Study On The Adsorption Of Eu(Ⅲ) On Mangnese Oxide-biochar Composite

Two kinds of biochar,peanut shell biochar（HBC）and corn stalk biochar（YBC）,were prepared by pyrolysis of peanut shell and corn stalk at different temperatures.Then two kinds of composite materials,MnO_x-HBC and MnO_x-YBC,were prepared by modification of manganese oxides.The surface morphology,functional groups and structures of HBC,YBC,MnO_x-HBC and MnO_x-YBC were characterized by scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray powder diffraction（XRD）and specific surface area and aperture analysis（BET）.The effects of pH value,adsorbent dosage,reaction temperature and adsorption time on the adsorption of Eu（Ⅲ）were investigated by batch experiments.Langmuir isotherm adsorption model,Freundlich isotherm adsorption model,quasi-first-order adsorption kinetics model,quasi-second-order adsorption kinetics model and intra-particle diffusion adsorption kinetics model were used to fit the adsorption thermodynamics,isotherm and kinetics data,respectively,to analyze the relevant adsorption mechanism and evaluate the adsorption effect.In addition,the effects of different coexisting ion types and different coexisting ion concentrations on the adsorption efficiency were investigated.The main research results are as follows:（1）Pyrolytic temperature has an effect on the yield of biochar.The higher the pyrolysis temperature,the lower the yield of biochar.The highest yield of biochar at different final pyrolysis temperatures is 47.26%at 300℃,42.34%at 500℃,and34.68%at 700℃.The ratio of C/H and C/N of biochar increases with the increase of pyrolysis temperature.（2）SEM results showed that the surface of YBC was slightly smooth,mostly with pore structure,while the surface of HBC was mostly with sheet structure.The SEM-EDX map indicated that manganese was successfully loaded on the biochar.Compared with the original biochar,the specific surface area of the modified biochar increased significantly,resulting in more contact sites.The characteristic peaks of FT-IR of YBC and HBC are basically the same.The XRD results showed that the Mnand O content on MnO_x-YBC and MnO_x-HBC increased,and the characteristic absorption peak of Mn-O appeared,which further proved that Mnoxide was loaded on the biochar.（3）The adsorption experiment results showed that the higher the dosage of adsorption materials,the higher the removal rate of Eu（Ⅲ）.The optimal adsorption pH was 6,the optimal dosage of YBC and MnO_x-YBC was 0.3g/L,and the optimal dosage of HBC and MnO_x-HBC was 0.5g/L.When the temperature is 298K and the pH is 6,the maximum adsorption capacity of Eu（Ⅲ）by YBC is 33.24mg/g,and the maximum adsorption capacity of Eu（Ⅲ）by HBC is 30.54mg/g.The maximum adsorption capacity of MnO_x-YBC to Eu（Ⅲ）is 68.31mg/g,and the maximum adsorption capacity of MnO_x-HBC to Eu（Ⅲ）is 42.46mg/g.The adsorption process conforms to the Langmuir model and the quasi-second order adsorption kinetics model.Adsorption thermodynamics results show that adsorption is a spontaneous endothermic process and an entropy increasing process,and the adsorption effect increases with the rise of temperature（4）Different concentrations and different kinds of coexisting ions have an effect on the adsorption effect.The removal rates of both MnO_x-HBC and MnO_x-YBC on Eu（Ⅲ）decrease with the increase of coexisting ion concentration.The effect of coexisting ions on the adsorption of MnO_x-HBC and MnO_x-YBC on Eu（Ⅲ）was Ca²⁺>Mg²⁺>-NO₃^->Cl^-.