Selective partitioning of mercury from co-extracted actinides in a simulated acidic ICPP waste stream Page: 3 of 13
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efficient process to remove mercury from radioactive and non-radioactive waste streams may prove to
be advantageous. Mercury partitioning may result in hazardous waste volume reductions and provide
a mercury waste form suitable for final disposition or reuse.
Therefore, the scope of this work was to: 1) determine mercury extraction, scrub, and
stripping distribution coefficients (DHg) in a typical TRUEX flowsheet using simulated sodium waste,
and 2) develop a flowsheet that would either allow mercury to be partitioned from the co-extracted
actinides or selectively extracted from them. Actinide separations from ICPP SBW will most likely
be a gross separation rather than selective actinide partitioning. Therefore, the TRUEX.flowsheet
used for these tests deviates slightly in the stripping section from the TRUEX flowsheet developed by
Commercially purchased octyl(phenyl)N,N-diisobutyl-carbamoylmethyl-phosphine oxide
(CMPO) obtained from Elf Atochem and having a purity of >97% was sent to Argonne National
Laboratory and further purified by Vandegrift and co-workers. It should be noted that previous
CMPO purity tests show that the Elf Atochem CMPO is pure enough for use as received and that
further purification steps are probably not necessary . The TRUEX solvent was made up using
this CMPO by LITCO's Quality Control Laboratory to contain 0.2 M CMPO and 1.4 M TBP in
dodecane. The solvent was washed three times with 0.25 M Na2C03 (0/A = 5)  and filtered
through Whatman 542 filter paper prior to contact with the sodium waste simulant. To ascertain the
purity and concentration of the CMPO in this solvent, the solvent was contacted with nitric acid
solutions, ranging in acid concentrations between 0.01 - 8 M, containing 241Am . Americium
distribution coefficients using this solvent agree favorably with those found in literature  thereby
establishing the suitability of this solvent for use in this study.
A NIST traceable 203Hg standard in HCl was purchased from Amersham. One milliliter of
this standard was diluted to 100 mL with 2 M HNO3. The resulting activity of 203Hg in this solution
was 14,864 dps/mL at TO = December 1, 1993 and contained 163 ppm Cl-. Because of the short
2o3Hg half-life (46.8 days), all 203Hg results were decay corrected back to T0. Aliquots of the stock
2osHg solution were spiked into the sodium waste simulant. The spike was allowed to equilibrate
with the sodium waste for approximately 24 hours prior to contacting with the TRUEX solvent.
The'TRUEX solvent was pre-equilibrated with non-spiked sodium waste simulant prior to
contact with the spiked simulant. The composition of the non-spiked sodium waste simulant is
presented in Table 1. Mercury is expected to predominantly exist as HgCl2 in the waste simulant
because of the high acidity and low chloride concentrations . Pre-equilibrating the solvent has the
effect of loading it with all extractable species (HN03, Zr", etc), including non-radioactive mercury,
so that when the spiked sodium waste was contacted with the solvent, only the species of interest,
13 Hg, was extracted. Kinetic studies  show that the 103Hg should come to equilibrium with stable
mercury quickly. The distribution coefficient of stable mercury was assumed to be that determined
for 213Hg. To verify 203Hg distribution coefficients obtained from TRUEX solvent pre-equilibrated
with sodium waste simulant containing stable mercury, extractions were repeated using TRUEX
solvent pre-equilibrated with sodium waste simulant that did not contain mercury. This pre-
equilibrated solvent was then contacted with the 203Hg spiked simulant which did contain stable
Solvent pre-equilibration was performed by contacting the solvent three times with the
simulated waste at an 0/A = 1 . Pre-equilibration contacts were performed by mixing the two
phases in a glass test tube on a vortex mixer for one minute. Phase disengagements were achieved
by centrifuging the two phases for 5 minutes at 3500 rpm.
The ability to strip mercury from the TRUEX solvent using 0.25 M Na2CO3 was evaluated
according to the flowsheet shown in Figure 1. A 0.04 M HEDPA contact was performed prior to
contacts with 0.25 M Na2CO3 to remove any extracted metals, such as zirconium.
A second experimental procedure, shown in Figure 2, was used to evaluate solutions that
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Brewer, K.N.; Herbst, R.S. & Tranter, T.J. Selective partitioning of mercury from co-extracted actinides in a simulated acidic ICPP waste stream, article, December 1, 1995; Idaho Falls, Idaho. (https://digital.library.unt.edu/ark:/67531/metadc619350/m1/3/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.