Development of New Column Extraction Methods

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
• 500mL 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?
• Pu3, 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 Np5, Np6, Pu6

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. Ti3, 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/supplemen
  t 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. UTEVATRU
• 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 Pu4 instead of
  Pu3
• 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 (TEVATRU) 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
  (UTEVATRU) since Fe reduced to Fe2 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 Pu3 since Pu converts rapidly to Pu4

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