FR2516498A1 - Purifying uranium concentrate contg. zirconium and/or hafnium - by uranium peroxide pptn. followed by uranium leaching - Google Patents

Abstract

Uranium concentrate contg. zirconium and/or hafnium impurities is purified by (a) suspending the concentrate in an aq. medium; (b) slowly acidifying the suspension in a controlled manner; (c) treating with hydrogen peroxide to ppte. the uranium and almost all of the zirconium and/or hafnium; (d) sepg. the ppte. and treating it with an acid to solubilise the uranium as uranyl ions; and (e) sepg. the uranyl soln. from the solid phase contg. the zirconium and/or hafnium. The process gives an uranium liquor of improved purity by eliminating all impurities except Zr and/or Hf in a first leaching and pptn. stage (steps a-c) and then eliminating the Zr and/or Hf in a second uranium leaching stage (steps d and e).

Description

PURIFICATION TREATMENT OF A URANIFER CONCENTRATE
The invention relates to a process for the purification of uraniferous concentrates containing impurities, in particular zirconium and / or hafnium, which comprises, in a novel combination, in a first stage, the treatment of uraniferous concentrates, firstly by an acid agent introduced in a strictly controlled quantity, then by hydrogen peroxide for the purpose of forming impure uranium peroxide, and, in a second step, the treatment of the impure uraniferous solid phase resulting from the first step at medium of an acidic agent ensuring the obtaining of a purified uraniferous liquor.

For a long time now, it is known that uranium cone concentrates contain or are likely to contain many impurities whose presence proves to be troublesome during the final purification of uranium.

The treatment of such uraniferous concentrates usually involves, first, the solubilization of uranium in the form of salts of Kranyl and the impurities accompanying it, then the precipitation of uranium in a peroxidized appearance by the use of peroxide. hydrogen.

The literature describes such treatments and describes the difficulties in obtaining a sufficiently pure uranium compound due to the presence of impurities.

The most commonly applied method for the treatment of a uranium concentrate is described in "The Extractive Metallurgy of Uranium".
R. MERITT, 1971 edition - Colorado School of Mines Research Institute, pages 247 and 248, and in "Proceeding of the International Conference on the Peaceful Uses of Atomic Energy", United Nations, vol.

VIII, pp. 141 to 143 (1955) by EL ZIMMER on "Preparation and Separation of Uranium Peroxide, as a stage in the chemical purification of
Crude Uraniferous Products. "These articles mention that, if the precipitation of the uranium within the solution impure the container, theoretically makes it possible to keep in solution the impurities present, the uranium precipitate obtained retains non negligible quantities of impurities at the moment. where the separation of said precipitate takes place, despite a long and prolonged washing. Thus, the precipitation and washing of the uranium peroxide makes it possible to satisfactorily remove impurities such as arsenic, aluminum, boron, bismuth, calcium, magnesium, manganese, molybdenum, vanadium, sodium, nickel, antimony, tin and zinc, but do not provide a sufficiently reasonable elimination of iron, phosphorus and silicon, if other purification treatments are not practically carried out.

When the uraniferous concentrate also contains other impurities such as zirconium and / or hafnium, they generally precipitate simultaneously with the uranium, during the treatment with hydrogen peroxide aqueous solutions containing them, giving a peroxide uranium that does not lead to the production of sufficiently pure uranium for nuclear applications.

Starting from this general process for the treatment of uranium concentrates, the specialized literature describes improved processes, making the same use of hydrogen peroxide for precipitating uranium peroxide from aqueous uraniferous acid solutions also containing solubilized impurities, said processes differing from each other by means suitable for the removal of one or more specific impurities.

Thus, in the "Report of Investigations 7 931 of the US Bureau of Mines 1974", by M. SHABBIR and KE TAME, dealing with the "Pretci-pitation of uranium by hydrogen peroxide", describes a means for obtaining pure uranium peroxide which consists in treating, at ambient temperature, an acidic aqueous solution of uranium, enriched with molybdenum and vanadiferous inert purities, by means of hydrogen peroxide by regulating the pH of said solution has various values between 3 and 6 for a period of four hours. According to this study, the authors specify that the pH of said solution should be maintained between 3.5 and 5 to obtain a sufficiently purified uranium peroxide precipitate.

Such a process, if applied to impure uraniferous concentrates, containing particular impurities such as zirconium, and / or hafnium, could lead only to the attention of an impure uranium peroxide, since said particular impurities would precipitate with uranium upon introduction of hydrogen peroxide.

