Method for metal production

Abstract

This invention relates to a method for the production of metals from metal oxides (e.g. the production of titanium from titanium dioxide). More specifically, the method facilitates the large-scale production of metals from metal oxides, for example by avoiding one or more problems associated with the large-scale reduction of metal oxides.

Description

Method for Metal Production

[0001] This invention relates to a method for the production of metals from metal oxides. More specifically, the method of the invention facilitates the large-scale production of metals from metal oxides.BACKGROUND

[0002] The production of metals, such as transition and rare earth metals, has always presented several technical challenges. With specific reference to a particularly useful transition metal, titanium is the ninth most abundant element and possesses unique and desirable properties, such as high melting point, high corrosion resistance and the ability to form lightweight alloys, but it has not been used widely owing to its production costs. Titanium dioxide, which finds widespread use as a white pigment in paints, is readily available in the Earth's crust, but the separation of titanium metal from the oxygen in titanium dioxide has traditionally presented several challenges, in terms of time and energy requirements and handling difficulties associated with corrosive and volatile reagents and by-products.

[0003] Typically, the extraction of highly reactive metals requires the use of expensive electrolysis methods. The most commonly used processes for the production of titanium, however, are reductive processes. The Kroll process uses ilmenite or rutile as a starting material and this is carbo-chlorinated to obtain titanium tetrachloride, which is then reduced using magnesium metal. The magnesium chloride which is thus obtained is separated by distillation. This process, however, is time-consuming and takes several days for completion. Hunter’s process is similar to the Kroll process, but uses sodium, rather than magnesium, to effect the reduction of titanium tetrachloride. The FFC process, which was developed at the University of Cambridge, is also extremely time-consuming and involves the reduction of titanium dioxide pellets in a molten calcium chloride bath. However, despite extensive development work over a period of years, this process still fails to achieve complete removal of the oxide layer.

[0004] Alternative lengthy on-going research efforts have also failed to arrive at a cheaper production route. Several researchers, for example, have attempted electro-deposition of titanium from ionic solutions but have faced difficulties in eliminating multivalent titanium ions and highly reactive dendrite products.

[0005] Reductive processes for the manufacture of titanium metal from titanium dioxide typically encounter difficulties associated with the presence of various lower oxides or Magneli phases in the TiC>2, since titanium can exist in several oxidation states that makethe reduction more complicated and difficult. The present inventors have previously addressed this issue and have effectively reduced all the lower oxidation states of titanium, thereby allowing for the production of very high purity titanium metal (see WO 2014 / 060766).

[0006] WO 2014 / 060766 examined the direct de-oxidation of titanium dioxide using calcium metal in order to produce titanium metal and provided a process which is simple and rapid when compared with conventional methods and facilitates the production of titanium metal which is free from oxygen impurity whilst allowing for massive reductions in production costs.

[0007] Existing methods of forming metals from metal oxides by reduction can result in large and rapid increases in temperature within the reactor. When a process is performed at large scale, these ‘spikes’ in the exotherm of the reaction can be detrimental to the components of the reactor, which are unable to withstand the increased temperatures resulting from the ‘spike’.

[0008] Reduction of metal oxide with reducing metals can be conducted using a molten salt bath (see e.g. US 6,117,208). This can have benefits, including mitigating the effects of exothermic spikes, but it can be more difficult to obtain and clean the metal that is produced, resulting in further process steps and / or reduced purity.

[0009] There exists a need to scale the production of transition and rare earth metals, particularly titanium, in a safe and sustainable manner without compromising purity of the end product or introducing additional purification steps. It is an aim of the present invention to provide a method of producing a metal from a metal oxide that is able to be applied to larger-scale production of metals such as titanium.BRIEF SUMMARY OF THE DISCLOSURE

[0010] In accordance with a first aspect, there is provided a method for the production of a metal from a metal oxide, said method comprising the steps of:(i) heating a first component to a temperature, Ti;(ii) adding a second component to the first component to form a mixture of the first and second component, wherein the second component is added to the first component at a rate sufficient to maintain a reaction temperature that is at or above Ti, to form the metal; wherein: one of the first and second components is the metal oxide and the other of the first and second components is a reducing agent comprising a Group II metal or a hydride thereof; andTi is a temperature at or above which an exotherm occurs when the first and second components react. The method may be described as a solid state method.

