土壤溶液自由态重金属离子活度的Donnan膜技术测定与多表面模型预测

Free metal ions in soil solution are considered to be the most reactive species that interact directly with the biota. Accurate measurement of free metal ion activity in equilibrated soil solution was difficult by using traditional techniques, and the current researches based on these techniques lacked a clear understanding of the mechanism that dissolved organic matter (DOM), hydroxide colloids and competitive ions affected free metal ion activity. The objectives of this study are to assess the activities and the distribution of free metal ions in equilibrated solutions of contaminated red soils from the mining sites in Pearl River Basin by using Donnan membrane technique; and to explore the underlying mechanisms that control their activities and the distribution by prediction of combined NICA-Donnan model and DDL model taking into account the adsorption of DOM and hydroxide colloids, and the competitive adsorption of Fe3+ and Al3+ in model calculations. In the modeling, the quality of DOM will be characterized by using UV-VIS spectroscopy, and Fe/Al speciation will be estimated based on the chemical equilibrium. This study will be helpful to improve the model prediction of the free ion activities in soil solutions and to provide scientific basis for the risk prediction and control of heavy metal contamination in soils.

土壤溶液中自由态重金属离子是生物可直接吸收并产生生物毒性的关键形态。然而，传统分析方法难以准确测定其在土壤溶液动态平衡条件下的活度，并无法阐明溶解性有机质（DOM）、氧化物胶体等吸附界面及竞争离子影响重金属离子活度的内在机理。本研究以珠江流域矿区污染红壤为研究对象，采用Donnan膜技术准确表征土壤溶液动态平衡条件下自由态重金属离子活度，揭示其分布规律及生态风险；耦合NICA-Donnan模型和DDL模型，采用UV-VIS光谱参数校正DOM活性、依据化学平衡推算铁铝形态及含量，研究DOM、铁铝氧化物对重金属离子的吸附及铁、铝离子在腐殖质表面与重金属离子的竞争吸附，阐明土壤溶液中自由态重金属离子活度及分布的内在机理，提高模型对土壤重金属关键形态的预测能力，为土壤重金属污染预测及控制提供科学依据。

土壤溶液中自由态重金属离子是生物可直接吸收并产生生物毒性的关键形态。然而，传统分析方法难以准确测定其在土壤溶液动态平衡条件下的活度，并无法阐明溶解性有机质（DOM）、氧化物胶体等吸附界面及竞争离子影响重金属离子活度的内在机理。本研究以粤北韶关市内三个典型工矿区（仁化县凡口铅锌矿区（FK）、翁源县大宝山多金属矿区(SBB、SBN)、曲江区的韶关发电厂（QJ））周边土壤为研究对象，（1）采用了Donnan膜技术分析了水稻土溶液中自由态Cd、Pb离子活度，发现土壤溶液中Cd、Pb均以自由态离子为主，表层土壤中Cd较Pb更容易迁移出土体。（2）采用了批式分离、紫外-可见、三维荧光光谱、高效排阻色谱分析了土壤溶液中溶解性有机质组分、分布规律及光谱特征参数，表征DOM活性，代入NICA-Donnan模型模拟DOM对重金属离子的专性与非专性吸附。结果显示采用三维荧光光谱参数HIX校正DOM活性后，显著提高了自由态Cd、Pb离子含量的模型预测准确性。（3）考虑到南方红壤强酸性、富铁铝的特征，在三维荧光光谱技术原位表征土壤DOM活性的基础上，在NICA-Donnan模型模拟过程中，加入铝、铁离子竞争作用，进一步提高了自由态重金属离子活度的模拟精确度，同时揭示了铝、铁离子主要在高亲和力的酚羟基位点上与其他金属离子竞争吸附。以上研究结果为准确预测和评估珠江流域酸性水稻土中重金属活性及潜在环境风险提供了理论依据及技术支持。.