老冲积黄壤微团聚体对As(Ⅴ)与P竞争吸附—解吸特性

Competitive Adsorption and Desorption Characteristics of Micro-aggregates to Arsenic and Phosphorus in Old Alluvial Yellow Soil

土壤微团聚体是土壤的最基本结构单元,不同粒径微团聚体的理化性质的差异不同使得重金属离子在各粒径微团聚体中的吸附—解吸能力大小不同。以名山河流域老冲积黄壤为研究对象,将其划分为4个粒径（2~0.25mm,0.25~0.053mm,0.053~0.002mm,〈0.002mm）。采用批培养法研究原土及不同粒径微团聚体对As（Ⅴ）与P的竞争吸附—解吸特性。结果表明：原土及不同粒径微团聚体对As（Ⅴ）、P的吸附—解吸特性相似,等温吸附均符合Langmuir和Freundlich方程,但Langmuir方程拟合效果最佳;动力学吸附均符合伪一级方程和伪二级方程,但伪二级方程拟合效果更好。原土及各粒径微团聚体对As（Ⅴ）、P的吸附均以专性吸附为主,非专性吸附为辅。原土及不同粒径微团聚体对As（Ⅴ）、P的最大吸附量不仅与粒径大小有关,与土壤有机质、CEC、游离氧化铁含量呈正相关。由于〈0.002mm粒径的土壤比表面积大,有机质、CEC、游离氧化铁含量高,故其对As（Ⅴ）、P有最大吸附能力和最高初始吸附速率。As（Ⅴ）、P在各粒径微团聚体上解吸量与其吸附量呈指数关系。当As（Ⅴ）与P共存时,明显互相抑制对方的吸附,促进对方的解吸。As（Ⅴ）与P在〈0.002mm粒径土壤中存在的竞争吸附—解吸能力最小。

As the basic structural unit of soils,soil micro-aggregates with different particle size takes different ability in adsorbing and desorbing heavy metals in the environment because of their various physical and chemical properties.This study was conducted on the alluvial yellow soil of famous river basin,which was classified into 4particle sizes（2~0.25 mm,0.25~0.053 mm,0.053~0.002 mm and 〈0.002mm）,and the batch culture method was used to study the competitive adsorption and desorption characteristics of micro-aggregates to arsenic（As（Ⅴ））and phosphorus（P）.The results showed that the adsorption and desorption characteristics of natural soil and micro-aggregates with different particle sizes to arsenic and phosphorus were similar The isothermal adsorption data for As（Ⅴ）and P could be well fitted with Langmuir and Freundlich equation,but the fitting effect of Langmuiris equation was the best.Kinetic adsorption data for As（Ⅴ）and P were more successfully fitted with pseudo second-order equation than with pseudo firstorder equation.The adsorption of natural soil to As（Ⅴ）and P was characterized mainly by specific adsorption,and secondarily by non-specific adsorption.The maximum adsorption amount of natural soil to As（Ⅴ）and P was not only related to the soil particle size,but also positively associated with the contents of soil organic matter,CEC and free iron oxide.The 〈0.002 mm micro-aggregates had the maximum adsorption capacity and the highest initial adsorption rate because of its larger specific surface area and the higher contents in organic matter,CEC and free iron oxide.There was the index relationship between adsorption and desorption of soil micro-aggregates to As（Ⅴ）and P.When the As（Ⅴ）and P coexisted,the adsorption to them was significantly restrained and desorption of them was promoted by each other.The ability of adsorption and desorption between P and As（Ⅴ）in 〈0.002 mm micro-aggregates was the lowest.