WO2005103338A1

WO2005103338A1 - Production of iron/titanium alloys

Info

Publication number: WO2005103338A1
Application number: PCT/AU2005/000593
Authority: WO
Inventors: Raymond Walter Shaw
Original assignee: Technological Resources Pty. Limited
Priority date: 2004-04-27
Filing date: 2005-04-27
Publication date: 2005-11-03

Abstract

A method and an apparatus for producing titanium metal products is disclosed. The method and the apparatus are based on using ionic liquids as electrolytes and adding titanium and other metals to be incorporated in the final products either directly into a compartment (5) of the cell that contains the ionic liquid or indirectly into the cell via a membrane (7) or other suitable means that separates the ionic liquid compartment (3) from a co-joined aqueous liquid compartment of the cell.

Description

PRODUCTION OF IRON/TITANIUM ALLOYS

The present invention relates to producing titanium metal products .

The present invention is a method and apparatus for producing titanium metal products rom feed materials , particularly minerals such as ilmenite (FeO.Ti0₂) , that contain iron and titanium.

The present invention relates particularly, although by no means exclusively, to producing titanium metal products in the form of iron/titanium alloys . Iron/titanium alloys have a range of applications .

One application that is of particular interest to the applicant is the storage of hydrogen. Iron/titanium alloys are known to be materials that can reversibly store hydrogen efficiently.

The basic reversible reaction between hydrogen and iron/titanium alloys and other suitable materials that can store hydrogen reversibly, which are usually metals, intermetallic compounds , and metal alloys , is : X Abs Me+—H₂ <=> MeH_x + Q (1) 2 Des where Me is a metal, intermetallic compound, or a metal alloy.

The current production methods for titanium metal products, such as iron/titanium alloys, are difficult and expensive because of limitations in the technology used.

The only commercial methods for producing metallic titanium sponge that is required for producing titanium metal products are the Kroll process which uses magnesium metal as the reductant and the Hunter process which uses sodium metal as the reductant.

Many attempts have been made to produce titanium metal products using direct electrowinning technology such as is commonly used for aluminium and for copper but these have not been successful. Aqueous systems, such as are used for copper, cannot be used for titanium because the voltage required to produce the titanium is above that at which the water decomposes to give hydrogen. In that case very poor current efficiency is obtained in the electrolysis step. Molten salt electrolytes have also been trialled to overcome this problem but have not been successful because of difficulties in supplying a suitable titanium feedstock and problems with loss of current efficiency due to disproportionation reactions occurring between the different titanium valence states which can exist. Both BHP Billiton and Cambridge University are known to be carrying out research in this area and have filed new patent applications but there are still no commercial operations of this type. The key to avoiding this loss of current efficiency is to maintain some separation of the anolyte and the catholyte but this has proven to be very difficult because high temperatures and aggressive conditions within the electrolytic cell prevent the use of simple materials and make maintenance to clear blockages very complex.

The present invention arises from a recent discovery of a class of chemicals called "ionic liquids" which have many of the same properties as molten salt electrolytes but achieve those at much lower temperatures and can be used in the range 0-100°C where aqueous systems exist as liquids at atmospheric pressures. The term "ionic liquid" is understood to herein to mean a liquid that substantially consists of ions and can be used in a temperature range of 0-100°C. The applicant has realised that ionic liquids which have high conductivity and are stable to voltages above those required to be able to reduce titanium and similar metals can now be prepared. The applicant has also realised that, with these systems, a range of electrode, membrane and diaphragm materials can be used which are not possible with the molten salt cells . The low temperature involved also allows feed materials such as TiCl to be used as the source of titanium for electrowinning without major difficulties of this volatilising from the system such as is the case with the high temperature molten salts where TiCl is typically volatilised off with the chlorine which is generated at the anodes .

The present invention is an improved method for producing titanium metal products, such as iron/titanium alloys that are useful for hydrogen storage, in an electrolytic cell .

