氧气对零价铁去除三价砷过程的影响及其机制

为研究氧气对零价铁(Fe0)去除水中三价砷(As(Ⅲ))过程的影响,通过曝氮气、空气和氧气的实验研究了pH为4.0和6.0时As(Ⅲ)的去除动力学,并采用X射线精细吸收结构谱(XAFS)和X射线衍射谱(XRD)等表征手段探究其影响机制。结果表明:尽管高浓度的氧气有利于As(Ⅲ)被氧化为更容易被铁氧化物吸附的五价砷(As(Ⅴ)),但曝空气对于As(Ⅲ)的去除相对于曝氧气更为有利。在pH为4.0时,高浓度的氧气能够促进Fe0的溶解,从而抑制As(Ⅲ)的去除;而在pH为6.0时,高浓度的氧气会导致Fe0表面钝化,从而阻碍反应的进行。此外,曝氮气则几乎完全抑制了Fe0对水中As(Ⅲ)的去除,这是由于无氧条件不利于吸附性铁氧化物的生成;调控氧气的量可改进Fe0对As(Ⅲ)的去除效果。

Influence of oxygen on arsenite removal with zerovalent iron and involved mechanisms

The kinetics of the removal of As(III)with zerovalent iron(Fe⁰)was investigated under N₂, air, and O₂ purging conditions in well-mixed batch systems at pH values of 4. 0 and 6. 0, and the mechanisms were examined by X-ray absorption fine structure(XAFS)and X-ray diffraction(XRD)and other characterization methods, in order to study the influence of oxygen on the removal of As(III)with Fe⁰. Although high-concentration oxygen contributed to the oxidation of As(III)to As(V), which could be easily absorbed by iron oxides, the removal of As(III)was more effective under air-purging condition than under O₂-purging condition. At a pH value of 4. 0, high-concentration oxygen accelerated the dissolution of Fe⁰, and thus inhibited the removal of As(III). At a pH value of 6. 0, high-concentration oxygen resulted in passivation of Fe⁰ and hindered the reaction. In addition, the N₂-purging condition totally inhibited the removal of As(III), because iron oxides could hardly be generated under anoxic condition. Therefore, air supplement could be controlled to improve the efficiency of the removal of As(III)with Fe⁰.