FR2633606A1 - Process for separation by precipitation of the zirconium contained in uranium-containing carbonate solutions - Google Patents

Abstract

Process for separation of the zirconium and/or hafnium contained in an aqueous uranium-containing carbonate solution by selective precipitation of the zirconium (hafnium) using a hydroxamic acid dissolved in a water-miscible solvent, it being possible for the precipitate obtained to be floated.

Description

PROCESS FOR SEPARATING BY PRECIPITATION OF ZIRCONIUM
CONTENTS IN URBAN CARBONATE SOLUTIONS
TECHNICAL AREA
The invention relates to a process for the selective precipitation of zirconium contained in uranium carbonate solutions using an oragnic precipitation agent.

STATE OF THE ART
Depending on their origin, the uraniferous concentrates may contain among various impurities zirconium and / or hafnium. -In all that will follow the term zirconium also means "and / or hafnium". The zirconium content reported with uranium can reach very variable values often high and in the case of urano-zirconium ores they can be very high.

During the hydrometallurgical treatment of these ores destined to recover uranium in the form of concentrates, it is sometimes difficult to completely eliminate the zirconium which is then found at levels that may exceed 0.5% by weight relative to U in Uranium concentrate.

Such contents are unacceptable to subsequently obtain a uranium of nuclear purity (of the order of the ppm), zirconium being a highly disruptive element of the purification process usually used to obtain said nuclear purity.

Thus, those skilled in the art are led, when they are in the presence of a zirconium-containing uraniferous concentrate, to provide an additional treatment that is as inexpensive as possible for lowering the zirconium content, or even completely eliminating it, with a view to to carry out the final purification, at the nuclear level, in good conditions.

Said concentrate may come from any source, for example uranium or phosphate ore, retrieval of irradiated nuclear fuel, uranium residues, etc.), it may have any chemical nature (oxide, uranate, fluoride, etc.) or any physical state (solid, solution ...).

To carry out such a uranium-zirconium separation, various processes have been used, but they mainly concern uranium contained in aqueous acid solution.

For example, there are known liquid-liquid extraction processes using solvents, immiscible with the aqueous solution, the selectivity of the uranium-zirconium separation generally depends on the acidity of said solution; Moreover, these extraction processes are often difficult to implement because of problems of stability of the solvent in these media, problems of emulsion, formation of dirt interfaces ... They motivated the applicant in particular to to study precipitation separation processes, which do not have these disadvantages. It has thus developed a process consisting of simultaneously precipitating a uranium peroxide and a zircyrut peroxyfluoride by adding hydrogen peroxide and soluble fluoride to the solution. starting uranium, and selectively resolving the uranium with an acid (FR 2 531 698).

Precipitation methods have also been developed for the selective separation of molybdenum also contained in a uraniferous acid medium, using organic molecules solubilized in a water-miscible solvent, such as hydroxyoximes (FR 2 583 4ci3). ) or hydroxamic acids (FR 2 583 404).

But it is possible that during hydrometallurgical treatments of uranium products, such as ores, concentrates, residues, uranium and its impurities, including zirconium, are in aqueous solution in a carbonated place; this is the case when, for example, a so-called alkaline attack of a uranium ore is carried out, or uranium and certain impurities, including zirconium, are reextracted from an organic phase, with the aid of a carbonated aqueous phase. The applicant has thus sought to solve the problem of purification of the zirconium impurity of this type of solution.

OBJECT OF THE INVENTION
The object of the invention is to purlfler a zirconium carbonate aqueous uraniferous solution which may also contain other impurities, by selective precipitation of said zirconium. This precipitation is generally selective with respect to the uranium and such that the residual content of zirconium in the carbonate solution is as low as possible: it is thus interesting to obtain a ratio (Zr / U) in the purified carbonated solution which does not exceed 0.5t by weight, or even 0.28. The method is also such that simultaneously the amount of uranium entrained during the precipitation is low, which can be limited to 5% by weight of the precipitate of the zirconiferous complex, and the uranium loss can be less than 0.58 of the total uranium used. This entrained uranium comes in part from the impregnation of the zirconiferous precipitate by the mother liquors.

Another object is to use a zirconium-specific oragnetic precipitating agent with respect to uranium.

Another object is to have a zirconium-uranium separation process that is simple to implement using ionic flotation or molecular flotation.

