Adsorption Characteristics Of Modified Biochar For Cr(?) In Wastewater

In this study,water hyacinth and eucalyptus were used as experimental modified raw materials.Magnetic modified water hyacinth biochar and amino modified eucalyptus biochar were prepared by soaking,chemical modification and pyrolysis respectively.The two modified biochar were recorded as MBC and ABC respectively.MBC and ABC were used to simulate the adsorption of Cr(VI)wastewater.The effects of pH value,initial concentration and temperature,adsorption time and dosage of adsorbent on adsorption were studied by single factor adsorption experiment.The materials before and after modification and before and after adsorption of heavy metal of Cr(VI)were characterized and analyzed by means of SEM,XRD,BET and FT-IR etc.The adsorption mechanism was discussed by means of kinetic model and isotherm model.The main conclusions are as follows:(1)Preparation and characterization of MBC and ABC:the results of single factor and orthogonal preparation experiments showed that the preparation conditions of MBC were 450?carbonization temperature,0.2M concentration of iron nitrate and the mass ratio of potassium carbonate:water hyacinth=0.5:5,its adsorption capacity of Cr(VI)is 9.902mg/g.BET analysis showed that the specific surface area of MBC was 29.797m~2/g,and the specific surface area of water hyacinth biochar was5.528m~2/g.It can be seen that magnetic modification increases the specific surface area of primary biochar.FTIR showed the Fe-O stretching vibration peak on MBC.When pH was greater than 3,with small amount of iron precipitates,which is less than 0.9?g/g and the magnetic of MBC was stability.The ABC preparation were300?carbonization temperature,the ratio of nitric acid:sulfuric acid=2:1,and 15mL of ammonia its adsorption capacity of Cr(VI)is 19.23mg/g..The specific surface area of Eucalyptus biochar and ABC was 0.854 m~2/g and 0.767 m~2/g,respectively.The absorption peak of C-N and N-H was found in FT-IR.The SEM show that the water hyacinth biochar surface was more rough than Eucalyptus biochar.(2)The adsorption characteristics of MBC were as follows:the removal of Cr(VI)wastewater by MBC were positive relevant to the dosage,reaction time and reaction temperature,and were negative relevant to the initial concentration of Cr(VI)and pH value.By FT-IR and XRD analysis of the adsorbed MBC,some peaks were disappear,indicating that the adsorption process was accompanied with chemical adsorption.The quasi-secondary kinetic model and Freundlich isothermal adsorption model can be used to describe the adsorption process of the MBC.According to the D-R model,the free energy was less than 16kJ/mol,shown that the adsorption process was accompanied with physical adsorption.According to thermodynamics result,the adsorption process was a spontaneous adsorption of disordered endotherms.To sum up,the adsorption process is mainly physical adsorption,but also accompanied by chemical adsorption.(3)The adsorption characteristics of ABC were as follows:the removal of Cr(VI)wastewater by ABC were positive relevant to the dosage,reaction time and reaction temperature,and were negative relevant to the initial concentration of Cr(VI)and pH value.The quasi-secondary kinetic model and Langmuir isothermal adsorption model can be used to describe the kinetics and isothermal process of the ABC.According to the D-R model,the free energy was greater than 16kJ/mol,shown that the adsorption process was accompanied by chemical adsorption.According to thermodynamics result,the adsorption process was a spontaneous adsorption of disordered endotherms.In summary,the adsorption process was mainly monolayer adsorption and chemisorption.