的形成和铁位点的可用性，在控制砷酸盐保留中的作用。 通过定制矿物面和优化反应条件以提高铁位的可用性并促进双齿络合，可以在富含磷酸盐的水生环境中显著提高砷酸盐保留率，例如农业地区的河流和地下水。