DESCRIPTION OF THE INVENTION
The invention is a process for separating zirconium and / or hafnium contained in a uraniferous aqueous carbonate solution by precipitation of zirconium, characterized in that said solution is treated with a precipitating agent consisting of at least one hydroxamic acid solubilized in a solvent miscibilized with water.

 It is known that certain hydroxamic acids and a solution in a nickel-free magnesium solvent can extract, under certain operating conditions, zirconium, preferably from uranium, from aqueous acid solutions, for example see US Pat. No. 3,900,551 (Baroncelli) or US Pat. .Chem. Research (S) 1982, 90-91 (F. Vernon). But such extraction results in significant amounts of uranium and moreover generally has the drawbacks related to liquid-liquid extraction mentioned above.

Furthermore, the Applicant has found that the hydroxamic acids, solubilized in an acidic aqueous phase containing zirconium, do not precipitate. However, in view of these unfortunate results, she continued her research and unexpectedly found that in aqueous carbonate medium hydroxamic acids, soluble in a solvent miscible with water, precipitated zirconium without causing significant losses. uranium.

The carbonated medium contains carbonate and / or ammonium bicarbonate, or an alkali or alkaline earth metal, or a mixture of these carbonates and bicarbonates; they form with uranium a soluble complex of uranyl tricarbonate; zirconium as well as other metallic impurities, such as Mo, V, Ti ..., or others such as S04, C1, NO3,
P04 ... are also solubilized.

Such a medium can come from a wide variety of hydrometallurgical treatments carried out on urano-zirconium products, such as ores, phosphates, treatment residues, concentrates, etc. In particular, this is the case with carbonated solutions obtained after alkaline attack of ores, or solutions obtained by carbonated extraction of solvents for extraction of uraniferous acid solutions.

According to the invention the treatment is carried out in a carbonate medium and. The pH is usually greater than about 5, more preferably 6 to 10, and most preferably 7 to 9.

Beyond the limits described, the formation of insoluble complexes
Zr-hydroxatric acid can be hindered by other Zr precipitation phenomena: by nyirnlyse in areas of acidic pH or by coprecipitation of hydroxide. in areas of high pH, uranium can also precipitate in this case by degrading the selectivity of the process.

Concentratior. uranium can reach saturation but in general it is between a few fractions g / l and 60 g / l.

By this method, uranium solutions having a zirconium content, expressed in g / l, of up to about 5 g; it is also preferable that the zirconium content is greater than 5 mg / l.

The presence of other impurities, such as those already mentioned, is not a problem; if some of them are entrained or complexed during the precipitation treatment, it is sufficient to take into account in the determination of the amount of precipitation reagent to be used.

dans laquelle R et R' sont des chaînes alkyles, ethoxyalkyles, aryles et benzylalkyle. On préfère cependant utiliser les acides substitués sur le carbone, du type

et en particulier celui où R est en CSHl7 (acide octylhydroxamique).The hydroxamic acids used in the invention correspond to the general formula:

wherein R and R 'are alkyl, ethoxyalkyl, aryl and benzylalkyl chains. However, it is preferred to use the carbon-substituted acids of the type

and in particular that where R is CSH17 (octylhydroxamic acid).

They are used alone or in mixture.

To use such oragnic acids according to the process they must be soluble in a solvent miscible with water, for example water, alcohol, formaldehyde, sodium hydroxide solution, ammonia solution ... or directly soluble in carbonated media. .

In order to effect the precipitation of zirconium according to the invention, the molar ratio, +, of the hydroxamic acid on the zirconium initially present is generally greater than 0.5, usually between 2 and 20, and the best results are obtained when this ratio is between 3 and 6.

The ratio 2 is adjusted according to the initial concentrations between U and Zr and as a function of the desired purification rate. If the ratio (Zr / U) is high in the starting solution, a high ratio can be used to increase the amount of zirconium removed, the resulting uranium, partly by impregnation of the precipitate with the mother liquor, then increasing. On the other hand, if the initial ratio (Zr / U) is not very high, the use of a high ratio will have less impact on the quantity of U involved.

Conversely, the use of a high ratio may decrease the amount of zirconium removed and the amount of uranium involved will also be less.