[0011] In accordance with a second aspect, there is provided a metal formed by the method of the first aspect.

[0012] For the avoidance of doubt, the following paragraphs refer to embodiments falling within the first and second aspects of the invention, unless otherwise stated.Metals, Metal Oxides, Alloys, and Reducing Agents

[0013] It may be that the first component is the metal oxide and the second component is the reducing agent.

[0014] It may be that the first component is the reducing agent and the second component is the metal oxide.

[0015] Typically, the metal is a transition metal or a rare earth metal and the metal oxide is an oxide of a transition metal or an oxide of a rare earth metal.

[0016] Most commonly, the metal is a transition metal, examples of which include is titanium, tantalum, niobium, hafnium or zirconium.. Suitable oxides of the metals may, for example, be selected from and said oxide of the transition metal is titanium dioxide, tantalum pentoxide, niobium pentoxide, hafnium dioxide or zirconium dioxide.

[0017] The metal may be selected from titanium, tantalum, niobium, hafnium, vanadium, aluminium, iron, chromium, molybdenum, tin, silicon, and niobium.

[0018] In embodiments, the metal is titanium. In embodiments, the metal oxide is titanium dioxide.

[0019] In embodiments, the reducing agent is a Group II metal. In embodiments, the reducing agent is a hydride of a Group II metal. It may be that the reducing agent is selected from calcium, magnesium, calcium hydride, and magnesium hydride. It may be that the reducing agent is selected from calcium and magnesium. It may be that the reducing agent is selected from calcium and calcium hydride. It may be that the reducing agent is calcium.

[0020] It may be that the metal oxide is a bulk metal oxide. The term “bulk metal oxide” relates to materials wherein the metal, e.g. titanium, is present as an oxide in at least 50% by weight of the metal oxide component. It may be that the metal oxide component comprises at least 50% of the metal by weight in the form of an oxide. It may be that the metal oxide component comprises at least 90% of the metal by weight in the form of an oxide. It may be that the metal oxide component comprises at least 99% of the metal by weight in the form of an oxide. It may be that the metal oxide component comprises 100% of the metal by weight in the form of an oxide

[0021] It may be that the method is a method of making an alloy. Thus, the metal produced in step ii) may be an alloy. The method may involve one or more further component(s) in addition to the first and second components, said further component(s) being metal(s) and / or additional metal oxide(s).

[0022] It may be that one or more metal is present in step (i) in addition to the first component, i.e. step (i) comprises heating one or more metals and the first component. It may be that one metal is present. It may be that two metals are present. It may be that three metals are present.

[0023] Where the first component is the metal oxide, it may be that one or more additional metal oxide(s) is present in step (i), i.e. step (i) comprises heating the metal oxide and one or more additional metal oxides. It may be that one additional metal oxide is present. It may be that two additional metal oxides are present. It may be that three additional metal oxides are present.

[0024] It may be that one or more further metal oxide(s), and / or one or more metal(s), are present in step (i), i.e. step (i) comprises heating one or more metal(s), one or more additional metal oxide(s), and the first component. This will typically be the case where the first component is a metal oxide.

[0025] It may be that one or more metal is added in step (ii) in addition to the second component, i.e. step (ii) comprises adding the second component and one or more metals to the first component. It may be that one metal is added. It may be that two metals are added. It may be that three metals are added.

[0026] Where the second component is the metal oxide, it may be that one or more additional metal oxide(s) are added in step (ii), i.e. step (ii) comprises adding the metal oxide and one or more additional metal oxides. It may be that one additional metal oxide is added. It may be that two additional metal oxides are added. It may be that three additional metal oxides are added.

[0027] It may be that one or more further metal oxide(s), and / or one or more metal(s), are added in step (ii), i.e. step (ii) comprises adding one or more metal(s), one or more additional metal oxide(s), and the second component. This will typically be the case where the first component is a reducing agent and the second component is the metal oxide.