The method of the present invention includes using ionic liquids as electrolytes and adding titanium and other metals to be incorporated in the final products either directly into a compartment of the cell that contains the ionic liquid or indirectly into the cell via a membrane or other suitable means that separates the ionic liquid compartment from a co-joined aqueous liquid compartment of the cell. According to the present invention there is provided a method of producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium in an apparatus that includes a compartment that contains an ionic liquid, an anode in contact with the ionic liquid, a cathode in contact with the ionic liquid, and a means for applying a potential across the anode and the cathode, the method including the steps of:

(a) . supplying the titanium-containing feed material or materials into the compartment and forming titanium ions in the ionic liquid; and

(b) applying a potential across the anode and the cathode and depositing titanium metal on the cathode.

The method described in the preceding paragraph is characterised by using a single compartment that contains ionic liquid and adding the reactants , such as titanium-containing feed material (s) , in a suitable form to the compartment.

Commonly available sources of titanium-containing feed material (s) tend to be in oxide form. One option is to select an ionic liquid that has an acceptable solubility for titanium oxides so that titanium oxides can dissolve in the ionic liquid.

In situations where the titanium oxides have limited or no solubility in available ionic liquids another option is to provide the titanium-containing feed material (s) in a form that is more soluble in the available ionic liquids . One option in this regard is to provide the titanium-containing feed material (s) as chlorides.

The titanium-containing feed material (s) may be added in a solid form.

The titanium-containing feed material (s) may be added in a solid form act as the anode .

The titanium-containing feed material (s) may also be added in an aqueous solution, although in such situations it is preferable that the ionic liquid be hydrophobic with a high affinity for titanium and be stable in the presence of water.

Preferably the ionic liquid is selected on the basis that it stabilises only one valence state for the metals being electrowon (most probably Ti⁴⁺ and Fe³⁺) so as to minimise reverse reactions at the anode and disproportionation reactions .

Preferably the titanium metal product is an iron/titanium alloy.

According to the present invention there is provided a method of producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium in an apparatus that includes a first compartment, a second compartment containing an ionic liquid, a membrane, diaphragm or other suitable means that is permeable to titanium ions forming at least part of a wall adjoining the first and second compartments , an anode , a cathode in contact with the ionic liquid in the second compartment, and a means for applying a potential across the anode and the cathode, the method including the steps of:

(a) supplying one or more than one titanium- containing feed material and an acid to the first compartment and dissolving titanium from the feed material or materials and forming titanium ions ; and

(b) applying a potential across the anode and the cathode and depositing titanium metals on the cathode.

The method described in the preceding paragraph is characterised by the use of separate compartments , namely an aqueous compartment containing titanium ions (and iron ions in the case of producing iron/titanium alloys) and an ionic liquid compartment, that are separated by a membrane, diaphragm or other suitable means that is permeable to titanium ions (and iron ions in the case of the producing iron/titanium alloys) .

In this arrangement the driving force for the transfer of titanium ions from the aqueous compartment to the ionic liquid compartment can be, for example, a concentration gradient between the compartments and/or a consequence of positioning the anode in the aqueous compartment and the cathode in the ionic liquid compartment.

Preferably the ionic liquid stabilises only one valence state of the titanium ions, preferably Ti⁴⁺ and thereby minimises issues of disproportionation reactions due to multiple valence states .

Preferably the membrane, diaphragm, or other suitable permeable means stops the return of any lower valence states of the titanium ions from the ionic liquid compartment to the aqueous compartment.

Preferably the titanium metal product is an iron/ itanium alloy.

In this context, the above described method is based on the realisation that iron/titanium alloys can be produced efficiently by separating and optimising the different functions of (a) extracting iron and titanium from titanium-containing feed materials, such as ilmenite, into solution and (b) thereafter recovering the extracted iron and titanium.

Effective dissolution of iron and titanium from titanium-containing feed materials, such as ilmenite, requires highly acidic conditions that are not conducive to thereafter recovering iron and titanium ions from solution . Ionic liquids are a convenient medium for electrowinning iron and titanium metals . The use of a membrane, diaphragm or other suitable means that is permeable to iron and titanium ions makes it possible to transport ions from one reaction zone that is optimised for dissolving iron and titanium from feed materials, ie the aqueous compartment, to another reaction zone that is optimised for electrowinning iron and titanium metals , ie the ionic liquid compartment.

