Removal Performance and Mechanism of New Ternary Composites for Low Concentration Uranium Containing Wastewater
Due to its high toxicity and radioactivity,uraniumis a typical radioactive pollutant.The main sources of uranium contami-nation in the environment include nuclear power plants,coal-burning power plants,ore mills,and fertilizer use,among other things.Uranium must be quickly removed from the environment,especially from aqueous solutions,for the protection of the general people and the ecosystem.Many methods have been proposed and investigated to remove U(Ⅵ)ions from solutions,including ion-exchange procedures,biological therapy,solvent extraction,surface complexation,and adsorption.Notably,adsorption technology is widely employed in environmental management because it is simple to use,consumes little energy,is highly effective,and is ecologically beneficial.Traditional adsorbents,on the other hand,frequently struggle with limited capacity and/or high cost when it comes to trac-ing U(Ⅵ)in aqueous solution.Therefore,one of the greatest scientific difficulties in environmental science is the design of an effec-tive adsorbent with excellent adsorption capability.Bentonite(B),a cheap and easily accessible buffer material for the geological dis-posal of high-level radioactive waste,exhibits good radionuclide adsorption capacity.Bent's anions extraction is unsuccessful despite having a high cation-exchange capacity because of its negatively charged surface,which restricts its use in the adsorption of U(Ⅵ)an-ionic species.As a result,the alteration of clay minerals by cationic surfactants has been suggested.One quaternary ammonium salt with strong surface activity and acid-base stability is cetyltrimethylammonium bromide(CTAB).The surface charges are changed from negative to positive and the surface characteristics from hydrophilic to hydrophobic by the intercalation of CTAB into the Bent's inter-layer gap.In order to further increase U(Ⅵ)adsorption capacity,(Ca10(PO4)6(OH)2(HAP)was used as the second loaded particle in CTAB-bent.HAP was used to remove heavy metals from aqueous solutions including Cd2+,Zn2+,Pb2+,Co2+,UO22+,and others be-cause of its outstanding characteristics.In general,the creation of surfactant-modified composites might be broken down into two steps:the first involved preparing the materials for the composites,and the second involved utilizing surfactants to activate the surface of the composites.Cetyltrimethylammonium bromide modified hydroxyapatite-bentonite composites(CTAB-HAP-B)were initially cre-ated using a one-step hydrothermal process to take into account cost and operation optimization.The removal rate of low concentration uranium-containing wastewater could achieve nearly 99％with pH of 4.0,uranium(Ⅵ)concentration of 10 mg·L-1,time of 160 min,temperature of room temperature(298.15 K),dose of CTAB-HAP-B of 0.05 g,rotating speed of 165 r·min-1,and volume of wastewa-ter of 50 ml.Scanning electron microscope(SEM),energy dispersive spectrometer(EDS),X-ray diffraction(XRD),Brunauer-Em-mett-Teller(BET),Barret-Joyner-Halenda(BJH),X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectros-copy(FTIR)were used to characterize the morphology,specific surface area,pore diameter,element composition,crystal form,and surface functional groups of CTAB-HAP-B.Ion exchange and the coordination of functional groups constituted the majority of the ad-sorption mechanism.The maximal adsorption capacity of CTAB-HAP-B within the parameters of the tests was 220.03 mg·g1,and it had a high removal rate of uranium(Ⅵ)throughout a wide pH range.Under the influence of strong alkali,it still retained some adsorp-tion capacity that was anticipated to be exploited for uranium extraction from weakly alkaline saltwater.According to the Langmuir iso-therm and Pseudo-Second Order Kinetic(SODM)adsorption kinetic model,the adsorption process of uranium(Ⅵ)by CTAB-HAP-B was characterized by single-layer chemical adsorption.Uranium(Ⅵ)was spontaneously adsorbed by CTAB-HAP-B in an endother-mic,entropy-increasing process.This study suggested that the development of environmental adsorption materials should make use of the synergy between various materials to get around the limitations of single adsorption materials in order to improve the removal perfor-mance of bentonite-based adsorption materials for low concentration uranium containing wastewater.The development of promising en-vironmental functional adsorption materials was encouraged by this concept.
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