PROCESS FOR PRODUCING URANIUM OXIDES

METHODE DE PRODUCTION DES OXYDES D'URANIUM

English Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a process for producing a
uranium oxide by dissolving a yellow cake in sulfuric acid
or hydrochloric acid, bringing the obtained solution into
contact with a chelating resin of diaminocarboxylic acid
type and subjecting the product to neutralizing precipitation
followed by heat treatment. By the contact of the solution
with the chelating resin, iron, copper, molybdenum and
vanadium among the metallic impurities are removed and in
the subsequent neutralizing precipitation step, other metallic
impurities such as aluminum, calcium, magnesium, sodium and
potassium removed. This process can easily produce uranium
oxide having a high purity using a simple apparatus.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing uranium oxide from an acidic
aqueous solution of uranyl sulfate or uranyl chloride
containing sulfates or chlorides of metallic impurities, said
acidic aqueous solution being obtained from a milling of
uranium ore, which process comprising bringing said acidic
aqueous solution having a pH of 0.5 to 2.5 into contact with
chelating resin of diaminocarboxylic acid type, said
chelating resin being prepared by cross-linking a phenolic
compound of formula:
<IMG>
(wherein M represents an alkali metal or hydrogen, and R1 and
R2 each represent hydrogen or alkyl group having 1 to 3
carbon atoms)
with a phenol and aldehyde to form a three-dimensional
structure, subjecting the thus treated solution to
neutralizing precipitation by adding ammonia into the
solution to precipitate ammonium diuranate, and heating the
thus formed ammonium diuranate to form uranium oxide.
2. A process for producing uranium oxide from a yellow
cake which is a uranium oxide concentrate obtained from
milling of uranium ore, said process comprising dissolving a
yellow cake in an acid selected from the group consisting of
sulfuric acid and hydrochloric acid to form an acid solution
having a pH of 0.5 to 2.5, bringing said acid solution into
contact with a chelating resin of diaminocarboxylic acid
type, said chelating resin being prepared by cross-linking a
phenolic compound of formula:

<IMG>
(wherein M represents an alkali metal of hydrogen, and R1 and
R2 each represent hydrogen or alkyl group having 1 to 3
carbon atoms)
with a phenol and aldehyde to form a three-dimensional
structure, subjecting the thus treated solution to
neutralizing precipitation by adding ammonia into the
solution to precipitate ammonium diuranate, heating the thus
formed ammonium diuranate to form uranium oxide.
3. The process according to Claim 1 or 2 wherein the
acid solution contains at least one metallic impurity
selected from the group consisting of iron, copper, vanadium,
molybdenum, sodium, aluminum, calcium, potassium and
magnesium; wherein at least one of iron, copper, molybdenum
and vanadium are removed by said treatment with chelating
resin; and wherein the remaining metallic impurities not
removed by the treatment with said chelating resin are
removed by said neutralizing precipitation step.
16

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
10. A process as claimed in Claim 1, in which the aqueous acidic
solution is obtained by leeching a uranium ore with sulphuric
acid, and removing the solid residue therefrom.
11. A method as claimed in Claim 1, in which the acidic aqueous
solution is obtained by leeching uranium ore with sulphuric acid,
separating the leaching liquid, subjecting the leaching liquid to
solvent extraction with an organic solvent subjecting the organic
extract obtained to back extraction with an aqueous solution of
ammonium sulphate and ammonia, and separating the aqueous extract
obtained from waste liquid.

