Ra in Water using MnO2 Resin: Update

Sherrod L. Maxwell, III

Westinghouse Savannah River Company

Need for Improved Method for Ra-226, 228 in Groundwater Samples

• Cation Resin experience– slow flow-1 to 2 days load time– potential calcium interference

• 1 pCi/L MDA required– need large sample aliquot (1L) for Ra-228 via

Ac-228 (gas proportional counting)• Test MnO2 Resin developed by PGRF (Horwitz et

al) and W. Burnett et al (FSU)

Ra-226 and Ra-228 in Water

• 1.25 g MnO2 Resin (Eichrom)• 1 liter samples + Ba-133 tracer• pH adjustment to 6-7 / add 25 mg Ca• Flow rate ~15 mL/min• Vacuum box loading with inner liner

– ~ 1-2 hour loading

– speed & ability to deal with slow samples

• Strip MnO2 with 12 mL 4M HCL-1.5% H2O2

• Wait 36 hours if analyzing Ra-228

Ac-228 on DGA Resin

• Ln Resin (2 mL) + DGA-Normal (2mL) stacked– Ln resin (U,Th removal) and DGA (Ac-228 retention)

– loaded 12 mL strip solution from MnO2 resin on LN-DGA

– collect load + 5 mL 4M HCL rinse for Ra-226

– 10 mL 4M HCL rinse-discard

– Save LN Resin

– Strip Ac-228 from DGA with 10 mL 0.5M HCl

– 100 uL Ce and 1 mL con. HF

Improvements

• Use Ln -DGA Resin instead of TRU-DGA– better alpha resolution and consistency– even with large groundwater sample size– combines Ra-226 and Ra-228 sample

preparation

• Ac-228 on DGA (Ln Resin removes Th,U)

• Ra-226 after repass through Ln-Resin at low acid

10-2 10-1 100 101

10-1

100

101

102

103

104

105

106TN-DGA ResinTRU Resin

Np(V)

Am(III)

Np(IV)

U(VI)

Comparison of TRU and DGA Resins

k'

[HNO3]

10-2 10-1 100 10110-1

100

101

102

103

104

105

106

Am(III)

U(VI)

Th(IV)

Th(IV)

Pu(IV)

[HNO3]

Slide- E. P. Horwitz, May, 2004 User’s Meeting

10-2 10-1 100 101

10-2

10-1

100

101

102

103

104

105

106TN-DGA ResinTRU Resin

Am(III)

Np(IV)

U(VI)

Comparison of TRU and DGA Resins

k'

[HCl]10-2 10-1 100 101

10-2

10-1

100

101

102

103

104

105

106

Am(III)

U(VI)

Th(IV)

Th(IV)

Pu(IV)

[HCl]

Slide- E. P. Horwitz, May, 2004 User’s Meeting

Ra-226 in Water

• Evaporate load + rinse solutions from Ln-DGA

• Redissolve in 0.1M HCl

• Pass solution through same Ln cartridges to better remove alpha resolution interferences

• Precipitate Ra-226 (Ra-224) using Ba sulfate

• 100 uL of 0.70 mg/mL Ba + 5 mL 30% sodium sulfate place on ice

• 0.1 mL seeding suspension

• Count Ra-226 (Ra-224) by alpha spectrometry

• Count filter by gamma for Ba-133 tracer recovery

Column Loading

Column Stripping

Strip with 4M HCL-0.15% H2O2

Wait 36 hours and load to Ln/DGA

Ln/DGA Resin Separation

Ra-226/228 Recoveries

% Recovery % Recovery % Recovery

Ba-133 Ra-226 Ra-228

LCS (spiked DI H2O) 60% 106.2% 108.6%

River smp 108% N/A N/A

River smp spk 95% 102.7% 110.2%

River smp spk 100% 103.1% 93.7%Avg = 104 % 104%

1.5 L samples

Ba-133=1040 pCi

Ra-226 spk= 5 pCi

Ra-228 spk= 20 pCi

Spiked river water sample-1500 mL Ra-226 and Ra-228 daughters

Ra-226 in Groundwater % Recovery % Recovery

Ba-133 Ra-226

Blank (DI H2O) 86.3% N/A

LCS (spiked DI H2O) 88.6% 104%

Grndwater smp 87.3% N/A

Grndwater smp spk 88.6% 87.3%

Grndwater smp 92.4% N/A

Grndwater smp spk 92.7% 89.1%

Tapwater smp 84.6% N/A

Tapwater smp spk 91.2% 94.6%

Avg.= 89.0% Avg = 93.8% ±6.9%

• Ba-133= 1040 pCi, 500 mL sample, 5 pCi Ra-226 + 25 mg Ca, @ 15 mL/ min.

Spiked Groundwater sample-500 mL

Passed through TRU-DGA at 4M HCLevaporate and precipitate

Spiked LCS-1 liter

Better alpha resolution with repass through Ln-Resin after lowering acid to 0.1M HCL

Spiked Groundwater sample-1 literFWHM=81.6

Ra-226 and Ra-228 in Groundwater

% Recovery % Recovery % Recovery Ba-133 Ra-226 Ra-228

BLK 90% N/A N/A

LCS (spiked DI H2O) 95% 99.2% 99.7%

GRNDWATER smp 100% N/A N/A

GRNDWATER smp 89% N/A N/A

GRNDWATER smp 97% N/A N/A

GRNDWATER SPK 95% 96.5% 101.2%

Avg = 94% 97.8% 100.4%

1 L samples

Ba-133=1040 pCi; Ra-226 spk= 5 pCi: Ra-228 spk= 20 pCi

waited 36 hr/used Ln-DGA

Summary

• Ra-226 and Ra 228 using MnO2 resin– Ln/DGA Resin -Ra-228 via Ac-228– Ra-226 using barium sulfate micro-precipitation – Speed and selectivity

• Vacuum Box method– 1L loaded and stripped ~ 1.5-2 hours

• Benefits– Fast, easy separation for both Ra-226, 228– Short count for Ra-226 with large aliquot– Better alpha resolution