东北污灌区草甸棕壤吸附重金属铅的形态分布及解吸行为

以沈阳市沈抚污灌区的草甸棕壤为模型土,采用Tessier顺序提取法分析了吸附重金属Pb(Ⅱ)在土壤中的化学形态分布特点,研究了吸附Pb(Ⅱ)的解吸行为,特别考察了冷冻对吸附Pb(Ⅱ)化学形态分布及解吸行为的影响.研究表明,吸附Pb(Ⅱ)在东北草甸棕壤上的化学形态分布规律为:可交换态碳酸盐结合态铁锰氧化物结合态有机结合态残渣态;吸附Pb(Ⅱ)的解吸动力学过程可分为快速和慢速两个阶段,符合准二级动力学方程;冷冻对吸附Pb(Ⅱ)的形态分布基本无影响,而对平衡解吸率有明显影响,随冷冻时间延长,平衡解吸率逐渐降低;随pH值减小,平衡解吸率增大;pH值在5—10范围内,平衡解吸率变化幅度相对很小,而pH值低于5后,平衡解吸率急剧增大.随离子强度增大,平衡解吸率先急剧上升,后趋于平缓.提出Pb(Ⅱ)在东北草甸棕壤上的吸附机理:化学吸附和静电吸附,后者又可分为静电键合吸附和离子交换吸附.在实验条件下,静电吸附约占75%,化学吸附约占25%.

SPECIATION DISTRIBUTION AND DESORPTION OF LEAD ADSORBED ON MEADOW BROWN SOIL IN NORTHEASTERN SEWAGE IRRIGATION DISTRICT OF CHINA

In this paper, speciation distributions and desorption properties of Pb ( Ⅱ ) adsorbed on a meadow brown soil in northeast of China were studied, specially the effect of freezing on the speciation characteristics and desorption properties of Pb(Ⅱ) adsorbed was investigated.It was found that the order of speciation distribution of lead adsorbed was: ion exchange > carbonate fractions > Fe-Mn oxides > organic fractions > residue.Freezing did not alter the speciation distributions of Pb (Ⅱ) adsorbed, but significantly changed the equilibrium desorption rate (F_e) of Pb (Ⅱ) adsorbed, and F_e decreased with the increase of freezing time.With the increase of ion strength( NaNO_3 concentration) , the F_e increased.A possible adsorption mechanism of Pb(Ⅱ) on the soil was proposed.The adsorption of Pb(Ⅱ) on the soil arose from the chemical binding and electrostatic interaction, and the electrostatic interaction may be divided into anion exchange and electrostatic binding.In the experimental conditions, Pb (Ⅱ) adsorbed by electrostatic interaction was about 75 % , and that by chemical binding was about 25 %.