WO2023017265A1

WO2023017265A1 - Method for metal production

Info

Publication number: WO2023017265A1
Application number: PCT/GB2022/052085
Authority: WO
Inventors: Adam VOLLANS; Katerina HRUBANTOVA; Rajnikant Patel; Russell HODGETTS
Original assignee: University Of Bradford; Bradford Metallurgy Ltd
Priority date: 2021-08-11
Filing date: 2022-08-10
Publication date: 2023-02-16
Also published as: EP4384337A1

Abstract

This invention relates to a method for the production of reducible metal oxides (e.g. V₂O₃). The invention also relates to a method for the production of metals (e.g. vanadium) from said oxides. More specifically, the method facilitates the preparation of metal oxides that are capable of being further reduced to their respective metals with high purity.

Description

Method for Metal Production

[0001] This invention relates to a method for the production of reducible metal oxides. The invention also relates to a method for the production of metals from said oxides. More specifically, the method facilitates the preparation of metal oxides that are capable of being further reduced to their respective metals with high purity.

BACKGROUND

[0002] The production of metals, such as transition and rare earth metals, has always presented several technical challenges. In particular, certain metal oxides are incapable of being fully reduced to metal with conventional reduction methods. For example, when exposed to a single reduction step, vanadium pentoxide forms complex metal oxides that are not able to be further reduced to vanadium metal. The formation of these non-reducible oxides results in poor yields of extraction and poorer quality metals.

[0003] Vanadium metal is the most important rare metal in metallurgy, atomic energy, aviation and other industries due to its high melting point, hardness, good heat conductivity and chemical stability. Most of the Vanadium produced is used in ferrovanadium and, of this majority is used for alloying special steel used in bridges, industrial tools etc. In the titanium industry, Vanadium is used in compounds with Aluminium as a master alloy for Ti64, Ti5553 and other Titanium alloys. [1 , 2]

[0004] Although the commercial production of Fe-V and V-AI is relatively simple and economical the product contains only about 80% of Vanadium metal. In order to produce high-purity V metal, multiple post-processing steps such as electron beam remelting are necessary to obtain pure metal. Due to the current demand for new alloys such as the Vanadium-Titanium alloy used as an electrode material for hydrogen storage batteries or the V-Cr-Ti used in fusion reactors the production of pure Vanadium metal is now attracting considerable attention. [2, 3]

[0005] Commercially, pure Vanadium metal is produced metallothermically by aluminium or calcium. The aluminothermic reduction (ATR) is composed of two steps: First, V2O5 is reduced by ATR to Vanadium metal, containing a lot of residual Aluminium and Oxygen. In order to produce pure Vanadium metal, multiple melting steps by using the electron-beam melting process are necessary for the removal of residual aluminium and oxygen and other impurities. For this reason, the ATR production of pure Vanadium is highly time-consuming and energy-demanding which are the major factors contributing to its high cost. Alternatively, V2O5 can be reduced with Calcium and CaCI2. However, the calcium process results in low metal yields of 75-80% while requiring a large amount of reductant. Therefore, the development of a simple and efficient production process of high-purity Vanadium metal is strongly required. [2, 4]

[0006] WO 2006/089222 describes a process for producing metal, metal alloy and metal composite non-powders in large volume with a minimum of by-products. The metals, including tungsten, zirconium, titanium, and tungsten-hafnium, are produced from their respective metal oxides by mixing the metal oxide with a reducing metal and heating the resultant mixture in a metallothermic reduction.

[0007] Similarly, WO 2014/060766 describes a one step process in which oxides of transition or rare earth metals are exposed to a reducing agent, such as calcium or magnesium.

[0008] It is generally understood that certain metal oxides, such as vanadium pentoxide, cannot be fully reduced when subjected to metallothermic reduction conditions.

BRIEF SUMMARY OF THE DISCLOSURE

[0009] In accordance with a first aspect of the invention, there is provided a method for the production of a partially reduced metal oxide, said method comprising the steps of:

(a) mixing an oxide of a metal in a receptacle with a first reducing agent comprising a Group II metal or a hydride thereof, wherein the oxide of the metal and the reducing agent are present in a first mass ratio; and

(b) heating the mixture of the oxide of the metal and the first reducing agent to produce a partially reduced metal oxide.

