WO2017085404A1

WO2017085404A1 - Hydrometallurgical method for separating and purifying tantalum and niobium

Info

Publication number: WO2017085404A1
Application number: PCT/FR2016/052974
Authority: WO
Inventors: Gauthier DEBLONDE; Marie-Aude ROUX; Valérie WEIGEL; Alexandre CHAGNES; Gérard Cote
Original assignee: Eramet; Centre National De La Recherche Scientifique; L'ecole Nationale Superieure De Chimie Paris
Priority date: 2015-11-17
Filing date: 2016-11-16
Publication date: 2017-05-26
Also published as: FR3043696A1

Abstract

The present invention relates to a method for separating and purifying niobium and tantalum from a basic aqueous solution containing niobium and tantalum. Said method is characterized in that it includes the following steps: a) placing an aqueous solution, having pH > 8 and containing niobium and tantalum, in contact with a quaternary ammonium salt organic solution so as to extract all or part of the niobium and tantalum from the aqueous solution; b) recovering the organic solution containing niobium and tantalum; d) placing the organic solution, containing niobium and tantalum, in contact with an acidic aqueous solution containing nitrate ions and oxalate ions so as to selectively back-extract the niobium from the tantalum; e) recovering the acidic aqueous solution, containing the purified niobium, and neutralizing with a base so as to obtain, on the one hand, a niobium precipitate and, on the other hand, an aqueous solution of oxalate ions and nitrate ions; f) recovering the organic solution from step d), containing the purified tantalum, and placing said organic solution in contact with an acidic aqueous solution of chloride salts or nitrate salts so as to back-extract the tantalum from the organic solution via anion exchange; and g) recovering the acidic aqueous solution from step f), containing the purified tantalum, and neutralizing said acidic aqueous solution with a base so as to obtain a purified tantalum precipitate.

Description

HYDROMETALLURGICAL METHOD FOR THE SEPARATION AND PURIFICATION OF TANTALIUM AND NIOBIUM

The present invention relates to the separation and purification of niobium (Nb) and tantalum (Ta) contained in a basic aqueous solution (pH> 8).

Niobium and tantalum are two transition metals used by many industries. Niobium is used primarily for the production of alloys and superalloys but is also used in the preparation of superconducting magnets, electronic components, catalysts, cutting tools, optical materials, surgical implants or more coins. Tantalum is used mainly for the manufacture of electronic components but it is also part of the composition of some superalloys, cutting tools, anticorrosive agents, medical implants or projectiles.

Due to the many fields of application of niobium and tantalum, and the fact that they are often associated in natural minerals or recyclable materials, niobium and tantalum separation methods have been developed in order to achieve the necessary purities. These methods are mainly hydrometallurgical processes using fluorinated reagents, and often at high concentrations (Zhu & Cheng, Hydrometallurgy, 107, 1-12, 2011, "Solvent extraction technology for the separation and purification of niobium and tantalum: A review Ungerer et al., Hydrometallurgy, 144-145, 195-206, 2014, "Comparison of extractants for the separation of TaF ₅ and NbF ₅ in different acidic media", Anatoly Agulyansky, "The Chemistry of Tantalum and Niobium Fluoride Compounds"; Elsevier Science, 2004). The niobium-tantalum selectivity obtained with this kind of process is based on the formation of different fluorinated complexes for the niobium and tantalum. These hydrometallurgical processes using fluorinated reagents are currently used on an industrial scale, in particular by the Brazilian company CBMM (Companhia Brasileire de Metalurgigia e Mineraçao), world leader in the extraction of niobium.

Due to technological constraints and environmental risks associated with the use of fluorinated reagents, the recovery of niobium and / or tantalum via the use of non-fluorinated reagents is studied at academic and industrial levels. Alkaline media and oxalic media are particularly studied because of their lower environmental impact and the high solubilities that niobium and tantalum possess in these BrilieEix concerns oxalic media, the quantitative extraction of niobium and tantalum contained in an aqueous solution of oxalic acid and sulfuric acid, by a water-immiscible organic phase based on a tertiary amine, has been described by Djordjevic et al. (Journal of Less-Common Metals, 11, 343-350, 1966, "Solvent Extraction of Niobium and Tantalum: III.Extraction mechanism in oxalic solutions with long chain tertiary amines"). More recently, Yang et al. (Hydrometallurgy 151, 56-61, 2015, "Extraction kinetics of niobium by tertiary amine N235 using Lewis cell") investigated the mechanism of extraction of niobium by commercial tertiary amine N235 from oxalic acid solutions. The case of tantalum is not addressed in this publication.

The patent application CN 1904097 describes the extraction and purification of niobium from a concentrate whose initial molar ratio Nb Ta is greater than 200, via the extraction of niobium by a tertiary amine from a solution containing oxalic acid, tantalum and niobium. The niobium oxalate is then extracted with a nitric acid solution and calcined. The disadvantage of this type of method is to consume oxalic acid which is complexed with niobium and not recovering tantalum, which degrades the economics of the process.

With regard to alkaline media, patent application FR 3008425 describes a hydrometallurgical process for dissolving niobium and / or tantalum after an etching of an ore or a concentrate of niobium and / or tantalum, at the same time. using concentrated NaOH. However, this application uses an acid solution to precipitate the niobium / tantalum mixture from the basic solution containing them and does not describe a specific step of separation of niobium and tantalum.

The article by Wang et al. (Hydrometallurgy, 98, 219-223, 2009, "Leaching of niobium and tantalum from a low-grade using a roast-water leach system"), describes the quasi-quantitative solution of niobium and tantalum after decomposition. a natural mineral of niobium and tantalum using KOH. However, this article does not address the problem of the separation of niobium and tantalum.

Finally, the article by Zhou and Tokuda (Journal of Central South University of Technology, Volume 7, No. 4, December 2000, "Solvent Extraction of Niobium from Alkali Solution by Methyltrioctylammonium Chloride") describes the possibility of extracting niobium. contained in an aqueous solution based on KOH and KCl (10.7 <pH <13) with an organic phase based on the methyltrioctylammonium chloride salt and toluene. The case of tantalum is not discussed in this article, nor the extraction of niobium after its extraction in the organic phase. Due to the growing interest in the dissolution of niobium and tantalum in alkaline media, it is therefore necessary to find new processes for extracting niobium and tantalum from these solutions and especially to separate them to purify them. , without using bad fluorinated salts for the environment. The inventors have thus surprisingly discovered that it was possible to extract the niobium and tantalum present in a basic aqueous solution with the aid of an organic solution based on a quaternary ammonium salt and then to selectively desextract niobium with oxalic acid and nitrate ions before extracting tantalum. The process uses no fluorinated reagent and most of the oxalic acid can be recycled within the process itself. The solutions used are also less acidic than those found in the processes currently used in the niobium and tantalum industry. Such a method is therefore very advantageous compared to industrial processes already developed.

