【作者】 张平；

【导师】 杨志辉；

【作者基本信息】 中南大学 ， 环境工程， 2025， 博士

【摘要】 砷（As）、铅（Pb）和镉（Cd）是土壤中常见的毒性强、危害大的重金属元素,对生态系统和人类健康构成严重威胁。由于砷铅镉之间相互作用复杂、性质各异,单一的稳定化方法难以实现同步处理土壤砷铅镉重金属污染,且存在着长效稳定性差等问题。本论文旨在将土壤中重金属由亚稳态向稳定态转变,从形成稳定的铁锰氧化态角度出发,提出“表面活性剂辅助电化学修复稳定土壤砷铅镉”的策略。研究了电化学修复对土壤重金属污染的稳定化效果,阐明了表面活性剂辅助下电化学修复对砷铅镉复合污染的稳定化效果及形态转化机理,探明了土壤中电化学活化的Mn²⁺和固有优势相MnO₂影响下砷的化学归宿及其稳定化机理,深入阐述了表面活性剂辅助下电化学修复砷、镉、铅的稳定化机理及其电化学反应机理。主要创新性研究成果如下:（1）构建了电化学土壤修复体系,探究了电化学工艺参数对砷污染土壤的修复特性。在最佳工艺参数下,土壤中水溶性砷的去除率达到99.99%,有效砷的去除率为89%。通过土壤形态分析,发现电化学修复后土壤中的砷由不稳定态向稳定态转化,铁锰氧化态及残余态比例显著增加,进而砷的环境危害性明显降低。进一步探究了电化学修复对土壤中铅镉稳定化效果,镉从铁锰氧化态向有机质态转化,而铅的弱酸态比例减少,可还原态和可氧化态比例增加。此外,电化学修复砷铅镉复合污染,砷的去除效率较高,但铅和镉的去除率较低,这主要归因于不同重金属之间存在的拮抗作用,抑制了铅和镉的迁移和去除过程。（2）探究了表面活性剂辅助下电化学修复对砷铅镉复合污染的稳定化效果及形态转变机理。以土壤中砷铅镉复合污染为研究对象,探究了工艺参数对于复合污染稳定化的影响规律,实现了同时稳定砷、铅和镉污染。表面活性剂辅助电化学修复后,有效砷的去除效率提高到80%左右,有效铅和有效镉的去除效率分别提高到约75%和35%。结合土壤形态分析,引入表面活性剂后,土壤中铅与镉由不稳定态向稳定态转化,且易迁移形态比例降低。此外,修复后土壤的长效稳定性分析、模拟酸雨淋溶试验、毒性浸出程序测试、土壤性质分析结果表明,表面活性剂辅助电化学修复具有长效稳定性。（3）考虑到电场作用下土壤浸出液中存在活化的Mn²⁺,并且土壤中Mn元素主要以优势相MnO₂存在,形成MnO₂与Mn²⁺共存体系。基于电化学修复体系,分别解析了Mn²⁺离子和MnO₂与外源铁物种的协同作用及其对铁锰氧化态转化的影响机理,并阐明了电化学修复砷污染的反应机理。对于电化学活化的Mn²⁺,可以促进Fe-Mn-As化学归宿产物的快速形成,且铁锰物种的共存有利于亚砷酸盐向砷酸盐的氧化。根据化学归宿产物表征结果,发现砷污染稳定后主要以FeHAsO₄和MnHAsO₄的形式存在于化学归宿中。对于土壤中的优势相MnO₂,其在电化学处理过程中产生Mn⁴⁺,Fe³⁺和Mn⁴⁺的共同作用下As（III）被氧化为As（V）,然后与铁锰物种反应生成沉淀FeHAsO₄和MnHAsO₄·H₂O,从而实现砷的稳定。密度泛函计算结果表明,MnO₂@FeOOH对H₃AsO₃和HAsO₄^2-分子的吸附能更高,表明其具有更优越的砷固定能力,有助于提高砷的稳定化效果。（4）深入分析了表面活性剂辅助下电化学修复砷铅镉的稳定化机理及其电化学反应机理。土壤浸出液结果表明,阴离子表面活性剂通过静电作用和络合作用使得铅镉阳离子从土壤中解吸,有利于在后续电化学处理过程中实现同步固定。结合化学归宿产物的微观结构和物相组成等分析可知,修复过程中主要形成的沉淀物分别为FeHAsO₄/MnHAsO₄、PbO₂和Cd（OH）₂。同时,根据化学归宿产物的价态分析,As（III）到As（V）的氧化过程是稳定砷的必要步骤,铅主要是+4价形式存在,镉主要以+2价形式存在。结合循环伏安法分析,系统揭示了As、Pb、Cd在电化学过程中与铁锰物种的协同转化机制。结果表明,MnO₂与电化学生成的Fe³⁺共同作用,促进Pb和Cd分别转化为PbO₂和Cd（OH）₂沉淀。As（III）则在Fe³⁺与MnO₂的协同氧化下转化为As（V）,并进一步与Fe、Mn反应形成FeHAsO₄与MnHAsO₄·H₂O沉淀。因此,从电化学反应机理角度阐明了铁锰物种对As、Pb、Cd的稳定化作用,为电化学法修复复合重金属污染土壤提供了理论依据。图78幅,表6个,参考文献280篇更多还原