The feed material (s) and the acid may be supplied to the aqueous compartment separately or may be mixed together prior to being introduced into the aqueous compartment.

The acid may be any suitable acid, such as hydrochloric acid or sulfuric acid. The membrane, diaphragm or other suitable permeable means may be any suitable membrane that is resistant to attack by the acid and the ionic liquid and is permeable to iron and titanium ions and is impermeable to other constituents of the compartments of the electrolytic cell.

Typically, the membrane, diaphragm or other suitable permeable means is made from either an oxide material or a polymer.

Both methods described above may be operated on a continuous basis or on a batch basis, as required.

The titanium-containing feed material (s) for both methods may be any suitable material or materials . The titanium-containing feed material (s) may be any suitable material or materials that separately contain titanium and iron.

The feed material (s) may be mixtures of the above-described types of feed materials.

Specifically, both methods may be based on the use of an iron/titanium-containing feed material or materials , such as ilmenite .

Alternatively, both methods may be based on extracting required concentrations of iron and titanium to produce a desired end-point composition of the iron/titanium alloy from a range of different feed materials and a range of addition rates of the feed materials , some of which may contain both iron and titanium and others of which may contain one or other of iron and titanium only. Preferably the ionic liquid is a room temperature ionic liquid.

According to the present invention there is also provided an apparatus for producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium that includes : (a) a first compartment containing an acid,

(b) a second compartment containing an ionic liquid,

(c) a membrane, diaphragm or other suitable means that is permeable to titanium ions forming at least part of a wall adjoining the first and second compartments,

(d) an anode,

(e) a cathode in contact with the ionic liquid in the second compartment,

(f) a means for applying a potential across the anode and the cathode; (g) a means for supplying feed materials to the first compartment; and

(h) a means for supplying acid to the first compartment.

The anode may be in contact with the acid in the first compartment or in contact with the ionic liquid in the second compartment. The present invention is described further by reference to the accompanying drawing which is a schematic illustration of one embodiment of an electrolytic cell that forms part of an apparatus in accordance with the present invention .

The drawing illustrates an apparatus for producing an iron/titanium alloy that is characterised by an electrolytic cell that includes two separate compartments , namely an aqueous compartment and an ionic liquid compartment, separated by a membrane that is permeable to titanium and iron ions .

The main component of the apparatus shown in the Figure is an electrolytic cell that includes :

(a) a first (aqueous) compartment 3 that contains an acid,

(b) a second (ionic liquid) compartment 5 that contains an ionic liquid, preferably a room temperature ionic liquid,

(c) a membrane 7 that separates the compartments 3, 5 that is formed from a material that is resistant to attack by the acid and the ionic liquid and is permeable to iron ions and titanium ions,

(d) an anode 9 extending into and thereby in contact with the ionic liquid, (e) a cathode 11 extending into and thereby in contact with the ionic liquid, and

(f) an external circuit 13 connected to the anode 9 and the cathode 11 for applying a potential between the anode and the cathode .

The type and concentration of the acid used in the apparatus is dependent on a range of variables, including (but not limited to) the availability of acids and the acid requirements for the particular iron/titanium-containing feed materials supplied to the cell .

The apparatus may be operated on a "continuous" basis or a "batch" basis.

Operation on a continuous basis involves supplying titanium-containing feed materials (such as ilmenite or other suitable iron/titanium-containing materials and make-up acid) to the acid bath in the compartment 3 over a period of time and removing a part of the bath in the compartment 3 over the time period to balance the feed materials supplied to and consumed in the bath to maintain a controlled bath height. When operated on a continuous basis, the apparatus includes means (not shown) for supplying ilmenite or other suitable iron/titanium-containing feed materials and make-up acid into the acid bath in the compartment 3 and a means (not shown) for removing a part of the bath from the compartment 3.