The present invention therefore relates to a process for the separation and purification of niobium and tantalum from a basic aqueous solution containing niobium and tantalum and optionally iron and / or titanium, characterized in that it comprises the steps following:

a) contacting an aqueous solution having a pH greater than or equal to 8, advantageously between 9 and 14, in particular between 11 and 13, and containing niobium (Nb), tantalum (Ta) and, optionally, titanium (Ti) and / or iron (Fe), with an organic solution based on a quaternary ammonium salt so as to extract all or part of the Nb, Ta and optionally Ti and / or Fe from the aqueous solution to the organic solution;

b) recovering the organic solution containing Nb, Ta and optionally Ti and / or Fe;

c) optionally contacting the organic solution containing Nb, Ta and optionally Ti and / or Fe obtained in step b) with an aqueous solution of sulfuric acid so as to selectively extract the organic solution all or part of the iron and / or titanium, optionally extracted in step a), with respect to Nb and Ta and recovery of the organic solution containing niobium and tantalum;

d) contacting the organic solution containing Nb and Ta obtained in step b) or in the optional step c) with an acidic aqueous solution containing nitrate and oxalate ions so as to selectively extract the organic solution niobium vis-à-vis tantalum by formation of soluble complexes in aqueous solution between niobium and oxalate ions;

e) recovering the acidic aqueous solution resulting from stage d), containing the purified niobium, and neutralizing with a base (advantageously chosen from NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ and NH ₄ OH; among NaOH, KOH and NH ₄ OH, even more advantageously among NaOH and NH ₄ OH), advantageously up to a pH of between 1.5 and 10, more advantageously between 6 and 9, still more advantageously between 7 and 9 , so as to obtain, on the one hand, a purified niobium precipitate and, on the other hand, a solution of oxalate ions and nitrate ions which may optionally be recycled in step d) of the process;

f) recovering the organic solution from step d), containing the purified tantalum, and brought into contact with an acidic aqueous solution of chloride salts or nitrate salts in order to extract the tantalum from the organic solution by anion exchange ;

g) recovering the acidic aqueous solution resulting from stage f), containing the purified Ta, and neutralizing with a base (advantageously chosen from NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ and NH ₄ OH), advantageously to a pH of between 1 and 10, more preferably between 5 and 9, so as to obtain a purified tantalum precipitate. Step a) of the process according to the present invention thus makes it possible to extract part or all the niobium and tantalum from the aqueous solution having a pH greater than or equal to 8 containing them.

The aqueous solution having a pH greater than or equal to 8 containing niobium and tantalum and optionally titanium (Ti) and / or iron (Fe) to be treated in step a) of the process according to the present invention may consist of any aqueous solution, having a pH greater than or equal to 8, containing niobium and tantalum and optionally titanium (Ti) and / or iron (Fe). It contains at least one alkali metal, in particular chosen from lithium, sodium, potassium, rubidium and cesium, advantageously from lithium, sodium and potassium, more advantageously from lithium and sodium, advantageously it's sodium. For example, this solution may consist of a solution of salts of sodium hexaniobate and sodium hexatantalate, well known to those skilled in the art. Indeed at pH> 8, Nb and Ta form the ions H _x Nb ₆ 0i ₉ ^{x "8} and H _x Ta ₆ 0i ₉ ^{x" 8} (with 0 <x <3).

In solution, the negative charges are counterbalanced by alkaline ions. Nb and Ta then only form the salts of type:

As-xHxNb6Oig nH ₂ 0 (with A = alkaline)

Advantageously, the aqueous solution having a pH greater than or equal to 8 containing niobium and tantalum and optionally titanium (Ti) and / or iron (Fe) to be treated in step a) of the process according to the present invention more than niobium than tantalum, titanium and iron. Advantageously, its initial Nb / Ta ratio is greater than 30 g / g, in particular greater than 40 g / g, its initial Nb / Ti ratio is greater than 200 g / g, in particular greater than 300 g / g, and its initial Nb / Fe ratio is greater than 200 g / g, in particular 300 g / g. Very advantageously this solution typically contains 1 to 3 g / L of niobium and 25 to 100 mg / L of tantalum. It also contains 0 to 10 mg / L of iron, 0 to 10 mg / L of titanium and 1 to 2 g / L of alkali metal, especially sodium. In an advantageous embodiment, it is a solution of niobium and tantalum obtained in step d) of the process of patent application FR 3008425, that is to say of the solution of niobium and tantalum obtained by a process comprising the following successive steps: A) sodium conversion of a niobium and / or tantalum ore or concentrate containing titanium and / or iron by adding a solution of concentrated NaOH at a temperature of between 50 ° C. and 150 ° C;

B) solid / liquid separation and recovery of the solid obtained in step A);

C) washing the solid recovered in step B) with an aqueous solution containing at most 30 g / l of NaOH and recovery of the washed solid;

D) addition of water so as to dissolve the niobium and / or tantalum and recovery of an aqueous solution having a pH> 8 containing niobium and tantalum and optionally titanium and / or iron, in particular under the conditions as described in FR 3008425.

For the purposes of the present invention, the term "organic solution based on a quaternary ammonium salt" means any organic solution immiscible with water comprising at least one quaternary ammonium salt. Such a solution may contain a diluent, and optionally a phase modifying agent. Advantageously, the concentration of quaternary ammonium salt is between 0.1 and 10% by volume, advantageously it is between 1 and 5% by volume, in particular it is 2.5% by volume.

The diluent may be an aliphatic hydrocarbon, such as the product called "Elixore 205" marketed by Total Fluids, or an aromatic hydrocarbon, advantageously it is an aliphatic hydrocarbon. In particular, the diluent is the main constituent of the organic solution based on a hydrophobic quaternary ammonium salt. This solution therefore generally contains the diluent and the hydrophobic quaternary ammonium salt. Advantageously, the quaternary ammonium salt is a chloride, bromide, carbonate, sulfate, hydroxide or nitrate ion salt, more preferably a chloride, bromide, carbonate, sulfate or hydroxide ion salt, still more advantageously a sodium salt. chloride ion.

In one advantageous embodiment, the quaternary ammonium salt according to the invention is a long-chain alkyl ammonium salt, advantageously whose alkyl chains comprise in total between 20 and 50 carbon atoms, in particular between 25 and 31 carbon atoms. carbon atoms. More particularly, it is a compound of formula N ⁺ RiR ₂ R ₃ R 4 X ^" in which R 1, R ₂ , R 3 and R 4 represent, independently of each other, a linear or branched alkyl group, in particular a linear alkyl group, in that N ⁺ R R ₂ R ₃ R 4 comprises between 20 and 50 carbon atoms, in particular between 25 and 31 carbon atoms, and X ^" represents an anion, advantageously an anion chloride, carbonate, hydroxide, sulfate, bromide or nitrate, more preferably a chloride, bromide, carbonate, sulfate or hydroxide anion, more preferably a chloride anion. Advantageously, R 1 represents a methyl group and R ₂ , R 3 and R 4 represent, independently of each other, a linear or branched, in particular linear, C ₈ -C ₁₀ , in particular C ₈ , alkyl group. In particular, in this case, X ^" represents a chloride anion, for example methyltrioctylammonium of bromide, nitrate, sulfate, carbonate, chloride or hydroxide, in particular methyltrioctylammonium chloride, such as the product commercial called Aliquat® 336 from BASF.