[0028] 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 metaloxides 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. It may be that each of the metals and metal oxides are different.Step (i)

[0029] The production of a metal from a metal oxide according to the present invention involves the reaction of a metal oxide with a reducing agent. Without wishing to be bound by theory, such reduction reactions require heat in order to initiate the reaction. Once activated, the reduction reaction is itself exothermic. Accordingly, the temperature at which the reaction occurs can be described as the temperature at which an exotherm occurs. This temperature will vary according to the identity of the reducing agent and the identity of the metal oxide.

[0030] The method of the present invention requires that a first component is heated to at or above a temperature, Ti. Ti is a temperature at or above which the exotherm occurs, i.e. is a temperature at or above which the reaction between the first and second components would ordinarily be initiated.

[0031] Ti may be a temperature in the range from 500°C to 1000°C. It may be that Ti is a temperature in the range from 600°C to 800°C. It may be that Ti is a temperature in the range from 650°C to 750°C. It may be that, Ti is 600°C. It may be that Ti is 650°C. It may be that T 1 is 700°C. It may be that T 1 is 750°C. These embodiments are particularly preferred where the metal oxide is titanium and the reducing agent is calcium.

[0032] It may be that the second component is present in an amount of less than 10 mol% of the first component in step (i). It may be that the second component is present in an amount of less than 5 mol% of the first component in step (i). It may be that the second component is present in an amount of less than 1 mol% of the first component in step (i).

[0033] Where the first component is the metal oxide and the second component is the reducing agent, it may be that substantially no reducing agent is present in step (i).

[0034] Where the first component is the metal oxide and the second component is the reducing agent, it may be that the reducing agent is present in an amount of less than 10 mol% of the metal oxide in step (i). It may be that the reducing agent is present in an amount of less than 5 mol% of the metal oxide in step (i). It may be that the reducing agent is present in an amount of less than 1 mol% of the metal oxide in step (i).

[0035] Where the first component is the reducing agent and the second component is the metal oxide, it may be that substantially no metal oxide is present in step (i).

[0036] Where the first component is the reducing agent and the second component is the metal oxide, it may be that the metal oxide is present in an amount of less than 10 mol% of the reducing agent in step (i). It may be that the metal oxide is present in an amount of less than 5 mol% of the reducing agent in step (i). It may be that the metal oxide is present in an amount of less than 1 mol% of the reducing agent in step (i).

[0037] A pressure in the range of from 10 bar (gauge) to 10-9mbar (gauge) may suitably be employed during step (i). It may be that a pressure in the range of from 2 bar (gauge) to 10-3mbar (gauge) may suitably be employed during step (i). It may be that the first component is placed under vacuum during and prior to heating the first component in step (i). Thus, it may be that a pressure in the range of from 10'3mbar (gauge) to 10-9mbar (gauge) is used prior to heating the first component.

[0038] It may be that the pressure is increased when heating begins in step (i), such that a pressure in the range of 2000 mbar (gauge) to 1 mbar (gauge) is used in step (i). It may be that the pressure is increased when heating begins in step (i), such that a pressure in the range of 20 mbar (gauge) to 1 mbar (gauge) is used in step (i).

[0039] Where a positive pressure is used, an inert atmosphere may be used. Thus, it may be that step (i) is performed under an argon atmosphere.

[0040] It may be that at least 90% by weight of the total mass of material heated in step (i) is the first component. It may be that at least 95% by weight of the total mass of material heated in step (i) is the first component. It may be that at least 99% by weight of the total mass of material heated in step (i) is the first component.

[0041] For the avoidance of doubt, where at least 90%, 95%, or 99% by weight of the total mass of material heated in step (i) is the first component, it is not intended to exclude the presence of additional components described herein. For example, where the metal produced by the method of the invention is an alloy, and the first component is the metal oxide, one or more additional metals and / or metal oxides may be present in step (i).

[0042] It may be that at least 90% by weight of the total mass of material heated in step (i) is a metal oxide or metal oxide mixture. It may be that at least 95% by weight of the total mass of material heated in step (i) is a metal oxide or a metal oxide mixture. It may be that at least 99% by weight of the total mass of material heated in step (i) is a metal oxide or a metal oxide mixture. The metal oxide mixture may comprise the metal oxide of the first component and one or more additional metals and / or metal oxides.