Another method, more evolved with regard to the impurities present, is described in the USP. 2,770,521. This process proposes the treatment of a solution of uranyl sulphate firstly comprising the precipitation of impurities such as iron, copper, chromium, cobalt, nickel, manganese, molybdenum, by adjusting the pH of the solution between 3 and 4 by means of calcium carbonate, and then, after separation of the impurity precipitate, treating the depleted uraniferous solution with impurities by means of the hydrogen peroxide introduced into said solution, in order to precipitating the uranium peroxide, the precipitation medium being maintained at a temperature at most equal to 650C and at a pH between 2.5 and 3.5.

The interest of such a process appears limited when the uranyl sulphate solution to be treated contains not only the usual impurities, but also those consisting of zirconium and / or hafnium. Because this process practicing the selective precipitation of impurities by means of calcium carbonate, is likely to lower the content of SO4 ions in the uranium solution and consequently to cause a partial coprecipitation of uranium, zirconium and / or hafnium at the same time as the impurities to be removed, resulting in a significant loss of uranium. Moreover, only a fraction of the zirconium and / or hafnium being precipitated with the impurities, the other fraction remaining in solution in the uranium-containing liquor will be precipitated at the same time as the uranium peroxide.

Thus, the prior art proposes to those skilled in the art solutions that can not fully satisfy him, since a uraniferous liquor resulting from the solubilization of a concentrate by means of an acidic agent, is one of the impurities present zirconium and / or hafnium, because the proposed treatments lead to the simultaneous precipitation of uranium and some of the aforementioned specific impurities, subsequently requiring a purification treatment of uranium peroxide in order to obtain the required purity in nuclear applications.

Therefore, the recommended treatments can not meet the requirements of users, the applicant, continuing its research, has found and developed a process for purifying uranium concentrates, free from the aforementioned drawbacks and to obtain a uraniferous liquor d ' a very improved purity.

The process according to the invention for the purification of uraniferous concentrates containing impurities including, in particular, at least one of the elements constituting the formation group ofirconium and / or dehafnium, comprising the treatment of said concentrates in an acidic and hot aqueous medium at room temperature. medium of hydrogen peroxide to cause the formation of uranium peroxide, is characterized in that, in a first step and, in order to quantitatively precipitate uranium and solubilize all or part of the impurities, is suspended the uraniferous concentrate in the aqueous medium, then the suspension is acidified slowly and in a controlled manner by means of an acidic agent, the resulting acidified aqueous medium is treated with hydrogen peroxide, causing the formation of a precipitate containing for the most part uranium and almost all the zirconium and / or hafnium which is separated from the impurity-laden liquid phase, then, in a In the second step, the precipitate from the first step is treated with an acidic agent to cause the conversion and solubilization of the uranium to soluble uranyl ions, and the liquid phase containing the uranyl ions is separated. of the solid phase formed of a compound containing zirconium and / or hafnium.

The uraniferous concentrates subjected to the process according to the invention are those which come from hydrometallurgical treatments of uranium ores well known to those skilled in the art. They are generally in the form of a solid mixture, composed for the most part of uranium, and in minor part of impurities such as, for example, silver, arsenic, aluminum, aluminum, bismuth, calcium, magnesium, manganese, molybdenum, vanadium, sodium, nickel, antimony, tin and, in particular, at least one of the metals constituting the group formed by the zirconium and hafnium.

According to the first step of the treatment, the uraniferous concentrate to be purified is dispersed in an aqueous medium maintained under agitation, constituting a suspension which is treated with an acidic agent.

The acidic agent must then be slowly introduced into said suspension, so that the impurities present are preferably solubilized.

The slow introduction time of the acidic agent is genetically between 5 and 200 minutes, but it is preferably chosen between 10 and 120 minutes.

The quantity of the acidic agent to be introduced for preferentially solubilizing the impurities is generally determined in equivalent
H + with respect to the content of impurities present, possibly excluding zirconium and hafnium. In practice, the amount of acidic agent to be introduced is determined relative to the alkaline and / or assimilated cations.

The amount of acidic agent to be introduced in this first step of the process of the invention corresponds at least to the stoichiometry of said cations: it is preferably between 1.1 and 2.5 times this stoichiometry.

