不同水分条件下铁基氧化物对土壤砷的稳定化效应研究

Effects of iron-based oxides on arsenic stabilization in soils of different water contents

应用等温吸附试验及室内模拟培养的方法,研究了Fe2O3、Nano-Fe2O3和铁锰双金属氧化物(FMBO)等铁基氧化物对砷的吸附特性和对不同含水量土壤中砷的稳定化效应.从等温吸附试验结果来看,3种铁基氧化物对As(V)和As(Ⅲ)的吸附过程符合准二级动力学方程,12 h后基本达到吸附平衡,吸附等温线符合Langmuir方程,FMBO对As(V)和As(Ⅲ)的吸附容量显著大于Fe2O3和Nano-Fe2O3,且对As(Ⅲ)的饱和吸附容量大于As(V),能够起到氧化和吸附的双重作用.从对不同含水量土壤中砷的稳定化效果来看,Nano-Fe2O3和FMBO在风干和田间持水量土壤中均能达到90%以上的稳定化效率,显著高于Fe2O3;在土壤水分饱和条件下,FMBO的稳定化效率仍保持在93.5%以上,且能够将土壤中As(Ⅲ)氧化成As(V),而Fe2O3和Nano-Fe2O3分别仅为29.4%、81.4%.3种铁基氧化物的添加会使土壤中砷的结合态发生变化,Fe2O3、NanoFe2O3主要使砷由F1非专性吸附态和F2专性吸附态向F4结晶铁锰或铁铝水化氧化物结合态转变,添加FMBO主要向F3无定形或弱结晶铁锰或铁铝水化氧化物结合态转变.总体看来,在非饱和状态的土壤,Nano-Fe2O3和FMBO均为良好的稳定化材料,而对于长期淹水的稻田或地下水位较高的地区,或者由于降雨造成土壤滞水等情况,FMBO可以作为一种优良的稳定化材料用于土壤砷污染修复.

Batch adsorption tests and laboratory culture experiments were carried out to investigate the adsorption properties of Fe2O3,Nano-Fe2O3 and Fe-Mn binary oxides（ FMBO） to arsenic（ As） and stabilization effects in As-contaminated soils of different water contents. In the adsorption tests,the results showed that Pseudo-second-order kinetics model and Langmuir isotherm model could describe the adsorption process well. The adsorption equilibrium was obtained within 12 h,and the maximum adsorption capacities calculated by Langmuir model were 13.6,24.2,80.6 mg·g-1for As（ V）and 7.5,20.2,129.9 mg·g-1for As（ Ⅲ） on Fe2O3,Nano-Fe2O3 and FMBO respectively at pH 7. 0. FMBO was more effective for both As（ V） and As（ Ⅲ） removal,particularly for As（ Ⅲ） because of its oxidation. In the culture experiments,the results showed that Nano-Fe2O3 and FMBO could reach more than 90% efficiency of As stabilization in air-dried and field capacity soils. In saturated soils,FMBO could still maintain more than 93. 5%stabilization efficiency while oxidized part of soil As（ Ⅲ） to As（ V） in the process,much better than Fe2O3 of 29. 4% and Nano-Fe2O3 of 81. 4%,respectively. Fe2O3 and Nano-Fe2O3 could transform non-specially sorbed and specially sorbed As mainly to well-crystallized hydroxides of Fe,Al and Mn combined,while FMBO was mainly to amorphous and poorly-crystalline ones. In conclusion,Nano-Fe2O3 and FMBO were both high-efficiency stabilization materials in unsaturated soils,while FMBO could be applied as an economical and efficient amendment to stabilize As in soils as it has better stabilization effects in saturated soils,such as long-term flooded paddy fields,areas with high groundwater level or abundant rainfall,which could be applied as an economical and efficient amendment to stabilize As in them.