改性褐煤对酸性矿山废水中Fe^(2+)、Mn^(2+)的吸附特性研究

Study on adsorption characteristics of modified lignite for Fe^(2+),Mn^(2+)in acid mine drainage

针对酸性矿山废水(Acid Mine Drainage,AMD)中Fe^(2+)、Mn^(2+)含量高,褐煤吸附饱和量有限等问题,以褐煤为试验材料,利用扫描电镜(SEM)、傅里叶红外光谱仪(FT-IR)、X射线衍射仪(XRD)等手段分析褐煤的吸附机理。同时,采用静态烧杯试验,并基于NaCl浸泡改性、超声波辅助NaCl改性褐煤的方法以及吸附等温线、吸附动力学原理,研究褐煤及改性褐煤吸附Fe^(2+)、Mn^(2+)特性和机理。结果表明:褐煤的表面孔隙结构发达,褐煤主要由高岭石、方解石、菱铁矿、石英等矿物组成,含有丰富的—OH、—C=O、—CHO等活性基团。超声波辅助NaCl改性褐煤对Fe^(2+)、Mn^(2+)的吸附效果最佳,平衡时吸附饱和量分别为6.7750 mg/g和8.0925 mg/g,较未改性褐煤提高了28.44%、22.47%。褐煤及其改性褐煤对Fe^(2+)、Mn^(2+)的吸附过程均符合Langmuir等温模型。研究表明,褐煤及改性褐煤表面均匀并且为单分子层吸附,被吸附的Fe^(2+)、Mn^(2+)之间没有相互作用力。褐煤及改性褐煤的吸附能力大小为:超声波辅助NaCl改性褐煤>NaCl浸泡改性褐煤>褐煤。其中,吸附效果最好的超声波辅助NaCl改性褐煤对Fe^(2+)、Mn^(2+)的Langmuir拟合方程分别为y=0.06995x+0.13924、y=0.07073x+0.42516。褐煤对AMD中Fe^(2+)的吸附过程符合准二级动力学模型,说明褐煤对Fe^(2+)的吸附机理以离子交换作用为主;NaCl浸泡改性褐煤、超声波辅助NaCl改性褐煤对AMD中Fe^(2+)的吸附现象符合颗粒内扩散模型,表明该吸附过程是由膜扩散和颗粒内扩散共同控制。褐煤及改性褐煤对AMD中Mn^(2+)的吸附均符合准二级动力学模型,说明褐煤及改性褐煤对AMD中Mn^(2+)的吸附以化学吸附为主。其中吸附效果最好的超声波辅助NaCl改性褐煤对Fe^(2+)的颗粒内扩散模型方程为y=0.48024x+0.45312;对Mn^(2+)的准二级动力学拟合方程为y=0.10344x+3.41511。

In view of the high content of Fe^(2+) and Mn^(2+) in acid mine drainage(AMD)and the limited adsorption saturation of lignite,the adsorption mechanism of lignite was analyzed by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction(XRD).At the same time,the static beaker experiment was used to study the characteristics and mechanism of adsorption of Fe^(2+) and Mn^(2+) by lignite and modified lignite based on the methods of NaCl soaking modification,ultrasonic assisted NaCl mod⁃ification,adsorption isotherm and adsorption kinetics.The results show that the surface pore structure of lignite is developed.Lignite is mainly composed of kaolinite,calcite,siderite,quartz and other minerals,and rich in—OH,—C=O,—CHO and other active groups.The results show that the adsorption of Fe^(2+) and Mn^(2+) by ultrasonic assisted NaCl modified lignite is the best,and the saturated adsorption capacity is 6.7750 mg/g and 8.0925 mg/g respectively,which is 28.44%and 22.47%higher than that of unmodified lignite.The adsorp⁃tion process of Fe^(2+) and Mn^(2+) on lignite and its modified lignite conformed to Langmuir isotherm model.The results show that the surface of lignite and modified lignite is homogeneous and monolayer adsorption,and there is no interaction between Fe^(2+) and Mn^(2+) adsorbed.The adsorption capacity of lignite and modified lignite is as follows:ultrasonic assisted NaCl modified lignite>NaCl soaked modified lignite>lig⁃nite.Among them,the Langmuir fitting equations of Fe^(2+) and Mn^(2+) by ultrasonic assisted NaCl modified lignite were y=0.06995x+0.13924 and y=0.07073x+0.42516,respectively.The adsorption process of lignite for Fe^(2+) in AMD accords with the pseudo second order kinetic model,which indicates that the adsorption mechanism of lignite for Fe^(2+) is mainly ion exchange;the adsorption of Fe^(2+) in AMD by NaCl soaking modified lignite and ultrasonic assisted NaCl modified lignite conforms to the intra particle diffusion model,which indicates that the adsorption process is controlled by both membrane diffusion and intra particle diffusion.The adsorption of Mn^(2+) in AMD by lignite and modified lignite is consistent with the pseudo second order kinetic model,which indicates that the adsorption of Mn^(2+) in AMD by lignite and modified lignite is mainly chemical adsorption.Among them,the best adsorption effect of ultrasonic assisted NaCl modified lignite is y=0.48024x+0.45312 for Fe^(2+),and y=0.10344x+3.41511 for Mn^(2+).