Depending on the amount of the acidic agent introduced into the aqueous suspension of the uranium concentrate, the resulting acidified medium remains in the form of an aqueous suspension, or is in the form of a liquor possibly with a low turbidity. In the latter case, the liquor contains in solution all the uranium and the great majority of the impurities initially present in the uranium concentrate.

The temperature of the resulting acidified medium, whether in the form of a suspension or a solution, is controlled and must be at most equal to 800C; but, it is preferably maintained in a temperature range between 300C and 400C.

The resulting acidified aqueous medium, maintained at the desired temperature, is then treated with hydrogen peroxide introduced into said medium in an amount at least equal to twice the stoichiometry necessary for the precipitation of the only uranium peroxide.

The amount of hydrogen peroxide is at least 1.4 times the stoichiometric amount necessary for the precipitation of uranium peroxide, and preferably between two and three times said stoichiometry, so that uranium and impurities formed by at least one of the elements belonging to the group formed by zirconium and hafnium initially present in the uranium concentrate, are transformed and maintained in a solid form.

The transformation and the solid state maintenance of uranium and at least one of zirconium and hafnium elements is carried out, as is well known to those skilled in the art, at a pH generally between 2,5 and 4,5, which is controlled by the introduction of an alkaline agent such as sodium hydroxide, potassium hydroxide or ammonium hydroxide.

After the introduction of the hydrogen peroxide into the acidified medium, whose temperature and pH are maintained at the chosen values, the suspension resulting from said treatment is then subjected to a walling operation, consisting in keeping it in agitation in the field temperatures initially chosen for a time at most equal to 6 hours and preferably between 2 hours and 4 hours.

After said ripening operation, the suspension is subjected to a liquid-solid separation operation, by means known to those skilled in the art such as filtration, decantation or centrifugation, and the solid phase coming from this The separation is washed with water or a 0.2% aqueous solution of hydrogen peroxide in an amount sufficient to drive the solid phase impregnating liquor.

The solid phase thus separated and washed is formed of the precipitate containing uranium peroxide and at least one of zirconium compounds and / or hafnium, while the liquid phase contains in solution substantially all the other impurities.

According to the second stage of the treatment, the solid, essentially uraniferous, phase originating from the first stage is subjected to stirring and is then treated with an acidic agent, either in the pasty state under which it occurs or after having been suspended in an aqueous medium consisting of water or a recycling liquor.

The amount of acidic agent introduced in this second step into the uranium-containing solid phase, in the state or in aqueous suspension, corresponds to the only solubilization of the uranium present in said phase.

The uraniferous solid phase, before being subjected to the action of the acidic agent, in the state, or after formation of an aqueous suspension, can be brought to a temperature of between 60 and 1000.degree. C. and, preferably, between 85 and 950 ° C., but it may be desirable for the temperature to rise after the introduction of the acidic agent: in the latter case, the temperature rise is carried out in a slow ability to control the release of gas resulting from the dissolution of uranium.

The operation of dissolving the uranium is completed by an operation of ripening of the acidified medium at the temperature chosen in the abovementioned interval, which generally requires a time of at least one hour and, preferably, between 3 and 5 hours.

The suspension resulting from the dissolution and cure treatment is generally cooled to a temperature at most equal to 400C in order to reduce the solubility of the zirconium compound and / or hafnium in the aqueous phase. Then, said suspension is subjected to a separation operation making it possible to collect a purified uranium rich liquor, and to isolate a solid phase containing the impurities constituted by the zirconium and / or hafnium compounds.

The acidic agent used in the one and the other stage of the process according to the invention may be chosen from the group consisting of nitric acid, sulfuric acid and hydrochloric acid. This acidic agent may be the same in both steps, but it may be desirable that it be different and that it is even constituted by the mixture of at least two of these acids.

Thus, the process according to the invention is distinguished from the prior art by the solubilization and removal of most of the impurities in the first stage, while the second stage is characterized by the sole dissolution of the impure uranium from the first step and the removal of the last impurities in a solid form.

