Mobilization And Transformation Of Arsenic In Different As-Fe Minerals During Sufidization Process

The mobilization of arsenic in the natural water environment is affected by the dissolution and transformation of arsenite-bearing iron oxides.Under anoxic conditions,the presence of dissolved S（-Ⅱ）on the mobilization of As（Ⅴ）during the reductive dissolution of High arsenic-iron oxides and the hypoxic reductive dissolution of arsenic-contained iron oxides has rarely been investigated systematically.In addition,How can the crystalline structure affect the mechanism involved the reductive dissolution and transform of arsenic-contained iron is still poorly understand.In this study,reductive dissolution of AFA and Scorodite with different crystalline structure and hypoxic reductive dissolution of As（Ⅲ）-Ferrihydrite were investigated separately at near neutral pH,similai to natural water as well as mobilization kinetics of As（Ⅴ）and As（Ⅲ）during the process.XRD,FT-IR,TEM,as well as XPS were used to determine the morphology of the formed secondary minerals.The transformation of iron oxides on the mobilization of arsenate was also investigated.The dissolved S（-Ⅱ）initiated the reductive dissolution of AFA and Scorodite.More high S（-Ⅱ）resulted in a more complete dissolution of AFA and Scorodite.AFA and Scorodite have different crystal structure and stability,as well as specific surface area,thus showing different dissolution behaviors.AFA will release more Fe²⁺ and be greatly affected by the change of pH than Scorodite in the process of dissolution.The AFA will undergo rapid release of arsenate at the beginning of dissolution then a significant the adsorption equilibrium followed.The release of arsenic in Scorodite has a significant stasis in the initial 1 h,and the resorption process of arsenic in the end is not as obvious as in AFA.In the process of reductive dissolution,The main secondary mineral in AFA is clusters of amorphous ferrous arsenite and a small amount of Goethite and Mackinawite.while in Scorodite is the crystalline Parasymplesite and a small amount of Lepidocrosite.As（Ⅲ）loading showed a negative effect on the hypoxic reductive dissolution of As（Ⅲ）-Ferrihydrite under the alkaline condition of pH8.8.at the same time,The hypoxic condition also inhibit the reductive dissolution of As（Ⅲ）-Ferrihydrite than the anoxic condition.XPS confirmed that A few As（Ⅲ）were oxidized to As（Ⅴ）under the hypoxic condition,and most As（Ⅴ）is absorbed in the solid phase while in anoxic conditions,there is hardly any As（Ⅴ）formationThe significance of this study is to reveal the mobilization mechanism of arsenate during the reductive dissolution of ferric arsenite and the hypoxic reductive dissolution of As（Ⅲ）-Ferrihydrite,which can provide a theoretical basis and experimental data for the effective control of arsenic contamination in natural water environment.