Working Through Mistakes, Miscues, and Mishaps in Actinide Separations

Shane KnockemusUS EPA / NARELMontgomery, ALMay 4, 2004

Goal

To give some examples of laboratory goof ups that I have been victim of, and how to salvage a successful analysis without having to rerun the sample from square one.My examples include using the wrong strip solutions, omitting important oxidation/reduction steps, and arranging the cartridges in the wrong order.

TEVA / TRU separation scheme

TEVA

(Th)

TRU

(Am,Pu,U)

1 2 3

123

1 2 3 (Discard)

1 Load solution: 2.5 M HNO3/ 0.5 Al(NO3)3,

ferrous sulfamate, ascorbic acid. Elements are loaded in the following valence states: Am+3, Pu+3, Th+4, U+6, (Np+4).

2 Rinse: 2.5 M HNO3, ferrous sulfamate.

3 Rinse: 2.5 M HNO3.

Separation Scheme (part 1)Separation Scheme (part 1)

TEVA

(Th)

12 3

(Discard) 1

2 3Th

1. Rinse: 2.5 M HNO3

2. 9 M HCl3. 6 M HCl

TRU

2 3

1

4

5

(Discard) 1

2 3Am

5

U4

Pu

1. Rinse: 2.5 M HNO3

2.5 M/ 0.1 M NaNO2

2.5 M HNO3

2. 9 M HCl3. 4 M HCl

4. 0.1 M HCl/ 0.1 M H2C2O4

5. 0.1 M (NH4)2C2O4

Separation Scheme (part 2,3)Separation Scheme (part 2,3)

Goof up scenario #1

What went wrong?….I used the U strip solution (ammonium oxalate) to elute Pu fraction.Result: Pu and U were eluted together.Point of realization?How to salvage usable analyses….If the mistake is realized before it is too late the Pu. and U may be precipitated selectively.It may also be an option to precipitate Pu and U together if both were precipitated in the presence of TiCl3. Good resolution is a necessity.

Selective Precipitation Scenario

Sol’n w/ Pu+4 and U+6

Nd+3, HF

filter---save filtrate

NdF3--Pu

Sol’n w/ U+6

reduce volume

Nd+3, TiCl3, HF

NdF3--U

Clean Pu Spectrum

Clean U Spectrum

Precipitating the U fraction from the filtrate of the Pu pptn can diminish the recovery slightly (10-20%), but results are still within acceptable ranges.

Pu and U Together

With slightly improved resolution, which may be obtained by counting the sample on a lower shelf, Pu and U could possibly be determined simultaneously.

Goof Up Scenario #2

What went wrong?…ferrous sulfamate was not added to load solution.Result: Pu will remain in the +4 valence, and will be retained and eluted with Th fraction from TEVA.Point of realization?…If the mistake is realized after the Th fraction has already been filtered and counted then the filter must be leached and/or wet ashed to do chemistry that will enable Pu / Th separation. If the mistake is realized prior to the precipitation and filtration of Th, but after the elution of Th (and Pu), the solution containing the Pu / Th mixture may be used for subsequent chemistry.

Pu and Th Together

Th / Pu Separation Scheme

Sol’n w/ Th and Pu

SO4-2, BaCl2

BaSO4 (Th, Pu)

EDTA

Ti+3, KOH

Ti(OH)3 -- (Th, Pu)

HClO4, water, Nd+3

KMnO4, HF

NdF3 – Th(save filtrate)

Filtrate w/ PuO2+2

HClO4, heat

Water, Fe+2, Nd+3, HF

NdF3 -- Pu

Pu-less Th Spectrum

Pu Spectrum

Goof Up Scenario #3

What went wrong?….did not oxidize Pu to +4 valence prior to elution of Am from TRU.Result: Pu will remain in +3 valence, and will be eluted with Am fraction.Point of realization?…before or after precipitation.Subsequent chemistry involved in separating Am and Pu will be the same as the Th / Pu chemistry involved in “Goof up scenario #2”, whereas the Am will behave the same as Th.

Pu and Am Together

Pu-less Am Spectrum

Pu Spectrum

Goof Up Scenario #4

What went wrong?….cartridges set up in wrong order (TRU-TEVA rather than TEVA-TRU).Result: Everything retained on TRU.Point of realization?….at the time of disconnecting tandem arrangement.Subsequent chemistry involved in obtaining usable analyses involves a mixture of things already covered.

Spectrum of Everything Retained on TRU

Everything stripped from TRU with 0.1 M ammonium oxalate

How to Salvage Usable Analyses

Everything on TRU (Am+3, Pu+3, Th+4, U+6).Am eluted with 4 M HCl.Pu / Th eluted together with 1 M HCl / 0.1 M oxalic acid. Pu and Th separated by chemistry demonstrated in ‘Goof Up Scenario #2’.U eluted with 0.1 M ammonium oxalate.

Spectra From Goof Up #4

Super Goof Up Scenario

What went wrong?….cartridges were arranged in the wrong order, ferrous sulfamate reduction of Pu omitted, sodium nitrite oxidation of Pu omitted, and wrong stripping solutions were used.

How To Fix Super Goof Up

Get out of the lab!Sober up.Consider a desk job.

Problems Encountered

The behavior and stability of Pu at the +6 valence proved to be hard to predict at times.In scenario # 2, 3, and 4 getting Pu to maintain a +6 valence during the NdF3 precipitation of both Th and Am proved to be difficult and at times not complete.Don’t co-precipitate samples with CeF3 in the presence of a strong oxidizer, as it will oxidize the Ce to +4 valence and will render the fluoride precipitation impossible.

Pu Contamination in Th Spectra

Pu Contamination in Am Spectrum

Acknowledgements

The chemistry involved in obtaining successful separations was borrowed / learned from David Sill and Steven Bohrer from RESL in Idaho Falls, ID.

Conclusions

Mistakes are inevitable as long as humans are involved.Don’t be too quick to dump a sample and start over when a mistake is made. Something can be learned from most mistakes.Successful separations are still quite possible in most situations when mistakes are made.