[0010] Typically, the partially reduced metal oxide is suitable for further reduction to form a metal.

[0011] In accordance with a second aspect, there is provided a method for the production of a metal, said method comprising the steps of:

(c) mixing the partially reduced metal oxide formed in step (b) of the first aspect of the invention with a second reducing agent comprising a Group II metal or a hydride thereof, wherein the partially reduced metal oxide and the second reducing agent are present in a second mass ratio; and

(d) heating the mixture of the partially reduced metal oxide and second reducing agent to form the metal.

[0012] Thus, the invention provides a method for the production of a metal, said method comprising the steps of: (a) mixing an oxide of a metal in a receptacle with a first reducing agent comprising a Group II metal or a hydride thereof, wherein the oxide of the metal and the reducing agent are present in a first mass ratio;

(b) heating the mixture of the oxide of the metal and the first reducing agent to produce a partially reduced metal oxide;

[0013] For the avoidance of doubt, the following paragraphs refer to embodiments falling within the first and second aspects of the invention, unless otherwise stated.

[0014] Typically, the metal is a transition metal or a rare earth metal and the oxide of the metal is an oxide of a transition metal or an oxide of a rare earth metal.

[0015] Most commonly, the metal is a transition metal, examples of which include vanadium, titanium, tantalum, niobium, hafnium and zirconium. Suitable oxides of the metals may, for example, be selected from vanadium pentoxide, vanadium trioxide, titanium dioxide, tantalum pentoxide, niobium pentoxide, hafnium dioxide and zirconium dioxide.

[0016] The metal may be selected from titanium, vanadium, aluminium, iron, chromium, zirconium, molybdenum, tin, silicon, and niobium.

[0017] The metal may be selected from vanadium, niobium, and tantalum. The metal may be niobium. The metal may be tantalum. The metal may be vanadium. Where the metal is vanadium, the oxide of the metal may be vanadium pentoxide.

[0018] The metal may be aluminium.

[0019] The metal oxide may be selected such that it is a metal that forms non-reducible metal oxides when reduced with calcium in a mass ratio of 1 :2 (metal oxide : calcium).

[0020] The metal oxide used in step a) may be a mixture of different metal oxides, e.g. a mixture of oxides of two different metals. The product of step b) in this case will typically be a mixture of partially reduced metal oxides, e.g. a mixture of partially reduced metal oxides that comprise different metals. This mixture may be used in step c). Accordingly, the method of the second aspect may be a method of producing a metal alloy.

Step (a) [0021] The metal oxide may be annealed prior to mixing with the first reducing agent.

[0022] The first reducing agent may be selected from calcium or magnesium or the hydrides of calcium or magnesium. The first reducing agent may be magnesium. The first reducing agent may be calcium.

[0023] Where the metal oxide is vanadium pentoxide, the first reducing agent is preferably calcium.

[0024] The metal oxide and first reducing agent may be mixed together in the presence of water or an organic solvent. In certain embodiments of the invention, the resulting mixture is dried under vacuum prior to reduction in the heating step.

[0025] The metal oxide and first reducing agent may be mixed together in the presence of an organic solvent.

[0026] Any organic solvent may be used for the purpose of mixing including, for example, alcohols, aldehydes, ketones, ethers, esters, alkanes or cycloalkanes. Specific examples of solvents include methanol, ethanol, butanol, isopropyl alcohol, isobutyl alcohol, ethylene glycol, glycerol, propylene glycol, amyl alcohol, cetyl alcohol, sorbitol, cyclohexane- 1 ,2,3,4,5,6-hexol, menthol, formaldehyde, acetaldehyde, cinnamaldehyde, glucose, fructose, acetophenone, benzophenone, acetone, acetyl acetone, cyclopropanone, methyl vinyl ketone, cyclobutanone, dimethyl ether, diethyl ether, dioxane, tetrahydrofuran, anisole, crown ethers, butyl acetate, lactones, hexane and cyclohexane. The organic solvent may be diethyl ether. The organic solvent may be isopropyl alcohol. The organic solvent may be cyclohexane. The organic solvent may be acetone.

