铅(Pb2+)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,Pb2+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Pb2+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Pb2+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Pb2+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Pb2+的吸附,高浓度柠檬酸则起抑制作用,降低土壤对Pb2+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Pb2+的吸附为不均匀表面的多层吸附;易解吸率随初始Pb2+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Pb2+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 active sites, which affecting the adsorption- desorption of heavy metals in the soil.In order to understand the accumulation and migration characteristics of Pb2+ in soil, simulated culture method and citric acid, HCl desorption method was used to studied the effect of citric acid on the adsorption and desorption of Pb2+ by aggregates with different particle size. The results showed that the adsorption capacity of Pb2+ by different particle size aggregates increased with the increasing initial concentration of Pb2+, in the order of (<0.002 mm)> 2~0.25 mm> raw soil >0.053~0.002 mm>0.25 mm~0.053 mm. The adsorption amount of Pb2+ increased under citric acid concentration from 0 mmol?L-1 to 1 mmol?L-1, and decreased from 10 mmol?L-1 to 100 mmol?L-1, indicating that low concentration of citric acid played a catalytic role but high concentration of citric acid play inhibition role on the the adsorption of Pb2+ by aggregates. The Freundlich equation is suitable for the simulating of the isothermal adsorption process, indicating that the adsorption of Pb2+ by soil and different particle size of micro-aggregates was a multilayered adsorption of heterogeneous surface. The easy desorption rate of Pb2+ increased with the increasing concentration of Pb2+, and the easy desorption rate increased further after the 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 of Pb2+ in the area of calcareous purple soil, and which is of great significance to the safety and regulation of agricultural environment.
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