Sulphate quantification using Raman spectroscopy in borosilicate glass matrix

Transcription

1 Sulphate quantification using Raman spectroscopy in borosilicate glass matrix Agnès GRANDJEAN 1, Marion LENOIR 1,2, Sylvie POISSONNET 3, Daniel R. NEUVILLE 2 1 CEA Nuclear Energy Division/ Waste Treatment and Conditioning Department, Marcoule (France) 2 Physique des Minéraux et des Magmas, UMR 7047 CNRS, Institut de Physique du Globe de Paris 3 CEA Nuclear Energy Division / DMN/SRMP, Saclay Silicate Melts Worshop La petite Pierre October

2 Sulphur in oxide glasses Commercially produced soda-lime-silica glasses Sulphur deliberately added (low level) : - as sulphate : refining agent - as sulphide : amber colour Silicate melts of geological : may contain substantial quantities of sulphur. Sulphur species : present in radioactive and toxic wastes. -> immobilization through vitrification In case of radiaoactive wastes : Sulphur solubility can be the «limiting factor» for the glass waste loading. Silicate Melts Worshop La petite Pierre October

3 Investigated Glasses Compound SiO 2 B 2 O 3 Na 2 O Analysed glasses Glass sample SBN SBN Nomi nal (mol %) EDS- XRF * (mol %) 56 ± ± 0.5 Nomi nal (mol %) EDS- XRF * (mol %) 25 ± ± 0.5 Nomi nal (mol %) EDS- XRF * (mol %) 19 ± ± 1 Relative Intensity S 6+ K-edge range SBN wt.% SO 3 ANaP 0.9 wt.% SO 3 SBN25Cs5 0.7 wt.% SO 3 SBN25Cs5V7 0.8 wt.% SO 3 Added around 6% mol Na 2 SO sulphur speciation S (+VI) sulphate S(+IV) sulphite S(0) S(-II) sulphide Energy / kev SO SO 2 3 ( gas), SO, S O ( gas), SO 2! 4 2 2! 7 2! 3 Silicate Melts Worshop La petite Pierre October

4 Raman spectroscopy Non destructive and very flexible technique. In situ measurement T64000 Jobin-Yvon Source = nm line of a coherent 70 Ar+ laser, Power = 1 W at the sample surface. Spectral resolution = ± 1 cm -1 Spatial resolution = around 1µm 3 IPGP High temperature cell = using a micro heater. A single PtRh alloy wire, heated by Joule effect. Small hole. B.O. Mysen and J.D. Frantz, Chem. Geol. 96 (1992) 321. Silicate Melts Worshop La petite Pierre October

5 Raman spectra : effect of sulphate Intensity (a.u) ν1 S-O stretching sulfate (Na 2+ SO 2-4 ) SBN cm -1 SBN Na 2 SO 4 ν1 S-O stretching sulphate (Na 2+ SO 4 2- ) 990 cm Na 2 SO Raman shift (cm -1 ) Si-O stretching ( cm -1 ) B-O stretching ( cm -1 ) Interesting region studied = cm -1 Silicate Melts Worshop La petite Pierre October

6 Reconvolution of Raman spectra Correction for temperature and frequency dependent scattering intensity I & ' hc = kt $. + 0 e ( I 4! obs. $ (. 0 '. )! % - ' Linear baseline. Frequency region = cm -1, * ) # " ν 0 = nm. 300 Q 3 Si-O - stretching Intensity (a. u.) Q 2 Q to 980 cm -1 : Q to 1100 cm -1 : Q to 1190 cm -1 : Q to 1050 cm -1 : Si-O 0 bridging oxygen stretching mode Raman shift (cm -1 ) Silicate Melts Worshop La petite Pierre October

7 Reconvolution of Raman spectra 1500 Stretching sulphate band (around 990 cm -1 ) 1200 Q 3 Intensity (a.u.) Q 2 Q 4 [ ] (!1 area 990cm ) " SO3 glass area! ( entire region) Raman shift (cm -1 ) Relative SO 3 content obtained from Raman spectra Silicate Melts Worshop La petite Pierre October

8 Reconvolution of Raman spectra various content of sulphate Intensity (u.a.) Raman shift (cm -1 ) Comparison with microprobe analysis (calibration curve) % SO3 (weight) SBN47-30 SBN20 % SO3 = ( ) * area (%) % SO3 = ( )*area (%) Thanks to S. Poissonnet (CEA Saclay, SRMP) for microprobe analysis Area Raman (relative %) Silicate Melts Worshop La petite Pierre October

9 Application Raman spectroscopy in the frequency region cm -1 allows the quantification of relative sulphate content in a simple borosilicate glass using 5 to 6 gaussian bands for the reconvolution -> in situ measurement in high temperature easy Example : decomposition of sulphate from a borosilicate melt at high temperature C 800 C 1200 C [SO3 (t)] / [SO3 (init)] time (min) Silicate Melts Worshop La petite Pierre October

10 Kinetics of sulphate decomposition At high temperature : diffusion of gaseous SO 3 species :fast reaction t $ exp' % ( SO 2-4 (melt) SO 3 (g) + O 2- (melt) & # ( )! " C( t) = Ceq + C0 ' C eq [SO3 ]equivalent (weight %) SBN C Time (min) Silicate Melts Worshop La petite Pierre October

11 At low temperature : SBN C [SO3 ]equivalent (weight %) Time (min) [SO3 ]equivalent (weight %) SBN C Time (min) Silicate Melts Worshop La petite Pierre October

12 Kinetics of sulphate decomposition At lower temperature : viscous flow diffusion of gaseous SO 3 species limiting reaction. «Re»formation of [SO 4 2- ] from gaseous SO 3 species already present in the glass sample. Competition between formation and decomposition of ionic sulphate species. C( t) & ( ), t ), t )# C - C exp* - ' - * - '! " =. 2 C0 + 0 eq $ * ' exp* % +. 1 ( + ' ( Decomposition time characteristic Formation time characteristic Silicate Melts Worshop La petite Pierre October

13 Kinetics of sulphate decomposition 1000 C [SO3 ]equivalent (weight %) SBN C C Time (min) [SO3 ]equivalent (weight %) C 0 = 0.45 C eq = 0.18 τ(decomposition) =546 min τ(formation) = 208 min SBN C C 0 = C eq = 0.82 τ(decomposition) =2825 min τ(formation) = 26 min Time (min) Silicate Melts Worshop La petite Pierre October

14 Conclusion 1. Raman spectroscopy in the frequency region cm -1 allows the quantification of relative sulphate content in a simple borosilicate glass using 5 to 6 gaussian bands for the reconvolution 2. in situ measurement of time dependence of sulphate content at high temperature (in the molten state). 3. At 800 C and 1000 C : decomposition of sulphate present into the melt : very low compared to kinetics at 1000 C. 4. Fit of the kinetics data : sulphate variation at least at 800 C implies a competition between departure and formation of ionic sulphate content inside the melt. Silicate Melts Worshop La petite Pierre October