[0027] The mass ratio of metal oxide to first reducing agent may be in the range of from 1 :10 to 10:1. It may be that the mass ratio of metal oxide to first reducing agent is in the range of from 1 :0.5 to 1 :1.5, more typically from 1 :0.8 to 1 :1.5. In preferred embodiments, the mass ratio of metal oxide to first reducing agent is in the range of from 1 :0.8 to 1 :1.1. In some embodiments, the mass ratio of metal oxide to first reducing agent is 1 :1.

[0028] For some metals, e.g. vanadium, the inventors have surprisingly found that using a smaller amount of first reducing agent in a first reduction step, gives rise to the formation of partially reduced metal oxides that may subsequently be fully reduced to metal in a subsequent reduction step. For certain metals, e.g. vanadium, conventional methods of reducing metal oxides, where more reducing agent is used in a single reduction step can give rise to complex metal oxides that cannot be fully reduced to the metal. Therefore, the presently described method allows metal oxides that are susceptible to forming such nonreducible oxides during conventional reduction methods to be fully reduced to metal. As a result, the presently described methods may be more efficient, more economical and/or give rise to purer products.

[0029] It may be that the present method is used for any metal found to form non-reducible oxides when reduced with calcium in a 1 :3 oxide:Ca mass ratio at a pressure of 10'⁴ mbar and at a temperature of 1000 °C. In particular, vanadium pentoxide forms complex, nonreducible oxides, when reduced under these conditions. Titanium oxide does not form nonreducible oxides when reduced under these conditions. The presently described method avoids the production of these non-reducible complex metal oxides, and instead forms partially reduced metal oxides that may be further reduced in a subsequent reduction step.

Step (b)

[0030] Heating the mixture of metal oxide and first reducing agent is typically carried out in a chamber or furnace.

[0031] Step (b) may be performed at a temperature in the range of from 350 to 1300°C. The temperature may be in the range of from 750 to 1200°C, typically from 800° to 1000°C. The temperature may be 900°C.

[0032] The temperature of the reaction may be determined according to the metal oxide being reduced. For example, reduction of aluminium oxides in the present method may be performed at relatively low temperatures, e.g. in the range of from 450 to 900°C. Reduction of vanadium pentoxide may be performed at relatively high temperatures, e.g. in the range of from 800 to 1200°C, preferably at 900°C.

[0033] A pressure in the range of from 0 to 10^-3 mbar may suitably be employed during step (b).

[0034] Step (b) may be carried out for a period in the range of from 2 to 48 hours. Step (b) may be carried out for a period in the range of from 2 to 24 hours. Step (b) may be carried out for a period in the range of from 2 to 12 hours. Step (b) may be carried out for a period in the range of from of from 5 to 10 hours. Step (b) may be carried out for a period of about 5 hours.

[0035] The partially reduced metal oxides formed by step (b) are reducible metal oxides, i.e. they are metal oxides capable of being further reduced to their respective metal by the method of the second aspect of the invention.

[0036] It may be that greater than 50 wt% of the partially reduced metal oxides formed by step (b) do not contain any metal from the first reducing agent. For example, where the reducing agent is calcium or calcium hydride, it may be that greater than 50 wt% of the partially reduced metal oxides formed by step (b) do not contain calcium. In other words, it may be that less than 50 wt% of the partially reduced metal oxides formed in step (b) are complex metal oxides, such as CaMCh or Ca / C (where M is the metal).

[0037] It may be that greater than 60 wt% of the partially reduced metal oxides formed by step (b) do not contain any metal from the first reducing agent. It may be that greater than 70 wt% of the partially reduced metal oxides formed by step (b) do not contain any metal from the first reducing agent. It may be that greater than 90 wt% of the partially reduced metal oxides formed by step (b) do not contain any metal from the first reducing agent.

[0038] Typically, where the first reducing agent is calcium, it may be that complex metal oxides such as Ca / C (where M is the metal in the metal oxide) are present in the product of step (b) in an amount of less than 50 wt%, less than 40 wt%, less than 30 wt%, or less than 10 wt%. M may be vanadium.

[0039] Typically, where the first reducing agent is calcium, it may be that complex metal oxides such as CaMCh (where M is the metal) are substantially absent in the product of step (b). M may be vanadium.

