mdp.39015006050176-117
TRANSCRIPT
UKANIUM OKK PROCESSING
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sulfate, precipitation as peroxide containing 81.5% uranium has re-
covered 99% of the uranium content of the original scrap.
If a stream of uranyl nitrate solution is mixed continuously with a
stream of ammonium hydroxide solution, ammonium diuranate will
precipitate at a constant pH and all the U02 produced from it will have
identical characteristics.36 The pH should be between 7 and 8. A pH
less than 8 is desirable for filterability of the ADU, but a pH above 7 is
desirable for best sinterability of the UO2 produced from it.
Precipitation methods are more common with alkaline systems than
with acid.6 The usual method, as shown in Fig. 42, is to raise the pH to
about 11, precipitating a diuranate by the following reaction :31
2NH«+or (NH,)2U20,or
2UO!(CO,),-« + 60H- + — + CO,-* + 3H20
2Na+ Na2U20,
Cold precipitation is more nearly complete than hot, but it results in
such fine crystals that hot precipitation is preferred for ease of filtering;
air dilution, when ammonia is the reagent, also leads to a coarser pre-
cipitate. Incomplete precipitation does not matter if the nearly barren
solution is to be reused, but losses, of course, result if some of this solu-
tion is bled off to prevent excessive build-up of impurities.
Neutralizing a carbonate leach solution from carnotite precipitates
a synthetic carnotite or "yellow cake," as shown in Fig. 30, more or less
in accordance with the following reaction31:
Xa,UO,(C03)3 + NaVO, + 6H2S()4 — Na-TJ02V(VnH20
L NajV()4 J yellow cake
+ 6NaSO< + 3CO, + 3H20
When the yellow cake has been filtered off, additional acidification
precipitates V206, or "red cake," which is actually an orange-tan color.
Quantitative precipitation of the uranium on acidifying the leach solu-
tion while coprecipitating a minimum amount of vanadium involves neu-
tralizing with HzSO* to pH 6.0 to 7.1. A suitable solution temperature
is 90°C, and holding at temperature 2 to 4 hours facilitates filtering."
Essentially the same procedure has been used before the advent of
atomic energy as a means of recovering red cake and rejecting uranium.
The rejected uranium was, however, kept in tailing dumps in case a use
for uranium should materialize. Since then the procedure was patented
as a means for recovering uranium.
If yellow cake is roasted with salt, soda ash, and sawdust the products
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