Description

lZ9~ 7
The present inven-tion relates -to a process for efficiently
producing uranium oxides, and more particularly, to a process for
effectively removing metallic impurities from an acidic aqueous
solutions oE uranyl sulfate and uranyl chloride containing
sulfates and chlorides, of metallic impurities obtained from the
milling of uranium ore and in a particular embodiment thereof
such a solution obtained by dissolving a yellow cake in
hydrochloric acid or sulEuric acid, to produce uranium oxides
with a high purity.
The term ~yellow cake~ used herein means a uranium oxide
concentrate that results from milling uranium ore. It typically
contains about ~0 to 90% U3O8.
~5 Various processes for reEining uranium have been proposed. Among
then, a process wherein a uranium oxide is produced as an
intermediate is employed widely in many countries. When a yellow
cake used as a starting material in this process contains
metallic impurities such as iron, copper, molybdenum, vanadlum,
aluminum, calclum, magnesium, sodium, potassium and the like, the
purities o~ these resulting uranium oxide or uranlulll hexafluoride
obtained by further refining thereoE a~e reduced. There~ore,
these metallic impuri-ties must be removed.
~rhese motallic impurlties have conventionally becn removed by
solvent extraction in a trlbutyl phosphate/ni-tric acld system.
In thls proces~, the yellow cako containlng the impurities is
dissolved in nitric acld and then the impurities are removed by
extraction wi-th tributyl phosphato (TBP) solvent. Then a
solution oE uranyl nitrate UO2(NO3)2 thus obtained is thickened
by evaporation to precipitate uranyl nitrate hydra-te (UNH
process) or, alternatively, ammonla is added to the uranyl
nitrate solution to crystallize ammonium diuranate
(NH4)2U2O7~2H2O (ADU process). The uranyl nitrate hydrate (UNH)
or ammonium diuranate (ADU) ls thermally decomposed by roasting
3~$
, ~,

1292~357
i-t at a -tempe~ature of 500C or higher to form uranium oxide and
to recover ni-tric acid or ammonia.
The above-mentioned so~vent extraction process is not preferred
from the viewpoint of environmental pollution, since a waste
liquor containing nitrogen and phosphorus ls formed in a large
amount because nitric acid and tributyl phosphate are used.
Further, materials of apparatus employed ln the process are
limited, since nitric acid is used. In addition, this process is
economically disadvantageous, since the solvent extraction is
conduc-ted in multiple steps with a mi~er-settler and, therefore,
a large apparatus and a large area for the installatlon thereof
are required. Another problem is that an explosion-proof
apparatus is necessi-tated, since the solvent is easily
lnflammable.
The presen-t invention provides a process capable of producing
uranium oxide having a high purity by removing the above-
mentioned metallic lmpurities from the a~oresald acid aqueoussolutions and par-ticularly an acid solution obtained by
dissolving yellow cake ln sulfuric or hydrochlorlc acld.
The present invention also provldes a process for produclng
~5 uranlum oxide wherein solven-t extraction process using nitrlc
acid and tributyl phosphate ls not employed so that no waste
li~uor containing nitrogen and phosphate is formed, and no large
production unit such as a mlxer-settler and no large area for the
ins-talla-tion -thereoE are required.
The invention again provides a process for producing uranium
oxide wherein no inflammable solven-t ls used so that an
explosion-proof apparatus is not required.

~ j~2B~'7
The inventors have found that iron, copper, molybdenum and
vanidium among the metallic impurities can be efficiently removed
by dissolving the yellow cake containing the metallic impurities
in hydrochloric acid or sulfuric acid in place of nitric acid and
then bringing the resulting solution into contact with a
chèlating resin of diaminocarboxylic acid type, and then the
other metallic impurities such as aluminum, calcium, magnesium
and the like can be removed in the subsequent neutralization
step. According to a broad aspect of the present invention there
is provided a process for producing uranium oxide from an acidic
aqueous solution of uranyl sulfate or uranyl chloride containing
sulfates or chlorides of metallic impurities, said acidic aqueous
solution being obtained from a milling of uranium ore, which
process comprising bringing said acidic aqueous solution into
. contact with a chelating resin of diaminocarboxylic acid type,
sub~ecting the thus treated solution to neutralizing
precipitation by adding ammonia into the solution to precipitate
ammonium diuranate, and heating the thus formed ammonium
diuranate to form uranium oxide.
According to the present invention, there is provided a
process for producing uranium o~ide from an acidic aqueous
solution of uranyl sulfate or uranyl chloride containing
sulfates or chlorides of metallic impurities, said acidic
aqueous solution being obtained from a milling of uranium
ore, which procass comprising bringing said acidic aqueous
solution having a pH o 0.5 to 2.5 into contact with
chelating resin of diaminocarboxylic acid type, said
chelating resin being prepared by cross-linking a phenolic
compound of formula:

