Removal Of Uranyl By Bacillus Cereus And Sodium Alginate-Polyethylene Coated Smectite Clay Minerals

As a new energy source,uranium has been exploited in large quantities.However,due to the immaturity of uranium technology in mining and processing,uranium energy flows into water resources along with groundwater and rivers.Finally,it affects the ecological environment and threatens the human health through the transmission of the food chain.At present,polymer materials are expected to be industrial materials for uranyl adsorption removal,and the microplastics contained in the soil have a potential impact on the cycle of the biosphere.Therefore,the factor of microplastics should be paid attention to in the treatment of uranium pollution under natural conditions,which will lay a solid foundation for solving the practical problem of uranium pollution.In this paper,Bacillus ceraceus（Bc）,polyethylene（PE）,sodium alginate（SA）and smectite clay minerals（Beidellite-Bd,montmorillite-Mt nontronite-Nt）were used as raw materials.Three different blocking systems in natural soil were simulated by cross-linking method（Bc-SA-PE@Bd,Bc-SA-PE@Mt,Bc-SA-PE@Nt）.The removal effect of UO₂²⁺under three blocking systems was studied by single factor experiment,and the influences of acid-base environment,PE mass,PE molecular weight,UO₂²⁺concentration and contact time were discussed.Finally,the adsorption effects of metal ions(Xⁿ⁺=Cd²⁺,Cr³⁺,Cu²⁺,Mn²⁺,Ni²⁺and Pb²⁺)on UO₂²⁺were also discussed.The adsorption process of UO₂²⁺and Xⁿ⁺was studied after fitting the experimental data with the kinetic model（pseudo-first-order and second-order kinetic）and isothermal adsorption model（Langmuir,Freundlich and Dubinin-Radushkevich models）,and the adsorption mechanism of UO₂²⁺was explored in the blocking system.The adsorption experiments and performance analysis of UO₂²⁺were carried out in three different blocking system,and it was found that the optimal mass ratio of SA,mineral,Bc and PE was 1:1:25:0.5.The optimal conditions for the adsorption of metal ions are as follows:the ratio of solid to liquid is 1:100,the p H value of solution is 5,the initial concentration of UO₂²⁺is 50 mg·g^-1,the oscillation time is 12 h,and the molecular weight of PE is 5000.In the kinetic study,it was found that the adsorption under the three blocking system matched the pseudo-second-order kinetic model respectively（the fit degree reached 0.99）,indicating that the adsorption was mainly chemisorption.The maximum adsorption capacities were 66.98,91.74 and 81.77mg·g^-1,respectively.In the isothermal adsorption study,two or three models of Langmuir,Freundlich and Dubinin-Radushkevich model were matched respectively,and the fitting degree reached 0.99.It shows that the adsorption behavior is the coexistence of single layer,multilayer and interlayer adsorption.The maximum adsorption capacities were 64.09,87.31 and 143.96 mg·g^-1,respectively.In the competitive adsorption experiment,it is found that a large number of functional groups in the blocking system have good affinity for UO₂²⁺,Cr³⁺,Mn²⁺and Pb²⁺.These functional groups react with metal ions to show selectivity,and the maximum adsorption capacities were 126.87,19.33,36.75 and 97.43 mg·g^-1,respectively.Through the study of the characterization of blocking system and the change value of metal ions,the following conclusions are drawn:SEM showed the presence of columnar or reticular structures in the blocking system;XRD show that the obvious change of mineral structure,especially the collapse of（001）crystal plane,is one of the reasons for the change of structure.FTIR and Raman revealed the bonding condition of the blocking system surface,and found that the blocking system contained more functional groups than the surface of the raw material.Amino,carboxyl and hydroxyl groups reacted with metal ions in the adsorption.By comparing the electrochemical cyclic voltammetry curves of UO₂²⁺and Xⁿ⁺,it is found that there is a REDOX reaction between UO₂²⁺and UO₂²⁺-Cr³⁺,indicating that U has a valence change phenomenon.The co-redox phenomenon of UO₂²⁺and Cr³⁺was found in UO₂²⁺-Cr³⁺solution system,so the REDOX reaction was weakened in this process.Three-dimensional fluorescence spectra showed that UO₂²⁺,Xⁿ⁺had complex reactions with groups（amino,carboxyl,hydroxyl,amide,etc.）on the blocking system surface to achieve the purpose of removing metal ions.Compared with AO-UHMWPE(1.97 mg·g^-1)synthesized by radiation grafting,it was found that the adsorption effect of the three blocking systems was superior,and showed better selectivity to UO₂²⁺.EDS showed that the blocking system could block the migration of metal ions,and the blocking system successfully recombined,and the metal ions were uniformly adsorbed on the blocking system.Therefore,the addition of SA in a specific environment（containing PE）can effectively enhance the adsorption of minerals to UO₂²⁺,which will provide a new theoretical idea for the retardation and mineralization of uranyl in plastic-containing soil.