[0040] Where the metal is vanadium, it may be that V2O3 is present in the product of step (b) in an amount of greater than 50 wt%, greater than 70 wt%, or greater than 90 wt%.

Processing the product of step (b)

[0041] The method may further comprise the step of removing impurities from the partially reduced metal oxide formed during step (b). Thus, the method may further comprise the step of cooling the product of step (b). The cooled product of step (b) may subsequently be washed. The product of step (b) may be washed with water and/or acid.

[0042] The washing/leaching step after reduction may conveniently be performed at a temperature in the range of from 15 to 100°C. The washing/leaching step after reduction may be performed for a duration in the range of from 30 minutes to 3 hours. This washing/leaching step may be repeated until substantially no such impurities are present.

[0043] Washing/leaching of the material may be carried out using dilute aqueous mineral acids, including inorganic acids such as hydrochloric, sulphuric, phosphoric or nitric acid. The acids are generally used at a concentration in the range of from 0.01 and 3M. In particular, the acid may be used at a concentration in the range of from 0.1 to 1 M. Preferably, the acid will be used at a concentration of 0.4M. Acid washing is typically performed at a temperature in the range of from 15 to 30°C.

[0044] The acid may be hydrochloric acid. In particular, the hydrochloric acid may be used at a concentration of 0.4M. [0045] Washing/leaching of the partially reduced metal oxides obtained from step (b) with acid results in the removal of oxides formed from the first reducing agent in step (b). For example, washing with acid may remove CaO and/or MgO from the partially reduced metal oxides, where Ca and/or Mg, or their respective hydrides are the first reducing agent.

Step (c)

[0046] The second reducing agent may be selected from calcium or magnesium or the hydrides of calcium or magnesium. The second reducing agent may be magnesium. The second reducing agent may be calcium.

[0047] The second reducing agent may be different to the first reducing agent. The second reducing agent may be the same as the first reducing agent. Thus, the first and second reducing agent may be selected from magnesium, magnesium hydride, calcium, and calcium hydride. The first and second reducing agent may be magnesium. The first and second reducing agent may be calcium. It may be that the second reducing agent is calcium, irrespective of the identity of the first reducing agent.

[0048] The partially reduced metal oxide produced in step (b) and the second reducing agent may be mixed together in the presence of water or an organic solvent and, in certain embodiments of the invention, the resulting mixture is dried under vacuum prior to reduction in the heating step.

[0049] For the avoidance of doubt, the product of step (b) may be the direct product of step (b), or the product of step (b) after any of the processes described under the “Processing the product of step (b)’’ section above.

[0050] The metal oxide and first reducing agent may be mixed together in the presence of an organic solvent.

[0051] Any organic solvent may be used for the purpose of mixing including, for example, alcohols, aldehydes, ketones, ethers, esters, alkanes or cycloalkanes. Specific examples of solvents include methanol, ethanol, butanol, isopropyl alcohol, isobutyl alcohol, ethylene glycol, glycerol, propylene glycol, amyl alcohol, cetyl alcohol, sorbitol, cyclohexane- 1 ,2,3,4,5,6-hexol, menthol, formaldehyde, acetaldehyde, cinnamaldehyde, glucose, fructose, acetophenone, benzophenone, acetone, acetyl acetone, cyclopropanone, methyl vinyl ketone, cyclobutanone, dimethyl ether, diethyl ether, dioxane, tetrahydrofuran, anisole, crown ethers, butyl acetate, lactones, hexane and cyclohexane. The organic solvent may be diethyl ether. The organic solvent may be isopropyl alcohol. The organic solvent may be cyclohexane. The organic solvent may be acetone.

[0052] Step (c) may further comprise the step of mixing the product of step (b) and the second reducing agent with one or more additional metals. Step (c) may further comprise the step of mixing the product of step (b) and the second reducing agent with one or more additional metal oxides. Step (c) may further comprise the step of mixing the product of step (b) and the second reducing agent with one or more additional metals and one or more additional metal oxides.

