腐植酸对重金属铅镉的吸附特征

The adsorption behavior of lead and cadmium by humic acid

为了揭示腐植酸对单一Pb、单一Cd和Pb、Cd复合污染物的吸附特征,笔者通过吸附模拟实验分析了pH、温度、反应时间和初始浓度等因素变化对风化煤腐植酸吸附重金属离子Pb^(2+)和Cd^(2+)的影响.结果表明,腐植酸对Pb^(2+)的吸附受pH值变化的影响很小,但对Cd^(2+)的吸附随着pH增加而增加;腐植酸对Pb^(2+)和Cd^(2+)吸附饱和的时间均为240 min;对Pb^(2+)和Cd^(2+)的吸附量均随温度的增加而增加;Langmuir吸附模型对腐植酸吸附单一Pb^(2+)、单一Cd^(2+)和铅镉复合态中Pb^(2+)的拟合较好,Freundlich吸附模型则对腐植酸吸附铅镉复合态中Cd^(2+)的拟合较好;准二级动力学模型能较好地拟合腐植酸吸附Pb^(2+)和Cd^(2+)的过程,说明腐植酸对铅镉的吸附为物理吸附和化学吸附的复合吸附过程;铅镉复合态下Pb^(2+)和Cd^(2+)存在竞争吸附,单一Pb^(2+)溶液中加入Cd^(2+)对腐植酸吸附Pb^(2+)基本无影响,但单一Cd^(2+)溶液中加入Pb^(2+)时,Pb^(2+)会与Cd^(2+)产生竞争吸附,从而降低Cd^(2+)的吸附量.本研究结果可为利用腐植酸稳定土壤中Pb^(2+)、Cd^(2+)等重金属离子的技术开发提供参考.

In order to explore the adsorption behavior and mechanism of Pb^2＋,Cd^2＋and their composite byhumic acid,adsorption experiments are conducted under various influencing factors such as pH,temperature,reaction time,initial concentrations,etc. The results show that adsorption capacity of Pb^2＋by humic acid is insignificant corelated with pH,but adsorption capacity of Cd^2＋increases with the raising pH. The saturation adsorption time of Pb^2＋and Cd^2＋by humic acid is 240 min. The adsorption capacity of Pb^2＋and Cd^2＋increase with the raising of temperature. Langmuir isotherm adsorption model well fit the adsorption of Pb^2＋,Cd^2＋and Pb^2＋in the composite of Pb^2＋and Cd^2＋,while the Freundlich isotherm adsorption model well fits the adsorption Cd^2＋in the composite of Pb^2＋and Cd2 ＋. Pseudo-second-order kinetics model can preferably fit the adsorption of Pb^2＋and Cd^2＋by humic acid,it means that the adsorption process of Pb^2＋and Cd^2＋belongs to physisorption and chemisorption. There exists competitive adsorption between Pb^2＋and Cd^2＋when both ions are present. The addition of Cd^2＋in Pb^2＋solution has no effect on the adsorption of Pb^2＋. However,when Pb^2＋is added into Cd^2＋solution,Pb^2＋will compete with Cd^2＋and the adsorption of Cd^2＋will bereduced. The results provide reference for the study of humic acid in the research of Pb^2＋and Cd^2＋stabilization technology in soil.