- ~Z~3Z85~
OH
(cH2cooM)2NcH2 ~ CH~N(CH2COOH)~
Rl R2
wherein M represents an alkali metal or hydrogen, and Rl and
R2 each represent hydrogen or alkyl group having 1 to 3
carbon atoms)
with a phenol and aldehyde to form a three-dimensional
structure, subjecting the thus treated solution to
neutralizing precipitation by adding ammonia into the
solution to precipitate ammonium diuranate, and heating the
thus formed ammonium diuranate to form uranium oxide.
- 3a -

lZ9Z8~j7
The yellow cake employed as a start:Lng material in the present
invention usually contains ther~in, in addition to uranium,
metallic impurities such as iron, copper, vanadium, molybdenum,
sodium, aluminum, calcium, potassium, magnesium and the like. By
the treatment of the solution of yellow cake with the chelating
resin the metallic impurities of iron, copper, molybdenum and
vanadium are removed. The remaining metallic impurities which
have not been removed by the treatment with the chelating resin
are removed in -the subse~uen~ neu-tralizing preclpitation step.
;~ ~

12~2t~57
Ammonium diuranate formed in the neutralizing
precipitation step is heated to a temperature of 350 to 550
CC to form uranium trioxide. When ammonium diuranate is
heated to a temperature of 550 DC or above, triuranium
octoxide is formed.
DETAILI:D DE~IPTIOI~ 01~ Tll~:; INV~;NTIOI~
As described hereinabove, the chelating resins of
diaminocarboxylic acid type used in the present invention
are capable of effectively removing iron, copper, molybdenum
and vanadium in the solution of the yellow cake in sulfuric
acid or hydrochloric acid. Examples of the chelating resins
of diaminocarboxylic acid type capable of selectively
removing iron, copper, molybdenum and vanadium from the
yellow cake solution include chelating resins prepared by
crosslinking a phenolic compound of the following general
formula:
OH
~CH2COOM)2NcH2 ~ CH2N~CH2cOoH)2
Rl R2
(wherein M represents an alkali metal or hydrogen, and
R1 and R2 each represent a hydrogen or an alkyl group
having 1 to 3 carbon atoms)
with phenols and aldehydes to form a three-dimensional

lZ9Z8S}7
structure. As for these chelating resins, those capable of
reducing iron concentration of an acidic electrogalvanizing
bath are known from Japanese Patent Laid-Open Specification
No. 54-121241 (laid-open on September 20, 1979) and
particularly that known under a trade name of Uniselec UR-50
(a registered trademark, a product of Unitika Ltd.) is
suitably used.
The solution of the starting yellow cake contains
uranium and at least one of the above-mentioned metallic
impurities such as iron, copper, molybdenum, vanadium,
sodium, aluminum, calcium, potassium or magnesium. The
content of the metallic impurities in the yellow cake is not
particularly limited.
In the treatment of the yellow cake solution with the
chelating resin of diaminocarboxylic acid type, it
is preferred to adjust the pH of the solution to 0.5 to 2.5.
When the pH exceeds 2.5, uranium in the yellow cake solution
begins to be precipitated to cause a loss thereof and to
orm a radioa~tive wasSe unfavorably. On the contrary, when
the pH is lower than 0.S, iron, copper, molybdenum and
vanadium contained as the metallic impurities in the yellow
cake solution cannot be sufficiently adsorbed on the
chelating resin. The yellow cake solution can be brought
into contact with the chelating resin by mixing them
together by stirring or by means of a column in the same
manner as in an ordinary treatment with an ion exchange
resin. The latter method is preferable to the former method