[0053] The one or more additional metals may be selected from aluminium, titanium, molybdenum, zirconium, tin, silicon, niobium, iron, and chromium. The one or more additional metal oxides may be selected from an oxide of aluminium, titanium, molybdenum, zirconium, tin, silicon, niobium, iron, and chromium. The one or more additional metals may be selected from aluminium, titanium, and molybdenum. The one or more additional metal oxides may be selected from aluminium oxide, titanium dioxide and molybdenum oxide. The one or more additional metal oxides may be titanium dioxide. The one or more additional metal oxides may be aluminium oxide. The one or more additional metal oxides may be molybdenum dioxide. The one or more additional metal oxides may be titanium dioxide and aluminium oxide. The one or more additional metal oxides may be titanium dioxide, aluminium oxide, and molybdenum oxide.

[0054] The mass ratio of partially reduced metal oxide to second reducing agent may be in the range of from 1 :10 to 10:1. It may be that the mass ratio of partially reduced metal oxide to second reducing agent is in the range of from 1 :1 to 1 :5, more typically in the range of from 1 :1 to 1 :3. In preferred embodiments, the mass ratio of partially reduced metal oxide to second reducing agent is 1 :3.

[0055] Where additional metal oxide(s) are added in step (c), the mass ratio is the mass of all metal oxides, i.e. the partially reduced metal oxide from step (b) and additional metal oxide(s) added in step (c), combined to the mass of the second reducing agent.

[0056] For the avoidance of doubt, where the product of the method of the second aspect is an alloy, additional metals and/or metal oxide(s) may be added to the mixture in step (c).

[0057] Where titanium dioxide is present in any step, it is preferred that the reducing agent used in that step is calcium.

Step (d)

[0058] Heating the mixture of partially reduced metal oxide and second reducing agent is typically carried out in a chamber or furnace.

[0059] Heating the mixture of partially reduced metal oxide and second reducing agent may be performed at a temperature in the range of from 350 to 1300°C. The temperature may in the range of from 750 to 1200°C, typically from 800° to 1000°C. The temperature may be 900°C. [0060] A pressure in the range of from 0 to 10^-3 mbar may suitably be employed during step (d).

[0061] Step (d) may typically be carried out for a period in the range of from 2 to 48 hours. Step (d) may be carried out for a period in the range of from 2 to 24 hours. Step (d) may be carried out for a period in the range of from 2 to 12 hours. Step (d) may be carried out for a period in the range of from 5 to 10 hours. Step (d) may be carried out for a period of about 5 hours.

[0062] The metal or alloy produced during step (d) may be pure metal(s), i.e. the metal or metal alloy may comprise no metal oxide(s). For example, the metal or alloy may be 100% pure metal(s). The metal or alloy may be 90% pure metal(s). The metal or alloy may be 85% pure metal(s). The metal or alloy may be 80% pure metal(s). Where the metal or alloy produced during step (d) is not 100% pure metal(s), the metal or metal alloy may comprise metal oxides that have not been fully reduced to their respective metal form. It may be that the metal or alloy produced during step (d) comprises up to 10 wt% metal oxide(s). It may be that the metal or alloy produced during step (d) comprises up to 15 wt% metal oxide(s). It may be that the metal or alloy produced during step (d) comprises up to 20 wt% metal oxide(s).

[0063] Where the metal in step (a) is vanadium, the metal produced during step (d) may comprise up to 10 wt% vanadium oxide (VO). Where the metal in step (a) is vanadium, the metal produced during step (d) may comprise up to 15 wt% vanadium oxide (VO).

[0064] The metal or alloy produced during step (d) may be 100 wt% metal(s), i.e. the metal or metal alloy may comprise no metal oxide(s). The metal or alloy may be 90% wt% metal(s). The metal or alloy may be 85% wt% metal(s). The metal or alloy may be 80% wt% metal(s). The wt% of metal(s) may be determined by SEM-EDX analysis.

[0065] Where the metal or alloy produced during step (d) is not 100% pure metal(s), the metal or metal alloy may comprise metal oxides that have not been fully reduced to their respective metal form. It may be that the product of step (d) comprises up to 10 wt% oxygen. It may be that the product of step (d) comprises up to 15 wt% oxygen. It may be that the product of step (d) comprises up to 20 wt% oxygen. The wt% of oxygen may be determined by SEM-EDX analysis.

