Process for producing metallic niobium or metallic tantalum

Abstract

 Metallic niobium or metallic tantalum is produced by a process which comprises bringing a fluorine containing compound of niobium or tantalum:

(A) into contact with a gas comprising hydrogen at a temperature of at least 400°C; or

(B) into contact with metallic aluminium, metallic magnesium or metallic lead, at a temperature of at least 300°C;

to convert the fluorine containing compound into the corresponding metal.

Description

[0001] The present invention relates to a process for producing metallic niobium or metallic tantalum.

[0002] Conventional processes for producing metallic niobium (Nb) or metallic tantalum (Ta) include reducing their chlorides with metallic magnesium or metallic sodium; using the aluminium Thermit process; and molten salt electrolysis. These conventional processes are complex and the use of metallic magnesium or metallic sodium is costly.

[0003] The present invention provides a new, improved, process. In this process, a fluorine containing compound of niobium or tantalum is reacted with hydrogen gas, metallic magnesium, metallic aluminium or metallic lead, to produce metallic niobium or metallic tantalum.

[0004] Accordingly, the invention provides a process for producing metallic niobium or metallic tantalum, which process comprises bringing a fluorine containing compound of niobium or tantalum:

(A) into contact with a gas comprising hydrogen at a temperature of at least 400°C; or

(B) into contact with metallic aluminium, metallic magnesium or metallic lead, at a temperature of at least 300°C;

to convert the fluorine containing compound into the corresponding metal.

[0005] The reaction should naturally not be conducted in the presence of material which mars the reaction. Oxygen, for example air, mars the reaction and hence should be avoided. The reaction in (B) can be conducted in the presence of an inert gas or a reducing gas. Alternatively in (B), the reaction can be conducted "in vacuum", i.e. with no other gas being present besides any from the fluorine containing compound and the aluminium, magnesium or lead.

[0006] Preferably, the fluorine containing compound in the present reaction is gaseous. The compound may contact initially as a solid with the aluminium, magnesium or lead and then be heated to make it gaseous. In a preferred embodiment, in (B) the reaction is conducted with the compound being gaseous and being in an inert gas or a reducing gas.

[0007] Thus, the present reaction is preferably between gaseous NbF₅ or gaseous TaF₅ and the hydrogen, aluminium, magnesium or lead, the gaseous NbF₅ or gaseous TaF₅ being comprised in the gaseous fluorine containing compound of niobium or tantalum. The gaseous NbF₅ or gaseous TaF₅ in (B) is preferably employed in the inert gas or reducing gas mentioned above.

[0008] Gaseous fluorine containing compound is generally produced by heating solid fluorine containing compound. The fluorine containing compound of niobium or tantalum can be produced by extracting a niobium or tantalum compound into an organic solvent, and bringing the solution into contact with an aqueous solution containing NH₄⁺ (and preferably also F^- ) to extract into the aqueous phase niobium or tantalum in the form of a fluorine containing compound of niobium or tantalum. The fluorine containing compound can then be crystallized from the aqueous solution. The organic solvent can be regarded as comprising an extracting agent which can be in admixture with a diluent. In a preferred embodiment, the organic solvent comprises at least one extracting agent (for example one or two) selected from the group consisting of (a) alkylphosphoric acids, (b) neutral phosphoric esters, (c) alkylamines and (d) ketones. Preferably, the organic solvent comprises (i) at least one extracting agent selected from (a), (b), (c) and (d), and (ii) a diluent which is a petroleum hydrocarbon.

[0009] The invention is illustrated by the accompanying drawings, in which:

Fig. 1 is a flow sheet illustrating the production using hydrogen gas as reducing agent;

Fig. 2 is a flow sheet illustrating the production using as reducing agent metallic Al, metallic Mg or metallic Pb;

Fig. 3 is a flow sheet illustrating the production of metallic Nb or metallic Ta including the preparation of fluorine containing compounds of Nb or Ta; and

Fig. 4 is a flow sheet similar to Fig. 3 containing a stage for treating by-product gases produced in the reaction stage.

