黑土不同粒径有机-矿质复合体对镉的吸附特性

采用振荡平衡法研究了黑土不同粒级有机-矿质复合体对Cd2+的吸附等温过程和吸附动力学过程，并采用常见数值模型进行了拟合. 结果表明，原土及各粒级复合体对Cd2+的吸附量随平衡液中ρ(Cd2+)的增加而增加. 各粒级组分对Cd2+的吸附量表现为黏粒＞粉粒＞原土＞粗砂＞细砂. Langmuir和Freundlich方程对Cd2+的等温吸附过程均有较好的拟合效果，线性方程拟合效果较差. 最大吸附量与吸附作用强度均呈随粒径增大而减小的趋势. 对影响最大吸附量和吸附作用强度的因子进行回归分析表明，w(有机质)、CEC(阳离子交换量)和比表面积的影响较大，其中w(有机质)是最主要因素，CEC和比表面积的影响次之. 各粒级复合体对土壤吸附Cd2+的贡献率为粉粒＞细砂＞黏粒＞粗砂，99%的Cd2+吸附在＜200 μm的组分上. 不同粒级组分对Cd2+的吸附动力学过程可分为0~20 min的快速反应阶段（吸附量均达到饱和吸附量的90%以上）和慢速反应阶段. 各组分对Cd2+的吸附符合二级动力学过程，表明吸附过程以化学吸附为主，并且吸附速率随颗粒粒径的增大而减小. 

Adsorption Characteristics of Cadmium on Particle-Sized Aggregates from Black Soil

A batch method was used to investigate the thermodynamics and kinetics of cadmium adsorption on different particle-sized aggregates derived from black soil.The results showed that the Cd2+ capacity on different particle-sized fractions increased with increasing concentration in the adsorption equilibrium,which decreased in the order of clay > silt > bulk soil > coarse sand > fine sand.The adsorption isotherm of Cd2+ on different organic-mineral aggregates could significantly conform to the Langmuir and Freundlich equations,while linear equations were not feasible or suitable.When the size of the particle increased,its sorption amount and intensity decreased.With regard to the contents of the fractions in the soils,the contribution of each fraction decreased in the order of silt > fine sand > clay > coarse sand.The amount of Cd2+ adsorbed by clay,silt and fine sand exceeded 99%.The results indicated that the adsorption of Cd2+ to the aggregates could be divided into two stages: a fast reaction in the first 20 minutes,and a slow reaction later.The amount of capacity by the fast reaction exceeded 90% of the maximum adsorption capacity.The adsorption process for Cd2+ on the four fractions was found to follow pseudo second-order adsorption kinetics,which indicated that the adsorption is mainly a chemical process,and the adsorption speed decreased with increase of particle size.