Post-production

[0066] The method may further comprise the step of removing impurities formed during step (d). Thus, the method may further comprise the step of cooling the product of step (d). The cooled product of step (d) may subsequently be washed. The product of step (d) may be washed with water and/or acid. [0067] The washing/leaching step after reduction may conveniently be performed at a temperature in the range of from 15 to 100°C. The washing/leaching step after reduction may be performed for a period in the range of from 30 minutes to 3 hours. This washing/leaching step may be repeated until substantially no such impurities are present.

[0068] Washing/leaching of the material may be carried out using dilute aqueous mineral acids, including inorganic acids such as hydrochloric, sulphuric, phosphoric or nitric acid. The acids are generally used at a concentration in the range of from 0.01 to 1 M. In particular, the acid may be used at a concentration in the range of from 0.1 to 1M. Preferably, the acid will be used at a concentration of 0.4M. Acid washing is typically performed at a temperature in the range of from 15 to 30°C.

[0069] The acid may be hydrochloric acid. In particular, the hydrochloric acid may be used at a concentration of 0.4M.

[0070] Washing/leaching of the metal or metal alloy obtained from step (d) with acid results in the removal of oxides formed from the second reducing agent in step (d). For example, washing with acid may remove CaO and/or MgO from the metal or metal alloy, where Ca and/or Mg, or their respective hydrides are the second reducing agent.

[0071] The washing/leaching step may result in the metal or alloy being obtained in substantially pure form, i.e. the metal or alloy may comprise no metal oxide and/or no oxide of the first and/or second reducing agent. The metal or alloy may be obtained with at least 95% purity. The metal or alloy may be obtained with at least 90% purity. The metal or alloy may be obtained with at least 85% purity. The metal or alloy may be obtained with at least 80% purity.

[0072] The metal or alloy produced may be a powder.

[0073] It may be that the metal or metal alloy is melted and cast in to any required shape/form. Thus, the method may additionally comprise the step of melting the washed product of step (d) and casting the molten metal or alloy in to a desired shape/form.

[0074] It may be that the metal or metal alloy is subject to an electron beam remelting step. Electron beam remelting may reduce the oxygen content in the metal or alloy.

[0075] The metal or alloy may be subjected to a gas atomisation step. The gas atomisation step may be used to form metal powder particles. The metal powder particles may be spherical metal powders.

[0076] The metal or alloy may be subjected to a hydride-dehydride process. Such processes may result in the production of an angular / irregular shaped powders of more uniform particle size range. Such processes may result in the metal or alloy being less porous, thereby improving the use of these powders in additive manufacturing applications.

[0077] In a further aspect, the present invention provides a partially reduced metal oxide obtained by a method of the first aspect of the invention.

[0078] In a further aspect, the present invention provides a metal or metal alloy obtained by a method of the second aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows the XRD spectrum for the samples obtained by the method described in Example 1 .

Figure 2 shows the XRD spectrum for the samples obtained by the method described in Example 1 .

Figure 3 shows the XRD spectra for the samples obtained by the method described in Comparative Examples 1 and 2.

Figure 4 shows the XRD spectra for the samples obtained by the method described in Comparative Examples 3 and 4.

Figure 5 depicts a flow diagram detailing a typical method for producing partially reduced vanadium oxides according to the first aspect (stage 1) and for producing metal or vanadium-titanium alloy, according to the second aspect (stage 2).

DETAILED DESCRIPTION

[0080] The terms ‘metal oxide’ and ‘oxide of the metal’ are used interchangeably throughout this specification.

[0081] The term ‘partially reduced metal oxide’, as used throughout this specification, may refers to a metal oxide formed in a process of the invention, in which the metal is in a lower oxidation state than in the metal oxide starting material. Certain such oxides are capable of being further reduced to a metal under any of the conditions described with respect to the second aspect. The term ‘partially reduced metal oxide’ may refer to a metal oxide comprising cations of only one metallic element.

[0082] The term ‘complex metal oxide’ may refer to a metal oxide that is unable to be reduced to metal under metallothermic reduction conditions. The term ‘complex metal oxide’, as used throughout this specification, may refer to a metal oxide that is unable to be reduced to a metal under any of the conditions described with respect to the second aspect. The term ‘complex metal oxide’ may refer to a metal oxide that comprises more than one metal.

