电动/PRB联合修复砷污染土壤协同机制研究

Arsenic, as one of the most common poisonous elements, can lead to severe public health problems. One of the reasons is that the arsenic existing in soil and groundwater can be assimilated by human body through drinking water and food chains. Due to its harmful characteristic to human health, the environment issues caused by arsenic have drawn great attention worldwide. Therefore, the treatment of soil and groundwater arsenic pollution is particularly important so as to guarantee the drinking water safety. By reviewing the disadvantages of the present groundwater arsenic pollution control methods, this project use electrokinetic remediation (EK) and permeable reactive barrier (PRB) joint method to remove soil and groundwater arsenic. The research intensively focuses on the following aspects: (1)studying the migration rules of arsenic in ground water under the electric driven conditions, the impact of pH variation of the soil on the arsenic removal efficiency and its morphological changes, to determine the economical efficient treatment parameters; (2)using zero-valent iron as PRB active media for the remediation of arsenic, studying the arsenic removal mechanism under the co-effect of EK/Fe-PRB joint remediation, analysing the synergy mechanism of hydrogen ions generated from anode electrode reaction and Fe for arsenic removal, studying the influence of co-existed pullutants, humus, chromate, nitrate, bicarbonate, to the arsenic morphological changes and its removal efficiency. With the purpose of exploring and determining the best control technology parameters of arsenic removal from soil and groundwater,the results of the study will provide scientific support and reliable theoretical basis for the appicaiton of electrokinetic remediation and PRB joint method in the high arsenic areas.

在环境化学污染物中，砷是目前常见、对公众健康危害严重的污染物之一，土壤（地下水）中的砷可以通过饮水和食物链进入人体，对人体健康造成危害，土壤及地下水中由砷引起的环境问题广泛存在于世界范围内。项目针对土壤（地下水）砷污染治理的技术需求，采用电动/PRB联合技术对砷污染土壤（地下水）进行修复研究。分析不同价态砷在电场作用下的迁移规律和去除机理，土壤pH变化对砷的去除效率和形态变化影响，确定经济有效的电动修复技术参数；以零价铁（Fe）作为PRB反应介质，研究电动/Fe-PRB联合修复砷污染土壤的去除机理，分析阳极电极反应产生的氢离子与零价铁反应协同去除砷的机制，研究腐殖质、铬酸盐、硝酸根、碳酸氢根等共存污染物对砷形态变化和去除效率影响。研究结果为电动和PRB联合技术修复受砷污染土壤的实地修复提供理论指导和技术支撑。

土壤及地下水中由砷引起的环境问题广泛存在于世界范围内。针对土壤（地下水）砷污染治理的技术需求，采用电动-渗透反应格栅技术（Electrokinetic-Permeable Reactive Barriers, EK-PRB）对砷污染土壤（地下水）的机理进行研究。通过批次实验研究了PRB介质零价铁（Fe0）对砷的吸附性能。考察了PRB在电动系统中的位置、阴极电解液pH、共存离子（Fe3+、Ca2+、Al3+、HCO3-、NO3-、PO43-）以及络合剂等因素对砷污染土壤修复的影响，探讨了砷在EK-PRB作用下的迁移转化规律及PRB反应介质与砷的反应机理，为EK-PRB技术修复砷污染土壤实际应用提供理论指导和技术支撑。结果表明：Fe0可有效吸附溶液中的砷，去除率为80%。pH为5~9时，吸附效果最好。Ca2+和Mg2+促进Fe0对砷的吸附，HCO3-抑制Fe0对砷的吸附。Fe0对As(Ⅲ)的吸附过程符合Freundlich模型和拟二级动力学。EK/PRB对砷的去除率为24-40%，比EK单独作用时对砷的去除率提高了8-15%；PRB位置距离阳极15 cm时，砷的去除效果最好，去除率可提高9%。添加乙二胺四乙酸（EDTA）和柠檬酸（CA）后，去除率可提高10-13%，并且能耗由7.15kWh/g降至5.73kWh/g。采用BCR法分析EK-PRB修复后土壤中砷的形态，酸溶态由29.66%升至56.18%，可还原态由78.81%降至33.89%，残渣态由11.98%降至5.96%；添加共存离子后，残渣态由11.98%升至39.81%；EDTA可使残渣态转化成酸溶态，转化率高达80%~90%。EK-PRB联合修复砷污染土壤时，以PRB的去除作用为主，在电场作用下PRB可将土壤中的铁锰氧化态砷转化成酸溶态砷，从而提高砷的去除率。EK-PRB去除土壤中砷的主要机理为铁氧化物对砷的吸附作用。XPS分析表明，反应后Fe0表面存在As(III)和As(V)，无As(0)，砷通过Fe0表面氧化物的吸附作用去除。EK/PRB可有效去除土壤中的砷，添加EDTA和CA不仅提高了砷的去除率，而且降低了能耗。