In practice, the process for purifying uranium concentrates according to the invention, which can be carried out in a continuous or discontinuous manner, comprises the following sequences: a) suspending the uraniferous concentrate purifying, in a
aqueous medium maintained in stirring state, b) introduction of an acidic agent in a controlled amount and
in a slow manner, the agitated suspension being maintained at a
adequate temperature, c) introduction of hydrogen peroxide into the resulting aqueous medium
both of the sequence b) in an amount at least equal to twice
the stoichiometry necessary for the soleprecipitation of the pero
uranium, the pH of the aqueous medium being maintained in the
2.5 to 4.5, d) suspension of the suspension from sequence c) by
maintained under agitation for not more than 6 hours, under
selected temperature and pH conditions in the sequences
b) and c), e) separation of a liquor charged with solubilized impurities and
a solid phase containing essentially uranium under the
peroxide form, f) washing the solid phase from sequence e), g) suspending the solid uranium phase in a medium
aqueous, consisting of water or a liquor recycling, h) dissolution of uranium with a quantity at most stoe
chiometric relative to the uranium present of an acidic agent
in the uranium suspension from sequence g), heated
before or during acidification, i) ripening of the suspension from sequence h) by
keeping stirring for at least one hour and at a time
chosen temperature, (j) cooling of the suspension from sequence (i) to
a temperature at most equal to 400 C, k) separation of a liquor rich in purified uranium and a phase
solid containing at least one of the impurities constituted by a
composed of zirconium and / or hafnium.

The invention will be better understood thanks to the numerical description of the diagram illustrating the two steps of the method.

According to the figure, the uraniferous concentrate S1 is suspended in (A) in a stirred aqueous medium consisting of the mixture of recycling liquors L13 and L15.

The suspension L1 thus obtained is then treated in (B) by the slow introduction of the acidic agent L20 to solubilize all or part of the impurities initially present in the uranium concentrate, while the temperature of the controlled medium is at most equal. at 800C.

The suspension acidified L2, maintained at the above temperature and with stirring, is treated in (C), at controlled temperature and pH, with an aqueous solution of hydrogen peroxide, the active amount is at least 1.4 times the stoichiometric amount required for the formation of uranium peroxide.

The suspension L 3 of uranium peroxide from (C 1 is subjected to a walling operation in (D), of keeping it under agitation in the range of temperatures initially selected and for a time at most equal to 6 hours.

At the end of this walling operation, the resulting suspension L4 is subjected to a liquid-solid separation to give a liquor L5, loaded with impurities and a cake Sg containing almost all the uranium initially present in the uranium concentrate, accompanied by impurities of zirconium and / or hafnium.

The cake S5 is then washed in (F) by means of an aqueous solution L23 to give a liquor L6 entraining the impure liquor for impregnating the cake S5, and a cake
The mixed liquors L5 and L6 constitute a liquor L14, of which one part L15 is recycled in (A), while the other part L16 is extracted from the treatment cycle.

The cake S6 is suspended in (G) in an aqueous recycle liquor L18, and the resulting suspension L7 is acidified in (H) by an acidic liquor L24, whose amount of acid corresponds to the solubilization only of the uranium, and said suspension is brought to a temperature at most equal to 1000C.

The resultant suspension t8 is subjected to a ripening operation
resulting in (I) at a temperature identical to that practiced in (H) and for a time of at least one hour.

At the end of the ripening operation, the resulting slurry Lg is subjected to a separation operation to give a purified L1o liquor, rich in uranium, and a S10 precipitate, mainly consisting of zirconium and / or hafnium compounds.

The precipitate S10 is then washed in (K) with an aqueous liquor L25, giving a liquor L11 and a cake S11, practically free of uranium.

The uranium liquors L10 and L11 are mixed to give the liquor L17, part of which L18 is recycled to (G), while the other part Llg corresponds to the uranium production liquor.

The cake S11 is subjected in (M) to a repulping operation using an aqueous liquor L26, giving a suspension L12 which is subjected to a liquid-solid separation operation in (N).

The solid S consists essentially of only zirconium impurities
13 'and / or hafnium, is removed from the treatment cycle, while the liquor L13 is recycled to (A).

EXAMPLE 1
This example serves the purpose of illustrating the importance of the operation of the walling in (d), during the first stage, of the acidic aqueous suspension after the introduction of hydrogen peroxide on the precipitation yield of water. uranium in a peroxidized form.

To this end, 200 g of an ammonium uranate concentrate were suspended in 200 g of water.

The ammonium uranate concentrate had the following composition in percent by weight
U: 61.16 X
Mo: 0.39%
Zr: 1.33%
NH4: 4.78 z
Miscellaneous: 32.34%
30 g of 10% HNO 3 and then 57 g of 100% H 2 O 2 were added to the suspension thus formed in the course of 20 minutes, the pH of the medium being checked to the value 3, while the temperature of the said suspension was maintained at 350C.

