CA1292857C - Process for producing uranium oxides - Google Patents
Process for producing uranium oxidesInfo
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- CA1292857C CA1292857C CA000554518A CA554518A CA1292857C CA 1292857 C CA1292857 C CA 1292857C CA 000554518 A CA000554518 A CA 000554518A CA 554518 A CA554518 A CA 554518A CA 1292857 C CA1292857 C CA 1292857C
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- acid
- uranium
- chelating resin
- uranium oxide
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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.
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.
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 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.
, .
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 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.
, .
Claims (3)
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:
(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.
(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:
(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.
(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.
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.
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.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000554518A CA1292857C (en) | 1987-12-16 | 1987-12-16 | Process for producing uranium oxides |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000554518A CA1292857C (en) | 1987-12-16 | 1987-12-16 | Process for producing uranium oxides |
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| Publication Number | Publication Date |
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| CA1292857C true CA1292857C (en) | 1991-12-10 |
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| Application Number | Title | Priority Date | Filing Date |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111410231A (en) * | 2020-04-24 | 2020-07-14 | 核工业北京化工冶金研究院 | Method for preparing triuranium octoxide from excellent slag |
| CN117587277A (en) * | 2023-11-13 | 2024-02-23 | 湖南中核金原新材料有限责任公司 | Method for preparing uranate by fractional precipitation |
-
1987
- 1987-12-16 CA CA000554518A patent/CA1292857C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111410231A (en) * | 2020-04-24 | 2020-07-14 | 核工业北京化工冶金研究院 | Method for preparing triuranium octoxide from excellent slag |
| CN117587277A (en) * | 2023-11-13 | 2024-02-23 | 湖南中核金原新材料有限责任公司 | Method for preparing uranate by fractional precipitation |
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