[0010] Referring to the drawings, Fig. 1 illustrates the production of Nb or Ta. Fluorine containing compounds (A) of Nb or Ta are supplied to the vaporization stage (B) to produce gaseous NbF₅ or TaF₅. The gaseous NbF₅ or TaFS is transferred to a reactor which is full of hydrogen gas (C) and the temperature is maintained at above 400°C (Reaction stage (D) ). In this stage, metallic Nb or metallic Ta can be produced according to the following equations:

[0011] Fig. 2 illustrates the production using as reducing agent metallic aluminium, metallic magnesium or metallic lead, instead of hydrogen gas. Gaseous TaF₅ or NbF₅ is prepared by supplying fluorine containing compounds of Ta or Nb (A), such as crystals of (^NH₄)₂TaF₇ or (NH₄)₂NbF₇, respectively, to the vaporization stage (B) and heating them at a temperature above 150°C, as expressed by the following equations:

[0012] In the reaction stage (D), an inert gas or a reducing gas fills the reactor and metallic aluminium, metallic magnesium or metallic lead heated to above 300°C is supplied to the reactor. The NbF₅ or TaF₅ supplied from the vaporization stage (B) to the reaction stage (D) produces metallic Nb or Ta, respectively, by reduction. This reaction stage (D) may be carried out in vacuum.

[0013] Fig. 3 illustrates the process of the invention including the preparation of fluorine containing compounds (A) of Nb or Ta and also the recovery of HF produced as by-product in the reaction stage.

[0014] The organic solution (H) containing extracted Nb or Ta is delivered to the stripping stage (J) and allowed to contact with the aqueous solution (K) containing F and NH₄⁺. The Nb or Ta is transferred to the aqueous phase, and the organic solvent (P) is transferred to the circulation route to the extraction stage. The transfer can be expressed by the following equations:











In these equations, TBP represents tributyl phosphate and R is such that RH represents an extracting agent having an H-type exchanging group. It should be understood that the chemical species of the niobium or tantalum compound crystal obtained varies according to the molar ratio NH₄+/F^- in the solution containing both NH₄⁺ and F^- as well as the species appearing in the equations above.

[0015] The crystals formed are separated by filtration in the separation stage (L), and the subsequent operations to obtain metallic Nb or Ta are as shown in Fig.1. The by-product HF gas (F) in the reaction stage (D) is absorbed for recovery in the gas absorbing stage (M) where a solution containing NH₄⁺ and F^- circulates.

[0016] The process illustrated in Fig.4 is basically the same as that in Fig. 3, but differs in that as reducing agent (C) there is used metallic aluminium, metallic magnesium or metallic lead, and by-product gases produced in the reaction stage (D) are AlF₃, MgF₂ or PbF₂ as illustrated in equations (5) to (10) above.

[0017] The gases (F), AlF₃, MgF₂ or PbF₂, produced as by-product in the reaction stage (D) react with H₂0 or moist air supplied in the oxidation stage (N) and are converted into easily recoverable HF gas, as expressed by the following equations:

[0018] The oxides produced, Al₂O₃, MgO or PbO, contain as little fluorine as is permissible for commercial material. The HF gas is recovered in the gas absorbing stage (M).

[0019] It is an advantage of the present invention that the fluoride content of the by-product produced in the present basic reaction, i.e. of the HF, AlF₃, MgF₂ or PbF₂, can be recovered and recycled for use in the aqueous solution discussed above which is preferably employed to produce the fluorine containing compound of niobium or tantalum.

[0020] In the present invention, gaseous TaF_S or NbF₅ can be produced by vaporization of fluorine containing compounds of Nb or Ta such as (NH₄)₂NbF₇ or (NH₄)₂TaF₇. The vaporization can be carried out using an external heating furnace, an external heating type rotary furnace or naturally a flow type external heating furnace.

