我国几种典型土壤不同粒级组分对镉吸附行为影响的研究

Adsorption of Cd(II) By Particle-Sized Fractions of Four Typical Soils in China

土壤各粒级组分在理化性质上有显著差异,必然导致不同组分吸附的镉其环境学归宿的差异。本文采用热力学平衡法研究了黑土、黄棕壤、黄泥土、红壤不同粒级组分(粘粒≤2μm,粉粒2～20μm,细砂粒20～200μm,粗砂粒200～2000μm)对镉的等温吸附,得出了各组分对土壤吸附镉的贡献率,并采用SPSS软件对影响吸附的因子进行了回归分析。结果表明,不同粒级组分对镉的吸附量在4种土壤中均表现为粘粒>粉粒>粗砂粒>细砂粒,且粒级间的差异都达到显著水平;吸附量最小的细砂粒组分对镉的平均最大吸附量为(47.00±9.450)mmol·kg-1,粘粒、粉粒、粗砂粒对镉的最大吸附量分别平均是细砂粒的4.22±0.67、2.86±0.49、1.7±0.47倍;各组分对镉的吸附量之间的差异随着镉浓度的增大而增大。各组分对土壤吸附镉的贡献率为粉粒>粘粒>细砂粒>粗砂粒(只有红壤中粘粒>粉粒),土壤80%～90%的镉吸附在<20μm的组分上,粗砂粒的贡献基本可以忽略不计。各因素对吸附的影响大小为粒级>有机质>平衡pH,而游离氧化铁无显著影响。

Cadmium adsorbed by differently sized organic-mineral particles will have different fate in the environment due to the significant differences in size and physic-chemical properties of the particles. In this paper, batch experiments were conducted to investigate the equilibrium sorption isotherms for Cd^2＋ onto particle-sized fractions（2000-200μm, 200-20μm, 20-2μm and 2-0 μm, which were named coarse sand, fine sand, silt and clay respectively according to international system） derived from four typical soils （black soil, yellow brown soil, huangnitu paddy soil and red soil） in China by using a novel technology combined with wet sieving, sedimentation-siphoning and centrifugation method. The results showed that the adsorption of Cd^2＋ by these fractions could be described by the Langmiur equation Ce=Xm. Ce/X-k^-1 and Frendlich equation X=Kd.Ce^n. The maximum adsorption of Cd^2＋ （Xm） and distribution coefficient （Kd） decreased in an order.clay〉silt〉 coarse sand〉fine sand in the four soils. The average maximum adsorption of Cd^2＋ by fine sands of the four soils was 47.00±9.450 mmol. kg^-1, and the maximum adsorption of Cd^2＋＋ by clay, silt and coarse sand were 4.22±0.67, 2.86±0.49 and 1.7±0.47 times over those by the fine sands averagely. In consideration of the contents of the fractions in the soils, the contribution of each fraction followed the order, silt 〉 clay 〉 fine sand〉 coarse sand. The amount of Cd^2＋ adsorbed by silt and clay of the four soils exceeded 80%. Choosing particle size, organic matter, iron oxide and equilibrium pH value as parameters, using SPSS software and multivariate statistical analysis, the regression model of adsorption of Cd^2＋ was set up and the effect of these factors was evaluated. Particle size, organic matter and equilibrium pH value significantly affected the adsorption of Cd^2＋, but iron oxide had no significant effect on the adsorption.