Hydroxyl Radical Production And Arsenic Removal By Iron-bearing Materials

Arsenic（As）has been frequently detected in wastewater and groundwater throughout the world.Due to its high mobility,As is hard to be removed by existing technologies.Therefore,it is crucial to develop more powerful and efficient methods for As removal from wastewater and As-contaminated groundwater.In this study,Fe-bearing materials（including Synthesized Siderite-High Temperature and Pressure（SID-HTP）and Activated Iron Media（AIM））were developed to remove As from aqueous solutions.Characterisitics of As adsorption,radical hydroxyl production,and removal mechanisms were delineated in those Fe-bearing material systems.The main conclusions are shown as follows.（1）SID-HTP had a good crystallinity and high content of siderite.More As was removed by SID-HTP under oxic conditions than under anoxic conditions.SID-HTP can efficiently remove As from solutions in a wide pH range.The transformation from siderite to goethite/lepidocrocite was the major cause of the high performance of As removal.（2）Hydroxyl radical（·OH）production increased with increasing dosage of the SID-HTP.·OH was mainly produced on the surface Fe（II）of SID-HTP（80%）,and secondarily by dissolved Fe²⁺.·OH production was affected by solution pH.Low pH increased the production of·OH,where more Fe²⁺was dissolved from SID-HTP into solution.·OH production was slightly enhanced with the addition of SO₄^2-,Ca²⁺and Mg²⁺,but was constrained by Cl^-,HCO₃^-,NO₃^-,SiO₃^2-and PO₄^3-.HCO₃^-inhibited the production of·OH most evidently.（3）Addition of Fe²⁺increased As（III）removal efficient by preconditioned AIM,hybrid ZVI（hZVI）and unprecondiationed ZVI/Magnetite.AIM had the best performance among the tested materials.In either anoxic conditions or oxic conditions,addition of Fe²⁺reactivated AIM for high efficiency of As removal.The high performance of AIM for As removal was the results of the synergistic interaction between inner ZVI and surficial magnetite and intermediate production of greenrust（GR）.（4）·OH produced from AIM enhanced As removal in the system.Under oxic conditions,·OH oxidized As（III）to As（V）.Contents of As（V）decreased under anoxic conditions afterwards.In SID-HTP system,a great amount of As（V）was detected on the surface of SID-HTP.As（III）was mainly oxidized on the surface of SID-HTP,although the·OH was generated from both dissolved Fe²⁺and surface Fe²⁺.The presence of·OH increased As removal efficiency via oxidation of As（III）and promotion of Fe（II）/Fe（III）cycle.