不同浓度柠檬酸溶液中石灰性紫色土微团聚体对Pb^(2+)的吸附解吸特性变化

Adsorption and Desorption Characteristics of Pb^(2+) by Aggregates of Calcareous Purple Soil under Citric Acid

铅(Pb^(2+))因溶解度较小,易在土壤中长期滞留,从而造成严重的土壤铅污染。柠檬酸(Citric Acid)作为植物根系分泌的典型天然有机酸,含有大量羧基功能团和活性点位,影响着土壤中重金属的吸附和解吸。为深入了解柠檬酸输入土壤后,Pb^(2+)在土壤中的积累与迁移规律,以石灰性紫色土为研究对象,通过模拟试验,采用平衡液吸附法及柠檬酸、HCl解吸法,研究了不同浓度柠檬酸溶液中石灰性紫色土及各粒径微团聚体对Pb^(2+)的吸附-解吸特性。结果表明:在不同浓度柠檬酸溶液中,石灰性紫色土全土及各粒径微团聚体对Pb^(2+)的吸附量随其初始浓度增大而增加,各粒径间吸附量大小顺序为:(<0.002 mm)>2~0.25 mm>全土>0.053~0.002 mm>0.25 mm^0.053 mm;柠檬酸浓度在0~1 mmol·L^(-1)范围内,石灰性紫色土全土及各粒径微微团聚体对Pb^(2+)的吸附量明显上升,1~100 mmol·L^(-1)范围内吸附量下降,低浓度的柠檬酸能够有效促进全土及各粒径微团聚体对Pb^(2+)的吸附,高浓度柠檬酸则起抑制作用,降低土壤对Pb^(2+)的吸附量;Freundlich方程对等温吸附过程的拟合达到极显著水平(R2=0.985-0.999),全土和不同粒径微团聚体对Pb^(2+)的吸附为不均匀表面的多层吸附;易解吸率随初始Pb^(2+)质量浓度上升而不断增大,难解吸率不断下降,加入柠檬酸后,易解吸率进一步上升,且随柠檬酸浓度升高而增大。研究柠檬酸溶液中石灰性紫色土对Pb^(2+)的吸附-解吸特性,能够有效预测石灰性紫色土区域重金属的环境效应,对农业环境安全调控具有重要意义。

Lead(Pb2+)is easy to stay in the soil for a long time because of its low solubility,and which leads to serious soil pollution.As a typical natural organic acid secreted by plant roots,citric acid contains a large number of carboxyl functional groups and activesites,which affecting the adsorption-desorption of heavy metals in the soil.In order to understand the accumulation and migrationcharacteristics of Pb2+in soil,simulated culture method and citric acid,HCl desorption method was used to studied the effect of citricacid on the adsorption and desorption of Pb2+by aggregates with different particle size.The results showed that the adsorptioncapacity of Pb2+by different particle size aggregates increased with the increasing initial concentration of Pb2+,in the order of(<0.002mm)>2~0.25mm>raw soil>0.053~0.002mm>0.25mm^0.053mm.The adsorption amount of Pb2+increased under citricacid concentration from0mmol·L-1to1mmol·L-1,and decreased from10mmol·L-1to100mmol·L-1,indicating that lowconcentration of citric acid played a catalytic role but high concentration of citric acid play inhibition role on the the adsorption ofPb2+by aggregates.The Freundlich equation is suitable for the simulating of the isothermal adsorption process,indicating that theadsorption of Pb2+by soil and different particle size of micro-aggregates was a multilayered adsorption of heterogeneous surface.Theeasy desorption rate of Pb2+increased with the increasing concentration of Pb2+,and the easy desorption rate increased further afterthe addition of citric acid,and such effect was increased with the increasing concentration of citric acid.It is important to understand.the adsorption-desorption characteristics of Pb2+under citric acid,which helpful for effectively predict the environmental effect ofPb2+in the area of calcareous purple soil,and which is of great significance to the safety and regulation of agricultural environment.