Advantageously, the phase modifier is a linear or branched alcohol, in particular a branched alcohol, more particularly a primary alcohol, comprising at least 6 carbon atoms, advantageously between 10 and 15 carbon atoms. In particular it may be tridecanol, more preferably tris-tridecanol. Advantageously, the phase modifier has a concentration between 0.5 and 5% by volume, in particular between 1 and 2.5% by volume. The phase modifier is added to facilitate phase separation and to avoid the formation of a third phase.

Advantageously, step (a) is carried out with stirring.

Advantageously, the volume ratio organic phase / aqueous phase (O / A) of step a) depends on the niobium and tantalum content of the aqueous solution to be extracted. Advantageously it is> 0.5, in particular between 0.8 and 3, more particularly equal to 1.

Step (a) of the process according to the present invention can be carried out batchwise, semi-continuously or continuously.

In the case where it is implemented continuously, the contacting takes place against the current. It may further comprise several extraction stages, in particular at least two floors. Advantageously, it comprises only two extraction stages.

In a particular embodiment, the process according to the present invention is a continuous process comprising at least 2 extraction stages for step a) and extraction yields of niobium and tantalum at the end of step a), are greater than 90%.

The extraction efficiency of an element is calculated as follows:

Extraction yield (in%) = [(amount of the element in the organic solution after extraction) / (amount of the element in the aqueous solution before extraction)] * 100

Step (b) of the process according to the present invention makes it possible to recover the organic solution containing tantalum and niobium.

In particular this step is carried out by decantation or centrifugation, more advantageously by decantation. The optional step c) of the process according to the present invention makes it possible to purify the organic solution by eliminating all or part of the titanium and / or iron that could have been extracted in step a).

It is optional because its implementation depends on two elements:

the presence of titanium or iron in the organic solution obtained in step b) and

- the need to eliminate these elements (depending on their concentration and the inconvenience they cause).

This step therefore comprises a titanium and iron de-extraction step of the organic solution with the aid of an aqueous sulfuric acid solution and a separation step in order to recover the organic solution containing niobium and tantalum.

In an advantageous embodiment, the sulfuric acid solution of step c) has a concentration of between 1 and 4 mol / l, advantageously it is 2 mol / l.

Advantageously, the step of extracting the optional step (c) of the process according to the present invention is carried out with stirring. It can be implemented in batch, semi-continuous or continuous.

In the case where it is implemented continuously, the contacting between the two solutions takes place against the current. Advantageously, it comprises only one de-extraction stage.

Advantageously, the step of separating optional step (c) from the process according to the present invention is carried out by decantation or centrifugation, more advantageously by decantation.

Advantageously, the volume ratio organic phase / aqueous phase (O / A) of step c) depends on the content of iron and / or titanium of the organic solution to be extracted. Advantageously it is> 3, in particular> 4. Step d) of the process according to the present invention makes it possible to selectively extract the niobium from the organic solution according to the invention, vis-à-vis the tantalum, which remains in the organic solution. For this purpose, an aqueous acidic solution containing nitrate and oxalate ions is used because it will allow the formation of soluble complexes in aqueous solution between the oxalate ions and the niobium.

Advantageously, the aqueous acid solution containing nitrate and oxalate ions of step d) is an aqueous solution such that 0.2 <[H2C2O4] ≤ 0.8 mol / L and 0.1 ≤ [HNO3] ≤ 0.8 mol / L, advantageously 0.3 [[H ₂ C ₂ O ₄ ] <0.6 mol / L and 0.2 [[HN0 ₃ ] 0,5 0.5 mol / L, even more advantageously [H ₂ C ₂ 0 ₄ ] = 0.5 mol / L and [HN0 ₃ ] = 0.45 mol / L.

In a particular embodiment of the present invention, the acidic aqueous solution containing nitrate and oxalate ions of step d) is an aqueous solution of oxalic acid also containing nitric acid, a mixture of nitric acid and sodium nitrate, a mixture of nitric acid and potassium nitrate or a mixture of nitric acid and ammonium nitrate, advantageously, containing a mixture NH ₄ NO ₃ / HN0 ₃ / H ₂ C ₂ O 4, so advantageous in contents such that 0.05 ≤ [NH ₄ N0 ₃ ] ≤ 0.30 mol / L, in particular equal to 0.15 mol / L, 0.20 <[HN0 ₃ ] ≤ 0.45 mol / L , in particular equal to 0.30 mol / l, and [H ₂ C ₂ O ₄ ] = 0.5 mol / l.

Advantageously, step (d) is carried out with stirring.

Advantageously, the volume ratio organic phase / aqueous phase (O / A) of step d) depends on the niobium content of the organic solution to be extracted. Advantageously it is> 3, in particular> 4.

Step (d) of the process according to the present invention can be carried out batchwise, semi-continuously or continuously. In the case where it is implemented continuously, the contacting takes place against the current. It may also comprise several stages of desextraction, in particular at most four stages. Step e) of the process according to the present invention makes it possible to recover the niobium in solid form.

For this it has two steps:

the step of recovering the acidic aqueous solution resulting from stage d) and

the step of precipitation of niobium, in particular in the form of Nb ₂ 0 ₅ , nH ₂ 0, by neutralization using a base.

In particular, the recovery step of step e) is carried out by decantation or centrifugation, more advantageously by decantation.

Advantageously, the base of step e) is chosen from NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ and NH ₄ OH, advantageously from NaOH, KOH and NH ₄ OH, even more advantageously from NaOH and NH ₄ OH. . In particular, the base used is not Ca (OH) ₂ . Advantageously, the neutralization of step e) is carried out up to a pH of between 1.5 and 10, even more advantageously between 6 and 9, in particular between 7 and 9.

In a particular embodiment of the present invention, the method according to the invention comprises an additional step j) of recovering the solution of oxalate ions and nitrate ions resulting from step e), of concentration of said solution in order to selectively precipitate oxalate ions against nitrate ions, conversion of precipitated oxalate ions to oxalic acid and oxalic acid recycle obtained in step d) of the process.

Thus, the solution of oxalate ions and nitrate ions from step e) (after precipitation of niobium) can be concentrated, for example by evaporation, in order to selectively precipitate oxalate ions vis-à-vis ions nitrate and facilitate their recycling upstream of the process. For example in the case where the solution resulting from step e) is a mixture of sodium nitrate and sodium oxalate, sodium nitrate is much more soluble in water than sodium oxalate (~ 10 mol / L for NaN0 ₃ versus ~ 0.25 mol / L for Na ₂ C ₂₀ 04 at 25 ° C) which allows their separation by selective precipitation. Reasoning can be done if the solution resulting from step e) consists of a mixture of ammonium nitrate and ammonium oxalate (solubility of> 20 mol / L for NH ₄ N0 ₃ versus ~ 0.35 mol / L for (NH ₄ ) ₂ C ₂ O ₄ at 25 ° C). The solution of sodium nitrate or ammonium nitrate, resulting from the selective precipitation of the oxalate ions, is then recycled partly upstream of the process, for example in step d).

In another particular embodiment, the selective precipitation of the oxalate ions can also be carried out by adding a salt, for example sodium nitrate or ammonium nitrate, in order to displace the equilibrium of solubility of the ions. oxalate.