9Z~357
from the viewpoint of simplification of the apparatus or the
selective adsorption efficiency. In passing the yellow cake
solution through the column, the solution is passed through
an ion exchange column packed with the chelating resin at a
space velocity of 10 (1/hr) or less, preferably 0.5 to 2.0
(1/hr). By the contact with the chelating resin, iron,
copper, molybdenum and vanadium are selectively adsorbed and
removed.
The solution thus treated with the chelating resin is
then neutralized with gaseous ammonia to form a precipitate
of ammonium diuranate. A continuous multi-stage
neutralizing precipitation method is preferably employed in
this neutralizing precipitation step. For example, a
continuous two-stage neutralizing precipitation method is
employed. In the first stage of this method, the p~-l of the
solution is adjusted in the range of 2.5 to 4.0 with calcium
oxide or calcium hydroxide to remove aluminum, contained as
an impurity in the solution, in the form of aluminum
hydroxide. In the second stage, ammonia is introduced into
a supernatant part of the solution to precipitate ammonium
diuranate. Ammonia used as the neutralizing agent is
preferably gaseous ammonia, since it can be handled more
easily than liquid ammonia and ammonium diuranate thus
formed can be precipitated, filtered and washed easily. In
this neutralizing precipitation step, only ammonium
diuranate is precipitated, leaving aluminum, calcium,
magnesium, sodium, potassium and the like contained as the

lZ~Zti357
metallic impurities in the supernatant liquid.
The resulting ammonium diuranate precipitate is
separated from the supernatant liquid and then heated or
calcinated at 350 to 550C to form uranium trioxide or at
550 C or above to form triuranium octoxide. These uranium
oxides can be reduced to form uranium dioxide, which can be
treated with hydrogen fluoride to form uranium tetrafluoride
and further uranium hexafluoride. The uranium oxide produced
by the process of the present invention is usable as a
yellow cake having a high purity. This product can be used
as a starting material (yellow cake) in a conversion process
for producing uranium hexafluoride from a yellow cake of a
high purity such as a dry process employed by Allied
Chemical Corp. in U.S.A.
The following example is illustrative of the present
invention.
EXAMPLE
A solution of yellow ea~e ln sulfuric acid having a pH
of 1.0 and having a composition shown in Table 1 was passed
through a column packed with S0 ml of a chelating resin of
diaminocarboxylic acid type at a space velocity of 1.0 (1/hr).
The amount of the solution passed through the column was 10
~ R. The analytical results of the solution thus treated
are shown in Table 2.

lZ~Z~
_ ~_ (.~ I __ = .
d 1 D ~ ~
_ ~ ~ d
Z ~ o Z E
E ~ o OD
_ O d O
E ~ u E d`
? _ ? __
U d O 3 d O
¢ E ~ R ¢ ~ _ _ .
E~ E ~D E~ E __
d ,~ :1 _
E __ t_~ ~ o
d r~ t~ ~ O
E ~ E ~
E E o
.,1 _ l / .
E / u c E ~ c
7 E 3 / v v
/ E o / o

129Zl35~7
It is apparent from the results that iron, copper,
molybdenum and vanadium were removed well by the treatment
with the chelating resin but aluminum, clacium, potassium,
magnesium and sodium could not be removed at all.
Calcium hydroxide was added to the solution thus treated
with the chelating resin to adjust the pH of the solution to
3.0 and to form a precipitate. After solid-liquid
separation, gaseous ammonia was blown into the supernatant
liquid to form a precipitate of ammonium diuranate. The
resulting ammonium diuranate precipitate was separated from
liquid, washed with water and calcinated at 600C to remove
ammonia to thereby obtain uranium trioxide. The quality
level of uranium trioxide thus obtained is shown in Table 3.
It can be seen from the results that uranium trioxide having
a high quality level could be produced by the present
invention which comprises the combination of the chelating
resin treatment with the neutralizing precipitation.
Table 3
¦Elements ¦ AQ ¦ Ca ¦ Cu ~ Fe ~ K ~ M
¦ Analytical ¦ 5 ¦o 21 0 1 ¦ ln ¦ 8 10-4 10-5 ¦ 12¦ 2
(unit: ppm/U)
As is apparent from the foregoing, according to the
process of the present invention wherein no nitric acid is
used at all for the dissolution of the yellow cake, no waste
liquid containing nitric acid or ammonium nitrate is formed
at all. Iron, copper, molybdenum and vanadium can be
- 10 -

lZ~2857
effectively removed by the treatment with the chelating
resin and other metals such as aluminum are removed by the
neutralizing precipitation step to produce a uranium oxide
having a high purity.
Since the process of the present invention can be
conducted without resort to the solvent extraction step, no
large production unit such as a mixer-settler is necessary.
Since, further, no inflammable solvent is used, any special
countermeasure need not be taken for protection against high
pressure and explosion, either.
I

