Exchanges of Uranium(VI) Species in Amidoxime-Functionalized Sorbents

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• 作者：Sadananda Das ; Ashok K. Pandey ; Anjali A. Athawale ; Vijay K. Manchanda
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：May 7, 2009
• 年：2009
• 卷：113
• 期：18
• 页码：6328-6335
• 全文大小：247K
• 年卷期：v.113,no.18(May 7, 2009)
• ISSN：1520-5207

文摘

Amidoxime (AO)-functionalized polymer sorbents used in this study were prepared by two different routes involving UV grafting and electron-beam grafting of acrylonitrile (AN) into poly(propylene) fibrous and microporous sheets, and subsequent conversion of AN to AO groups by reacting the precursor sorbent with hydroxylamine. The values of self-diffusion coefficient (D_s) of UO₂²⁺ in fibrous and sheet AO sorbents were found to be 1.1 × 10⁻⁶ and 2.3 × 10⁻¹⁰ cm² s⁻¹, respectively. The higher diffusion mobility of UO₂²⁺ in the fibrous AO sorbent was attributed to its higher free volume as observed in scanning electron microscopic studies. The water content was also found to be maximum in AO-fibrous sorbent (165−200 wt %) and minimum in AO-sheet sorbent (70 wt %). In fibrous AO sorbent, the values of D_s for Na⁺ and Sr²⁺ were found to be comparable to their self-diffusion coefficients in the aqueous medium. This indicated that the retardation in diffusion mobility of the ions was a minimum in the fibrous AO sorbent. However, D_s of UO₂²⁺ in the fibrous membrane was found to be significantly lower than that of Sr²⁺, which has a self-diffusion coefficient comparable to that of UO₂²⁺ in aqueous medium. This could be attributed to stronger binding of UO₂²⁺ with AO groups as compared to Sr²⁺. To understand the parameters affecting the U(VI) sorption from seawater, the U(VI) exchange rates between fibrous AO sorbent (S) and seawater (aq) involving (H⁺/Na⁺)_S ([UO₂(CO₃)₃]⁴⁻)_aq and (UO₂²⁺)_S ([UO₂(CO₃)₃]⁴⁻)_aq systems were experimentally measured. The exchange profiles thus obtained were found to be non-Fickian and much slower than (H⁺)_S (UO₂²⁺)_aq and (UO₂²⁺)_S (UO₂²⁺)_aq exchanges. This seems to suggest that the reaction kinetics involved in decomplexation of [UO₂(CO₃)₃]⁴⁻ into UO₂²⁺, which forms a complex with AO groups, is the rate-determining step in sorption of U(VI) from seawater. The kinetics of U(VI) sorption in AO-gel and AO-fibrous sorbents followed the pseudo-second-order rate equation. The density of AO groups in the sorbents and their conditioning were found to influence the U(VI) sorption from seawater.