Study on adsorption characteristics of modified lignite for Fe2+, Mn2+ in acid mine drainage

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 modification, 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〖KG-*5〗〖FY=,1〗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 6.775 0 mg/g and 8.092 5 mg/g respectively, which is 28.44% and 22.47% higher than that of unmodified lignite. The adsorption 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>lignite. 〖JP2〗Among them, the Langmuir fitting equations of Fe2+ and Mn2+ by ultrasonic assisted NaCl modified lignite were y=0.069 95x+ 0.139 24 〖JP〗and y=0.070 73x+0.425 16, 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=0.480 24x+0.453 12 for Fe2+, and y=0.103 44x+3.415 11 for Mn2+.