Preparation And Adsorption Capability Of Modified Biochar Composites

A new type of composite modified biochar was prepared in this paper to remove heavy metal ions in the effluent.In this study,corn straw stalk biomass was unitarily modified by four elements such as manganese,iron,titanium,and silicon through a"one-step sintering method",and the modified biochar were prepared and named by MnBC,FeBC,Ti BC,and SiBC.Binary modification of the biochar was carried out with manganese and silicon as the substrate to overcome the shortcomings of the one-component modified composite material and to improve comprehensive effect of the materials.1.Surface morphology,elemental composition,crystal structure and surface area of modified biochars were analyzed by XRD,FTIR,SEM+EDS,and BET before and after modification.Firstly,XRD showed that the modified elements were loaded as the form of oxides.Secondly,FTIR results showed that the modification enhanced the oxygen-containing functional groups on the surface of biochars,which were beneficial to the adsorption of heavy metal ions.Thirdly,the surface of the modified biochars were all rougher than the pure biochar（PBC）,and the particles were visible under high magnification.Finally,the specific surface area of the MnBC,FeBC,Ti BC and SiBC had increased from 2.2859 m²/g（PBC）to 68.1343,29.8803,98.2928 and 4.4598 m²/g,respectively.2.Batch adsorption experiments were conducted to explore the adsorption performance of modifed biochars in this study.The ratio between modified elements and biomass,the initial pH of the solution,and the dosage of adsorbent all effected the results of adsorption,experiments results showed that the optimal adsorption conditions were pH=6,dosage of adsorbent=2 g/L,Mn BC and SiBC’s ratio mass=1:5.The results of adsorption isotherm models and adsorption kinetics models showed that the maximum adsorption capacity of MnBC and SiBC were 187.76 mg/g and 152.61 mg/g,respectively.The kinetic fitting results showed that the adsorption of Cu（II）by SiBC could reach the adsorption equilibrium in about 10 minutes and the removal rate was more than 97%.And the MnBC had to take 500 minutes to achieve the same adsorption effect.The kinetic rate constant k₂ of SiBC could reach 268 times of Mn BC.According to the fitting results of Webber-Morris model,adsorption of SiBC could could be devided into only two stages,those were film diffusion stage and intraparticle diffusion stage,while MnBC needs three stages to complete adsorption equilibrium.3.The adsorption mechanisms were analyzed by FTIR and XPS before and after adsorption of modified biochar.The results showed that the adsorption mechanism of SiBC were mainly precipitation and surface complexation,while the main adsorption mechanism of MnBC were exclusive adsorption,ion exchange and intra-particle diffusion.4.Binary modification of the biomass was carried with elements of silicon and manganese,which had good adsorption properties.The adsorption ability and mechanism of binary modified biochar（SMBC）were analyzed by characterizations,batch adsorption experiments and adsorption model fittings.The adsorption of Cu（II）by SMBC could reach at 97%of removal rate within 10 min,and the maximum adsorption capacity was 825.07 mg/g fitted by isotherm models,and the monolayer and chemical adsorption were dominated.Combined with of adsorption isotherms,adsorption kinetics,FTIR and XPS before and after adsorption,the adsorption mechanisms were analysized as precipitation,surface complexation and ion exchange.The commen effect of three adsorption mechanisms to achieve the purpose of fast and high-capacity adsorption.In addition,the binary modification well controls the potential risk of leaching of Mn during the adsorption process.The manganese ion exchange capacity of SMBC（0.65 mg/L）was much smaller than the ion exchange capacity of MnBC（39.39 mg/L）.