FeCl_3-柠檬酸对低浓度As^(3+)污染土壤的淋洗特性

Characteristics of FeCl_3-Citric Acid Leaching Arsenic From Soil Low in As^(3+) Contamination Level

以人工采集制备的w=100 mg·kg^(-1)砷污染土壤为研究对象,采用超声溶解的方式获得FeCl_3-柠檬酸复合淋洗剂,对不同淋洗剂配比、pH值、温度和常见共存阴阳离子(Ca^(2+)、Al^(3+)、SO_4^(2-)、PO_4^(3-))对砷污染土壤淋洗特性的影响和机理进行研究。结果表明,在相同的土液比(1∶10)条件下,m(FeCl_3)∶m(柠檬酸)=3∶1时对土壤中As的淋洗效果最佳,复合淋洗剂的淋洗效果优于单一淋洗剂。pH值和一定范围内温度的升高均有助于增加淋洗量。在pH值为7、8、9、10和温度为25、35、45℃时,淋洗动力学均符合Elovich方程,说明FeCl_3-柠檬酸对As^(3+)污染土壤的淋洗属于非均相的扩散过程。不同浓度(0.01~0.2 mol·L^(-1))的Ca^(2+)、Al^(3+)、SO_4^(2-)、PO_4^(3-)对淋洗效果均有一定影响。除SO_4^(2-)外,其他共存离子浓度越大,淋洗效果越好。

As contaminated-soil samples were prepared artificially with As concentration being 100 mg·kg^(-1) for the study on the use of FeCl_3-citric acid,a compound leachate prepared by means of ultrasonic dissolution,to leach As from As contaminated soils and effects of ratio,p H,temperature of the leachate and commonly coexisting anions or cations( Ca^(2+),Al^(3+),SO_4^(2-) and PO_4^(3-)) on leaching characteristics and their mechanisms. Results show that in solutions the same in soilto-liquid ratio( 1 ∶ 10),the compound leachate maximized its effect of leaching As from As-contaminated soils when its m( FeCl_3) ∶ m( citric acid) was 3 ∶ 1 and was better than simple leachates in leaching effect. Rising pH and temperature within a certain range contributed to leaching. In solutions with pH being 7,8,9 or 10 and temperature at 25,35 or 45℃,the leaching kinetics could be better described with the Elovich equation,which indicates that the leaching of As with FeCl_3-citric acid from As^(3+) contaminated soil is a heterogeneous diffusion process. The coexisting ions,such as Ca^(2+),Al^(3+),SO_4^(2-) and PO_4^(3-),0.01 ~ 0.2 mol·L^(-1) in concentration also had certain impacts on leaching of As. The higher the concentrations of the other coexisting ions,except for SO_4^(2-),the better the leaching effect. The compound leachate is expected to have a bright prospect for its application thanks to its low cost and wide availability.