Transcript Ra in Water using MnO2 Resin: Update Sherrod L. Maxwell, III

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 LNDGA
– 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
Comparison of TRU and DGA Resins
10
6
10
5
TRU Resin
10
6
10
5
10
4
10
3
10
2
10
1
10
0
TN-DGA Resin
Pu(IV)
Np(IV)
Am(III)
10
4
Th(IV)
3
10
2
10
1
10
0
U(VI)
Th(IV)
k'
10
Am(III)
U(VI)
10
Np(V)
-1
10
10
-2
10
-1
10
[HNO3]
0
10
1
-1
10
-2
10
-1
10
0
10
1
[HNO3]
Slide- E. P. Horwitz, May, 2004 User’s Meeting
Comparison of TRU and DGA Resins
10
6
10
5
10
4
10
3
10
2
10
1
TRU Resin
10
6
10
5
10
4
10
3
10
2
10
1
10
0
TN-DGA Resin
Pu(IV)
k'
Np(IV)
Th(IV)
U(VI)
Th(IV)
Am(III)
Am(III)
10
0
U(VI)
10
-1
10
-2
10
-2
10
-1
10
[HCl]
0
10
1
10
-1
10
-2
10
-2
10
-1
10
0
10
1
[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
Ba-133
LCS (spiked DI H2O)
River smp
River smp spk
River smp spk
% Recovery
Ra-226
60%
108%
95%
100%
Avg =
1.5 L samples
Ba-133=1040 pCi
Ra-226 spk= 5 pCi
Ra-228 spk= 20 pCi
106.2%
N/A
102.7%
103.1%
104 %
% Recovery
Ra-228
108.6%
N/A
110.2%
93.7%
104%
Spiked river water sample-1500 mL
Ra-226 and Ra-228 daughters
Ra-226 in Groundwater
% Recovery
Ba-133
Blank (DI H2O)
86.3%
LCS (spiked DI H2O)
88.6%
Grndwater smp
87.3%
Grndwater smp spk
88.6%
Grndwater smp
92.4%
Grndwater smp spk
92.7%
Tapwater smp
84.6%
Tapwater smp spk
91.2%
Avg.= 89.0%
% Recovery
Ra-226
N/A
104%
N/A
87.3%
N/A
89.1%
N/A
94.6%
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 HCL
evaporate and precipitate
Better alpha resolution with repass through LnResin after lowering acid to 0.1M HCL
Spiked LCS-1 liter
Spiked Groundwater sample-1 liter
FWHM=81.6
Ra-226 and Ra-228 in Groundwater
% Recovery
Ba-133
% Recovery
Ra-226
% Recovery
Ra-228
BLK
90%
N/A
LCS (spiked DI H2O)
95%
99.2%
GRNDWATER smp
100%
N/A
GRNDWATER smp
89%
N/A
GRNDWATER smp
97%
N/A
GRNDWATER SPK
95%
96.5%
Avg = 94%
97.8%
1 L samples
Ba-133=1040 pCi; Ra-226 spk= 5 pCi: Ra-228 spk= 20 pCi
waited 36 hr/used Ln-DGA
N/A
99.7%
N/A
N/A
N/A
101.2%
100.4%
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