Adsorption Of U(Ⅵ) In Aqueous Solution By Functionalized Carbon Aerogel

It is of important scientific and realistic significance to achieve efficient separation and enrichment of uranium from wastewater and seawater. The carbon aerogel is a new nano-materials, and it has a high specific surface area, porosity, conductivity and thermal conduction and excellent mechanical performance. Thus it is a promising materials to be the adsorbent of uranium. In this paper, based on the as-prepared carbon aerogel(CA), the phosphorylated CA(CA-PO4) and sulfonated CA(CA-SO3H) was prepared. The SEM, Raman spectra and FT-IR have been used to observe the structure and functional groups on the surface of the adsorbents. The adsorption of U(VI) from aqueous solution was systematically investigated by both static adsorption and dynamic column adsorption.The CA was prepared by the self-assembly of graphene and carbon nanotubes using the sol-cryo method. The CA showed poriferous and lax structure. The adsorption of U(VI) by CA were fitted well with pseudo-second-order kinetics model and Langmuir isotherms, the maximum monolayer adsorption capacity can reach 98.0 mg·g-1. The adsorption process was feasible, spontaneous and endothermic. The U(VI) adsorbed on CA can be desorbed by 1.0 mol·L-1 HCl solution, the rate of elution up to 96%.The CA-PO4 was prepared by the reaction of CA with concentrated phosphoric acid. The structure of CA remained poriferous and porosity, and the content of oxygen-containing groups increasing from 0.54 mmol·g-1 to 1.41 mmol·g-1. Adsorption of U(VI) onto CA-PO4 can be well described with pseudo-second-order kinetics model and Langmuir isotherms, the maximum monolayer adsorption capacity can reach 152.0 mg·g-1. The adsorption process was spontaneous and endothermic. The U(VI) adsorbed on CA-PO4 can be desorbed by 1.0 mol·L-1 HCl solution, the rate of elution up to 98.5%.The CA-SO3 H was prepared by the vapor-solid transfer reaction by oleum(50% SO3/H2SO4). The structure of CA was not destroyed after sulfonation, and the content of sulfonic groups on the surface of CA-SO3 H is about 2.02 mmol·g-1. The adsorption of U(VI) over CA-SO3 H can be well defined by pseudo-second-order kinetics model and Langmuir isotherms, suggesting that the adsorption was mainly dominated by chemical force, and adsorption capacity is 141.0 mg·g-1. The adsorption process was endothermic and spontaneous. The U(VI) adsorbed on CA-SO3 H can be eluated by 1.0 mol·L-1 H2SO4 solution, the rate of elution up to 95.4%.Continuous fixed-bed column studies showed that the exhaustion point decreased with the increase of flow rate and decrease of bed depth. Thomas model indicate that the kTh increased with the increase of flow rate and decrease of bed depth, while the q0 is decrease. This simplified-design model ignores both the intraparticle mass transfer resistance and the external resistance directly. Yoon-Nelson model indicate that the required for 50% absorbate breakthrough τ decreased with the increase of flow rate and decrease of bed depth.