不同形态氧化铁对黄土性土壤吸附铅的影响

Effects of iron oxides on adsorption of Pb^(2+) by several loessial soils

针对土壤含氧化铁的普遍性以及氧化铁对土壤理化性质的重要影响,探求氧化铁对土壤吸附重金属离子的作用与影响。采用了化学选择性溶提技术,分别去除黄土性母质上发育的古土壤、淋溶褐土和黄褐土中不同形态的氧化铁,采用了等温吸附试验,并以Langmuir和Freundlich方程拟合参数为指标,分析去除不同形态氧化铁前后土壤对Pb^(2+)的吸附特征。结果表明:原土壤对Pb^(2+)的吸附曲线逐渐递增,并无明显阶段特征,且更符合Freundlich方程;而去除不同形态氧化铁后的3类土壤对Pb^(2+)的吸附曲线均为L型,阶段特征显著,更加符合Langmuir方程,且土壤对Pb^(2+)的亲和力(KL)成倍增加;去除络合态铁和无定形氧化铁后,土壤对Pb^(2+)的最大吸附量均有不同程度增加,其中去除无定形氧化铁之后,古土壤对Pb^(2+)的最大吸附量增幅最大,增加了14.71 mg·g-1;去除游离态氧化铁后古土壤、淋溶褐土对Pb^(2+)的吸附量分别下降了5.95、3.10 mg·g-1,黄褐土对Pb^(2+)的吸附量则增加了2.98 mg·g-1。土壤中氧化铁对Pb^(2+)吸附能力与吸附容量的影响不完全依赖于氧化铁的含量,在很大程度上依赖于土壤中氧化铁的形态。对于不同氧化铁形态的土壤采用相应的化学溶提技术,能够获得具有较高吸附性能的粘土矿物环境材料。

Considering the ubiquity of iron oxide in soil and the important impact of iron oxide on soil physical and chemical properties,this paper studied the effects of different forms of iron oxide on the adsorption of heavy metals in soil. After removal of different forms of Fe oxide from Loessial soils by chemical selective stripping technique,the adsorption characteristics of Pb^2＋ on several loessial soils were studied by isothermal adsorption experiments and the Langmuir equation and Freundlich equation were used to analyze Pb^2＋ adsorption characteristics of soil before and after removal of different forms of iron oxide. The adsorption process of Pb^2＋ in three kinds of original soils increased gradually,the isotherm curve of Pb^2＋ adsorbed was more fitted by Freundlich equation and with no significant stage characteristics; after removal of different forms of Fe oxide,the isotherm curve of Pb^2＋ adsorbed was L-shaped,which was more fitted by Langmuir equation,and the phase characteristics was significant,while the bonding strength and the affinity of lead by soil multiplied; after removal complexing Fe oxides and amorphous Fe oxides in different soils could increase the amount of Pb^2＋ absorption,and after removal of amorphous Fe oxides,the adsorption amount of Pb^2＋ by paleosol increased by 14. 71 mg·g^-1; after removal free Fe oxides,the adsorption amount of Pb^2＋ by paleosol and eluvial cinnamon soil decreased by 5. 95、3. 10 mg·g^-1compared to their original soils,but increased by yellow cinnamon soil. In nature soil,the effect of iron oxide on the adsorption capacity of Pb^2＋was not entirely depend on the content of iron oxide,but also affected by the state of iron oxide in the soil. Using chemical selective stripping technique to remove different forms of Fe oxide can obtain clay mineral materials with high adsorption capacity.