多元重金属吸附质与泥沙颗粒的微界面作用机理研究

Sediment is an important carrier of pollutants in natural water, so the migration and conversion of most pollutants are closely related to sediment movement. At present, the related researches focus more on the total adsorption relationship and the adsorption characteristics of sediment and single pollutant, but the study on the micro-interfacial action between sediment and multiple pollutants is still less involved. Through the interfacial experiments between sediment particles and multiple heavy metal adsorbates, this project identified the competitive adsorption characteristics and the mode of micro-interfacial action. Electron microscopy and BET experiments were carried out to analyze the dynamic changes of the complex morphology and structure of sediment particles under competitive adsorption, and to qualitatively and quantitatively describe the distribution of multiple heavy metal adsorbates on the complex morphology of sediment particles and the scale relevance of the pore adsorption of sediment particles. The kinetic equation of competitive adsorption micro-interfacial action was deduced, and the competitive adsorption micro-interfacial action model of sediment- multiple heavy metal adsorbates was established to simulate the micro-interfacial action process of liquid film diffusion, external surface adsorption and diffusion, pore diffusion and so on, through which this project integrated phase separation mathematical model and build an entire process model about micro-interfacial action. This project perfected and enriched the theoretical method and application system of environmental sediment micro-interfacial action, which provided a scientific basis for studying the interaction between sediment particles and pollutants.

泥沙是天然水体中污染物质的重要载体，大多数污染物的迁移转化与泥沙运动密切相关。当前研究较多关注泥沙与单一污染物的吸附总量关系和吸附特征，泥沙与多元污染物的微界面作用研究仍较少涉及。本项目以河流泥沙为对象，通过泥沙颗粒与多元重金属吸附质的界面作用实验，识别竞争吸附特征及其微界面作用模式；开展电镜与BET实验，分析竞争吸附下泥沙颗粒复杂形貌结构的动态变化过程，定性与定量描述多元重金属吸附质在泥沙颗粒复杂形貌上的分布规律以及泥沙颗粒孔隙吸附的尺度关联性。推导竞争吸附微界面作用动力学方程，建立竞争吸附微界面作用模型，模拟液膜扩散、外表面吸附与扩散、孔隙扩散等分相微界面作用过程，整合分相数学模型，构建微界面作用全过程模型。通过本项目完善与丰富环境泥沙微界面作用的理论方法与应用体系，为研究泥沙颗粒与污染物质相互作用关系提供科学基础。

泥沙颗粒是天然水体中重金属污染物的吸附剂，理解与善用泥沙颗粒与重金属污染物的微界面作用关系，有助于流域与区域的水生态治理与修复。当前相关研究多聚焦于单一重金属污染物的宏观吸附过程，多元重金属污染物与泥沙颗粒的微界面作用机理较少涉及，其中“多元重金属吸附质在泥沙颗粒上的微界面作用存在何种特征”、“多元竞争体系下的微界面动力学响应机理”、及“微米尺度下的多元吸附质的微界面作用模拟”等机理与理论问题为本文研究的重点。本项目研究成果有：（1）揭示了多元竞争体系的分配关系。铅-铜-镉体系的分配系数分别为40.08%、39.03%与20.89%，表明多元重金属离子在泥沙颗粒上的吸附竞争性和分配效应顺序为Pb＞Cu＞Cd，离子的水合离子半径和电负性具有主导作用。（2）阐明了多元竞争体系下的微界面作用特征。10min后，离子的液相浓度波动变化，吸附速率变化呈“N型”、“倒N型”、“W型”和“倒W型”特征，此阶段为膜扩散和颗粒内扩散并存；60min后，离子的液相浓度较稳定和吸附速率较小，微界面作用趋于稳定，为扩散速率较小的颗粒内扩散阶段。（3）构建了颗粒物复杂微界面作用模型，展示了复杂微界面作用全过程。初期（0~10min）以膜扩散为主，膜扩散速率较大；中期（10~60min）为膜扩散和颗粒内扩散并存阶段，颗粒内扩散逐渐变大，铅和镉粒子向空腔聚集；后期（60~180min）以颗粒内扩散为主，孔道基本被填满，空腔的铅和镉粒子数较多，扩散速率较低。狭长孔道的铅和镉粒子数比宽短孔道多出174倍左右，狭长孔道可吸附点位多于宽短孔道，这与狭长孔道的形貌比宽短孔道复杂密切相关。研究成果可为微米与纳米尺度下多元竞争体系的液-固相微界面作用研究、动力学响应机理研究、微米尺度下水-沙-多元污染物交互作用模型构建等提供理论支撑，完善与丰富环境泥沙的理论体系。