In another particular embodiment of the present invention, the oxalate ions are selectively precipitated from nitrate ions in the form of sodium or ammonium oxalate. The sodium or ammonium oxalate precipitate is then converted to oxalic acid by contacting with a mineral acid (H ₂ SO ₄ , HCl or HNO ₃ ) in order to be recycled upstream of the process, for example to step d).

Step f) of the process according to the present invention makes it possible to extract the tantalum from the organic solution by anionic exchange using an acidic aqueous solution of chloride salts or nitrate salts. Advantageously, the concentration of chloride salts is 2 mol / l. Advantageously, the concentration of nitrate salts is 1 mol / L.

In a particular embodiment of the present invention, the acid solution of chloride salts or nitrate salts of step f) is selected from an aqueous solution of hydrochloric acid (HCl), a mixture of hydrochloric acid and a chloride salt, an aqueous solution of nitric acid (HN0 ₃ ) and a mixture of nitric acid and a nitrate salt . Advantageously, it is chosen from a solution of hydrochloric acid at 2 mol / l, a mixture of 1 mol / l HCl and 1 mol / l NaCl, a 1 mol / l nitric acid solution, a mixture of HN0 ₃ at 0.5 mol / L and NaN0 ₃ at 0.5 mol / L and a mixture of HNO3 at 0.5 mol / L and NH ₄ NO ₃ at 0.5 mol / L. Advantageously, it is a mixture of 0.5 mol / L HN0 ₃ and 0.5 mol / L NH ₄ NO ₃ or a mixture of 1 mol / l HCl and 1 mol / l NaCl, even more advantageously 0.5 mol / l nitric acid mixture and 0.5 mol / l NH 4 NO 3.

Advantageously, step (f) is carried out with stirring.

Advantageously, the volume ratio organic phase / aqueous phase (O / A) of step f) depends on the tantalum content of the organic solution to be extracted. Advantageously it is> 1, in particular between 10 and 20. Step (f) of the process according to the present invention can be carried out batchwise, semi-continuously or continuously.

In the case where it is implemented continuously, the contacting takes place against the current. It may furthermore comprise several stages of desextraction, in particular at least two stages. Advantageously, it comprises only two stages of desextraction.

Step g) of the process according to the present invention makes it possible to recover the tantalum in solid form.

For this it has two steps:

the step of recovering the acidic aqueous solution resulting from stage f) and the step of precipitating tantalum, in particular in the form of Ta ₂ 0 ₅ , nH ₂ 0, by neutralization with the aid of a base. In particular, the recovery step of step g) is carried out by decantation or centrifugation, more advantageously by decantation.

Advantageously, the base of step g) is chosen from NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ and NH ₄ OH, even more advantageously from NaOH and NH ₄ OH. Advantageously, the neutralization is carried out up to a pH of between 1 and 10, advantageously between 1.5 and 10, advantageously between 5 and 9, and even more advantageously between 6 and 9.

In a particular embodiment of the present invention, the solution of oxalate ions and nitrate ions from step e) (after precipitation of niobium), is recycled upstream of the process, for example at the level of the step

0-

Advantageously, the organic phase based on quaternary ammonium salt obtained at the end of step f) after the extraction of tantalum is recycled. In this case, an additional step of regeneration of the solvent can be carried out before its reintroduction at the beginning of the process (in step a)). For example, the regeneration of the solvent can be carried out by contacting the organic phase with a solution based on chloride ions (such as a solution of hydrochloric acid or a mixture of hydrochloric acid and of ion salts chloride) or sulfate ions.

In an advantageous embodiment, the process according to the present invention comprises an additional step h) of recovering the purified niobium precipitate obtained in step e), washing the purified niobium precipitate, advantageously with water, and calcining the precipitate washed.

In the same manner, the process according to the present invention may comprise an additional step i) of recovering the purified tantalum precipitate obtained in step g), washing the tantalum precipitate, advantageously with water, and calcining the washed precipitate . The invention will be better understood in the light of the examples and figures which follow. Of course, these are given as illustrations and in no way constitute a limitation.

FIG. 1 represents a schematic diagram of a preferred embodiment of the process of the invention, designed to separate and purify the niobium and tantalum initially contained in an aqueous alkaline solution of the type described in the application of patent FR 3008425.

FIG. 2 shows the scheme of the process which was tested in example 9. In FIG. 1, the rectangles represent either multi-stage extractors such as those conventionally used in liquid-liquid extraction processes (mixer-settlers, pulsed columns, centrifugal extractors), or reactors such as those conventionally used in hydrometallurgical processes.

The organic phases entering and leaving these extractors are symbolized by double lines, while the aqueous phases are symbolized by simple lines. The dashed single lines represent possible recycling of reagents within the process.

In Figure 1, the initial aqueous solution typically contains 1 to 3 g / L of niobium and 25 to 100 mg / L of tantalum. It also contains 0 to 10 mg / L of iron, 0 to 10 mg / L of titanium and 1 to 2 g / L of sodium. The pH of the initial aqueous solution is close to 12.

The initial aqueous solution undergoes a first step, called "Extraction", which consists in extracting quantitatively niobium, tantalum and a part of the iron and / or titanium initially present. For this, the aqueous solution is brought into contact, against the current, with an organic phase containing 2.5% by volume of Aliquat® 336 diluted in a hydrocarbon (called "diluent") which may, for example be the Elixore 205 marketed by the Total Fluid company. This first step is non-selective with respect to niobium and tantalum. The number of extraction stages is of the order of 2 for a ratio of flow rates of organic and aqueous phases close to 1.

The organic phase resulting from the first step then undergoes a step called "Washing Fe, Ti" which consists of selectively removing all or part of the iron and / or titanium vis-à-vis niobium and tantalum. For this, the organic phase is contacted, against the current, with a solution containing about 2 mol / l of sulfuric acid. The flow rate of the aqueous phase is typically 4 times lower than the flow rate of the organic phase and there is only one de-extraction stage.

The organic phase is then sent to the "Desextraction Nb" step which consists of selectively extracting the niobium from the tantalum. For this, the organic phase is brought into contact, against the current, with an aqueous solution containing about 0.5 mol / l of oxalic acid, 0.15 mol / l of ammonium nitrate and 0.30 mol / l. L nitric acid. The flow rate of the aqueous phase is then typically 4 to 7 times lower than the flow rate of the organic phase and the number of de-extraction stages is less than or equal to 4.

The aqueous solution leaving the "Desextraction Nb" stage, containing the purified niobium, is then sent to the unit called "neutralization eluate Nb". At this stage, a base is added (for example NaOH or NH ₄ OH) to increase the pH of the solution to a value between 6 and 8. The increase in pH causes the selective precipitation of niobium oxide. purified (as Nb ₂ Os, nH ₂ O) with respect to the oxalate and nitrate ions. Part of the precipitation filtrates, containing the oxalate and nitrate ions, can then be recycled directly upstream of the process, for example at the "Desextraction Nb" stage. Alternatively, intermediate steps (not shown in Figure 1) may be added such as the concentration of the filtrates to separate the oxalate and nitrate ions, by selective precipitation oxalate ions, or the conversion of the oxalate precipitate to oxalic acid. These intermediate steps are intended to recycle most of the oxalic acid consumed in the "Desextraction Nb" step but also limit the consumption of nitrate ions of the process.

