Embed Size (px)
Citation preview
Alkaline Fusion for Radioanalytical Chemistry
Abstract
Borate fusion is well established and widely used to digest a vastrange of oxide materials like soils, sludges, ashes, cements,ceramics, slags, ores and minerals. It is the optimal techniqueoffering high accuracy in sample preparation for X-rayfluorescence analysis (XRF), but it is also very advantageous forliquid preparation for downstream trace elemental analysis whencompared to acid leaching. Given the beneficial characteristics offusion, it is an ideal technique for radioanalytical chemistry. Thispaper will describe the current issues associated with acidleaching and how fusion can overcome them. It will become clearto you that fusion is the ultimate preparation for inorganicsamples, especially for radionuclides.
Safe and Effective Sample Preparation for the Extraction of Radionuclides from Complex Matrices
Contents
First Reported Application of Borate Fusion in Radioanalytical Sample Preparation
Applications for Nuclear Sectors
Why Fusion for Radionuclides?
Reasons to Avoid Acid Leaching
Advantages Specific to Nuclear Application
Things to Consider
Conclusions
References
2
3
3
4
5
6
7
8
9
3
First Reported Application of Borate Fusion in Radioanalytical SamplePreparation
Applications for Nuclear Sectors
✓Nuclear Decommissioning Civil power stations and military installations → 438 power stations worldwide → 149 being or about to be
decommissioned
✓Nuclear Waste and NORM CharacterizationNaturally Occurring Radioactive Materials
→ IAEA (International Atomic Energy Agency) & ALMERA(Analytical Laboratories for the Measurement of Environmental Radioactivity) lab network
→ 176 labs in 89 countries
✓Nuclear ForensicsIllicit trafficking and events involving nuclear and other radioactive material outside regulatory control→ Emergency responses
The application in a radioanalyticalcontext was pioneered by ProfessorIan Croudace (Director of theGeosciences Advisory Unit). In a 1996research contract, the lab had toanalyse U and Pu isotopes from 650soils samples within 3 months, whereborate fusion was chosen primarilydue to its speed, safety and ability forcomplete dissolution (Croudace et al.1998). This high-profile public studyfocused on investigating groundcontamination from alleged damage ofa nuclear weapon at the former USAFairbase at Greenham Common in theUK. Prior to this work, radioanalyticalspecialists would traditionally haveused one or more sample digestionapproaches to extract U, Pu and allother radioactive species from soils.
« around 80% of participatinglaboratories […] failed to provide
accurate results […] using acidleaching methods »
Effective digestion depends on thesample matrix and the nature of theradionuclide(s) present, but thetipping point is when one faces arefractory matrix, which is reputed tocause problems with a widespreaddigestion technique like acid leaching.In fact, around 80% of participatinglaboratories from a recentPerformance Evaluation Program(MAPEP, Session 30) by the USDepartment of Energy failed toprovide accurate results for uraniumisotopes in soil samples due toincomplete dissolution of refractoryparticles using acid leaching methods(Maxwell et al. 2015). Moreover, evenwith the use of strong, hazardoushydrofluoric acid, some results werealmost 50% lower than the referencevalues.
Why Fusion for Radionuclides?
There is no denying the importance ofcomplete sample digestion foraccurate radionuclide character-isation, mainly for naturally-occurringradioactive materials (NORM),decommissioning materials, industrialwastes and by-products. The assess-ment needs to be effective, quick andprecise whether it is for storage,disposal or for forensic investigation.It has been known for a long time thatincomplete dissolution is the primarycause for poor analytical performanceand that if a procedure is known tohave the capability to dissolvecompletely the most problematicsamples, all other digestiontechniques should not be botheredwith (Sill and Sill 1995).
« incomplete dissolution isthe primary cause for pooranalytical performance »
4
Reasons to Avoid Acid Leaching:
Risk of incomplete digestion, especially refractory elements
Analytical errors
Safety reasonsWorking with HF to decompose silicates can be very harmful, in addition to being complicated and expensiveRisks associated with strong acidsCannot be automated
Time consumingSlow, can take hours to digestRequires a lot of manipulations
5
A cold to cold operation withautomated pouring function has aduration of less than 20 minutes!
The X-600 six-positions heavy-dutyfully automated electric fusionfluxer can process safely up to 18samples per hour.
Prepares glass disks for XRF,solutions for ICP/AA and peroxideor pyrosulfate fusions.
changed for solubility reasons or ifcontaminated by analyte of interest,and sample-to-flux ratio can beoptimized easily. Also, a non-negligibleaspect of using fusion is the increasein laboratory workflow that comesfrom the speed of the technique whencompared to other methods.Automating the process has made iteasy to change the fusion conditionsdepending on the needs.