The removed bath includes "spent" acid, and the apparatus may include an acid regeneration circuit (not shown) for regenerating spent acid and returning the regenerated acid to the compartment 3 as part of the makeup acid stream.

The removed bath also includes partially extracted ilmenite, and the partially extracted ilmenite may be recycled to the compartment 3 for subsequent treatment in the bath or may be transferred to a downstream cell (not shown) .

When operated on a continuous basis , the apparatus also includes a means (not shown) for supplying make-up ionic liquid to the compartment 5 and for removing ionic liquid from the compartment 5. The apparatus may also include a means (not shown) for regenerating the ionic liquid.

In use of the apparatus on a continuous basis , ilmenite and other suitable iron/titanium-containing feed materials and make-up acid are supplied to the compartment 3 over a period of time and acid in the bath dissolves iron and titanium in the feed materials into solution. The so-formed iron ions and titanium ions migrate through the membrane 7 into the ionic liquid in the second compartment 5. The driving force for the migration is the concentration gradient between the two compartments . An applied potential between the anode 9 and cathode 11 causes movement of the iron ions and the titanium ions to the cathode 11 and deposition of iron and titanium metals on the cathode 11. Periodically, the cathode 11 is removed and replaced with a new cathode 11 and iron/titanium alloy is separated from the removed cathode 11. The separated iron and titanium are thereafter processed as required for particular end-use applications.

As described above, when operated on a continuous basis there is timed removal of a part of the bath in the compartment 3 over the time period of cell operation to balance the timed supply of feed materials to the bath. Consequently, the average residence time of ilmenite and other suitable iron/titanium-containing feed materials varies with the rate of supply and removal of material to and from the bath.

The above-described method and apparatus is an efficient option for producing iron/titanium alloys.

Many modifications may be made to the embodiment of the present invention described above in relation to the drawing without departing from the spirit and scope of the present invention. By way of example, whilst the above embodiment relies on the concentration gradient of iron ions and titanium ions as the driving force for migration of the ions from the compartment 3 to the compartment 5 via the membrane 7 , the present invention is not so limited and extends to other options .

One such option is an apparatus similar to that shown in the Figure, with the exception that the anode 9 is positioned in the compartment 3 in contact with the aqueous liquid in the compartment rather than the compartment 5 and the applied potential between the anode 9 in the compartment 3. With this arrangement the cathode 11 in the compartment 5 provides the driving force for migration of the iron and titanium ions from the compartment 3 to the compartment 5 via the membrane 7.

By way of further example, whilst the above embodiment is a two compartment cell with a membrane 7 that separates the compartments 3 , 5 , the present invention is not so limited and extends to a single compartment cell that contains the ionic liquid and includes an anode and a cathode in contact with the ionic liquid.

By way of further example, whilst the above embodiment includes a membrane 7 that allows migration of ions from compartment 3 to compartment 5 , the present invention is not so limited and extends to any other suitable permeable member .

By way of further example, whilst the above embodiment is described in the context of producing an iron/titanium alloy, the present invention is not so limited and also applies to other titanium metal products provided the other components that form the products can exist in a suitable chemical form for addition to the cell and/or a suitable membrane can be developed and they are not so electrochemically stable that they are outside the range of stability of the available ionic liquids . In the simplest form, the target additives are added to the cell in the appropriate amounts . The metal product can include "pure" titanium metal, binary alloys such as the iron/titanium alloys discussed, and more complex systems with three or more metals present to provide alloys with specific properties for their applications.

Claims

CLAIMS :

1. A method of producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium in an apparatus that includes a compartment that contains an ionic liquid, an anode in contact with the ionic liquid, a cathode in contact with the ionic liquid, and a means for applying a potential across the anode and the cathode, the method including the steps of:

(a) supplying the titanium-containing feed material or materials into the compartment and forming titanium ions ; and

2. The method defined in claim 1 wherein the titanium-containing feed material is in an oxide form and the ionic liquid has an acceptable solubility for titanium oxides and therefore can dissolve titanium oxides .

