腐植酸对重金属铅镉的吸附特征

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.

The adsorption behavior of lead and cadmium by humic acid

In order to explore the adsorption behavior and mechanism of Pb²⁺, Cd²⁺ 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 Pb²⁺ by humic acid is insignificant corelated with pH, but adsorption capacity of Cd²⁺ increases with the raising pH. The saturation adsorption time of Pb²⁺ and Cd²⁺ by humic acid is 240 min. The adsorption capacity of Pb²⁺ and Cd²⁺ increase with the raising of temperature. Langmuir isotherm adsorption model well fit the adsorption of Pb²⁺, Cd²⁺ and Pb²⁺ in the composite of Pb²⁺ and Cd²⁺, while the Freundlich isotherm adsorption model well fits the adsorption Cd²⁺ in the composite of Pb²⁺ and Cd²⁺. Pseudo-second-order kinetics model can preferably fit the adsorption of Pb²⁺ and Cd²⁺ by humic acid, it means that the adsorption process of Pb²⁺ and Cd²⁺ belongs to physisorption and chemisorption. There exists competitive adsorption between Pb²⁺ and Cd²⁺ when both ions are present. The addition of Cd²⁺ in Pb²⁺ solution has no effect on the adsorption of Pb²⁺. However, when Pb²⁺ is added into Cd²⁺ solution, Pb²⁺ will compete with Cd²⁺ and the adsorption of Cd²⁺ will bereduced. The results provide reference for the study of humic acid in the research of Pb²⁺ and Cd²⁺ stabilization technology in soil.