The hydroxamic acids are chelating agents of zirconium and give an insoluble complex. It is possible that they complex other metal ions present in the carbonated solution, the complexes obtained being able to be soluble or insoluble. In this case the amount of hydroxamic acid introduced into the carbonated solution must be increased accordingly. On the other hand, it is not necessary to take into account impurities that do not react with hydroxamic acids, for example Mo Vl.

The precipitation temperature can be chosen in a wide range; however, temperatures are preferred. between ambient and 800C, high temperatures to better flocculate the precipitate.

 It is therefore sufficient to add the hydroxamic acid to the uraniferous carbonate solution containing zirconium to cause the formation of a precipitate which can then be recovered by any known means such as, for example, decantation, centrifugation, filtration or a combination thereof. means.

But the Applicant has also found that when the groups P and R 'or of hydroxamic acids have a certain hydrophobicity com? Re, for example, in the case of octylhydroxamic acid, the precipitate formed between this molecule and zirconium could be recovered by fottation. This technique consists of passing an ascending stream of gas bubbles (air or nitrogen) into the reaction medium. Due to the hydrophobic nature of the precipitate, it is adsorbed on the gas bubbles and rises to the surface where it can be collected from the formed foams. The flotation is complete and rapid, which can be less than 4 minutes, and the entrainment of liquid is reduced.

The invention can be illustrated by the following examples:
EXAMPLE 1
This example illustrates the precipitation of a carbonated synthetic solution containing only zirconium introduced in nitrate form.

Its concentration of HCO3Na is 0.3 M and in Zr of 100 mg / l.

The precipitation of zirconium was carried out at room temperature; the precipitating agent, or collector, is a solution of octylhydroxamic acid in 0.5 M sodium hydroxide; different molar ratios b (collector on zirconium) were used. The final pH value is between 7 and 8. The purification results are given in Table 1 below:
TABLE 1

<tb> N <SEP> TEST <SEP> REPORT <SEP> MOLAR: <SEP> Zr <SEP> PERFORMANCE
<tb>: <SEP>: <SEP> @ <SEP> collector <SEP>: RESIDUAL <SEP> IN <SEP> LA <SEP>: ELIMINATION:
<tb> zirconium <SEP> SOLUTION <SEP> CARBONATE <SEP>: <SEP> of <SEP> Zr
<tb>: <SEP>: <SEP>: <SEP> mg / l <SEP>: <SEP>
<tb><SEP> 1 <SEP> 1 <SEP>: <SEP> 2 <SEP>: <SEP><SEP> 16.7 <SEP>: <SEP> 83.3
<tb>: <SEP> 2 <SEP>: <SEP> 4 <SEP>: <SEP><SEP><0.5<SEP>:<SEP> 99.9
<tb>: <SEP> 3 <SEP>: <SEP> 6 <SEP>: <SEP><SEP><0.5<SEP>:<SEP> 99.9
<Tb>
It shows that the treatment rate in Zr is already very good for a relatively low P ratio. and that his elimination is total as soon as =
EXAMPLE 2
Other series of tests were carried out using industrial type solutions obtained from a uranium ore of sedimentary origin.

In this example, two starting solutions are used whose concentrations in U, Zr and, incidentally, MQ are given in FIG.
Table 2 and having a pH of 7.7. The ratio (Zr / U) varies from 1.9 to 2.2% by weight.

The tests were carried out starting from 100 cm3 of the uranium carbonate solution to which is added a solution of octylhydroxamic acid in 0.5 M sodium hydroxide to selectively precipitate zirconium with respect to uranium.

The tests were carried out at 200 ° C. and the precipitation pH used was 7.7.

The results are given in Table 2 below:
TABLE 2

<tb> I <SEP> I <SEP> I <SEP> I <SEP> | <SEP> I <SEP> I <SEP> I <SEP> I
<tb> | <SEP> N <SEP> COMPOSIT.DE <SEP><SEP> I <SEP> REPOR <SEP> I <SEP> DILUTION <SEP> I <SEP> Zr <SEP> RESID. <SEP> @ <SEP> YIELD <SEP> I <SEP> U <SEP> IN <SEP> I <SEP> U <SEP> RESIDUAL <SEP> I <SEP> (Zr / U) <SEP> I
<tb> I <SEP> TEST <SEP> I <SEP> SOL.CARBONATE <SEP> I <SEP> MOLAR @@ <SEP><SEP> DUE <SEP> AT <SEP> I <SEP> IN <SEP> SOL.I <SEP> ELIMINATE. <SEP> I <SEP> SOLUT. <SEP> I <SEP> IN <SEP> PRECIP.I <SEP> IN <SEP> I
<tb><SEP> A <SEP> SPLIT <SEP> Collect <SEP> COLLECT. <SEP> CARBONAT. <SEP> FROM <SEP> Zr <SEP> CARBON. <SEP> ZIRCONIFER <SEP> SOLUT.
<Tb>