The organic solution leaving the step called "Nbextraction" is then sent to the "Taextraction" step in order to quantitatively extract the tantalum. For this, the organic phase is contacted, against the current, with an acidic solution containing chloride ions or nitrate ions to perform anion exchange. The concentration is typically 2 mol / L in the case of chloride ions or 1 mol / L in the case of nitrate ions. The ratio between the flow rate of the organic phase and that of the aqueous phase is greater than unity, typically between 10 and 20, in order to maximize the concentration of tantalum in the aqueous solution leaving the step. The number of de-extraction stages is at least 2. This step is non-selective, the traces of niobium, iron and / or titanium potentially present in the organic phase entering this stage are then coexextracted with tantalum.

The aqueous solution leaving the "Ta extraction" stage, containing the purified tantalum, is sent to the unit called "Ta neutralization eluate". At this stage, a base is added (for example NaOH or NH ₄ OH) to increase the pH of the solution to a value between 5 and 9. The increase in pH causes the selective precipitation of tantalum oxide purified (as Ta ₂ O ₅ , nH ₂ O) vis-a-vis the chloride or nitrate ions initially present in the solution. Part of the precipitation filtrates containing the chloride or nitrate ions may optionally be recycled upstream of the process, for example at the "Ta-extraction" stage.

The organic phase leaving the "Ta extraction" stage can be recycled at the beginning of the process, at the stage called "Extraction". In which case, a step called "Solvent Regeneration" can be added. It aims to regenerate the quaternary ammonium salt, present in the organic phase, in its initial form. In the case of Aliquat® 336, the quaternary ammonium salt is a chloride salt. The "Regeneration solvent" step may, in this case, consist in bringing the organic phase into contact with a concentrated solution of chloride ions, for example a solution of hydrochloric acid or a mixture of hydrochloric acid and a salt. of chloride ions.

Example 1: Extraction of niobium from various aqueous alkaline solutions using an organic solution based on a quaternary ammonium salt The organic solution consists of:

the extractant: quaternary ammonium (Aliquat® 336), at a concentration of 0.5% by volume;

the phase modifier: 1% by volume of / so-tridecanol;

- the diluent: aliphatic (Elixore 205).

Three different aqueous solutions are used:

Solution A (lithium medium): contains 1 g / L of niobium obtained by dissolving the lithium hexanoobate salt ϋ ₈ Γ¾Οι ₉ , 22Η ₂ 0, and 0.050 mol / L of lithium chloride. Its pH is adjusted to 12 by addition of LiOH;

Solution B (sodium medium): contains 1 g / l of niobium obtained by dissolving the salt of sodium hexaniobate Na7H b ₆ 0i9,15H ₂ 0, and 0.050 mol / l of sodium chloride. Its pH is adjusted to 12 by adding NaOH;

- Solution C (potassium medium) containing 1 g / L of niobium obtained by dissolving potassium salt hexaniobate Κ8Γ¾ΟΙ9,16Η ₂ 0, and 0.050 mol / L of potassium chloride. Its pH is adjusted to 12 by adding KOH. For the three solutions A, B and C, the extraction of niobium is carried out in batch as follows. 20 ml of aqueous solution are brought into contact with 40 ml of organic solution and the mixture of the two solutions is stirred for minutes (thermoshaker, 100 movements per minute) at a temperature of 25 ° C. Each mixture is then introduced into a separating funnel for phase separation. For each mixture, the aqueous solution is collected for analysis. The extraction yield of niobium is calculated by difference of its concentration in aqueous solution before and after contact with the organic solution (Table 1).

Table 1

Example 2: Extraction of niobium and / or tantalum from aqueous sodium solutions using an organic solution based on a quaternary ammonium salt.

The organic solution consists of:

the phase modifier: 1% by volume of / so-tridecanol;

- the diluent: aliphatic (Elixore 205).

Three different aqueous solutions are used:

Solution A (niobium alone): contains 0.02 mol / l of niobium obtained by dissolving the salt of sodium hexaniobate Na ₇ HNb ₆ O ₉ , 15H ₂ O. Its pH is adjusted to 12 by adding NaOH; Solution B (tantalum alone): contains 0.02 mol / L of tantalum obtained by dissolving sodium hexatantalate salt Na ₈ Ta ₆ O ₉ , 24.5H ₂ O. Its pH is adjusted to 12 by adding NaOH ;

Solution C (tantalum + niobium): contains 0.01 mol / l of tantalum and 0.01 mol / l of niobium obtained by dissolving the Na ₈ Ta ₆ 0g, 24.5H ₂ O salts and

Na ₇ HNb ₆ 0i ₉ , 15H ₂ 0. Its pH is adjusted to 12 by adding NaOH.

For the three solutions A, B and C, the extraction of niobium and / or tantalum is performed in batch as follows. 20 ml of aqueous solution are brought into contact with 60 ml of organic solution and the mixture of the two solutions is stirred for 15 minutes (thermoshaker, 100 movements per minute) at a controlled temperature and equal to 25 ° C. Each mixture is then introduced into a separating funnel for phase separation. For each mixture, the aqueous solution is collected for analysis. The extraction yield of niobium (and tantalum) is calculated by difference of its concentration in aqueous solution before and after contact with the organic solution (Table 2).

Table 2

Example 3: Extraction of niobium, tantalum, titanium and iron from an aqueous alkaline solution using an organic solution based on Aliquat® 336.

The organic solution consists of:

the extractant: quaternary ammonium (Aliquat® 336), at a concentration of 2.5% by volume; - the phase modifier: 2% by volume of / sotridecanol;

- the diluent: aliphatic (Elixore 205).

The aqueous solution has the composition shown in Table 3. Its pH is close to 12.

Table 3

The extraction elements is carried out in batch by contacting the organic solution to a _golden ratio V g / Vaq 0.8 in a beaker with stirring (500 revolutions / minute). The contact time is 5 minutes, at room temperature, and the mixture is then introduced into a separating funnel for phase separation.

The aqueous solution is collected for analysis. The extraction yields of niobium, tantalum, titanium, iron and sodium are calculated by difference of their concentration in aqueous solution before and after contact with the organic solution (Table 4).

Table 4

Example 4: Extraction of niobium, tantalum and / or titanium from an aqueous alkaline solution using an organic solution based on different quaternary ammonium salts.

This example is similar to the previous one but my nature of the quaternary ammonium salt in the organic solution is varied. The quaternary ammonium salts used are described in Table 5. The salts are then used to prepare various organic solutions. Each of them contains salt of ammonium at a concentration of 2.5% by volume and Elixore 205 at a concentration of 97.5% by volume.

Table 5

The initial aqueous solution has a pH of about 12 and contains 1900 mg / L of niobium, 41.4 mg / L of tantalum and 13.0 mg / L of titanium.

The extraction elements is carried out in batch by contacting the organic solution at a ratio V ₀ rg / _V q 1 into a beaker with stirring (500 revolutions / minute). The contact time is 10 minutes at room temperature, and the mixture is then introduced into a separating funnel for phase separation.

