土壤中腐殖酸-水铁矿复合胶体促进砷迁移的微界面机制

The adsorption and co-transport of arsenic (As) with humus and ferrihydrite colloid regulate the solid-solution distribution of As in porous soil medium. A lack of good understanding of this phenomenon hampers accurate prediction of environmental risks and remediation of As. In our previous study, the mechanism of enhanced ferrihydrite colloid transport by chain-shaped humic acid colloid has been illustrated. However, in the complex soil environment, the micro-interfacial process of competitive adsorption between humus colloid (fulvic acid and humic acid) and As at the surface of ferrihydrite colloid is not well understood yet, neither the mechanism of facilitated As transport by compound colloid of humus-ferrihydrite. Therefore, this project will firstly employ adsorption experiments and Ligand Charge Distribution (LCD) model to quantify As adsorption on humus-ferrihydrite assemblages and to clarify the micro-interfacial mechanisms in the adsorption. Secondly, transport experiments will be combined with colloid transport modeling and XDLVO theory calculations to investigate the facilitated transport of ferrihydrite colloid in the presence of humus colloids with different solubility. Finally, the results of adsorption and transport will be coupled and compared with the fraction and speciation analysis using synchrotron radiation spectroscopy technique and sequential extraction procedure. This combination will lead to better insight into the distribution ratio and fractions of As in the colloidal phase, soil solid phase, and liquid phase, as well as the micro-interfacial mechanism of facilitated As transport by humus-ferrihydrite compound colloid. Achievement of this project will provide theoretical support for study of As environmental geochemistry and remediation of As contaminated soils.

土壤中的腐殖酸胶体、水铁矿胶体与砷的相互吸附及共迁移影响着砷在土壤固相和孔隙中的固液动态分配，干扰了对砷污染环境风险的准确预测和修复治理。在前期的研究中，我们明确了链状胡敏酸胶体对水铁矿胶体迁移的促进机制。但在复杂的土壤环境中，腐殖酸胶体（富里酸和胡敏酸）与砷在水铁矿胶体表面上的竞争吸附微界面过程，以及腐殖酸-水铁矿复合胶体对砷迁移的促进机制还并不明确。因此，本项目拟采用吸附试验，通过电荷-配体分配模型量化砷在腐殖酸-水铁矿胶体上的吸附，明晰其微界面过程；采用迁移实验，通过胶体迁移模型和扩展DLVO理论，讨论腐殖酸胶体对水铁矿胶体迁移的促进机制；最后，耦合腐殖酸-水铁矿胶体迁移和其对砷的吸附结果，结合同步辐射和连续提取技术，阐明砷在胶体相、土壤固相和液相的分配比例和结合形态，揭示腐殖酸-水铁矿胶体促进砷迁移的微界面机制。项目成果可为砷环境地球化学研究和土壤砷污染修复提供理论支撑。

土壤中的腐殖酸胶体、水铁矿胶体与砷的相互吸附及共迁移影响着砷在土壤固相和孔隙中的固液动态分配，干扰了对砷污染环境风险的准确预测和修复治理。在复杂的土壤环境中，腐殖酸胶体与砷在水铁矿胶体表面上的竞争吸附微界面过程，以及腐殖酸-水铁矿复合胶体对砷迁移的促进机制还并不明确。项目顺利执行，采用吸附试验，明确了不同离子体系下As在铁矿物上的吸附机制，明晰不同来源的HA对As吸附的差异影响，不同FA对As吸附影响差异较小，FA与As的竞争吸附作用强于HA；利用沉降试验，阐明了不同体系中铁矿物纳米颗粒稳定性和影响因素，针铁矿和水铁矿纳米颗粒混合会产生明显的异质聚沉现象，纳米颗粒浓度越高自凝聚显现越明显，针铁矿纳米颗粒浓度越高异质聚沉越明显；利用迁移试验，结合农业实际阐明了农业有机投入品对水铁矿纳米颗粒迁移的影响，尽管农业有机投入物可以释放溶解性有机质来增强水铁矿胶体的迁移，但是农业有机投入物在土壤老化的过程中，释放DOC的能力降低、表面粗糙度增加，这就会导致水铁矿胶体的迁移从增强变为减弱；同样利用吸附试验，明晰水铁矿吸附的As和中性条件下颗粒状胡敏酸水铁矿复合胶体更容易与As共沉积在砂上，而链状胡敏酸水铁矿复合胶体容易携带As迁移，胡敏酸浓度越高携带量越少；在实际土壤中辨析了长株潭地区稻田土壤中As淋溶特征和控制规律和铅锌尾矿、冶炼污染土壤和稻田土壤中砷形态赋存规律。项目成果可为砷环境地球化学研究和土壤砷污染修复提供理论支撑。