| Nuclear energy has been the hot issue of common concern in the energy field all over the world.With the development and utilization of nuclear energy,such as mining,nuclear reactors and nuclear weapons manufacturing,various radionuclides are released into the environment.Uranium,a major pollutant in radioactive wastewater has chemical toxicity and radiotoxicity,and can pose great risks to human health and ecological environment.Therefore,it is of great significance to study the materials and methods for extracting uranium in radioactive waste water with high efficiency for the recycling of uranium and the protection of the ecological environment.Through the magnetic nanoparticles modified by surface functionalization,the efficient composite adsorbents with the more selectivity and easy magnetic-separation can be obtained.At the same time,it will also make the adsorbent having the characteristics of easy magnetic separation.Therefore,magnetic nano-sorbents have a good application prospect for the extraction of uranium in radioactive wastewater.Calixarene is a new generation of supramolecular ligand after crown ether and cyclodextrin.It is composed of several phenol units connected through ortho methylene(or hetero atoms such as oxygen,sulfur,nitrogen,etc.)at the ortho position of phenolic hydroxyl group.The resulting cyclic oligomers have a size-adjustable cavity and are highly selective to metal ions,and can form host-guest complexes with many metal ions through a plurality of coordination atoms.As an efficient and economical biosorbent,aspergillus niger is characterized by safety,non-toxicity,low cost,stable source,large treated amount of wastewater,and easy resolution after adsorption,whose surface is rich in functional groups such as hydroxyl,carboxyl,and amino groups.In this paper,a novel functionalized magnetic biosorbent was prepared by using calixarenes and aspergillus niger as functional materials.And,it was studied that the adsorption properties of the functionalized magnetic biosorbent for radioactive uranium wastewater.Through a series of tests,the following research results were mainly obtained:(1)4-sulfonylcalix[6] arene modified Fe3O4 magnetic nanoparticles(MFS)were synthesized by co-precipitation method.Its structure was characterized by infrared(IR),scanning electron microscopy(SEM),vibrating sample magnetometer(VSM)and thermal comprehensive analyzer(TGA).The experimental results showed that MFS was spherical with the diameter of 10 ~ 40 nm and the saturation magnetization 64.99 emu/g and had good superparamagnetism and good thermal stability.The adsorption behavior of U(?)solution by MFS under conditions of solution p H,adsorbent dosage,adsorption time,initial U(?)concentration and temperature was explored,and the optimal adsorption conditions for MFS on U(?)solution were determined: p H 6,initial uranium concentration 2.5 mg/L,adsorption time 60 min,adsorbent dosage 15 mg/100 m L and temperature 50 ?.The maximum adsorption efficiency of MFS for U(?)was 94.39 %,which was significantly improved compared with the maximum adsorption rate of Fe3O4(65.22 %).Interference experiments showed that the magnetic nanoparticles Fe3O4 surface modified calixarene functional molecules,its multiple coordination and cavity recognition dual effects,so that MFS on uranyl ions have a better selective adsorption capacity.In the presence of metal ions such as Na+,Mg2+,Ca2+,the maximum adsorption of U(?)by MFS can still reach 93.62 %.The adsorption kinetics of MFS for U(?)accorded with the second-order kinetic model,indicating that the adsorption was a chemical reaction.The adsorption behavior accorded with Langmuir isothermal adsorption model,indicating that the adsorption reaction was monolayer adsorption.By analyzing the Gibbs free energy change of MFS for U(?)adsorption behavior,it was see that the adsorption was a spontaneous endothermic reaction.(2)On the basis of MFS,a new type of multi-coordination magnetic biosorbent(MFSC)was prepared in combination with biomaterial aspergillus niger,aiming to improve the mechanical properties and identification for uranyl ions of biosorbent through the combination of magnetic nanoparticles,functional recognition molecules and biosorbents.The resulting MFSC was characterized by IR,SEM,VSM and TGA,indicating that the MFSC with the saturation magnetization of 5.74 emu/g was folding and stratiform and had good superparamagnetic and thermal stability.The adsorption behavior of U(?)solution by MFSC under conditions of solution p H,adsorbent dosage,adsorption time,initial U(?)concentration and temperature were explored,and the optimum adsorption conditions for U(?)solution by MFSC were determined.At p H 6,initial uranium concentration 3 mg/L,adsorption time 8 h,adsorbent dosage 20 mg/100 m L and temperature 30 ?,the maximum adsorption efficiency of MFSC for U(?)was 91.18 %.Interference experiments showed that compared with MFS,the anti-interference ability of MFSC was decreased,which indicated that the adsorption capacity of the calixarene molecules was reduced when MFS was carried on the surface of aspergillus niger,but MFSC still had some selective adsorption performance.In the presence of metal ions such as K+,Na+,Cu2+,the maximum adsorption rate can reach 72.41 %.Adsorption-desorption experiments showed that the adsorption rate could still reach over 80 % after repeated adsorption-desorption of MFSC for 3 times,indicating that the MFS was carried on the surface of aspergillus niger,which overcomes the loss of biosorbent during adsorption-desorption.It made aspergillus niger obtain good mechanical properties,and it was easy to separate solids and liquids after adsorption.Therefore,when MFSC adsorbs U(?),it can be recycled.The adsorption behavior of MFSC for U(?)was in line with the second-order kinetic model,indicating that the adsorption was a chemical reaction;the adsorption behavior in line with Langmuir isothermal adsorption model showed the adsorption was monolayer.By analyzing the Gibbs free energy change of MFSC for U(?)adsorption behavior,it was suggested that the adsorption was a spontaneous endothermic reaction. |
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