Chemical Stability of Purex and Uranium Recovery Process Solvent Page: 2 of 16
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An attempt has been made in the choice of experimental conditions to
evaluate separately the effect of temperature and aqueous phase
composition on the diluent and on TBP decomposition, rather than to
test only Purex flowsheet operating conditions. This approach is
reasonable in that the conditions can be varied to bracket most actual
flowsheet chemical compositions.
This report presents data covering the first phases of this investi-
gation, namely, the effect of nitric and nitrous acid on "the solvent
at 71 C. or higher temperatures.
II. SUMMARY AND CONCLUSIONS
(1) Thirty per cent TBP solutions in Shell Spray Base, Soltrol 170,
Bayol-D, and Ultrasene have been found to be satisfactorily
stable at 71 C in nitric acid concentrations up to 6.0 M
providing nitrous acid is excluded.
(2) In the presence of nitrous acid, all of the above solvents,
or the diluents alone, are unstable when in contact with aqueous
nitric acid at 71 C and react at rates which increase with
increasing nitric acid concentration. Soltrol 170 shows greater
resistance to attack than does Shell Spray Base.
(3) The effect of nitrous acid in promoting chemical instability
can be eliminated by the addition of nitrite inhibitors to
aqueous phases to be contacted with an organic phase. Experi-
ments have shown that 0.2 M urea or 0.2 M sulfamic acid completely
eliminates effects due to nitrous acid.
(4) Nitrous acid is not a catalyst but enters directly into the
reactions. By analysis, nitrite esters, nitroso compounds,
and oxidation products are found among the impurities in
solvents exposed to combined nitric acid - nitrous acid attack.
(5) The impurities resulting from the chemical decomposition of
Shell Spray Base cause increases in uranium distribution co-
efficients under dilute 'C" column conditions, increases in
coalescence times, lowering of the uranium transfer rate,
lowering of dispersion time, enhanced fission product retention
by the solvent, and enhanced foaming during the course of UNH
(6) The aromatic content of diluents of the Shell Spray Base type
seems to have little effect on the solvent as regards its use
in a Purex type process. This seems to be due to the fact that
the impurities arising from the aromatic constituents are among
those readily removed by aqueous carbonate washing.
In general, the diluent or solvent-(diluent and TBP) was contacted with
an aqueous phase under conditions of controlled or known temperature and
with stirring, shaking, or mild ebullition. Samples were withdrawn at
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Moore, R. H. Chemical Stability of Purex and Uranium Recovery Process Solvent, report, March 1, 1955; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc1017318/m1/2/: accessed December 10, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.