几种亚热带土壤铁锰胶膜和基质的表面化学特征

Surface chemical characteristics of iron-manganese cutan and matrix in several subtropic soils in Central China

以我国亚热带的黄褐土、黄棕壤和红壤为材料,研究了土壤铁锰胶膜和其基质的表面化学性质及其对重金属元素的吸附和氧化特点。结果表明,与基质土壤相比,铁锰胶膜的比表面积大,电荷零点(PZC)低,这与其富含粘粒、有机质和铁锰氧化物等有关;铁锰胶膜经脱锰处理后,比表面积明显降低。由盐滴定-电位滴定(STPT)法测得黄褐土、黄棕壤、红壤基质的PZC分别为3.13、3.65和3.90;黄棕壤和红壤铁锰胶膜的PZC分别为3.26和3.42。铁锰胶膜对Pb2+、Cu2+、Cd2+和Zn2+的吸附和对Cr3+的氧化能力比基质的强。铁锰胶膜经脱锰处理后,对Pb2+、Cu2+、Cd2+和Zn2+的最大吸附量比未处理时降低了53%～100%;其氧化Cr3+生成Cr6+的量比铁锰胶膜的降低了87%～100%。说明黄褐土、黄棕壤和红壤的铁锰胶膜中,氧化锰是吸附重金属离子和氧化Cr3+的主体。

The surface chemical properties, adsorption and oxidation characteristics on heavy metal elements between iron-manganese cutans and their matrix soils in yellow cinnamon soil, yellow brown earth and red soil were studied in subtropical zone in China. The results show that the specific surface area is larger and point of zero charge （PZC） is lower in the cutan than that in the matrix soil which related to the high contents of clays, organic matters and iron-manganese oxides in the iron-manganese cutans. PZC measured by STPT method are 3.13, 3.65 and 3.90 for the matrixes of the yellow cinnamon soil, yellow brown earth and red soil, and 3.26 and 3.42 for the iron-manganese cutans of the yellow brown earth and red soil. The cutans adsorbed more Pb^2＋, Cu^2＋, Cd^2＋ and Zn^2＋ and oxidized more Cr^3＋ than the matrix soils. The maximum of heavy metal elements （Pb^2＋, Cu^2＋, Cd^2＋ and Zn^2＋） adsorbed by the cutans deprived of manganese oxides decreased 53% - 100% compared with those adsorbed by the cutans in the three soils. The maximum of Cr^3＋ oxidized by the cutans deprived of the manganese oxides decreased 87% - 100% compared with those oxidized by the cutans of the soils. These show that manganese oxides in the tested iron-manganese cutans were the main sorbents in adsorbing heavy metal ions and main oxidants in oxidizing Cr^3＋.