Raman Study of Aluminum Speciation in Simulated Alkaline Nuclear Waste
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- 作者：Cliff T. Johnston ; Stephen F. Agnew ; Jon R. Schoonover ; John W. Kenney ; III ; Bobbi Page ; Jill Osborn ; and Rob Corbin
- 刊名：Environmental Science & Technology
- 出版年：2002
- 出版时间：June 1, 2002
- 年：2002
- 卷：36
- 期：11
- 页码：2451 - 2458
- 全文大小：110K
- 年卷期：v.36,no.11(June 1, 2002)
- ISSN：1520-5851
文摘
The chemistry of concentrated sodium aluminate solutionsstored in many of the large, underground storage tankscontaining high-level waste (HLW) at the Hanford andSavannah River Nuclear Reservations is an area of recentresearch interest. Not only is the presence of aluminatein solution important for continued safe storage of thesewastes, the nature of both solid and solution aluminumoxyhydroxides is important for waste pretreatment. Moreover,for many tanks that have leaked high aluminum waste inthe past, little is known about the speciation of Al in the soil.In this study, Raman spectroscopy has been used toinvestigate the speciation of the aqueous species in the Al2O3-Na2O-H2O system over a wide range of solutioncompositions and hydration. A ternary phase diagram hasbeen used to correlate the observed changes in thespectra with the composition of the solution and withdimerization of aluminate that occurs at elevated aluminateconcentrations (>1.5 M). Dimerization is evidenced bygrowth of new Al-O stretching bands at 535 and 695 cm-1at the expense of the aluminate monomer band at 620cm-1. The spectrum of water was strongly influenced bythe high concentrations of Na+ and OH- (>17 M). Uponincreasing the concentration of NaOH in solution, the 
(H-O-H) bending band of water (
2 mode) increased infrequency to 1663 cm-1, indicating that the water containedin the concentrated caustic solution was more stronglyhydrogen bonded at the higher base content. In addition,the sharp, well-resolved band at 3610 cm-1, assigned to the(O-H) of free OH-, increased in intensity with increasingNaOH. Analysis of the (O-H) bands in the 3800-2600cm-1 region supported the overall increase in hydrogenbonding as evidenced by the increase in relative intensityof a strongly hydrated water band at 3118 cm-1. Takinginto consideration the activity of water, the molarconcentrations of the monomeric and dimeric aluminatespecies were estimated using the relative intensities of theAl-O stretching bands from the Raman spectra. Aconstant apparent log Kdimer value was obtained at aluminateconcentrations >1.5 M with a value of 0.97 ± 0.04 at~25 
C. This study represents the first spectral-basedestimation of a thermodynamic equilibrium constant for theAl2O3-Na2O-H2O system.
(H-O-H) bending band of water (2 mode) increased infrequency to 1663 cm-1, indicating that the water containedin the concentrated caustic solution was more stronglyhydrogen bonded at the higher base content. In addition,the sharp, well-resolved band at 3610 cm-1, assigned to the(O-H) of free OH-, increased in intensity with increasingNaOH. Analysis of the (O-H) bands in the 3800-2600cm-1 region supported the overall increase in hydrogenbonding as evidenced by the increase in relative intensityof a strongly hydrated water band at 3118 cm-1. Takinginto consideration the activity of water, the molarconcentrations of the monomeric and dimeric aluminatespecies were estimated using the relative intensities of theAl-O stretching bands from the Raman spectra. Aconstant apparent log Kdimer value was obtained at aluminateconcentrations >1.5 M with a value of 0.97 ± 0.04 at~25 C. This study represents the first spectral-basedestimation of a thermodynamic equilibrium constant for theAl2O3-Na2O-H2O system.