The influence of the weathering time is perceptible by the observation of the results mentioned in the following Table 1, which were established according to the time spent on the actual walling operation, after separation and washing of the cake.

Six tests were carried out for times ranging from 0 to 4 hours 30 minutes after introduction of hydrogen peroxide into the acid suspension.

TABLE I

<tb> TEST <SEP> TIME <SEP> FILTRAT <SEP> GATEAU
<tb><SEP> h, <SEP> mn <SEP> Umg / 1 <SEP> Momg / 1 <SEP> H2O <SEP>% <SEP> MB / sec <SEP> Z / sec
<tb><SEP> in <SEP> ppm <SEP> in <SEP> ppm
<tb><SEP> A <SEP> O <SEP> 127 <SEP> 1 <SEP> 250 <SEP> 31 <SEP> 476 <SEP> 13483
<tb><SEP> B <SEP> 0.30 <SEP> 11 <SEP> 1 <SEP> 150 <SEP> 32 <SEP> 509 <SEP> 13 <SEP> 070
<tb><SEP> C <SEP> 1.30 <SEP><<SEP> 10 <SEP> 1 <SEP> 150 <SEP> - <SEP> 30 <SEP> 360 <SEP>! <SEP><SEP> 13 <SEP> 106
<tb><SEP> D <SEP> 2.30 <SEP> 1 <<SEP> 10 <SEP> 1 <SEP> 100 <SEP>! <SEP><SEP> 30 <SEP> r <SEP> 389 <SEP> 11 <SEP> 357
<tb><SEP> E <SEP> 3.30 <SEP> 10 <SEP> 10 <SEP> 1 <SEP> 350 <SEP> 1 <SEP><SEP> 32 <SEP> 416 <SEP> 13 <SEP > 600
<tb><SEP> F <SEP> 4.30 <SEP>'<<SEP> 10 <SEP> 1 <SEP> 450 <SEP> 31 <SEP> 489 <SEP> 13 <SEP> 405
<Tb>
The table shows that the cure time must be at least one hour for the solubilized uranium to be fully precipitated.

EXAMPLE 2
This example makes it possible to illustrate the influence of the quantity of the acid agent introduced, during the second stage, to effect the total dissolution of the uranium contained in the uranium peroxide, obtained during the first stage. .

Two attempts were made by varying the amount of the acidic agent introduced. The influence of the amount of said acidic agent is evidenced by the results mentioned in Table II.

For this, the first step of the process was carried out using the uraniferous concentrate defined in Example 1, which led to the production of a wet cake S6, subjected to the second stage of the process according to the invention. .

For each test, 200 g of the cake S6, formed of impure uranium peroxide, was used.

TABLE II

<tb><SEP> Content <SEP> in <SEP> U, <SEP> MB, <SEP> Zr <SEP> and <SEP> H <SEP> in <SEP><SEP> li
<tb><SEP> result <SEP> result <SEP> of <SEP><SEP> dissolution <SEP> and <SEP> of
<tb><SEP> ripening <SEP> of the <SEP> precipitate <SEP> from <SEP> of
<tb><SEP> the <SEP> first <SEP> step
<tb> TEST <SEP> HN03 <SEP> U <SEP> MB <SEP> Zr <SEP> r <SEP><SEP> Acidity
<tb> (100 <SEP>, (100 <SEP> Z) <SEP> g / l <SEP> mg / l <SEP> mg / l <SEP> free
<tb><SEP> G <SEP> 39.65 <SEP> 430.8 <SEP> 150 <SEP> 200 <SEP> 0.1 <SE> N
<tb><SEP> H <SEP> 55.81 <SEP> 1409 <SEP> 230 <SEP> 8 <SEP> 236 <SEP> 2 <SEP> N
<Tb>
According to this table, it appears that from a free acidity 0.1 N to 2 N, the impurity content Zr increases by about 40 times, thus showing the need to closely control the amount of acid introduced to achieve the dissolution uraniferous precipitate from the first step.

EXAMPLE 3
This example reveals the importance that must be given to the duration of the ripening operation (I) in the second step, which follows the operation of dissolution of the uranium from the precipitate resulting from the first step.

For this, five successive tests were carried out, using the same amounts of materials to be treated (200 g) and treatment (39.65 g of 100% HNO3) as in the test (G) of Example 2 .

