Study On Preparation And Adsorption Properties Of Magnetic Biochar From Sludge

Sludge biochar（SBC）was prepared from surplus sludge of municipal sewage treatment plant,and modified sludge biochar was used for adsorption of methylene blue（MB）,the results showed that the adsorption capacity of SBC to methylene blue at a concentration of 100 mg/L was 27.65 mg/g,and the removal rate was 53.88%.SBC was modified by HCl、HNO₃、H₃PO₄、NaOH、KOH、Na₂CO₃、K₂CO₃、ZnCl₂and NaHCO₃,the results showed that the modified sludge biochar（SBC-NaOH）with NaOH as modifier had the best adsorption effect on methylene blue,the adsorption capacity reached 48.08 mg/g,and the removal rate was 93.44%.To further research on the optimization of SBC modification conditions by NaOH modifier is as follows:the modifier NaOH concentration is 7%,the modification reaction time is 2 h,the modification temperature is 40℃,the modified products MSBC-NaOH reached the maximum adsorption capacity of methylene blue was 52.48 mg/g,and the removal rate reached 99.72%,compared with SBC,the removal rate increased by 45.84%..The optimal preparation conditions for the adsorption of methylene blue by the prepared MSBC-NaOH negative magnetic were as follows:MSBC-NaOH dosage was 3.0 g/L,reaction time was 2 h,temperature was 80℃,and the obtained magnetic sludge-based biochar（MSBC-NaOH/Fe₃O₄）,and the adsorption capacity of methylene blue reached 47.01 mg/g,and the removal rate reached 98.43%.The MSBC-NaOH/Fe₃O₄ after adsorption of methylene blue was recycled and reused,after 5 times of reuse,the adsorption and removal rates decreased by 8.67%and8.72%,respectively.Three kinds of materials,SBC,MSBC-NaOH and MSBC-NaOH/Fe₃O₄,were characterized by BET,XRD,SEM and FTIR.The BET measurement results show that after SBC is modified and negatively magnetized,the specific surface area of MSBC-NaOH and MSBC-NaOH/Fe₃O₄ increased from 42.6 m²/g to 66.3 m²/g and58.8 m²/g,respectively;the pore diameter decreased from 22.0 nm to 6.91 nm and12.3 nm,respectively.The total pore volume was reduced from 0.24 cm³/g to 0.10cm³/g and 0.20 cm³/g,respectively.The results of XRD showed that the diffraction peak of Fe₃O₄ appeared in the sample MSBC-NaOH/Fe₃O₄,indicating that the MSBC-NaOH/Fe₃O₄ material contained Fe₃O₄.The results of SEM showed that the modified MSBC-NaOH pores were more developed than SBC,these developed pores increased the specific surface area of MSBC-NaOH.After negative magnetic,MSBC-NaOH/Fe₃O₄ has a certain decrease in the number of pores compared with MSBC-NaOH,and the specific surface area is lower than that of MSBC-NaOH.FTIR analysis showed that SBC,MSBC-NaOH and MSBC-NaOH/Fe₃O₄ all contained similar groups,including-OH,C=O,C-O and Si-O.Among them,the absorption peak of MSBC-NaOH/Fe₃O₄ at 582.03 cm^-1 after negative magnetic is mainly the Fe-O stretching vibration peak,indicating the presence of iron oxide.The results of adsorption of ammonia nitrogen by MSBC-NaOH/Fe₃O₄ showed that the pH of 7,MSBC-NaOH/Fe₃O₄ dosage of 10 g/L,the temperature of 20℃ when the initial mass concentration of 200 mg/L oscillation simulation of ammonia nitrogen wastewater 15 h adsorption,the adsorption quantity can reach 3.66 mg/g.The adsorption of Cr（VI）by MSBC-NaOH/Fe₃O₄ showed that the PH of 3,MSBC-NaOH/Fe₃O₄ dosage of 10 g/L,when the temperature is 40℃ on the initial mass concentration of 200 mg/L Cr（VI）to simulate wastewater oscillation adsorption24 h,the adsorption quantity can reach 13.38 mg/g.The results of adsorption isotherm and kinetics fitting showed that the adsorption of methylene blue,ammonia nitrogen and Cr（VI）by MSBC-NaOH/Fe₃O₄accorded with Langmuir isotherm adsorption model and quasi-secondary kinetic model.The results of thermodynamic analysis showed that the adsorption process of methylene blue and Cr（VI）by MSBC-NaOH/Fe₃O₄ was spontaneously endothermic,while the adsorption process of ammonia nitrogen by MSBC-NaOH/Fe₃O₄ was self-heating.