Effect Of Lanthanum Modification On Phosphate Adsorption Of Lees Sludge Biochar And Its Mechanism

As the urbanization process in China continues to advance,the amount of municipal sludge generated from wastewater treatment is increasing,and the treatment and disposal of municipal sludge and its utilization has attracted more and more attention,and has been identified as“the future waste problem”.Traditional municipal sludge treatment and disposal methods often have problems such as causing secondary pollution to the environment,so it is necessary to find a resource recovery and harmless treatment and disposal method for municipal sludge.This paper proposes a method of preparing adsorbents from municipal sludge by pyrolysis,which can be used to adsorb and desorb phosphorus in wastewater.This method can not only realize the resource recovery and harmless treatment of municipal sludge,but also realize the recycling of phosphorus.In this study,distiller’s grains sludge biochar was prepared by pyrolysis using municipal sludge and corn distiller’s grains as biomass raw materials,and lanthanum-loaded modified distiller’s grains sludge biochar was prepared by co-precipitation method.The optimal preparation conditions of biochar and modification conditions were determined by single-factor experiments;the adsorption performance and its influencing factors were investigated by phosphorus adsorption experiments;the adsorption mechanism was analyzed by material characterization and DFT calculation.The optimal preparation conditions of wine lees sludge biochar were determined by single-factor experiments as follows:Zn Cl₂(2 mol·L^-1)was used as an activator,the proportion of wine lees added was 30%,the impregnation ratio of biomass raw materials to activator was 1:3（g:m L）,the pyrolysis temperature was 450℃,and the pyrolysis time was 1.5 h.The wine lees sludge biochar prepared under these conditions was denoted as LBC_Z.The optimal modification conditions for modified wine lees sludge biochar were as follows:La Cl₃·7H₂O(0.1 mol·L^-1)was used as a modifier,the modification time was 60 min,and the modification temperature was 40℃.The lanthanum-modified wine lees sludge biochar prepared under these conditions was denoted as La-LBC_Z.LBC_Z and La-LBC_Z were characterized by SEM-EDS,BET,XRD,FTIR and XPS to determine the effect of modification on the physicochemical properties of biochar.The results showed that the surface of the LBC_Z was rougher with many small particles and a relative decrease in specific surface area.The relative content of La element on the surface of the biochar increased to 8.53 and was loaded in the form of La（OH）₃ onto the surface of the La-LBC_Z.The adsorption experiment results showed that the adsorption capacity of LBC_Z for phosphate was 11.56 mg·g^-1,which increased to 68.32mg·g^-1 after modification,and the adsorption capacity was increased by about 6 times.Kinetic analysis results showed that LBC_Z adsorption process for phosphate was in accordance with pseudo-second-order kinetic model and Freundlich model;La-LBC_Zadsorption process for phosphate was in accordance with pseudo-second-order kinetic model and Langmuir model.Coexisting ion experiments,adsorption-desorption experiments and actual wastewater adsorption experiments showed that La-LBC_Z has better application prospects than LBC_Z and still has excellent adsorption-desorption performance after 5 cycles of adsorption-desorption experiments.The biochar before and after adsorption of phosphate was characterized and analyzed to explore the adsorption mechanism.The results showed that the surface of LBC_Z produced electrostatic attraction to phosphate,and at the same time,Zn ions were leached out during the adsorption process and combined with phosphate to form precipitation.Physical adsorption and chemical adsorption coexisted,with physical adsorption being dominant.The surface of La-LBC_Z produced electrostatic attraction to phosphate,and phosphate replaced-OH groups to form inner coordination compounds to achieve adsorption effect,mainly chemical adsorption.DFT calculation results confirmed the above mechanism.The adsorption energies of La-LBC_Z for phosphate were all negative,indicating that the adsorption of La-LBC_Z for phosphate was spontaneous and easy to occur.The differential charge diagram showed that the charge exchange of La-LBC_Z in the process of adsorbing phosphate was much stronger than that of LBC_Z in the process of adsorbing phosphate,which also indicated that the adsorption of LBC_Z for phosphate tended to be physical adsorption,while the adsorption of La-LBC_Z for phosphate was chemical adsorption.This paper prepared wine lees biochar from municipal sludge and corn wine lees by pyrolysis,and modified the wine lees biochar by co-precipitation method to obtain lanthanum-modified wine lees biochar with high phosphate adsorption performance.The biochar before and after modification was used to adsorb phosphorus in domestic wastewater,providing a basis for the resource utilization of municipal sludge and the adsorption of phosphorus-containing wastewater.