Investigation On The Sorption Of Radionuclides And Heavy Metals By Titanate Compsites

With the fast growing of the nuclear industry and industrialization,the removal and recovery of the hazardous radionuclides and heavy metals from wastewater has been paid an increasing attention in environmental researches.The hazardous radionuclides and heavy metals can do seriously harm to living beings.Therefore,it is crucial to eliminate of hazardous radionuclides and heavy metals from the wastewater before it enters into the environment.The sorption is regarded as an efficient way to remove radionuclides and heavy metals due to its most economically favorable,simple operation and high efficiency.The choice of adsorbent should meet some criteria such as having large surface area,mechanical stability,possibility of recycling and biodegradability.Due to the selective ion-exchange processes for target cations and high-performance adsorption due to their large surface area and the layered structure arranged by unique Ti06 octahedral.Titanate has attracted great attention due to its extraordinarily application potential in the disposal of wastewater to remove the metal ions.However,titanates also have certain drawbacks including aggregation which may limit their adsorption capacity.To solve these problems,dispersing titanate onto a support material is an attractive strategy.The finely dispersed titanate on the supporting material may help to increase the effective surface area and enhance the number of available active sites and thus improve the adsorption ability.Carbon materials have recently been utilized as supporting material in many cases.In this paper,various carbon materil supported sodium titanate(C/Na2Ti3O7)was synthesized via a facile hydrothermal method,which was applied to remove several metal ions from aqueous solution.The C/Na2Ti3O7 composites are characterized using SEM,TEM,FT-IR,XRD,BET and XPS.And batch techniques were utilized to investigate the various effects such as pH,ionic strength,contact time,temperature on the adsorption of metal ions on the C/Na2Ti3O7 composites.Meanwhile,based on the analysis of spectroscopic techniques,the adsorption mechanism of metal ions on the C/Na2Ti3O7 composites is also explored.The main research findings are listed as follows:(1)The GO are used as the carbon support materials and the GO/Na2Ti3O7 was synthesized via a facile hydrothermal method.GO/Na2Ti3O7 was applied to remove Co(II)from aqueous solution and the maximum sorption capacity of GO/Na2Ti3O7 was calculated to be 590.7 mg/g for Co(II)at pH = 5.5 and T=318 K,which is much higher than Na2Ti3O7(114.1 mg/g).The sorption is attributed to the outer sphere surface complexation at pH<7.0 and inner sphere surface complexation at pH>7.0.The kinetics data can be better simulated by pseudo-second-order model and steady state of the sorption is reached within 8 h.The sorption of Co(?)decreases by approximately 16%from 157.0 to 132.2 mg/g after seven sorption/desorption cycles indicating the excellent chemical stability and reusability.XRD analysis suggest that the Na2Ti3O7 contributes to the Co(?)sorption on GO-Na2Ti3O7 by the ion exchange process.FT-IR and XPS technologies analyses indicate that the-OH groups are responsible to the high effective sorption of Co(?)on GO-Na2Ti3O7.(2)The carbon aerogel(CA)are used as the carbon support materials and the CA/Na2Ti307 was synthesized via a facile hydrothermal method.Compared to the Na2Ti3O7,CA/Na2Ti3O7 exhibited higher adsorption capacities for Rb+(70.5 mg/g),Cd(?)(133.4 mg/g),Eu(?)(224.1 mg/g)and U(VI)(264.5 mg/g)at T = 298 K and pH 5.5,indicating the combination with CA has synergistically improved the adsorption ability of Na2Ti3O7.FT-IR and XPS analyses suggested that the adsorption process was mainly ascribed to the ion exchange process between Na+ and target metals cations within the interlayer space.Meanwhile,the interaction of metals with-OH groups on CA/Na2Ti3O7 surfaces is also responsible for the adsorption processes.One can conclude the adsorption process on CA/Na2Ti3O7 was mainly dominated by ion exchange or outer-sphere surface complexation(low pH values),and by innersphere surface complexation(high pH values).The pseudo-second-order model could simulate the kinetic data well and reached the equilibrium within 2 h.And CA/Na2Ti3O7 displayed good recyclability and recoverability.