[0021] The gaseous NbF₅ or gaseous TaF_S is preferably prepared by heating (NH₄)₂NbF₇ or (NH₄)₂TaF₇ at a temperature above 150°C.

[0022] For the reactor used in the invention, furnaces of various known types can be employed such as the closed type of electric furnace, shaft furnace, rotary or static type of external heating furnace. Metallic aluminium, magnesium or lead used as reducing agent may be employed in the form of a gas or liquid or mixture thereof.

[0023] The metallic Nb or Ta can be produced by bringing the gaseous fluoride in a stream of an inert gas or a reducing gas or in vacuum into contact with the metallic reducing agent.

[0024] The inert gas which can be employed to maintain the reaction condition of the reactor can be selected for example from the group consisting of argon, helium and nitrogen. Reducing gases which can be employed in the invention include H₂, CO and various gaseous hydrocarbons C H .

[0025] The alkylphosphoric acids which can be employed as extracting agents in the invention, to produce fluorine containing compounds of Nb or Ta, are selected from the group consisting of the following compounds:



where R represents an alkyl group, generally of 4 to 22 carbon atoms.

[0026] The neutral phosphoric esters which can be employed as extracting agents are selected from the following compounds:

R is as defined above. TBP (tributyl phosphate) used in the Examples and referred to above is of formula (a) where R C₄H₉.

[0027] The alkylamines which can be employed as extracting agents are selected from the following group of compounds:

Primary amines : Represented ty RNH₂, where R represents an alkyl group of 4 to 22 carbon atoms.

Secondary amines : Represented by k₂N^- or R₂NH, where R represents an alkyl group of 4 to 22 carbon atoms.

Tertiary amines : Represented by R₃N or R₃NH⁺, where R represents an alkyl group of 4 to 22 carbon atoms.

[0028] An example of a ketone which can be employed as extracting agent is as follows:

[0029] In addition to the above-mentioned compounds, cyclohexanone(C₆H₁₂O) is also often employed.

[0030] The diluents which can be employed are mostly petroleum hydrocarbons, but aromatic and aliphatic hydrocarbons and mixtures thereof may also be used. For example, kerosene, a mixture of many kinds of hydrocarbon, is commonly used.

[0031] The concentration of extracting agent should be chosen according to the character of the treated solution, the concentration of metal ions, the concentration and nature of impurities, and the nature of the chemical species to be extracted, but generally is 2 to 100% by volume.

[0032] The invention is illustrated by the following Examples, which describe preferred embodiments:

Example 1:

[0033] H₂TaF₇ extracted by a solvent consisting of 60% by volume TBP and 40% by volume aromatic (the aromatic being Shellsol AB), was stripped by an aqueous solution containing 250 g/1 of NH₄F, to obtain crystals of (NH₄)₂TaF₇. 20 g of these crystals were introduced into a vaporization furnace and heated to 220°C under a stream of H₂ gas. Gaseous TaF₅ formed in the vaporization furnace and was transferred to a reactor which was maintained at a temperature of 600°C. The reaction was continued for an hour, and then the reactor was cooled. A substance had adhered to the inner wall of the reactor, and this substance proved to be Ta, as confirmed by X-ray diffraction analysis. The substance amounted to10g.

Example 2:

[0034] H₂NbF₇ extracted by 100% MIBK (methyl isobutyl ketone) was stripped with an aqueous solution containing 250 g/1 of NH₄HF₂, to obtain crystals of (NH₄)₂NbF₇, of which 180 g was heated in an atmosphere of helium to produce NbF_S. The NbF₅ gas was continuously treated in a reactor in which the NbF₅ containing gas just obtained was blown onto an aluminium metal surface heated at 950°C in a helium stream. After 6 hours of continuous treatment, the reactor was cooled and disassembled. A substance was found on the aluminium surface in an amount of 62 g and this substance proved to be metallic Nb, as confirmed by X-ray diffraction analysis and chemical analysis.

