Preparation And Adsorption Mechanism Of Rare Earth Ions And Fluoride Ion Adsorbents Based On Halorubrum Ejinoor Sp.biomass

With the wide application of rare earth elements（REEs）in industry and agriculture,high-tech materials and devices,more and more REEs are released into the environment,and they enter the body of animals and human by bioaccumulation.In recent years,REEs have been recognized as an emerging pollutant,which can cause irreversible harm to animals,plants and people.Thus,the recovery of rare earth elements has been a hot issue for researchers.The recovery of rare earth elements has been a hot issue for scholars.Because of the strong selectivity between lanthanum and fluoride,the adsorption of halophilic bacteria-lanthanum composite adsorbent for fluoride ion was studied.Among many rare earth adsorbents,algae,fungi,bacteria,resins and activated carbon are the most widely used,among which microbial adsorbents are easy to obtain and low cost,in recent years,more attention has been paid to the study.Adsorption and desorption of rare earth elements La,Ce,Er in water by biomass and the adsorption of fluoride by H.e.-La³⁺composite adsorbent made by H.e.and La were studied.The effects of initial concentration（0～50 mmol/L）,contact time（0～160 min）,temperature（15～40℃）and Na Cl solution concentration（2.5%～25%）on the adsorption of rare earth elements on H.e.,and the effects of initial fluoride concentration（2～20 mg·L-1）,contact time（0～160 min）,p H value（4.5～8.5）,temperature（10～40℃）and ionic strength（2.5%～25%Na Cl）on the removal of fluorine by H.e.-La³⁺composite adsorbents were studied.The adsorption mechanism of H.e.biosorbents for lanthanum and H.e.-La³⁺complex adsorbents for fluoride ion were analyzed by using SEM,XPS and FT-IR.The results showed that:（1）the adsorption of La³⁺on H.e.reached equilibrium at 80 min,the adsorption kinetics fitting results showed that the adsorption can be well fitted by second-order kinetic model,R²=0.98.When the temperature reaches 40℃and the concentration of Na Cl solution is 2.5%,the adsorption capacity of H.e.to La³⁺reaches the maximum value of 7.15 mg/g,which follows Langmuir isothermal adsorption model,.Thermodynamic analysis showed that the enthalpy and Gibbs free energy changes were negative,which indicated that the biosorption of La³⁺on H.e.was endothermic and sp.ontaneous.（2）In the experiment of adsorption of cerium and erbium by H.e.adsorbent,the equilibrium time of adsorption of cerium and erbium with adsorbent H.e.was about 80 min,which accorded with the pseudo-second-order kinetic model.In the ionic strength test,the adsorption data of lanthanum were analyzed under the conditions of 2.5%and 25%Na Cl solution.The adsorption amount of lanthanum was increased by 2.7127 mg/g under the condition of 2.5%Na Cl solution,erbium ion increased 0.2675 mg/g,cerium ion decreased 0.09797mg/g.Compared with the data of lanthanum ion,the effect of ion strength on erbium and cerium is negligible.By analyzing the experimental data at30℃and 40℃,it can be found that the adsorption capacity of Ce³⁺and Er³⁺decreases with the increase of temperature.（3）In the experiment of adsorption of fluoride ion by H.e.-La³⁺complex adsorbent,the initial concentration of fluoride was 20 mg·L^-1,p H=4.5,temperature was 40℃,25%Na Cl solution was adsorbed for 80min,the maximum removal rate of fluoride was 94.22%.The adsorption kinetics fit the pseudo-second-order kinetic model,R²=0.9993,the adsorption isotherm fit the Freundlich isotherm,R²=0.9925.It is concluded that the physical adsorption of fluorine by halophilic bacteria-lanthanum complex adsorbent may take place during the adsorption process,meanwhile,chemical adsorption occurs as well.The thermodynamic data show that the adsorption process is endothermic,irreversible and spontaneous,so it can be concluded that the adsorption process of H.e.-La³⁺complex adsorbent is mainly chemical adsorption.（4）The H.e.,H.e.-La³⁺composite adsorbent and H.e.-La³⁺composite adsorbent after adsorption of fluoride were analyzed by SEM,FT-IR and XPS:La³⁺can be successfully adsorbed on H.e.,and the La³⁺bound on the surface of H.e.can combine with fluoride ions.The results showed that H.e.biomass is a potential material to recover REEs,and H.e.-La³⁺composite adsorbent is an effective material to remove fluorine.The results of this study will provide a new idea for the application of H.e.and a choice for the recovery of REEs and fluoride in water.