黏土矿物界面吸附Fe(Ⅱ)耦合对邻硝基苯酚还原转化的增强机理研究

The enhanced reductive transformation for 2-nitrophenol removal coupled to the Fe(Ⅱ) adsorbed at the interfaces of clay minerals

系统考查了Fe(Ⅱ)分别与高岭石、蒙脱石结合的界面结合系统对邻硝基苯酚(简称2-NP)的还原转化作用。研究表明,矿物表面结合态Fe(Ⅱ)能够有效提高2-NP的还原转化速率,2-NP的还原反应符合伪一级反应动力学方程,而且速率常数(k)随溶液pH值、亚铁离子初始浓度以及反应温度的升高而显著增大。当温度25℃,pH值6.7,Fe(Ⅱ)和2-NP初始浓度分别为3.0 mmol/L、0.022 mmol/L,以及黏土的投加量为4.0 g/L时,Fe(Ⅱ)/高岭石系统对2-NP的还原转化率在4.0 h内可达到100%。同样,pH值从6.0升高至7.3时,Fe(Ⅱ)/蒙脱石系统对2-NP的还原转化也显著增强;但在较低pH值和较低初始Fe(Ⅱ)浓度时,蒙脱石对Fe(Ⅱ)的还原催化性能不如高岭石,可归因于蒙脱石具有较高的离子交换性能。因此,Fe(Ⅱ)在上述两种矿物上吸附形态的差异是导致该系统对2-NP还原转化出现不同效应的根本原因。

In this study,the reductive transformations of 2-nitrophenol(2-NP)by interfacial complex systems of Fe(Ⅱ)associated with kaolinite and montmorillonite respectively were systematically investigated.The results showed that surface-bonded Fe(Ⅱ)species on the minerals can effectively improve the rate of reductive transformations.The reduction reactions of 2-NP over the complex systems can be described by the pseudo first-order kinetics.The rate constant(k)was increased with the pH,initial Fe(Ⅱ)concentration and reaction temperature.Moreover,2-NP removal efficiency can reach 100%within 4.0 h by the presence of Fe(Ⅱ)/kaolinite system under the conditions of pH 6.7 and temperature 25℃,initial concentrations of 3.0 mmol/L Fe(Ⅱ)and 0.022 mmol/L 2-NP as well as the dose of kaolinite at 4.0 g/L.Similarly,when the solution pH increased from 6.0 to 7.3,the transformation for 2-NP removal was also clearly enhanced by the presence of Fe(Ⅱ)/montmorillonite system,but the conditions with a lower pH and a lower initial Fe(Ⅱ)concentration were quite not favorable for montmorillonite to effectively catalyze 2-NP to be reduced by Fe(Ⅱ),and the performance was even lower than that of kaolinite.This may be ascribed to montmorillonite having a higher cation-exchange capacity.Therefore,the difference in speciationof adsorbed Fe(Ⅱ)is the intrinsic reason for controling the 2-NP reductive transformation in the mentionedmineral interfacial reduction systems.