铀在凹凸棒石上的吸附特性与机制研究

Adsorption Characteristics and Mechanism of Uranium on Attapulgite

采用静态实验方法研究了凹凸棒石对水溶液中铀的吸附特性,考察了溶液pH值、初始浓度、吸附时间对吸附的影响,用扫描电镜(SEM)、X射线衍射仪(XRD)表征凹凸棒石的形貌和结构,用傅里叶变换红外光谱仪(FTIR)表征凹凸棒石吸附铀前后结构的变化,探讨了凹凸棒石对铀的吸附动力学及吸附机制.结果表明,pH值对凹凸棒石吸附铀的影响显著,且在pH=5时吸附量最大.吸附量随着时间增大而增大,在2 h内可以达到平衡,吸附等温线方程符合Langmuir等温吸附模型,吸附过程为准二级动力学模型.由FTIR分析可得,凹凸棒石吸附铀后,在高频区3 700～3 000 cm-1内吸光度减弱,可能是由于铀与凹凸棒石的R—OH发生配位作用形成了R—OUO2+或(R—O)2UO2等络合物;在中频区1 700～800 cm-1内吸光度减弱,可能是铀离子和镁离子产生离子交换作用.铀在凹凸棒石上的吸附机制主要表现为离子交换和配位作用.

The adsorption characteristics of uranium on attapulgite were investigated by conducting a series of batch adsorption experiments in this study.The influence of solution pH,initial uranium concentration and contact time was investigated.Scanning electron microscope（SEM） and X-ray diffraction（XRD） were used to characterize the surface structure of the attapulgite,Fourier transform infrared spectrometer（FTIR） were used to characterize the surface properties of the attapulgite before and after uranium adsorption,and to analyze the adsorption mechanism and adsorption kinetics of uranium on attapulgite.The experimental results showed that sorption of uranium on attapulgite was strongly dependent on pH,and the highest adsorption reached at pH=5.The adsorption quantity increased with time,adsorption could achieve balance in 2 h.The adsorption isotherm equation conformed to the Langmuir isothermal adsorption model and adsorption process could be described by the two-order kinetics model.According to FTIR spectral,the absorbance of attapulgite decreased,which may result from R—OUO＋2or（R—O）2UO2 formed by the bond between uranium and R-OH of attapulgite in the high frequency area 3 700-3 000 cm-1,and which uranium ion and magnesium ions may produce ion exchanges in the intermediate frequency area 1 700-800 cm-1.Adsorption mechanism of uranium on attapulgite was mainly ion exchange and complexation.