[0043] It may be that less than 10% by total weight of the material heated in step (i) is a metal halide salt, e.g. CaCl2. It may be that less than 5% by total weight of the material heated in step (i) is a metal halide salt, e.g. CaCh. It may be that less than 1% by total weight of the material heated in step (i) is a metal halide salt, e.g. CaCh. It may be that step (i) is performed in the absence of a metal halide salt, e.g. CaCl2. It may be that the metal halide salt is CaCh. It may be that the metal halide salt is CaF2. It may be that the metal halide salt is CaCh and CaF2.

[0044] The method is typically carried out in the absence of a molten salt bath. The method is typically carried out in the absence of zinc.Step (ii)

[0045] Once the first component has been heated to Ti, a second component is added to the first component to form a mixture of the first and second component. The second component is added to the first component at a rate sufficient to maintain a reaction temperature that is at or above Ti.

[0046] The second component may be added in a manner sufficient to maintain a reaction temperature that is below a temperature, T2, wherein T2 is the maximum temperature at which the reactor in which the reaction takes place can operate without damage.

[0047] It may be that the second component is added continuously or portionwise, provided that a reaction temperature that is above Ti is maintained. It may be that the second component is added continuously or portionwise, provided that a reaction temperature that is above Ti and below T2 is maintained.

[0048] It may be that the second component is added at a rate sufficient to maintain a reaction temperature in the range Ti to Ti+300°C (i.e. if Ti is 500 °C , a range between 500°C and 800°C). It may be that the second component is added at a rate sufficient to maintain a reaction temperature in the range Ti to Ti+200°C (i.e. if Ti is 600°C, a range between 600°C and 800°C). It may be that the second component is added at a rate sufficient to maintain a reaction temperature in the range from Ti to Ti+100°C (i.e. if Ti is 700°C, a range between 700°C and 800°C).

[0049] It may be that T2 is a temperature in the range of from 1000°C to 1500°C. It may be that T2 is 1200°C. It may be that T2 is a temperature below the melting point of the material from which the reactor is made. It may be that T2 is a temperature below the a temperature that is 80% of the melting point of the material from which the reactor is made. For example, where the reactor is made from stainless steel, it may be that T2 is in the range of 1400°C to 1500°C, e.g. 1440°C, or it may be that T2 is 80% of the melting point of stainless steel, such that T2 is in the range of 1100°C to 1200°C, e.g. 1150°C.

[0050] Conventional methods of forming metals from metal oxides, where the first and second components are mixed prior to heating, result in large and rapid increases in temperature within the reactor. These ‘spikes’ in the exotherm of the reaction can be detrimental to the components of the reactor, which are unable to withstand the increased temperatures resulting from the ‘spike’. This can be particularly problematic for large-scale production of metals from metal oxides. The inventors have surprisingly found that by first heating a first component of the reduction reaction to at or above a temperature at which an exotherm occurs, and subsequently adding in a second component of the reduction reaction, large and rapid increases in temperature within the reactor are avoided.

[0051] The avoidance of a spike in the exotherm of the reaction results in a process that is workable for large quantities of material. Accordingly, it may be that the total mass of metal oxide used in the present invention is only limited by practicalities such as the size of the reaction vessel (e.g. crucible / furnace) used.

[0052] It may be that the total mass of metal oxide used in the method is an amount in excess of 4500 Kg, for example in an amount of from 4500 Kg to 12000 Kg. It may be that the total mass of metal oxide used in the method is an amount in the range of from 500 Kg (e.g. 600 Kg, 700 Kg, 800 Kg, 900 Kg, 1000 Kg, 1500 Kg, or 2000 Kg) to 4500 Kg (e.g. 1000 Kg, 1500 Kg, 2000 Kg, 2500 Kg, 3000 Kg, 3500 Kg, or 4000 Kg).

[0053] It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 1 Kg. It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 750g. It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 600g. It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 500g. It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 400g. It may be that the total mass of metal oxide used in the method is an amount in the range of from 100g to 300g.