【Abstract】 Arsenic（As）,lead（Pb）,and cadmium（Cd）are common heavy metals in soil that exhibit high toxicity and pose significant threats to both ecosystems and human health.Due to the complex interactions and distinct physicochemical properties among As,Pb,and Cd,conventional single stabilization approaches often face challenges such as poor synchrony in remediation and limited long-term stability when addressing co-contaminated soils.This study aims to transform metastable heavy metal species in soil into stable forms by promoting the formation of stable-manganese oxide species,and proposes a novel strategy of“surfactant-assisted electrochemical remediation”for the stabilization of As,Pb,and Cd in contaminated soils.The stabilization performance of electrochemical remediation for heavy metal-contaminated soil was systematically investigated,with a particular focus on the influence of surfactants in enhancing the stabilization efficiency and elucidating the associated species transformation mechanisms of As,Pb,and Cd.The study further clarified the chemical fate of arsenic and its stabilization mechanism under the influence of electrochemically activated Mn²⁺and naturally occurring MnO₂in the soil matrix.Moreover,the stabilization mechanisms and electrochemical reaction pathways of As,Cd,and Pb were comprehensively elucidated under surfactant-assisted electrochemical conditions.The main innovative research findings are as follows:（1）An electrochemical remediation system was constructed to explore the remediation characteristics of As-contaminated soil by different electrochemical process parameters.Under the optimal process parameters,the removal rate of water-soluble arsenic in the soil reached99.99%,and the removal rate of effective arsenic was 89%.Soil species analysis showed that after electrochemical remediation,arsenic in the soil was transformed from an unstable state to a stable state,and the proportion of iron-manganese oxidation species and residual species increased significantly,thereby significantly reducing the environmental hazard of arsenic.The effect of electrochemical remediation on the stabilization of lead and cadmium in the soil was further explored.Cadmium was transformed from the iron-manganese oxidation species to the organic matter state,while the weak acid species proportion of lead decreased,and the proportion of reducible and oxidizable species increased.In addition,in the electrochemical remediation of arsenic-lead-cadmium pollution,the removal efficiency of arsenic was high,but the removal rates of lead and cadmium were low,which was mainly attributed to the antagonism between different heavy metals,which inhibits the migration and removal process of lead and cadmium.（2）The stabilization performance and speciation transformation mechanism of electrochemical remediation assisted by surfactants on As-Pb-Cd co-contaminated soil were investigated.Using As-Pb-Cd co-contaminated soil as the research subject,the effects of process parameters on the stabilization of multiple heavy metals were examined,achieving simultaneous stabilization of arsenic,lead,and cadmium.After surfactant-assisted electrochemical remediation,the removal efficiency of available arsenic increased to approximately 80%,while that of available lead and cadmium rose to around 75%and 35%,respectively.Combined with soil species analysis,it was showed that the addition of surfactants promoted the transformation of lead and cadmium from unstable to more stable forms,with a reduction in the proportion of mobile fractions.Furthermore,long-term stability analysis,simulated acid rain leaching tests,toxicity characteristic leaching procedure（TCLP）tests,and soil property evaluations confirmed that the surfactant-assisted electrochemical remediation process has long-term stability.（3）Under the influence of the electric field,Mn²⁺is activated and released into the soil leachate,while Mn in the soil primarily exists as the dominant MnO₂phase,forming a coexistence system of MnO₂and Mn²⁺.Based on the electrochemical remediation system,the synergistic effects of Mn²⁺ions and MnO₂with exogenous Fe species were systematically analyzed to elucidate the mechanisms governing the transformation of iron-manganese oxidation species and the electrochemical remediation pathways of arsenic pollution.The electrochemically activated Mn²⁺was found to promote the rapid formation of Fe-Mn-As complex products,and the coexistence of Fe and Mn species facilitated the oxidation of arsenite to arsenate.Phase characterization of the stabilization products confirmed that arsenic was predominantly immobilized in the form of FeHAsO₄and MnHAsO₄.For MnO₂,the dominant phase in soil,Mn⁴⁺was generated during electrochemical treatment.The combined action of Fe³⁺and Mn⁴⁺led to the oxidation of As（III）to As（V）,followed by precipitation with iron and manganese species to form FeHAsO₄and MnHAsO₄·H₂O,thus achieving arsenic stabilization.Density functional theory（DFT）calculations reveal that MnO₂@FeOOH exhibits higher adsorption energy for H₃AsO₃and HAsO₄^2-molecules,indicating superior arsenic fixation capability,which enhances As stabilization efficiency.（4）The stabilization mechanism and electrochemical reaction pathways of As,Pb,and Cd under electrochemical remediation assisted by surfactants were systematically investigated.Results from soil leachate analysis indicated that anionic surfactants promote the desorption of Pb²⁺and Cd²⁺from soil through electrostatic interactions and complexation,facilitating their subsequent co-immobilization during the electrochemical process.Analysis of the microstructure and phase composition of the chemical sequestration products revealed that the main precipitates formed during remediation were FeHAsO₄/MnHAsO₄,PbO₂and Cd（OH）₂.Furthermore,valence state analysis of the sequestration products demonstrated that the oxidation of As（III）to As（V）is a necessary step for effective arsenic stabilization,while Pb and Cd primarily exist in the+4 and+2 oxidation states,respectively.Combined with cyclic voltammetry analysis,the study elucidated the synergistic transformation mechanisms of As,Pb,and Cd with Fe and Mn species during the electrochemical process.The results showed that the combined action of MnO₂and electrochemically generated Fe³⁺promoted the transformation of Pb and Cd into PbO₂and Cd（OH）₂precipitates,respectively.As（III）was oxidized to As（V）through the synergistic effect of Fe³⁺and MnO₂,and subsequently reacted with Fe and Mn species to form FeHAsO₄and MnHAsO₄·H₂O precipitates.Thus,from the perspective of electrochemical reaction mechanisms,the stabilizing roles of Fe and Mn species on As,Pb,and Cd were clarified,providing a theoretical foundation for the electrochemical remediation of complex heavy metal-contaminated soils..78 Figures,6 Tables,280 References更多还原