Accumulation Mechanism Of U(?) On Bacteria Or Al-goethite In Soils

The migration and ecotoxicity of uranium in environment were closely related to its chemical speciation under different soil or aquatic conditions and its interaction with environmental media.Therefore,this study choosed Pantoea sp.TW18 and S.epidermidis separated from radionuclide-contaminated soils and synthetic Al-goethite.Based on the combination of batch experiments and modern instrumental analysis techniques,the adsorption behavior and mechanism of U???on the single system?bacteria,minerals?and coexistence system of bacteria-mineral were investigated under the different environment,which is critical to both for understanding the biogeochemical cycles of uranium and the remediation of uranium pollution.The main research findings were listed as follows:1)The results of Zeta potential showed that the surface charge of the bacterial cells was negative at pH>2.5,which was beneficial to the binding of U???cations.In addition,Al-goethite and bacterial cells at pH 2.5-8.0 were easily combined with each other by electrostatic attraction.The results of SEM/TEM characterization indicated that there was a large amount of secretion?such as EPS?on the surface of Pantoea sp.TW18cells compared with S.epidermidis,and the cell wall was the main site of U???adsorption.2)The adsorption rate of U???on the bacterial cells was much higher than that of Al-goethite.In 10 min,the adsorption capacity of U???on S.epidermidis was 92%of the maximum adsorption capacity,and then the adsorption saturation was reached within 60 min.The maximum adsorption capacities of U???on S.epidermidis and Al-goethite at pH=4.0 and T=300K were calculated from Langmuir equation to be 121.18 and 11.34 mg?g^-1,respectively.3)The concentration of carbonate and pH in the environment affected chemical speciation of U???on bacteria or minerals,and the U???adsorption decreased with the increase of carbonate concentration.In the Al-goethite+S.epidermidis system,Al-goethite promoted U???adsorption on S.epidermidis at pH<9.0,while inhibiting the adsorption of U???on S.epidermidis at pH>9.0.In addition,the adsorption of U???by the bacterial cells was hardly affected by ionic strength.4)Based on the results of FTIR and XPS analysis,abundant functional groups on the bacterial cells could bind with U???,which improved the U???adsorption.In addition,Pantoea sp.TW18 had no the property of reducing U???,while S.epidermidis could reduce U???to U?IV?.However,Al-goethite inhibited reduction of U???on S.epidermidis when S.epidermidis and Al-goethite coexisted,and the inhibition was especially noticeable at high pH.This inhibition may result from the bonding between functional groups of S.epidermidis?e.g.,carboxyl and phosphoryl?and structural Fe???of Al-goethite,thereby occupying the active site of S.epidermidis reducing U???.