RE: Actinide Analysis

["Akbarzadeh, Mansour" <AkbarzM@wipp.carlsbad.nm.us>]

Tony Harrison wrote,
Does anyone have a good method for digesting environmental samples for
actinide analysis that does not include wet ashing with hydrofluoric acid?
Matrices to be digested are soils and air filters, so silica is the main
issue.  Respond to me, as I don't think too many others will care.

Tony,
Wet ashing is usually used in conjunction with muffling to destroy organic
compounds and prepare the sample for the next step (digestion). Normally,
conc. HNO3 and H2O2 are used for wet ashing. For glass fiber air filters, HF
must be used to achieve a complete digestion and dissolution. For other types
of filters (i.e. cellulose, plastic, paper...etc), muffling at higher
temperature will ash the sample. For plastic and cellulose filters, use wet
ashing with HNO3 and H2O2 first, then dry and muffle, finally, digest the
sample with HNO3/HCl to be ready for actinide separation. In general, you can
use fusion method for dissolution of solid samples using Pt, or Zr crucibles,
however silica might not be removed from the sample completely, and a
secondary process will be necessary. Please, See the following:
Before any sample preparation (i.e. wet ashing,or fusion), the tracers are
added to a known amount of sample in a crucible. After muffling, LiBO2(Na2O2,
or NaOH...etc, may also be used) is added and the crucible is directly
heated(using tongs for better control of applied heat)on a Bunsen-burner.
Fusion is complete when a uniform mixture is formed. Finally, the crucible
with the sample is transferred to a large beaker containing D.I. H20 or weak
acid solution to dissolve the mixture (heating the solution on hot plate might
be necessary). Remove the crucible from the beaker by using tongs. Wash the
crucible with D.I. and add to the original solution. Any undissolved portion
of the sample should be separated(by centrifuging)and reprocessed. Using conc.
HNO3 and HCl, digest the samples. Prepare anion resin,or Eichrom for actinide
separation.  
Using microwave leaching is another method for sample preparation. In this
method, a weak solution of HF can be used. 
Microwave the solid sample with ~ 20 ml of 3part Conc. HNO3 + 1part Conc. HCl
for 20 minutes
(temperature @ ~200C Pressure@ minimum 600psi). Filter the solution and
evaporate. Add 10-20ml mixture of 1.5N HCl-1N HF to sample and dry. Fuse the
sample as described above.
Sherrod Maxwell and Sheldon Nichols from Westinghouse Savannah River Site have
a paper which describes the details. Of course, you can modify the procedure
based on your needs.
You can also do a study by using a spiked sample (i.e. EML Soil, or air
filter)leaving out the HF from the above microwave method and follow-up with
fusion to see % recovery at the final step. 

Regards, 

Mansour Akbarzadeh
WIPP Laboratories
(505)234-8617
akbarzm@wipp.carlsbad.nm.us

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