RUSTED <SEP> RUSTED <SEP> CARBON.
<tb><SEP> Zr <SEP> EPURATED
<tb> U <SEP> Zr <SEP> MB
<tb> g / l <SEP> g / l <SEP> g / l <SEP> cm3 <SEP> mg / l <SEP>% <SEP> g / l <SEP>% <SEP> Weight <SEP>% weight
<tb> 1 <SEP> 61 <SEP> 1 <SEP> 41,110,767 <SEP> 13,3 <SEP> i <SEP> 2,4 <SEP> 1 <SEP> 20 <SEP> 1 <SEP> 198,2 <SEP> 1 <SEP> 69 <SEP> 1 <SEP> 39.4 <SEP> 1 <SEP> - <SEP> 1 <SEP> 0.60 <SEP> | <September>
<tb> I <SEP> I <SEP><SEP> I <SEP><SEP> I <SEP>(<SEP> I <SEP> I
<tb> I <SEP> 99 <SEP> 1 <SEP> 37.4 <SEP> 0.762 <SEP> @ 3.2 <SEP><SEP> I <SEP> 4 <SEP> i <SEP> 16 <SEP > | <SEP> 6.4 <SEP> | <SEP> 99 <SEP> 1 <SEP> 32.9 <SEP> 1 <SEP> 2,3 <SEP> 1 <SEP> 0.02 <SEP> I
<tb> 100 <SEP> 37.4 <SEP> 0.762 <SEP> 3.2 <SEP> 6 <SEP> 24 <SEP> 5.1 <SEP> 99 <SEP> 29.2 <SEP> 4.2 <SEP> 0.02
<Tb>
It is observed that the purification is done under acceptable conditions using a low ratio i since, in the test 64, about 70% of the zirconium has been removed and the Zr content of the purified uranium is very close to 0 5t which is the value usually desired.

This tends to show that, in order to improve the purity of recovered uranium, it is desirable to increase the ratio when the zirconium content of the initial solution is high.

Moreover, it can be seen that the selectivity of the U-Zr separation is very good since only a very small amount of Uranium is found in the zirconium precipitate: this precipitate weighs approximately 0.6 to 0.7 g. Uranium is less than 1% of the U used.

EXAMPLE 3
This test is intended to illustrate the selectivity of uranium-zirconium separation.

The carbonated starting solution is from the same ore as in Example 2. It has the following composition:
U 36.4 9/1 pH 7.7 2r 760 mg./l (Zr U = 1.9t)
Total carbonate: 40.9 g / l
Other impurities
As <0.02 g / l V <0.04 g / l
Ca <0.04 g / l Mo 3.4 g / l
PO 4 0.16 g
SiO2 <0.04 g / l
150 cm3 of this solution were added. octylhydroxamic acid in solution in 0.5M sodium hydroxide. The other operating conditions were as follows: temperature 200C} = mole collector = 4.6
mole Zr dilution due to the collector: 25 cm3.

After precipitation, a purified solution and a precipitate of 1.05 g were obtained, which were analyzed and are the subject of the following Table 3:
TABLE 3

<tb>: <SEP>: <SEP> SOLUTION <SEP> OUR <SEP>: <SEP> PRECIPIT
<tb><SEP> g / l <SEP>: <SEP>
<tb> As <SEP> As <SEP><0.02<SEP>:<SEP><SEP> 0.072
<tb> Ca <SEP><G, 03 <SEP>: <SEP><SEP> 0.12
<tb>: <SEP> PO4 <SEP>: <SEP> 0.14 <SEP>: <SEP><SEP> 0.02
<tb> SiO2 <SEP><0.03<SEP><0.10
<tb> Mo <SEP>: <SEP> 3.0 <SEP>: <SEP><SEP> 0.035
<tb>: <SEP> V <SEP>: <SEP><0.03<SEP>:<SEP><SEP><0.10
<tb> Th <SEP>: <SEP>. <SEP> 0.32
<tb> Zr <SEP><0.03
<tb>. <SEP> U <SEP>: <SEP> 30.85 <SEP>. <SEP> 2,6
<Tb>
This test makes it possible to see the different behavior of each of the impurities: in particular uranium, although being the main element in the starting solution, is not entrained during precipitation, the loss of uranium in the precipitate zirconium is very low and represents only 0.4% by weight of the starting uranium, part of which is constituted by mother liquors impregnating said precipitate.