For each test, the acid suspension was maintained at a temperature of 900C, with stirring, for a variable time.

The results expressing the Zr contents in the aqueous phase, collected after ripening and separation, are collated in Table III.
TABLE III

<tb> TEST <SEP> I <SEP> J <SEP> K <SEP> L <SEP> M
<tb> Time <SEP> of <SEP> mu
<tb> rissement <SEP> in <SEP> i <SEP> 2 <SEP> - <SEP> 3 <SEP> 4 <SEP> 5
<tb> hour
<tb> Zr <SEP> soluble
<tb><SEP> 365 <SEP> 260 <SEP> 220 <SEP> 200 <SEP> 190
<tb> in <SEP> mg / l <SEP>
<tb> Mo <SEP> soluble
<tb> in <SEP> mg / l <SEP>! <September>
<tb> iU <SEP> soluble <SEP> i
<tb> in <SEP> gil <SEP> I <SEP> L <SEP> t <SEP>
<Tb>
The table reveals the need to practice a cure time of at least 2 hours and, more preferably, of the order of 4 hours, time for which the levels of impurities Zr and Mo are acceptable.

EXAMPLE 4: (According to the figure)
In this example, the demander illustrates the method of the invention comprising the two processing steps.

According to the method, and in the first treatment step, 200 parts by weight of a uranium-containing concentrate having the following composition, expressed in% by weight on a dry basis, were introduced into the suspension zone (A).
U: 61.16%
Mo: 0.39 X
Zt: 1.33%
NH4: 4.78%
Other + H20: 32.34 Z
In this same zone (A), 200 parts by weight of water were introduced and then stirred for the time necessary to produce a homogeneous suspension.

To this suspension was added in 20 minutes the equivalent of 30 parts of 100% HNO 3 (zone B).

Then, to the acid suspension thus obtained, (Zone C) 57.0 g of H 2 O 2 (100%) (L 21) was added in 20 minutes at controlled pH 3 by addition of sodium hydroxide. (L22).

The suspension t3 exiting the zone (C) was subjected to a walling operation in (D), consisting in maintaining said suspension under stirring at a temperature of 350 ° C. for 2 hours 30 minutes.

The L4 suspension from (D) was then subjected to a separation operation at (E), giving a liquor L5 and a solid phase S5.

The solid phase Sg was then subjected to an operation in (F) by means of 200 parts by weight of water, giving a washing liquor and a solid phase S6.
The liquors L5 and L6 were mixed to give a liquor L14 of which a L15 fraction was recycled in (A) to the suspension of the uranium concentrate, while the L16 fraction was removed from the cycle to avoid the accumulation of impurities in the first one. step.

The L14 liquor represented 323 parts by weight, and had the following composition by weight
Mo 0.35 X
U: 2 ppm 2Dpm
H2'O2 5s0 z
NH4N03 12.9 Z
NaNO3: 1.7% H20 + Other 89, o5:
Thus, 90.0% of the molybdenum initially present in the uranium concentrate was removed using the L14 liquor.

The cake S6 leaving the wash (F) represented 349 parts by weight of a wet cake. This cake, after drying at 600C, had the following composition in percent by weight
U: 65.4%
Mo: 0.05%
Zr: 1.34%
NH4: 0.4%
Other + H20: 32.81%
In the second step of the treatment according to the invention, the cake resulting from the first treatment step, was treated in (H) with 65 parts of HNO 3 at 100 Z. This acid was introduced slowly in 20 minutes, the suspension thus obtained L8 , being brought to 900C in (I) and maintained at this temperature for 4 hours.

The Lg slurry from zone (I) was separated at (J) to give a liquor L10 and cake S10, which was washed at (K) with 22 parts by weight of water (L25). ) giving a cake S11 and liquor L11.

The liquors L10 and L11 were mixed and constituted a liquor L17 which represented 450 parts by weight. This L17 liquor had the following composition
U: 27.2%
Mo: 0.016%
Zr: 0.005%
H20 + NO: 72.779%
+ various
A fraction of the purified liquor L17 was recycled in (G) to the slaking of the S6 cake resulting from the first step while the L1o fraction constituted the uranium production liquor.

the S11 cake after drying at 600 ° C represented a mass of 5.6 parts by weight. This cake contained practically 99.1% of the zirconium initially present in the uranium concentrate, and its uranium content was such that it represented a 0.4% loss relative to the uranium initially present in the concentrate which, in the framework of the continuous process was resuspended in (M) in a weakly acidic liquor L26, to be recycled to (A) according to the liquor L13 after filtration (N).

