地下水系统中富里酸-铁-砷的共沉淀行为

Coprecipitation behaviors of fulvic acid-Fe(Ⅲ)-arsenate in groundwater system

地下水系统中砷酸盐与Fe(Ⅲ)的共沉淀可以有效减少砷向水生环境的释放。有机质易参与Fe(Ⅲ)的沉淀过程,从而影响砷的固定,但目前对基于共沉淀反应的C-Fe-As耦合机制的认识还非常有限。选取富里酸(FA)为典型有机质,通过开展室内批试验,探讨不同Fe(Ⅲ)浓度和pH值条件下地下水系统中FA-Fe(Ⅲ)-As(Ⅴ)的共沉淀行为,并综合采用三维荧光光谱(3D-EEMs)、X射线衍射(XRD)、扫描电子显微镜与能谱分析(SEM-EDS)和X射线光电子能谱(XPS)等表征手段,揭示地下水系统中有机质-铁(氢)氧化物共沉淀(OFC)的固砷机理。结果表明:地下水系统中较高的Fe(Ⅲ)浓度促进水解共沉淀发生,有利于砷的固定及FA的组分分馏,FA中大分子量、强芳香性组分优先与水铁矿结合形成OFC;As(Ⅴ)通过占据OFC中类腐殖质组分与水铁矿的结合位点而被固定;地下水系统中较高的pH值抑制共沉淀发生,FA提高了Fe(Ⅲ)的溶解度,不利于砷的固定。该研究结果有助于深入理解地下水系统中砷与碳元素的地球化学循环过程,可为地下水砷污染的治理与防治提供理论基础。

The coprecipitation of arsenate and Fe(Ⅲ)in groundwater system can effectively reduce the release of arsenic to the aquatic environment.Organic matter is easily involved in the precipitation process of Fe(Ⅲ),which affects the sequestration of arsenate.However,the C-Fe-As coupled mechanism based on coprecipitation has been poorly understood at present.In this research,we chose FA as the typical organic matter to conduct batch experiments,and explored the coprecipitation behaviors of FA-Fe(Ⅲ)-As(Ⅴ)in groundwater system under different Fe(Ⅲ)concentrations and pH conditions.The mechanism of arsenate immobilization by organo-Fe hydroxides coprecipitates(OFC)in groundwater system was revealed by comprehensively using methods of 3D-EEMs,XRD,SEM-EDS,and XPS.The results show that the higher Fe(Ⅲ)concentration in groundwater system promotes the hydrolysis coprecipitation,which is beneficial to the sequestration of arsenate and the component fractionation of FA.The macromolecular and strong aromatic components in FA preferentially bind with ferrihydrite to form OFC.As(Ⅴ)is immobilized by occupying the binding sites of humus-like components with ferrihydrite in OFC.The higher pH condition in groundwater system inhibits the hydrolysis coprecipitation and promotes the dissolution of Fe(Ⅲ),which is not conducive to the sequestration of arsenate.The results are helpful to understand the geochemical cycle of arsenic and carbon in groundwater system,and provide a theoretical basis for the treatment and prevention of arsenic pollution in groundwater.