[0083] The term ‘non-reducible metal oxide’, as used throughout this specification, refers to a metal oxide that is not able to be reduced to a metal under any of the conditions described with respect to the first and/or second aspect. The ‘non-reducible metal oxide’ may be a metal oxide comprising cations of only one metallic element, or it may be a complex metal oxide, as defined herein.

[0084] It is to be understood that the term ‘metal’, as used throughout this specification, may be considered to encompass semi-metals. For example, the term ‘metal’ may be considered to encompass silicon. The term ‘metal’ may also be understood to refer only to metals. Thus, the term ‘metal’ may exclude semi-metals, such as silicon. In these embodiments, the term metal may only refer to transition metals and rare earth metals.

[0085] The present invention provides a method for the production of a reducible partially reduced metal oxide, as defined herein. The present invention also provides a method for the production of a metal or metal alloy, as defined herein. The process is particularly suited to the production of metals from metal oxides that are susceptible to forming non-reducible metal oxides that are not easily further reduced to their respective metal.

METHODS AND EXAMPLES

Methods

X-ray Diffraction (XRD)

[0086] X-ray diffractometry was performed with Cu Ka radiation (XRD, Bruker D8 AXS Advance X-ray diffractometer with linxeye detector). The PXRD run in Braggs-Brentano with a copper source operating at a wavelength of 0.15406nm, voltage of 40kV and a filament emission of 30mA.

Scanning Electron Microscopy - Energy Dispersive X-ray (SEM-EDX)

[0087] SEM-EDX analysis was performed utilising an Oxford Xplore 30 detector with the AZtec Live Software suite. The SEM-EDX was typically operated under "high" vacuum (1 E- 4 Torr); at an accelerating voltage of 20kV using tungsten filament, and magnifications between 10x - 600x, with the samples carbon coated prior to analysis.

Examples

[0088] Example 1 [0089] 5g of vanadium pentoxide (V2O5) was mixed with 3.81g of calcium. The resultant mixture was heated to 900°C for 5 hours at 10'³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.05M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 1.

Table 1 :

[0090] The XRD spectrum of Figure 1 shows that the product of the process described in Example 1 , i.e. a process according to the first aspect, includes V2O3 and CaV2O4.

[0091] Example 2

[0092] The partially reduced metal oxides obtained according to Example 1 were mixed with 4g of calcium. The resultant mixture was heated to 900°C for 5 hours at 10'³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.4M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 2.

Table 2:

[0093] The XRD spectrum of Figure 2 shows indicated that the product of the process described in Example 2, i.e. a process according to the second aspect of the invention, includes pure vanadium metal and a small amount (approximately 15-20 wt%) of vanadium oxide (VO).

[0094] Comparative Example 1

[0095] 2.5g of vanadium pentoxide (V2O5) was mixed with 5g of calcium. The resultant mixture was heated to 900°C for 7 hours at 10 '³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.05M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 3.

Table 3:

[0096] It is clear from the results shown in Table 3, and in Figure 3, that a one-step reduction process in which the mass ratio of vanadium pentoxide to calcium is 1 :2 (i.e. a process of the prior art), is insufficient to result in the production of vanadium metal.

[0097] Comparative Example 2

[0098] 2.5g of vanadium pentoxide (V2O5) was mixed with 5g of calcium. The resultant mixture was heated to 900°C for 10 hours at 10 '³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.05M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 4.

Table 4:

[0099] It is clear from the results shown in Table 4, and in Figure 3, that increasing the period of time for the prior art reduction process is insufficient to fully reduce vanadium pentoxide to vanadium metal.

[00100] Comparative Example 3

[00101] 2.5g of vanadium pentoxide (V2O5) was mixed with 5g of calcium. The resultant mixture was heated to 1050°C for 5 hours at 10 '³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.05M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 5.

Table 5:

[00102] It is clear from the results shown in Table 5, and in Figure 4, that increasing the temperature for the prior art reduction process is insufficient to fully reduce vanadium pentoxide to vanadium metal.

[00103] Comparative Example 4

[00104] 2.5g of vanadium pentoxide (V2O5) was mixed with 5g of calcium. The resultant mixture was heated to 1100°C for 5 hours at 10'³ mbar. The resultant mixture was cooled and washed with distilled water and diluted hydrochloric acid solution (0.05M). The washed product was then dried and analysed using SEM-EDX, the results of which are shown in Table 6.