Claims (16)

1. A process for purifying uraniferous concentrates containing impurities, in particular at least one of zirconium and / or hafnium elements, comprising treating said concentrates in an acidic and hot aqueous medium using hydrogen peroyxide to provoke the formation of uranium peroxide, characterized in that in a first step, and in order to precipitate the uranium quantitatively and to solubilize all or part of the impurities, the uraniferous con centrate is suspended in the aqueous medium, then the suspension is acidified slowly and in a controlled manner by means of an acidic agent, the resulting acidified aqueous medium is treated with hydrogen peroxide to form a precipitate containing substantially the uranium and almost all the zirconium, and / or hafnium which is separated from the impurity-laden liquid phase, then in a second step, the precipitated precipitate is treated. t of the first step using an acidic agent to cause the transformation and solubilization of uranium to soluble uranyl ions and separating the liquid phase containing the uranyl ions from the solid phase formed of a compound containing zirconium and hafnium. 2. Process for purifying uranium concentrates according to claim 1, characterized in that the time of introduction of the acidic agent in the first step is between 5 and 200 minutes, but preferably between 10 and 120 minutes. 3. Process for purifying uranium concentrates according to claims 1 and 2, characterized in that the amount of acidic agent introduced in the first step is determined in H + equivalent relative to the contents of the impurities present, and more particularly with respect to the contents. in alkaline and / or assimilated cations. 4. A method for purifying uranium concentrates according to any one of claims 1 to 3 characterized in that the amount of acidic agent introduced in the first step is at least equal to the stoichiometry of the alkali and / or assimilated cations present and of preferably between 1.1 times and 2.5 times said stoichiometry. 5. Process for purifying uranium concentrates according to any one of claims 1 to 4, characterized in that the acidified aqueous medium is a suspens ion or a solution. 6. A method for purifying uranium concentrates according to any one of claims 1 to 5, characterized in that the treatment with hydrogen peroxide acidified aqueous medium is carried out at a controlled temperature, at most equal to 800C, and preferably between 30 ° C and 400 ° C. 7. Process for purifying uranium concentrates according to claim 1, wherein the amount of hydrogen peroxide introduced into the acidified aqueous medium is at least 1.4 times the stoichiometric the precipitation of uranium peroxide and preferably between 2 and 3 times said stoichiometry. 8. A method for purifying uranium concentrates according to any one of claims 1 to 7, characterized in that the suspension resulting from treatment with hydrogen peroxide is kept stirring for a time at most equal to 6 hours, and preferably between 2 and 4 hours. 9. A method for purifying uranium concentrates according to any one of claims 1 to 8, characterized in that the suspension resulting from treatment with hydrogen peroxide is maintained at a temperature at most equal to 800C and preferably between 300C and 400C. 10. A method for purifying uranium concentrates according to any one of claims 1 to 9, characterized in that the precipitate resulting from the first step is treated in the state with an acidic agent. 11. A method for purifying uranium concentrates according to any one of claims 1 to 10, characterized in that the precipitate resulting from the first step is suspended in acidified water or in an acid recycling liquor. 12. A method for purifying uranium concentrates according to any one of claims 1 to 11, characterized in that the amount of acidic agent required for the treatment of the precipitate resulting from the first step is at most equal to the stoichiometric amount corresponding to the uranium present. 13. A method for purifying uranium concentrates according to any one of claims 1 to 12, characterized in that the treatment with the acidic agent of the precipitate resulting from the first step is carried out at a temperature between 600C and 1000C, and preferably between 850C and 950C. 14. Process for purifying uranium concentrates according to any one of claims 1 to 13, characterized in that the treatment with the acidic agent of the precipitate resulting from the first step takes place over a period of at least 1 hour. and preferably in a time between 3 and 5 hours. 15. A method for purifying uranium concentrates according to any one of claims 1 to 14, characterized in that the suspension resulting from the treatment with an acidic agent of the precipitate from the first stage, is cooled to a temperature at most equal to 400C . 16. A method for purifying uranium concentrates according to any one of claims 1 to 15, characterized in that the acidic agent introduced into the first and second stage belongs to the group consisting of nitric acid, sulfuric and hydrochloric acid and mixture at least from them.