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Development of New Column Extraction Methods

Development of New Column Extraction Methods. Sherrod L. Maxwell, III Westinghouse Savannah River Site. Approach. Ion exchange, solvent extraction, or extraction chromatography? Sample matrix, analyte levels, interferences?

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Development of New Column Extraction Methods

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  1. Development of New Column Extraction Methods Sherrod L. Maxwell, III Westinghouse Savannah River Site

  2. Approach • Ion exchange, solvent extraction, or extraction chromatography? • Sample matrix, analyte levels, interferences? • Separation efficiency vs. interferences, ruggedness, sample frequency, turnaround time, detection limit, consistency of chemical yields, cost, alpha peak resolution, radiological containment, space limitations, automation, sequential analysis, waste disposal • Ex.: low level Pu in urine • 500+mL sample size, handle high phosphate and calcium, ensure good Th-228 removal, sequential analysis for other actinides plus Sr, high throughput, minimize acid waste, good alpha peak resolution, high tracer recoveries, DOELAP accuracy and precision criteria, etc.

  3. Approach • Sample matrix, analyte levels, interferences? (contd) • Dissolution required? • fusion or complete digestion vs leach (microwave, hot plate, furnace) • Analyte stable in separation matrix? (Ex. Ti in fecal samples after dissolution, do I need HF to stabilize?, if so can I still extract?) • Tracer selection (Pu-242 vs. Pu-236 or Sr-85 vs. stable Sr) • traceability, tracer contamination level, equipment available, (e.g. gamma PHA for Sr-85) • Interference type • U-238 mass on Pu-238, Am-241 on Pu-241 (ICP-MS or TIMS) • Th-228 on Pu-238, Am-241 alpha spectrometry • U by KPA laser phosphorescence (quenchers such as Fe) • U, Pu spectral interferences on ICP-AES • Beta interferences on Tc-99, Sr-90

  4. Approach • Preconcentration/dilution required? • Evaporation • Precipitation (calcium phosphate, iron hydroxide, etc.) • Resin (cation resin for Sr in water, Diphonix or Dipex from soil, fecal) • Aliquot size limited by radiation levels (process dissolver samples) • Valence adjustment? • Pu+3, Pu +4, Pu +5, Pu +6 • Np +4, Np +5, Np +6 • U +4 ,U +6 • Am +3, Cm +3, rare earths • Th +4, Sr +2 • Oxidants/reductants (efficiency, interference, waste, corrosion, destruction, redissolution) • If evaporate strip solution, readjustment required? form Np+5, Np+6, Pu+6

  5. Approach • Analytes together, matrix limitations ? • Ex. Pu , Th, Np by ICP-MS • Pu and Np by alpha spectrometry (with Pu-236 tracer) • Process samples with high Pu (may not need Th removal) • Np assay in process samples with extremely high Pu (need Pu removed from Np due to tail overlap on Np-237) • Depends on levels and assay type (alpha spectrometry vs mass spectrometry)

  6. Approach • Final strip solution matrix: • Interferences on assay method • Low salt for alpha planchet, TIMS filament or ICP-MS assay • Evaporation needed/available (e.g. Ti+3, NH4I, HF) • Ex. second column separation required/hard to redissolve Ti • Ashing required for electrodeposition (optimal # of ashing cycles) • Extractant or resin bleed-off (Am on TRU resin) • Dilute sulfuric acid enhances destruction on ashing • REE removal on TEVA for Am from soil/destroy extractant bleed well

  7. Extraction chromatography options • Offers selectivity over ion exchange • Aluminum to complex matrix interferences/supplement nitrate levels • 0.5M to 1.25M aluminum nitrate • Gravity flow vs. vacuum • Vacuum 3X to 5X faster • Helps with stubborn sample flow/particluates • Need 50-100 micron size (now in cartridges from Eichrom) • Keep lid clean/control flow rate • Sequential options • Pu on TEVA or TRU • U on UTEVA or TRU • TEVA +TRU vs. UTEVA+TRU • Cerium fluoride vs. electrodeposition (alpha spectrometry)

  8. Pu on TEVA Approach • TEVA (Pu, Np, Th) +TRU (U, Am) approach • Can separate Pu and Np together; good U, Th removal • Pu loading as strongly retained Pu+4 instead of Pu+3 • Pu stripped with less difficult matrices for some types of assay • Better Th removal/recovery on TEVA with no competition from U (from soil for ex.) • Second TEVA column can be applied for additional Th, U removal

  9. Pu on TEVA Approach • TEVA (Pu, Np, Th) +TRU (U, Am) approach • No Th-228 in Am fraction from TRU resin • Any residual Th-228 on TRU in U strip does not interfere as it does with Pu-238 on TRU • For urine, with no iron in samples, stacked cartridges (TEVA+TRU) can be used • If iron in samples or is used in valence adjustment, evaporate load + rinse from TEVA, redissolve, add ascorbic acid + sulfamic acid and then load to TRU • Can insert UTEVA for U if you want low salt strip for TIMS or ICP-MS

  10. Pu on TRU Approach • UTEVA (U, Th) +TRU (Pu, Am) approach • Can separate Pu and Am from same resin (TRU) • Cartridges can be stacked in single column (UTEVA+TRU) since Fe reduced to Fe+2 in load solution for all samples (no evaporation step prior to TRU resin) • Pu can be stripped with HCL-Ti(III) for enhanced separation from U, Th vs. older TRU methods • TRU retention still high for Pu despite loading as Pu+3 since Pu converts rapidly to Pu+4

  11. Pu on TRU Approach • UTEVA (U, Th) +TRU (Pu, Am) approach • Retains uranium that may come through UTEVA • Th recovery on UTEVA not as good as TEVA (for soil, sediments) • Th occasionally in Am/Pu fractions • Np not recovered with Pu • Can insert TEVA prior to UTEVA to remove/recover Th and Np

  12. Examples • Actinides in water • Pu, Am, U, Sr at low levels • 500 mL water sample (10 liters?) • Evaporation or precipitation? • Interferences: how high can I tolerate? • Tracers? • Sequential options? • Valence adjustment? • Gravity flow or vacuum? • Add Np as analyte?

  13. Examples • Np-237 in mixed Pu/U oxide? • Dissolve? • Resin? • Valence adjustment? • Assay? • Interferences? • Tracers, spikes, or standards? • Gravity flow or vacuum? • Np in Pu metal?

  14. Summary • Many factors have to be considered/needs are different • Preconcentration methods and highly selective extraction chromatography methods are available • Information exchange valuable • User workshops • Journals/radchem message groups via email • Eichrom web page/procedures • Call Larry

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