On the other hand, Mo is not precipitated with Zr.

EXAMPLE 4
This example illustrates the influence of pH and temperature.

These tests were carried out with 100 cm3 of a starting carbonate solution, still from the same ore, containing:
U 38.1 g / l
Zr 730 mg / l
Octylhydroxamic acid was added using an alcohol solution in an amount such that j = 4, the dilution caused by this addition being 16 cm3.

The influence of pH is given in Table 4, where the tests were carried out at 20 ° C.

TABLE 4

<tb> N <SEP> TEST <SEP>: <SEP> pH <SEP>: <SEP> Zr <SEP> RESIDUAL <SEP>: <SEP><SEP> PERFORMANCE
<tb> IN <SEP> SOLUTION <SEP>: ELIMINATION
<tb>: <SEP>: <SEP>: <SEP> CARBONATE <SEP> SEPARATE <SEP>: <SEP> of <SEP> Zr <SEP>
<tb> mg / l <SEP>: <SEP> z <SEP><SEP> weight
<tb>: <SEP> 116 <SEP>: <SEP> 5.9 <SEP>: <SEP> 7 <SEP>: <SEP> 98.89
<tb>: <SEP> 115 <SEP>: <SEP> 7.7 <SEP>: <SEP> 7 <SEP>: <SEP> 98.89
<tb>: <SEP> 117 <SEP>: <SEP> 9.8 <SEP>: <SEP> 8 <SEP>: <SEP> 98.73
<Tb>
During these tests, the pH was controlled to maintain at least its initial value and not to exceed the prescribed limits. Thus it has always been lower respectively at 6.5 - 8.3 - 9.8.

It can be seen that the pH does not have a very pronounced influence on the precipitation of zirconium, provided that it remains within the limits prescribed according to the invention as has been said.

In run 115 the zirconium precipitate was flotation recovered by bubbling air through the slurry; it is total and fast (less than 4 minutes).

The influence of temperature is given in Table 5, where the tests were carried out at pH 8.8.

TABLE 5

<tb><SEP> NO <SEP> TEST <SEP>: <SEP> TEMPERATURE <SEP>: Zr <SEP> RESIDUAL <SEP> IN <SEP>: <SEP> PERFORMANCE
<tb> C <SEP>: <SEP> SOLUTION <SEP>: <SEP> ELIMINATION <SEP>:
<tb>: CARBONATE <SEP> SPRING: <SEP> FROM <SEP> Zr
<tb> mg / l <SEP>%
<tb>: <SEP> 118 <SEP>: <SEP> 20 <SEP>: <SEP> 8 <SEP>: <SEP> 98.73
<tb>: <SEP> 119 <SEP>: <SEP> 40 <SEP>: <SEP> 8 <SEP>: <SEP> 98.73
<tb> 120 <SEP>: <SEP> 60 <SEP>: <SEP> 8 <SEP>: <SEP> 98.73
<Tb>
The removal of zirconium is not affected by the temperature, however a high temperature improves the flocculation of the precipitate.

Claims (6)

1. Process for separating zirconium and / or hafnium  in a uraniferous aqueous carbonate solution by precipitation  zirconium (hafnium) characterized in that said solution is treated  with a precipitating agent consisting of at least one acid  hydroxamic solubilized in a solvent miscible with water. 2. Method according to claim 1 characterized in that it uses  the hydroxamic acids substituted on the carbon.  octylhydroxamic acid. 3 Process according to claim 2, characterized in that 4. Method according to any one of claims 1 to 3 characterized  in that the molar ratio between the precipitating agent introduced  and zirconium (hafnium) is greater than 0.5 and preferably  between 2 and 2C. 5. Process according to a yuelcorique of claims 1 to 4 characterized  in that the pH of the carbonated medium is greater than 5. 6. Method according to any one of claims 1 to 5 characterized  in that the zirconium precipitate obtained is recovered by stream  station.