The aqueous solution is collected for analysis. The extraction yields of niobium, tantalum, titanium, iron and sodium are calculated by difference in their concentration in aqueous solution before and after contact with the organic solution (Table 6). Table 6

It will be noted that the salt that is least effective is the salt containing nitrate ions but that the extraction of niobium and tantalum remains greater than 58%, and this in a single contact. Salts based on chloride ions (Aliquat® 336), bromide, sulfate, carbonate and hydroxide have quantitative yields for the extraction of niobium, tantalum and titanium.

Example 5: Selective removal of iron and titanium vis-à-vis niobium and tantalum in continuous mode

An organic solution having undergone step a) of the present invention consists of:

the extractant: quaternary ammonium (Aliquat® 336), at a concentration of 2.5% by volume;

the phase modifier: 2.5% by volume of isotridecanol;

diluent: aliphatic (Elixore 205);

- niobium, tantalum, titanium and iron at the concentrations given in Table 7. Table 7

The selective desextraction of all or part of the iron and titanium is carried out as follows. The organic solution is introduced into a glass mixer-decanter (capacity of 200 mL for the mixer and 400 mL for the decanter) with a flow rate of 1.44 L / h. The aqueous solution containing 1.5 mol / L sulfuric acid is introduced in countercurrent with a flow rate of 0.31. The system comprises 1 single mixer-settler. After obtaining a steady state, the aqueous solution containing the sulfuric acid is in order to calculate the extraction yields of niobium, tantalum, iron and titanium. The composition of the organic solution at the end of the washing step and the de-extraction yields of the various elements in the washing step are given in Table 8.

Table 8

It will be noted that the ratio Nb / Ti in the organic solution increases from 360 g / g to 404 g / g and that the Nb / Fe ratio increases from 1244 g / g to 2168 g / g.

Example 6a: Selective de-extraction of niobium from tantalum and titanium using mixtures of oxalic acid, nitric acid and sodium nitrate.

An organic solution having undergone the steps a), b) and c) of the present invention consists of: the extractant: quaternary ammonium (Aliquat® 336), at a concentration of 2.5% by volume;

the phase modifier: 1% by volume of / so-tridecanol;

diluent: aliphatic (Elixore 205);

- niobium and tantalum at the concentrations given in Table 9. Table 9

The selective desextraction of all or part of the niobium, tantalum and titanium is carried out as follows. The organic solution is divided equally and brought into contact with different aqueous solutions containing oxalic acid, nitric acid and sodium nitrate, the concentrations of which are given in Table 10.

The ratio V ₀ rg / _V q is 4 and the contact time is 15 minutes at room temperature. Each mixture is then introduced into a decanter for phase separation and the aqueous solution is collected for analysis. Table 10 shows the Nb, Ta and Ti concentrations obtained in each aqueous desextraction solution as well as the corresponding de-extraction yields and niobium / tantalum and niobium / titanium mass ratios.

Table 10

Solution used for Concentration Yield

desextraction desextraction (mg / L)

H ₂ C ₂ O ₄ HNO ₃ NaNO ₃ Nb / Ta Nb / Ti

Nb Ta Ti Nb Ta Ti

(mol / L) (mol / L) (mol / L) (g / g) (g / g)

79.3 11.7

0.5 0.5 0 17.8% 4460 22.3 8.1 200 551

%%

0.5 0.4 0.1 77.2 17.3% 11.1 4340 21.7 7.7 200 564 %%

74.7 10.7

0.5 0.3 0.2 17.2% 4200 21.5 7.4 195 568

%%

74.7 12.4

0.5 0.2 0.3 19.0% 4200 23.8 8.6 176 488

%%

74.7 13.3

0.5 0.15 0.35 19.9% 4200 24.9 9.2 169 457

%%

It will be noted that the mass ratio Nb / Ta in the initial solution increases from 45 g / g (Table 9) to 200 g / g in the de-extraction solution (Table 10), with only one desextraction stage. Ditto for the ratio Nb / Ti which goes from 81 g / g to more than 550 g / g. Of course, when the process is operated continuously, the number of stages of desextraction will determine the overall de-extraction yields of each of the elements. Mac Cabe-Thiele constructions have shown that 3 de-extraction stages are sufficient to recover more than 99% of the niobium contained in the organic phase described in this example, while de-extracting at most only 25% of the tantalum.

Example 6b: Selective de-extraction of niobium from tantalum and titanium using mixtures of oxalic acid, nitric acid and ammonium nitrate.

This example is similar to Example 6a. For the initial organic solution, only the concentrations of Nb, Ta and Ti are different. For aqueous solutions used to selectively remove all or part of niobium, tantalum and titanium, sodium nitrate is replaced by ammonium nitrate. In this example, the ratio V ₀ rg / _V q is 6 and the contact time is 15 minutes at room temperature. Table 11 gives the concentrations of niobium, tantalum and titanium in the initial organic solution. Table 12 shows the concentrations of Nb, Ta and Ti obtained in each aqueous desextraction solution as well as the corresponding niobium / tantalum and niobium / titanium mass yield ratios.

Table 11

Table 12

In this example, it is noted that the mass ratio Nb / Ta in the initial solution increases from 43 g / g (Table 11) to 173 g / g in the de-extraction solution (Table 12), and with only one stage of stripping. Idem for the ratio Nb / Ti which passes from 396 g / g to more than 2000 g / g Example 6c: selective extraction of niobium vis-à-vis tantalum, comparative tests using mixtures H ₂ C ₂ O ₄ / H ₂ SO ₄ , H ₂ C ₂ O ₄ / HCl, H ₂ C ₂ O ₄ / H 3 PO ₄ and H ₂ C ₂ O ₄ / HClO 4.

the phase modifier: 1% by volume of / so-tridecanol;

diluent: aliphatic (Elixore 205);

- niobium and tantalum at the concentrations given in Table 13.

Table 13

The selective desextraction of all or part of niobium and tantalum is carried out as follows. The organic solution is divided equally and brought into contact with different aqueous solutions containing 0.5 mol / L of oxalic acid and 0.5 mol / L of a mineral acid selected from nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid or perchloric acid.

The ratio V ₀ rg / _V q is 4 and the contact time is 15 minutes at room temperature. Each mixture is then introduced into a decanter for phase separation and the aqueous solution is collected for analysis. Table 14 shows the niobium and tantalum concentrations obtained in each aqueous desextraction solution as well as the corresponding de-extraction yields.

