Nano Fe ₃ O ₄ Load Characteristics And Mechanism Of Adsorption Of Uranium U (Ⅵ) Of Pseudomonas Aeruginosa

A novel biosorbent was prepared by loading pseudomonas aeruginosa ontonano-Fe₃O₄，Making it not only have the ability of microbial adsorption to uranium, butalso the ability of chemical adsorption to uranium. At the same time,it has thecharacteristics of fast magnetic separation under an external magnetic field.Static experiments were conducted on the effects of pH value, adsorbent dosage,temperature and co-existed cation and anion on the adsorption of uranium. Regenerationability and stability of the composite material were investigated. The adsorptionmechanisms of uranium by loading pseudomonas aeruginosa onto nano-Fe₃O₄were studiedby using SEM-EDS、FT-IR、XRD. The results show that uranium adsorption by loadingpseudomonas aeruginosa onto nano-Fe₃O₄has high efficiency at pH6.0, the adsorbentdosage of0.07g and30℃, adsorption rate was91.99%.The interference effect ofco-existed cations and anion on uranium adsorption respectively follows the order：Fe³⁺＞Al³⁺＞Cu²⁺＞Ca²⁺＞K⁺＞Na⁺, CO₃^2-＞HCO₃-＞SO₄^2-.The addition of1mol/L NaHCO₃has the best desorption efficiency on the composite material which is not separated fromeach other for its good stability. The surface morphology of the adsorbent changes greatlywith a decrease of gaps and grooves apparently and agglomerate phenomena. Theadsorption mainly complies with the mechanism of surface complexation between uraniumand groups such as-COOH、-OH、-NH2、PO₄3-, results in forming complexes in the process.The crystal structure turns to be incomplete after adsorption by NFPA, while generatingvery few crystalline substances.The dynamics, thermodynamics, particle diffusion types, activation energy andrate-controlling steps have been studied. The results indicated that the adsorption ofuranium by loading Pseudomonas aeruginosa onto nano-Fe₃O₄depended significantly onall the above-mentioned parameters. Kinetic study showed that the adsorption kineticsclosely followed the pseudo-second-order model （R2＞0.9995）; Fitting diffusion modelwell confirmed that liquid film diffusion and intra-particle diffusion was the controllingstep of adsorption; Bangham model yielded a somewhat good fit（R2＞0.9455）, showing that the intra-particle diffusion was not the only rate-controlling step, the influence ofliquid phase boundary layer and particle external mass transfer processes on adsorptioncouldn’t be ignored either. The apparent activation energy of reaction is15.705kJ/mol.Four theoretical adsorption isotherms, namely, Langmuir、Freundlich、Temkin and D-Rwere used to describe the experimental datas. The results showed that the adsorptionbehaviours of uranium onto nano-Fe₃O₄well fitted with the Langmuir and Freundlichisotherm models, which indicates that monolayer cover and multilayer adsorption wereboth involved in the adsorption process. The Langmuir adsorption capacity were found tobe92.483mg/g,103.875mg/g and107.918mg/g at298k、303k and308k respectively, inaddition, the adsorption capacity increased with the increase in temperature. The Langmuirand Freundlich coefficients, RLand1/n both having values in the range of0-1indicatedthat loading Pseudomonas aeruginosa onto nano-Fe₃O₄was an attractive compositematerials for removing uranium.Thermodynamic parameters such as ΔH^Θ, ΔS^Θand ΔG^Θfor the adsorption were evaluated. The positive values of ΔH^Θand ΔS^Θ, negative values ofΔG^Θindicated that adsorption was spontaneous and endothermic, the process existed allkinds of chemical bond force and van der waals force. And the adsorption mechanism wasmixed adsorption, including the physisorption and chemisorption.