3. The method defined in claim 1 wherein the titanium-containing feed material is an oxide form has no or low solubility in the ionic liquid and step (a) includes supplying the titanium-containing feed material in a form, such as chlorides, that is more soluble in the ionic liquids.

4. The method defined in any one of the preceding claims wherein the titanium-containing feed material (s) is in a solid form.

5. The method defined in claim 4 wherein the solid form of the titanium-containing material acts as the anode .

6. The method defined in any one of claims 1 to 4 wherein the titanium-containing feed material (s) is in an aqueous solution .

7. The method defined in claim 6 wherein the ionic liquid is hydrophobic with a high affinity for titanium and is stable in the presence of water.

8. The method defined in any one of the preceding claims wherein the ionic liquid is selected on the basis that it stabilises only one valence state for the metals being electrowon (most probably Ti⁺ and Fe³⁺) so as to minimise reverse reactions at the anode and disproportionation reactions .

9. The method defined in any one of the preceding claims wherein the titanium metal product is an iron/titanium alloy.

10. A method of producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium in an apparatus that includes a first compartment, a second compartment containing an ionic liquid, a membrane, diaphragm or other suitable means that is permeable to titanium ions forming at least part of a wall adjoining the first and second compartments, an anode, a cathode in contact with the ionic liquid in the second compartment, and a means for applying a potential across the anode and the cathode, the method including the steps of:

11. The method defined in claim 10 wherein the driving force for the transfer of titanium ions from the aqueous compartment to the ionic liquid compartment is a concentration gradient between the compartments and/or a consequence of positioning the anode in the aqueous compartment and the cathode in the ionic liquid compartment.

12. The method defined in claim 10 or claim 11 wherein the ionic liquid stabilises only one valence state of the titanium ions , preferably Ti⁴⁺ and thereby minimises issues of disproportionation reactions due to multiple valence states .

13. The method defined in any one of claims 10 to 12 wherein the membrane, diaphragm, or other permeable means stops the return of any lower valence states of the titanium ions from the ionic liquid compartment to the aqueous compartment.

14. The method defined in any one of claims 10 to 13 wherein step (a) includes supplying the feed material (s) and the acid to the aqueous compartment separately.

15. The method defined in any one of claims 10 to 13 wherein step (a) includes mixing the feed material (s) and the acid together prior to supplying the mixture into the aqueous compartment .

16. The method defined in any one of claims 10 to 15 wherein the acid is hydrochloric acid or sulfuric acid.

17. The method defined in any one of claims 10 to 16 wherein the membrane, diaphragm, or other permeable means is resistant to attack by the acid and the ionic liquid and is permeable to iron and titanium ions and is impermeable to other constituents of the compartments of the electrolytic cell.

18. The method defined in any one of claims 10 to 17 wherein the membrane, diaphragm, or other permeable means is made from either an oxide material or a polymer .

19. The method defined in any one of the preceding claims wherein the titanium metal product produced by the method is an iron/titanium alloy.

20. The method defined in any one of the preceding claims operated on a continuous basis or on a batch basis .

21. The method defined in any one of the preceding claims wherein the titanium-containing feed material (s) separately contain titanium and iron.

22. The method defined in any one of the preceding claims wherein the titanium-containing feed material (s) are mixtures of feed materials .

23. The method defined in any one of the preceding claims wherein the titanium-containing feed material (s) includes ilmenite.

24. The method defined in any one of the preceding claims wherein the ionic liquid is a room temperature ionic liquid.

25. An apparatus for producing a titanium metal product, such as an iron/titanium alloy, from one or more than one feed material that contains titanium that includes :

(a) a first compartment containing an acid,

(b) a second compartment containing an ionic liquid,

(d) an anode,

(e) a cathode in contact with the ionic liquid in the second compartment,

(f) a means for applying a potential across the anode and the cathode;

(g) a means for supplying feed materials to the first compartment; and (h) a means for supplying acid to the first compartment.

26. The apparatus defined in claim 25 wherein the anode is in contact with the acid in the first compartment or in contact with the ionic liquid in the second compartment .