Table 14

Concentration Yield of (mg / L) de-extraction

Solution used for Nb Ta

Nb Ta

stripping

H2C2O4 0.5 mol / L + HCIO ₄ 0.50 mol / L 5740 124 100% 100%

H ₂ C ₂ 0 ₄ 0.5 mol / L + HN0 ₃ 0.50 mol / L 4036 19 70.3% 15%

H ₂ C ₂ O ₄ 0.5 mol / L + H ₂ SO ₄ 0.50 mol / L 1467 3.3 26% 2.7% H ₂ C ₂ 0 ₄ 0.5 mol / L + HCl 0.50 mol / L 1217 2.4 21% 1.9%

H ₂ C ₂ O ₄ 0.5 mol / L + H ₃ PO ₄ 0.50 mol / L 478 1.6 8.3% 1.3%

It will be noted that the oxalic / nitric mixture offers the best compromise between recovery efficiency of niobium and niobium-tantalum selectivity. The mixture of oxalic acid and perchloric acid has no Nb-Ta selectivity. Mixtures H ₂ C ₂ O ₄ / HCl, H ₂ C ₂ O 4 / H ₂ SO ₄ and ₂ θ2θ4 Η / Η ₃ ΡΟ ₄ show some selectivity Nb-Ta but stripping niobium yields are low. Increasing the concentration of HCl, H ₂ SO ₄ or H ₃ PO ₄ makes it possible to increase the niobium deextraction efficiencies, but this has a negative impact on the steps downstream of the process, in particular the neutralization of the niobium eluate. The increase in the concentration of HCl, H ₂ SO ₄ or H ₃ PO ₄ can also cause the precipitation of oxalic acid making the use of such de-extraction solutions unattractive at the industrial level.

Finally, the mixture H ₂ C ₂ O ₄ / HNO 3, ensures the chemical stability of the mixture of desextraction since oxalic acid is synthesized industrially by oxidation of organic matter (sugars, wood ...) in concentrated nitric acid medium (US Patent 2057119. Article by Sullivan et al., Industrial & Chemical Chemistry Product Research and Development, 22, 699-709, 1983).

Example 7: Neutralization of the aqueous extraction solution containing purified niobium and separation of niobium vis-à-vis the oxalate and nitrate ions.

An aqueous desextraction solution containing the components described below is neutralized to different pHs by adding a solution of sodium hydroxide or ammonia solution.

The initial solution contains:

niobium at a concentration of 10 g / L; oxalic acid at a concentration of 0.50 mol / L;

nitric acid at a concentration of 0.50 mol / l.

Neutralization is carried out with stirring (400 rpm) at room temperature in a 500 ml beaker. 250 ml of initial solution are stirred, a pH probe is placed in the initial solution. Its pH is then close to the value 0.3. A solution of sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH ₄ OH) or concentrated sodium carbonate (Na 2 CO 3) is then added until the desired pH value is reached. A white precipitate appears when the pH is above 1.5. After stirring for 15 min, the precipitate is recovered by centrifugation and the filtrates are analyzed. Table 15 gives the percentage of niobium, oxalate and nitrate that precipitates as a function of pH.

Table 15

* Nb: niobium. Ox: oxalate ions. Nit: nitrate ions It will be noted that the neutralization of the desextraction solution at a pH greater than 2 causes the precipitation of niobium while leaving the oxalate and nitrate ions in solution. It will also be noted that the most effective bases are NaOH, KOH and NH ₄ OH; with a quantitative precipitation of niobium for a pH greater than 7. In the case of sodium carbonate, even if the precipitation of niobium vis-à-vis the oxalate and nitrate ions also observed, the precipitation yields of niobium are lower by compared to those obtained with NaOH, KOH or NH ₄ OH; a complexation of Nb (V) by the carbonate ions can be at the origin of this phenomenon. Chemical analyzes have shown that the precipitation reaction with NaOH, KOH or NH ₄ OH can be summarized as follows:

6 <pH <9

2 [NbO (C ₂ 0 ₄₎ 3] ^{3 "(aq)} + 6 ^HO" + n H ₂ 0 ≤ Nb ₂ 0 _5, nH ₂ 0 + 6 C ₂ 0 ₄ ^{2 _"(aq)}

Therefore, the neutralization of the de-extraction solution, resulting from step d) of the present invention, makes it possible both to recover the purified niobium in the form of a solid concentrate while recovering the oxalate ions initially complexed with niobium. Nitrate ions are also left in solution. This allows the oxalate and nitrate ions to be recycled upstream of the process, in particular to the selective desextraction of niobium. EXAMPLE 8 Destraction of Tantalum in Hydrochloric or Nitric Media

The extraction of tantalum is carried out by simple anion exchange; mechanism well known to those skilled in the art. An organic solution having undergone steps a), b), c) and d) of the present invention consists of:

the phase modifier: 2.5% by volume of / so-tridecanol; diluent: aliphatic (Elixore 205);

- tantalum at a concentration of 35 mg / L

The removal of all or part of the tantalum is carried out as follows. The organic solution is introduced into a glass mixer-decanter (capacity of 200 mL for the mixer and 400 mL for the decanter) with a flow rate of 1.4 L / h.

The aqueous solution is introduced in counter-current with a flow rate of 0.28 L / h. The system consists of 2 mixers-decanters arranged in series. The desextraction is carried out at 20 ° C. The operation was entirely repeated with five different aqueous solution (HCl 2 mol / L HCl or 1 mol / L + NaCl 1 mol / L HNO ₃ or 1 mol / L HNO ₃ or 0.5 mol / L NaNO ₃ + 0 5 mol / L or HNO ₃ 0.5 mol / L + NH 4 NOO 3 0.5 mol / L).

In each aqueous solution tested, once the system is operating in steady state, the aqueous solution leaving the second mixer is collected for analysis. Table 16 shows the tantalum extraction efficiency obtained for each aqueous solution tested.

Table 16

It will be noted that for the five aqueous solutions tested, the tantalum extraction efficiency is greater than or equal to 90%. It will also be appreciated that solutions containing nitrate ions are more effective in extracting tantalum. Example 9: Demonstration of the Feasibility of the Process in Continuous Mode

The process of the present invention has been tested in continuous mode. Figure 2 shows the process flow that has been tested. Of course, this example is given by way of illustration and in no way constitutes a limitation.

In this figure, the rectangles numbered from 1 to 9 represent 9 mixer-settlers. The arrows indicate the flow direction of the flows. The tables show the composition of the liquid streams and solutions at different points in the process. The flow rate of the various aqueous and organic streams are indicated in FIG. 2. The pumps allowing the circulation of the fluids and the stirrers have not been represented in the figure.

In Figure 2, the organic solution is composed of Aliquat® 336 at a concentration of 2.5% by volume, of / sotridecanol at a concentration of volume and diluent (Elixore 205). The iron and titanium de-extraction step (described in Example 5) was not implanted in the process scheme described in FIG. 2 because of the low iron content in the initial solution. The purity of the final Nb concentrate can nevertheless be increased by adding this step.

In Figure 2, it is noted that the entire niobium is recovered, first as an eluate containing 11.6 g / L Nb and then as a solid concentrate containing about 55% by mass Nb. Part of the tantalum is desextracted at the same time as the niobium with the process diagram described in FIG. 2. Nevertheless, the purity of the Nb concentrate is much greater than that of the feed solution, since the ratio Nb / It goes from 49 to 239 g / g, the Nb / Ti ratio goes from 376 to 2785 g / g, the Nb / Fe ratio goes from 1280 to 1638 g / g and the Nb / Na ratio goes from 1.8 to more. of 2142 g / g. The process of the present invention thus makes it possible to recover and purify the niobium initially contained in a basic aqueous solution. In FIG. 2, it is also noted that the tantalum is recovered in the form of a solution in a nitric medium and then in the form of a solid concentrate. Tantalum is thus recovered separately from niobium. The process of the present invention thus makes it possible to recover and purify the tantalum initially contained in a basic aqueous solution.