1~9~28~
S~PPLEMENTARY DISCLOSURE
In the original disclosure the acidic aqueous solution of uranyl
sulphate or uranyl chloride containing sulphates or chlorides of
metallic impurities, are in a preferred embodiment maintained by
dissolving ~yellow cake~' in sulphuric or hydrochloric acid.
~Yellow Cake~ is the final precipitate formed in the milling of
uranium ores, i.e., is the uranium concentrate. In the milling
of uranium ores the uranium ore is first subjected to leaching
with sulphuric acid, and the leaching liquid obtained sub~ected
to solvent extraction with an organic solvent. The organic
extract is sub;ected to back extraction in aqueous solution of
ammonium sulphate and ammonia, and the aqueous extract is treated
with alkali to effect precipitation of the ~yellow cake". The
"yellow cake" is in the form of a dried powder, and is a
convenlent form for transportation for further processing.
However, it will be readily seen that in the milling process the
leaching liquid from the leaching step and the aqueous extract
from the back extraction step are bo-th acidic aqueous solutions
of uranyl sulphates containing the metallic impurities, in a
simllar manner as the solution of the "yellow cake" is. Thus,
the process of the present invention can be readily applied to
these solutions also, to achieve the benefits of the present
invention.
The present invention will be further illustrated by way of the
following Examples:
Exam~le I.
A leaching liquid obtained by leaching uranium ore in a sulfuric
acid solution for 4 hrs., was treated by the process of the
present invention. The analytical results of the leaching
solution are shown in Table A.

lZ~2~3S7
The leaching solution having a pH of 0.61 (44g So~2 /1~ was
passed through a column packed with 50 ml of a chelating resin of
diaminocarboxylic type at a space velocity of 1.0 (l/hr.) The
amount of the solution passed through the column was 10 1/1-
Resin. The analytical results of the thus treated solution are
shown in Table B.
Table A (g/l)
u r Mo ¦ As ¦ Fe ¦ Ni
Leaching 5 . 25 0 . 109 3 . 04 0 . 306 2 . 95
so lut i on
Table E3 ( g/ ]. )
_ U Mo A s F e N i
Tr eat e d S . 2 5C 0 . 0 0 5 3 . 0 4 j 0 . 1 2 0 2 . 9 5
It is apparent from the results that iron and molybdenum were
removed well by the treatment wlth the chelating resin but
uranium was not removed at all.
To the thus ~Ar~ated solution was added calcium hydroxide to
ad~ust the pH o the solution to 3.0 and to form a preclpitate.
After solid-liquid separation, gaseous ammonia was blown into the
supernatant liquid to orm a precipitate of ammonium diuranate.
The resulting ammonium diuranate precipitate was separated from
liquid, washed with water and calcinated at 600C to remove
ammonia to thereby obtain uranium trioxide.

1~29Z857
EXAMPLE II
An aqueous solution which simulated an aqueous back extract
solution obtained by extraction step in the milling of uranium
ore, was treated by the process of the present invention. The
aqueous back extract solution was prepared by back-extracting a
simulated organic extract solution of tri-n-octylamine solvent
containing sulfates of uranium and other metallic impurities with
an aqueous solution acidified by sulfuric acid (3.5 mol SO42~
lo The analytical results of the aqueous back extract solution are
show in Table C.
The resulting aqueous back extract solution (3.0 mol SO42-/1) was
passed through a column packed with 30 ml of a chelating resin of
diaminocarboxylic type at a space velocity of l.0 ~1/hr.). The
amount of the solution passed through the column was 10 l/l-
Resin. The analytical results of the thus treated solution are
shown in Table D.
Table C (g/l~
.
U _ Mo _ As _
Back extract 20.2S 0.060 0.03
solution _ ___
rrable D (g/l)
~_ .., ~
I ~t M
Treated 20.2S ~o.oo~ 0 02
solution _ _
It is apparent from the results that molybdenum were removed well
by the treatment with the chelating resin but uranium was not
removed at all.
The subsequent neutralizing precipitation step and heating step
were carried out in the same manner and the same conditions as in
the EXAMPLE I, and uranium trioxide was obtained.
- 14 -
, .