Preparation Of Modified Biochar And Its Adsorption Performance On Uranium In Water

Nuclear energy,recognized for its efficiency and cleanliness,is increasingly considered a sustainable solution to the global energy crisis.Uranium,the primary raw material for nuclear energy,is extensively mined,smelted,and utilized.However,improper disposal of uranium slag and smelting wastewater can lead to severe pollution of surface water,soil,and groundwater,posing potential threats to human health and the ecological environment.Hexavalent uranium（U（VI））,characterized by its high solubility,mobility,and toxicity,is the predominant form of uranium found at contaminated sites.Consequently,the development of adsorbents for U（VI）removal from aqueous solutions and the exploration of their action mechanisms have emerged as critical research areas.In this study,we prepared biochar from rice husk（SBC）,wheat straw（MBC）,and moso bamboo（ZBC）using a high-temperature anoxic pyrolysis method.We then investigated the adsorption performance and mechanism of both unmodified and modified biochar for U（VI）.Our primary findings include:（1）Material characterization revealed that the biochars derived from rice husk（SBC）,wheat straw（MBC）,and moso bamboo（ZBC）exhibited a loose and porous structure with well-developed pores.Under specific conditions—1 g·L^-1of biochar,a solution p H of 5,a U（VI）concentration of 10 mg·L^-1,and an adsorption time of 180minutes—the adsorption rates of U（VI）for SBC,MBC,and ZBC were found to be66.9%,60.2%,and 61.7%,respectively.The theoretical maximum adsorption capacities for U（VI）were determined to be 30.22 mg·g^-1for SBC,23.31 mg·g^-1for MBC,and22.42 mg·g^-1for ZBC.Fourier-transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）analyses indicated that the biochar surfaces were rich in oxygen-containing functional groups.The mechanism of U（VI）adsorption by SBC was found to involve the complexation of these oxygen-containing functional groups with uranyl ions.Given its higher content of oxygen-containing functional groups and larger specific surface area and pore capacity,SBC demonstrated the most effective U（VI）adsorption.（2）While biochar exhibits a certain degree of adsorption effect on U（VI）,its adsorption capacity is notably limited.To enhance this performance,we produced modified biochar（ABC2 and ABC3）by treating rice husk biochar（SBC）with 20%and30%concentrations of H₂O₂,respectively.Material characterization revealed that ABC2and ABC3,both featuring an abundance of pore structures on their surfaces,underwent oxidation by H₂O₂,leading to surface erosion and consequent enrichment of the biochar’s pore structure.The specific surface areas of ABC2 and ABC3 increased to1.91 times and 3.25 times,respectively,compared to their pre-modification states.Under specific conditions—1 g·L^-1of biochar,a solution p H of 5,a U（VI）concentration of 10 mg·L^-1,and an adsorption time of 180 minutes—the removal rates of U（VI）by ABC2 and ABC3 were 87.5%and 93.8%,respectively.The theoretical maximum adsorption capacities of ABC2 and ABC3 for U（VI）were determined to be 46.51 mg·g^-1and 52.26 mg·g^-1,respectively,and these capacities remained consistent after four replicate adsorption experiments.FT-IR and XPS analyses indicated a significant increase in the number of oxygen-containing functional groups,such as hydroxyl and carboxyl groups,on the surfaces of ABC2 and ABC3 following modification.The mechanism of U（VI）adsorption by ABC3 involves complexation reactions between these oxygen-containing functional groups and uranyl ions.Owing to its higher content of oxygen-containing functional groups,larger specific surface area,and greater pore volume,ABC3 demonstrated superior adsorption performance for U（VI）.Therefore,the modification of biochar with 30%H₂O₂proved to be the most effective approach.（3）The improper recovery of used biochar can lead to secondary water pollution.To address this issue,we endowed ABC3 with magnetic properties through a co-precipitation process.Material characterization revealed that the surface of the magnetically modified biochar（MABC）was populated with a multitude of irregular pores.The introduction of Fe₃O₄microspheres to the biochar surface resulted in a rougher texture,thereby increasing its specific surface area.The specific surface area of MABC was determined to be 195.62 m²·g^-1,which is 11.11 and 3.41 times greater than that of SBC and ABC3,respectively.Under specific conditions—1 g·L^-1of biochar,a solution p H of 5,a U（VI）concentration of 10 mg·L^-1,and an adsorption time of 180minutes—MABC removed 95%of U（VI）.The theoretical maximum adsorption capacity of MABC for U（VI）was established to be 53.68 mg·g^-1.Even after four repeated adsorption experiments,the adsorption quantity of MABC for U（VI）remained at 90%of the initial adsorption amount.Due to its magnetic properties,MABC can be easily separated using magnets,underscoring its recoverability and economic value.FT-IR and XPS analyses indicated the addition of Fe-O and O-Fe-O functional groups to the surface of MABC following magnetization.The adsorption mechanism of MABC on U（VI）involves both electrostatic interaction and chemical complexation,implicating Fe-O,hydroxyl,carboxyl,and other oxygen-containing functional groups.In conclusion,our study presents a simple,cost-effective method for preparing magnetic modified biochar.Given its enhanced U（VI）adsorption performance and ease of recovery,this material holds significant promise for practical industrial applications.