镉砷在典型土壤铁氧化物-有机复合胶体微界面的共吸附机制

Soil contaminated with cadmium and arsenic is common in southern China. Due to the different elemental properties, the chemical behaviors of cadmium and arsenic at the soil colloid interfaces differ significantly. The active soil components normally coexist together to form mineral-organic composite, it is therefore needed to clarify the co-binding properties of cadmium and arsenic at the multi-colloid interfaces, in order to better predicting their mobility, transformation and fate in soil. This project aims to investigate the co-adsorption mechanism of cadmium and arsenic at typical iron oxide-organic (humic acid and bacteria) colloid interfaces, using surface property analysis, chemical equilibrium adsorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, electron microscope-energy dispersive spectroscopy and isothermal titration calorimetry. The adsorption quantity, affinity, binding functional group, chemical bond, distribution and thermodynamic characteristic of As and Cd will be evaluated, and the surface complexation model will be built. We will make clear the selective sorption features of different component for As and Cd; and clarify the sorption sites and their dynamic changes with the changes of soil environmental factor (pH, ironic strength). Our results therefore will contribute to a deep understanding in the field of soil mineral–organic matter–microorganism interaction and their regulation on contaminant behavior, and will also provide the scientific evidences for the remediation of cadmium and arsenic co-contaminated soils.

我国南方土壤常常受到镉砷复合污染，镉砷的化学特性截然不同，因此在土壤胶体界面的化学行为存在显著区别。土壤活性组分往往胶结在一起形成复杂的矿物–有机复合物，因此研究多组分互作界面镉砷的化学行为更能真实评价其在土壤中的迁移、转化和归趋。本项目拟模拟南方土壤典型铁氧化物–有机（腐殖酸、微生物）复合胶体体系，借助表面分析技术、化学平衡吸附、红外光谱、X射线光电子能谱、电镜-能谱及等温滴定量热等手段，从吸附量、亲和力、官能团、化学成键、结合丰度和热效应等方面，综合分析镉砷在铁氧化物–腐殖酸/微生物复合胶体上的共吸附特点和机制，并构建镉砷吸附的表面络合模型。重点明确镉砷在复合胶体微界面的选择吸附特性和分配规律；查明参与吸附的表面位点及其随土壤环境因素（pH、离子强度）的动态变化。研究结果将丰富土壤矿物–有机质–微生物相互作用对污染物界面反应调控的内容，为准确评价镉砷复合污染及指导土壤修复提供科学参考。

摸清镉砷复合污染物在土壤胶体微界面的化学行为，为调控其形态和转化提供理论参考，为镉砷复合污染土壤的治理与修复提供科学依据。项目选取代表性的铁氧化物（水铁矿、针铁矿）和几种有机组分（腐殖酸、细菌、真菌），合成典型铁氧化物–有机复合胶体，结合湿化学、原位谱学、表面络合模型和现代仪器分析手段，探讨镉、砷在铁氧化物–腐殖酸/微生物复合胶体微界面的共吸附特点和配位机理。主要研究成果有：1）在铁氧化物体系，镉砷共存时发生静电相互作用、表面三元络合和表面沉淀等多个过程，且高度依赖于溶液pH；2）在微生物体系，镉的存在显著抑制砷的吸附，而砷在酸性条件下促进镉的吸附，细菌表面羧基和少部分氨基参与了镉砷的竞争吸附反应；3）在铁氧化物–微生物/腐殖酸复合体系，镉砷的吸附为协同过程，在弱酸环境中，铁氧化物组分对砷的吸附固定起主要贡献作用，对镉则有机物组分贡献更大。研究结果揭示了镉砷在单一土壤组分及二元矿物–有机复合体上的共吸附差异，查明了复合胶体矿物和有机组分对镉砷的选择吸附特性及镉砷的分配丰度；阐明了参与共吸附反应的表面位点、官能团贡献及其随土壤环境因素的动态变化。为理解镉砷复合污染土壤中重金属的结合形态提供参考，为合理制定修复策略、提高土壤污染修复效率提供科学依据。