Table 6:

[00105] It is clear from the results shown in Table 6, and in Figure 4, that increasing the temperature for the prior art reduction process is insufficient to fully reduce vanadium pentoxide to vanadium metal.

[00106] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00107] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. [00108] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

REFERENCES

[1] "Vanadium processing - The metal and its alloys", Encyclopedia Britannica, 2021. [Online], Available: https://www.britannica.com/technology/vanadium-processing/The- metal-and-its-alloys. [Accessed: 27- Jul- 2021],

[2] R. Moskalyk and A. Alfantazi, "Processing of vanadium: a review", Minerals Engineering, vol. 16, no. 9, pp. 793-805, 2003. Available: 10.1016/s0892-6875(03)00213-9 [Accessed 14 February 2021],

[3] Y. Oka and R. Suzuki, "Direct Reduction of Vanadium Oxide in the Molten Calcium Chloride", Journal of the Japan Institute of Metals, vol. 72, no. 3, pp. 181-187, 2008. Available: 10.2320/jinstmet.72.181 [Accessed 14 February 2021],

[4] F. Wang, B. Xu, H. Wan, J. Yang, B. Yang and W. Jiang, "Preparation of vanadium powders by calcium vapor reduction of V2O3 under vacuum", Vacuum, vol. 173, p. 109133, 2020. Available: 10.1016/j. vacuum.2019.109133 [Accessed 14 February 2021],

Claims

1. A method for the production of a partially reduced metal oxide, said method comprising the steps of:

(b) heating the mixture of the oxide of the metal and the first reducing agent to produce a partially reduced metal oxide; wherein the partially reduced metal oxide is suitable for further reduction to form a metal.

2. The method of claim 1 , wherein the metal is selected from a transition metal, a rare earth metal, and aluminium.

3. The method of claim 1 or claim 2, wherein the metal is selected from vanadium, titanium, tantalum, niobium, hafnium, zirconium, and aluminium.

4. The method of any of claims 1 to 3, wherein the metal is vanadium and the oxide of the metal is vanadium pentoxide.

5. The method of any preceding claim, wherein the metal oxide used in step (a) is a mixture of different metal oxides.

6. The method of any preceding claim, wherein the first reducing agent is selected from calcium, magnesium, calcium hydride, and magnesium hydride.

7. The method of any preceding claim, wherein the first reducing agent is calcium.

8. The method of any preceding claim, wherein the mass ratio of metal oxide to first reducing agent is in the range of from 1 :0.5 to 1 : 1.5.

9. The method of any preceding claim, further comprising the step of washing the product of step (b) with an acid.

10. A method for the production of a metal, said method comprising the steps of:

(c) mixing the partially reduced metal oxide formed in step (b) of claim 1, with a second reducing agent comprising a Group II metal or a hydride thereof, wherein the partially reduced metal oxide and the second reducing agent are present in a second mass ratio; and

11. The method of claim 10, wherein the second reducing agent is selected from calcium, magnesium, calcium hydride, and magnesium hydride.

12. The method of claim 10 or claim 11, wherein step (c) further comprises the step of mixing the product of step (b) and the second reducing agent with one or more additional metals and/or metal oxides.

13. The method of claim 12, wherein the one or more additional metals or metal oxides is selected from aluminium, titanium, molybdenum, zirconium, tin, silicon, niobium, iron, and chromium, or an oxide thereof.

14. The method of any of claims 10 to 13, wherein the mass ratio of partially reduced metal oxide to second reducing agent is in the range of from 1:1 to 1:5.

15. The method of any of claims 10 to 14, further comprising the step of washing the product of step (d) with an acid.

16. The method of any of claims 10 to 15, further comprising the step of melting the washed metal or alloy product of step (d) and casting the molten metal or alloy in to a desired shape/form.

17. The method of any of claims 10 to 16, wherein the washed metal or alloy product of step (d) is subject to an electron beam remelting step.

18. The method of any of claims 10 to 16, wherein the washed metal or alloy product of step (d) is subjected to a gas atomisation step.

19. A partially reduced metal oxide obtainable by the method of any of claims 1 to 9.

20. A metal or metal alloy obtainable by the method of any of claims 10 to 18.