我国18种不同理化性质的土壤对硒酸盐的吸附解吸作用研究

硒在土壤中的环境化学行为及其生物有效性在很大程度受到吸附解吸作用的影响,土壤对硒的吸附解吸因为土壤理化性质的不同差异很大.本文采用批量吸附实验,选择土壤性质差异较大的我国18种农田土壤,探讨了土壤p H、无定形铁铝氧化物、有机质和机械组成等对SeO_4~(2-)吸附的影响.结果表明,18种土壤对SeO_4~(2-)的吸附均是一个先快后慢的过程,在24 h达到吸附平衡;二级动力学方程为描述SeO_4~(2-)吸附的最佳模型(R20.976),18种土壤对SeO_4~(2-)吸附大多符合Freundlich模型(R20.842);土壤对SeO_4~(2-)吸附量与p H值(P0.01)、碳酸盐含量(P0.05)呈显著负相关,而与无定型铁、铝含量(P0.01)及有机质含量(P0.05)呈正相关;18种土壤对SeO_4~(2-)吸附的固液分配系数(Kd值)均很低(0.99~18.18 L·kg~(-1));土壤SeO_4~(2-)解吸率均大于80%,表明吸附是可逆的;土壤吸附SeO_4~(2-)的低Kd值和高解吸率反映了硒酸盐易迁移淋溶的特性,这应当在区域环境硒的评价和调控中受到关注.

Selenate Adsorption and Desorption in 18 Kinds of Chinese Soil with Their Physicochemical Properties

The environmental behavior and bioavailability of selenium (Se) in soils are greatly affected by its adsorption on soil components, which are largely discrepant with the different physicochemical properties of soils. 18 kinds of farmland soils with various physicochemical properties in China were used in batch adsorption experiments in this study to explore the influencs of soil pH, amorphous iron, aluminum oxides, organic matter and mechanical composition on the adsorption of SeO₄^2-. The results showed that the adsorption of SeO₄^2- on 18 soils was an initially fast phase followed by a slow process, during which the adsorption equilibrium was reached at 24 h. Second-order kinetic model(R²>0.976)and Freundlich isothermal model(R²>0.842)were the fittest for most of the adsorption process. SeO₄^2- adsorption capacity of soil was negatively correlated with soil pH value (P<0.01) and the content of carbonate (P<0.05), while positively correlated with the content of amorphous iron, aluminum oxides (P<0.01) and organic matter content (P<0.05). The partition coefficient of solid to liquid (K_d values) of SeO₄^2- in adsorption process for all the 18 soil types were very low and without big differences(0.99 L·kg^-1-18.18 L·kg^-1). The desorption rates for all tested soils were above 80%, which indicated the reversibility of SeO₄^2- adsorption in soil. It was inferred from the above that the low K_d and high desorption rate reflected that selenate was featured by easy migration and leaching in soil, which should be emphasized in the regional evaluation and regulation of Se level.