Different fusion methods exist toenable multiple labs to use thetechnique, which include boratefusion (being the most attractive),Na2O2 fusion and NaOH fusion toname a few. Using an automatedfluxer improves repeat-ability, allowscold-to-cold operation in less than 20minutes and is the safest way to dofusion.
6
Advantages Specific to Nuclear Application
Fusion improves the accuracy byachieving complete destruction ofmineral lattice structures and easierdigestion of silicate materials moreeffectively than any other technique(Galindo et al. 2007). This is of greatimportance, since some radionuclidesare trapped inside the matrixstructures or associated with resistantmaterials. Consequently, higherrecoveries are reached by fusion,notably for Strontium (Russell et al.2017) Plutonium, Uranium andThorium isotopes (Maxwell et al.2015) and in the case of Cs evencomplete chemical yield recoverycompared to 78% with acid leachingusing aqua regia (Russell et al. 2014).
Figure 1: Example of lithium borate glassnetwork
Also, fusion parameters can be easilyadapted depending on the nature ofthe samples and radionuclide(s) ofinterest, which makes it a technique ofchoice due to its large flexibility andversatility (Braysher et al. 2019). Forinstance, the type of flux can be
7
The is a flux dosing machine thatautomatically calculates and accurately dispensesthe required amount of flux to the sample. Your labwill gain efficiency, precision and excellentreproducibility in sample and flux weighing.
Things to Consider
Although fusion has proven its efficiency in many applications, there are some basic considerations if one wishes to benefit entirely form its superiority:
Fusion is a more complex matrix that results in high total dissolved salts (TDS) solutions. The use of ion-exchange resins and extraction chromatography can help to overcome this problem.
The sample-to-flux ratio is low to moderate and can therefore limit the analysis of ultratrace elements. Traces of contaminants in flux can also raise concerns, but it is minimized nowadays with the use of high purity fluxes.
The solubility of the sample in the flux can vary depending on its composition. Consider also the solubility limit of borate flux in the final acid solution.
Initial investment in start up materials for fusion can seem expensive because of the high value of platinumware. However, it is so durable that platinum keeps its value even after thousands of fusions and is fully recyclable!
Conclusion
Fusion is the key to reach complete digestion of a variety of sample matrices withguaranteed accuracy. It is superior to acid leaching in many other ways: it is saferdue to the absence of strong acids and as a consequence of being an automatedprocess, but also by being quick and very efficient in digesting complex material.Flexible and robust, fusion can prevent incorrect results, which could bedetrimental to a laboratory reputation! It has proven its effectiveness in aradioanalytical context many times over and brings economic benefits for thenuclear industry. Progress in this sector is important and the need for propersample digestion will be even more relevant in the near future with the increasingrate of decommissioning worldwide.
8
References
• Braysher, E., Russell, B., Woods, S. et al.
(2019) Complete dissolution of solid
matrices using automated borate fusion in
support of nuclear decommissioning and
production of reference materials. J
Radioanal Nucl Chem 321, 183–196.
• Croudace I, Warwick P, Taylor R, Dee S
(1998) Rapid procedure for plutonium and
uranium determination in soils using a
borate fusion followed by ion-exchange
and extraction chromatography. Anal Chim
Acta 371:217–225.
• Galindo C, Mougin L, Nourreddine A
(2007) An improved radiochemical
separation of uranium and thorium in
environmental samples involving peroxide
fusion. Appl Radiat Isot 65:9–16.
https://doi.org/10.1016/j.apradiso.2006.05.
012
• Maxwell SL, Hutchison JB, McAlister DR
(2015) Rapid fusion method for the
determination of refractory thorium and
uranium isotopes in soil samples. J
Radioanal Nucl Chem 305:631–641.
https://doi.org/10.1007/s10967-015-3972-1
• Russell BC, Croudace IW, Warwick PE,
Milton JA (2014) Determination of precise
Cs-135/Cs-137 ratio in environmental
samples using sector field inductively
coupled plasma mass spectrometry. Anal
Chem 86:8719–8726.
https://doi.org/10.1021/ac501894a
• Sill CW, Sill DS (1995) Sample
dissolution. Radioact Radiochem 6:8–14
Katanax
100-2500 rue Jean-Perrin
Quebec, QC G2C 1X1 Canada
Tel: +1 (418) 915-4848
www.katanax.com
SPEX SamplePrep
65 Liberty Street
Metuchen, NJ 08840 USA
Tel: +1 (732) 623-0465
Toll Free: +1 855-GET-SPEX (855-438-7739)
www.spexsampleprep.com
SPEX Europe
Trinity Court, Church Street Rickmansworth, WD3 1RT, UK
Tel: +44 (0) 208 204 6654
www.spexeurope.com
9