Claims

1. A process for separating and purifying niobium and tantalum from a basic aqueous solution containing niobium and tantalum and optionally iron and / or titanium, characterized in that it comprises the following steps:

- a) contacting an aqueous solution having a pH> 8 containing niobium, tantalum and optionally titanium and / or iron, with an organic solution based on a quaternary ammonium salt so as to extract all or part of niobium, tantalum and optionally titanium and / or iron from the aqueous solution to the organic solution;

b) recovering the organic solution containing niobium, tantalum and optionally titanium and / or iron;

c) optionally contacting the organic solution containing niobium, tantalum and optionally titanium and / or iron obtained in step b) with an aqueous solution of sulfuric acid so as to selectively remove the organic solution all or part of the possible iron and / or titanium extracted in step a), vis-à-vis niobium and tantalum and recovery of the organic solution containing niobium and tantalum;

d) contacting the organic solution containing the niobium and the tantalum obtained in step b) or in the optional step c) with an aqueous acid solution containing nitrate and oxalate ions so as to selectively remove the solution organic niobium vis-a-vis tantalum by formation of soluble complexes in aqueous solution between niobium and oxalate ions;

e) recovering the acidic aqueous solution resulting from stage d), containing the purified niobium in the form of a complex with the oxalate ions, and neutralization with a base so as, on the one hand, to obtain a purified niobium precipitate; on the other hand, an aqueous solution of oxalate ions and nitrate ions which may optionally be recycled in step d) of the process;

f) recovering the organic solution resulting from stage d), containing the purified tantalum, and bringing it into contact with an acidic aqueous solution of chloride salts or nitrate salts in order to extract the tantalum from the organic solution by exchange anionic;

g) recovering the acidic aqueous solution resulting from stage f), containing the purified tantalum, and neutralizing with a base so as to obtain a purified tantalum precipitate.

2. Process according to claim 1, characterized in that the organic solution based on a quaternary ammonium salt comprises a diluent, advantageously an aliphatic hydrocarbon, and optionally a phase-modifying agent, advantageously 1α-so-tridecanol.

3. A method according to any one of claims 1 or 2, characterized in that the hydrophobic quaternary ammonium salt is a compound of formula N ⁺ R3R RIR ₂ X ^'wherein Ri, R _2, R ₃ and R * represents independently of one another a linear or branched alkyl group such that N ⁺ R ₁ R ₂ R ₃ R ₄ comprises between 20 and 50 carbon atoms, in particular between 25 and 31 carbon atoms, and X ^" represents a anion, preferably a chloride, carbonate, hydroxide or sulfate anion.

4. Process according to claim 3, characterized in that R 1 represents a methyl group, R ₂ , R 3 and R 4 represent, independently of one another, a C 6 -C 10 alkyl group and X ^" represents a chloride ion.

5. Method according to any one of claims 1 to 4, characterized in that the process is a continuous process comprising at least 2 extraction stages for step a) and in that the extraction yields of niobium and tantalum are greater than 90%.

6. Method according to any one of claims 1 to 5, characterized in that the sulfuric acid solution of optional step c) has a concentration of between 1 and 4 mol / L, advantageously it is 2 mol / L.

7. Method according to any one of claims 1 to 6, characterized in that the acidic aqueous solution containing nitrate and oxalate ions of step d) is an aqueous solution such that 0.2 <[H ₂ C ₂ 0 ₄ ] <0.8 mol / L and 0.1 <[HN0 ₃ ] <0.8 mol / L, advantageously 0.3 <[H ₂ C ₂ O ₄ ] <0.6 mol / L and 0.2 ≤ [HNO ₃ ] <0.5 mol / L, even more advantageously [H ₂ C ₂ O ₄ ] = 0.5 mol / L and [HNO 3] = 0.45 mol / L.

8. Process according to any one of claims 1 to 7, characterized in that the acidic aqueous solution containing nitrate and oxalate ions of step d) is an aqueous solution of oxalic acid also containing nitric acid. a mixture of nitric acid and sodium nitrate, a mixture of nitric acid and potassium nitrate, or a mixture of nitric acid and ammonium nitrate, advantageously containing a mixture of nitric acid and nitrate ammonium, advantageously in contents such that 0.05 [[NH ₄ NO ₃ ] ≤ 0.30 mol / L, 0.20 [[HN0 ₃ ] ≤ 0.45 mol / L and [H ₂ C ₂ O _4] ] = 0.5 mol / L.

9. Process according to any one of Claims 1 to 8, characterized in that the base of step e) and / or of step g) is chosen from NaOH, Na ₂ CO ₃ , KOH and K ₂ CO. ₃ and NH4OH, advantageously from NaOH and NH ₄ OH.

10. Process according to any one of claims 1 to 9, characterized in that the neutralization of step e) and / or step g) is carried out to a pH of between 1.5 and 10, advantageously between 6 and 9.

11. Process according to any one of claims 1 to 10, characterized in that the acid solution of chloride salts or of nitrate salts of step f) is chosen from an aqueous solution of hydrochloric acid, a mixture of hydrochloric acid and a chloride salt, an aqueous solution of nitric acid and a mixture of nitric acid and a nitrate salt, preferably from a 2 mol / l hydrochloric acid solution, a mixture of 1 mol / L hydrochloric acid and 1 mol / L NaCl, 1 mol / L nitric acid solution, 0.5 mol / L nitric acid mixture and 0.5 molar NaNO 3 / L, a mixture of nitric acid at 0.5 mol / L and NaNO ₃ at 0.5 mol / L and a mixture of nitric acid at 0.5 mol / L and NH4NO3 at 0.5 mol / L, even more advantageously it is the mixture of nitric acid at 0.5 mol / L and NH ₄ NO ₃ at 0.5 mol / L.

12. Process according to any one of claims 1 to 11, characterized in that the aqueous solution having a pH> 8 containing niobium and tantalum and optionally titanium and / or iron of step a) also contains at least one alkali metal selected from lithium, sodium, potassium, rubidium and cesium, advantageously it contains sodium and is obtained by a process comprising the following successive steps: A) sodium conversion of a niobium and / or tantalum ore or concentrate containing titanium and / or iron by addition of a concentrated NaOH solution at a temperature of between 50 ° C and 150 ° C;

B) solid / liquid separation and recovery of the solid obtained in step A);

D) addition of water to dissolve the niobium and / or tantalum and recovery of an aqueous solution having a pH> 8 containing niobium and tantalum and optionally titanium and / or iron.

13. Process according to any one of claims 1 to 12, characterized in that it comprises an additional step h) of recovering the purified niobium precipitate obtained in step e), washing the precipitate, advantageously with water. water, and calcination of the washed precipitate.

14. A method according to any one of claims 1 to 12, characterized in that it comprises an additional step i) recovery of the purified tantalum precipitate obtained in step g), washing the precipitate, preferably with the water, and calcination of the washed precipitate.

15. Method according to any one of claims 1 to 14, characterized in that it comprises an additional step j) recovery of the solution of oxalate ions and nitrate ions from step e), concentration of said solution for selectively precipitating the oxalate ions against nitrate ions, converting the precipitated oxalate ions to oxalic acid and recycling the oxalic acid obtained in step d) of the process.