玉米叶吸附剂对水溶液中Pb^(2+)的吸附性能研究

Adsorption properties of corn leaves for Pb^(2+) removal from the aqueous solutions

研究了玉米叶对水溶液中Pb^(2+)的吸附性能,借助正交和单因素试验探讨各因素对吸附率的影响,利用红外光谱研究吸附机理,并采用Langmuir、Freundlich和Temkin模型对吸附数据进行拟合。结果表明:金属初始质量浓度和体系pH值是影响吸附的重要因素;玉米叶吸附铅离子的最佳pH值为5.0,金属质量浓度和吸附剂投加量最佳比值为80 mg/L:0.170 g,在25℃时玉米叶对铅离子的吸附较快,180min后达到吸附平衡;吸附数据更加符合Freundlich和Femkin等温吸附模型,由Langmuir等温吸附模型可知玉米叶最大吸附量为103.266mg/g,吉布斯自由能△G°为负值,该过程吸热且自发进行。红外光谱分析表明,参与作用的官能团为羟基、羧基、酰胺或脂肪族C—X(X代表Cl、Br、I)。

The aim of this article is to assess the potential adsorptive properties of corn leaves in removing Pb（2＋） from the aqueous solutions.As is known,com leaves have been used for years to remove Pb（2＋） from aqueous solution as a new adsorbent under the batch method.The leaves have been used without any chemical additives or treating measures for the leaves＇ adsorption behavior for the lead ions in the solution.For the research purpose,we have done a multi-factor and multi-level orthogonal test in hoping to disclose the effect of initial Pb2＋ concentration,the solution pH,the contact time and the adsorbent dosage to be used to achieve the adsorption efficiency.Then,we have made an investigation over the effect of the afore-mentioned factors on the adsorption efficiency through a batch of experiments.At the same time,we have adopted the adsorption model of Langmuir,Freundlich and Temkin and discussed the adsorption mechanism by FT-IR spectrum for describing the equilibrium isotherms and the model parameters.The results show that it is the initial Pb2＋ concentration and the solution pH that mainly influence the adsorption.We have found that the adsorption rate tends to increase with the increase of pH value from 2.0 to 5.0,beyond which a decrease trend of the removal rate can be detected.In addition,the maximum adsorption rated would take place at pH 5.0 while the adsorption equilibrium time can be found at the point when the lasting time is 180 min at 25℃.The removal rate tends to increase with the increase of the initial concentrations of metal ions till it reaches a certain concentration（80 mg/L）.Beyond 80 mg/L,the increase in concentrations of metal ions may lead to the decrease of the adsorption rate.The maximum adsorption rate（78.70%） shall take place at 80mg/L.What is more,the thermodynamic studies indicate that the adsorption process is endothermic,whereas the thermodynamic parameters for the adsorption can be used to depict the spontaneous nature of the adsorption process.The experimental data we have gained are well in accord with the Freundlich and Temkin isotherm models.The maximum value of the uptake capacity has been found equal to103.266 mg/g,similar or a bit higher than the values encountered in the literature for other types of adsorbents.And the FT-IR spectrum shows that the chemical functional groups joining in the adsorption process are mainly OH—COOH—CONH2 and C—X（X represent Cl,Br,I）.