Fe（Ⅱ）与O2共存体系中地下水As（Ⅲ）的固化行为

Study on Immobilized Behavior of Arsenic(Ⅲ) in Groundwater Under the Coexistence of Iron(Ⅱ) and Oxygen

砷在地下含水层中的迁移转化、释放等地球化学行为与地下水的氧化还原环境及铁氧化物的存在形态密切相关。本文主要通过室内静态、动态实验及野外现场试验研究了Fe（Ⅱ）和O_2共存体系对模拟地下水中As（Ⅲ）固化效率与机理,研究表明：单纯的曝气行为对水体中铁和砷的价态改变均不明显,只有当Fe（Ⅱ）和O_2共存时才能有效改变砷的存在形态并通过发生吸附共沉淀作用使水体中As浓度降低下来。以质量比为Fe/As=20为例,有氧无氧两种条件下砷的去除率分别为81.3%和23.4%。模拟无氧条件下向流动相的含砷地下含水层中连续输入Fe（Ⅱ）时,溶液中的砷含量相比进水溶液浓度略有降低,出水溶液中以Fe（Ⅱ）和As（Ⅲ）为主。在有氧条件下持续30天向含砷试验砂柱内输入Fe（Ⅱ）,其总量累积可达到283.65 mg,被固定于砂柱内的总砷含量达到25 075μg,固化能力达到88.40μg/mg。Fe（Ⅱ）与O_2共存体系对地下水中As（Ⅲ）的固化行为主要包括O_2对As（Ⅲ）及Fe（Ⅱ）氧化和Fe（Ⅲ）与As（V）的吸附共沉淀作用,其中溶解氧的存在是所有反应发生的必要前提条件。

Geochemical behavior including migration and release of arsenic in underground aquifers is closely related to the redox environment of groundwater and the existence of iron oxides. In this paper,the curing efficiency and mechanism of As（Ⅲ） in the simulated groundwater under the coexistence condition of Fe（ Ⅱ） and O_2 were studied by static test,dynamic experiment and field experiment. Results show that the simple aeration behavior has inconspicuous change for both iron and arsenic. Only with the coexist of Fe（ Ⅱ） and O_2 can effectively reduce the concentration of As because of the adsorption and co-precipitation in the water. Taking Fe/As = 20 for example,under two different conditions with aerobic and anaerobic,the removal rates of arsenic are 81. 3% and 23. 4% respectively. The arsenic content in the solution is slightly lower than that of the aqueous solution when Fe（ Ⅱ） is continuously input into the arsenic-containing underground aquifer in the mobile phase under simulated anaerobic conditions,with Fe（ Ⅱ） and As（Ⅲ） as the main effluent. Another conclusion can be described that the amount of residual Fe in the sand column cumulative reaches to 283. 65 mg with the 30 days of continuous infusion under aerobic conditions. Meanwhile,the total arsenic content fixed in the sand column is25 075 μg,while the curing capacity of 88. 40 μg/mg with coexist of Fe（ Ⅱ） and O_2.The solidification behavior of As（Ⅲ） in groundwater by Fe（ II） and O_2 coexisting system mainly includes the oxidation of As（Ⅲ） and Fe（ II）,with the following adsorption of Fe（Ⅲ） and As（ V）. Besides,the existence of oxygen is a necessary prerequisite for all reactions to occur.