Example 3:

[0035] H₂NbF₅ extracted by a solvent consisting of 80% by volume cyclohexanone and 20% by volume Shellsol AB was stripped with an aqueous solution containing 200 g/1 of NH4HF2, to obtain crystals of (NH₄)₂NbF₇. These crystals and metallic lead were heated separately in an external heating furnace. Gases of metallic Pb and NbF₅ were led to a reactor and held for 2 hours at a reactor temperature of 750°C. The reactor was then cooled and disassembled. Powder adhering to the inner wall of the reactor proved to be metallic Nb by X-ray diffraction measurement and chemical analysis.

Claims

1. A process for producing metallic niobium or metallic tantalum, which process comprises bringing a fluorine containing compound of niobium or tantalum:

(A) into contact with a gas comprising hydrogen at a temperature of at least 400°C; or

(B) into contact with metallic aluminium, metallic magnesium or metallic lead, at a temperature of at least 300°C;

to convert the fluorine containing compound into the corresponding metal.

2. A process for producing metallic niobium or metallic tantalum, which process comprises bringing gaseous NbF₅ or gaseous TaF₅ into contact with a gas comprising hydrogen at a temperature of at least 400°C, to convert the NbF₅ or TaF₅ into the corresponding metal.

3. A process for producing metallic niobium or metallic tantalum, which process comprises bringing gaseous NbF₅ or gaseous TaF₅ into contact with metallic aluminium, metallic magnesium or metallic lead, at a temperature of at least 300°C, to convert the NbF₅ or TaF₅ into the corresponding metal.

4. A process according to claim 3 wherein the gaseous NbF₅ or gaseous TaF₅ is in an inert gas or a reducing gas.

5. A process according to claim 1 wherein the fluorine containing compound of niobium or tantalum is prepared by extracting a niobium or tantalum compound into an organic solvent comprising at least one extracting agent selected from the group consisting of (a) alkylphosphoric acids, (b) neutral phosphoric esters, (c) alkylamines and (d) ketones,and bringing the solution into contact with an aqueous solution containing NH₄⁺ to extract into the aqueous phase niobium or tantalum in the form of a fluorine containing compound of niobium or tantalum.

6. A process according to any one of claims 2-4 wherein the gaseous NbF₅ or gaseous TaF_S is prepared by heating a fluorine containing compound of niobium or tantalum, which compound has been produced by extracting a niobium or tantalum compound into an organic solvent comprising (i) at least one extracting agent selected from the group consisting of (a) alkylphosphoric acids, (b) neutral phosphoric esters, (c) alkylamines and (d) ketones, and (ii) a diluent which is a petroleum hydrocarbon. and bringing the solution into contact with an aqueous solution containing NH₄⁺ to extract into the aqueous phase niobium or tantalum in the form of a fluorine containing compound of niobium or tantalum.

7. A process according to any one of claims 2-4 and 6 wherein the gaseous NbF₅ or gaseous TaF₅ is prepared by heating (NH₄)₂NbF₇ or (NH₄)₂TaF₇ at a temperature above 150°C.

8. A process according to any one of claims 2-4 wherein the gaseous NbF₅ or gaseous TaF_S is prepared by heating a fluorine containing compound of niobium or tantalum, which compound is prepared as defined in claim 5.

9. A process according to any one of the preceding claims wherein metallic tantalum is produced by a process comprising bringing gaseous TaF5 into contact with a gas comprising hydrogen at a temperature of at least 400°C, to convert the TaF₅ into metallic tantalum.

10. A process according to any one of claims 1-8 wherein metallic niobium is produced by a process comprising bringing gaseous NbF_S:

(a) in helium into contact with metallic aluminium; or

(b) into contact with gaseous metallic lead;

at a temperature of at least 300°C, to convert the NbF₅ into metallic niobium.

Drawing