[0054] It may be that the method is configured to produce the metal in an amount of at least 200g. It may be that the method is configured to produce the metal in an amount of at least 300g. It may be that the method is configured to produce the metal in an amount of at least 500g. It may be that the method is configured to produce the metal in an amount of at least 1 Kg.

[0055] It may be that the molar ratio of the total amount of metal oxide to the total amount of reducing agent is from 1 :0.5 to 1 :4. The ratio of the total amount of metal oxide to total amount of reducing agent refers to the total amounts of each component added to the reaction.

[0056] It may be that the molar ratio of the metal oxide to the reducing agent is from 1 :0.5 to 1 :3. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 :0.5 to 1 :2. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 :0.5 to 1 :1.1. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 :0.5 to 1 :1.05.

[0057] It may be that the molar ratio of the metal oxide to the reducing agent is from 1 : 1 to 1 :4. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 : 1 to 1 :3. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 :1 to 1 :2. It may be that the molar ratio of the metal oxide to the reducing agent is from 1 : 1 to 1 : 1 .1.

[0058] It may be that, where the first component is the metal oxide, and the second component is the reducing agent, step (ii) involves adding the reducing agent alongside additional metal oxide. The additional metal oxide may be the same metal oxide, i.e. the metal oxide is the same as the first component. The additional metal oxide may be a different metal oxide to that of the first component.

[0059] It may be that the method further comprises the step of mixing the components of the reaction by any appropriate method known to the skilled person. It may be that the method further comprises the step of mechanically mixing the components of the reaction. It may be that the step of mechanically mixing is performed concurrently with step (ii). Accordingly, step (ii) may also comprise mechanically mixing the components of the reaction. It may be that the mechanical mixing is performed in step (i) and step (ii).

[0060] It may be that the mechanical mixing is performed by a fluidised bed reactor. It may be that the mechanical mixing is performed by a rotary kiln.

[0061] A pressure in the range of 2000 mbar (gauge) to 1 mbar (gauge) may be used in step (ii). A pressure in the range of 20 mbar (gauge) to 1 mbar (gauge) may be used in step (ii). A pressure in the range of 10 mbar (gauge) to 1 mbar (gauge) may be used in step (ii).

[0062] Where a positive pressure is used, an inert atmosphere may be used. Thus, it may be that step (ii) is performed under an argon atmosphere.

[0063] Step (ii) may typically be carried out for a period in the range of from 1 to 200 hours. Step (ii) may typically be carried out for a period in the range of from 2 to 48 hours. Step (ii) may be carried out for a period in the range of from 2 to 24 hours. Step (ii) may be carried out for a period in the range of from 2 to 12 hours. Step (ii) may be carried out for a period in the range of from 5 to 10 hours. Step (ii) may be carried out for a period of about 5 hours.

[0064] It may be that, after the second component has been added in step (ii), the reaction mixture is heated further. It may be that the reaction mixture is heated to a temperature sufficient to ensure that the reaction goes to completion. It may be that the reaction mixtureis heated to a temperature in the range of from 800°C to 1000°C, for example where the metal oxide is titanium dioxide and the reducing agent is calcium. It may be that the reaction mixture is heated to a temperature of approximately 900°C, for example where the metal oxide is titanium dioxide and the reducing agent is calcium.

[0065] The metal produced during step (ii) may be pure metal (or where the metal produced in step (ii) is an alloy, the alloy comprises only metals). Thus, the metal or metal alloy produced in step (ii) may comprise no metal oxide(s). For example, the metal or alloy produced in step (ii) may be 100% pure metal(s). The metal or alloy produced in step (ii) may be from 90% to 100% pure metal(s). The metal or alloy produced in step (ii) may be from 85% to 100% pure metal(s). The metal or alloy produced in step (ii) may be from 80% to 100% pure metal(s). The metal or alloy produced in step (ii) may be from 80% to 100% pure metal(s). The metal or alloy produced in step (ii) may be from 70% to 100% pure metal(s). The metal or alloy produced in step (ii) may be from 60% to 100% pure metal(s). Where the metal or alloy produced during step (ii) 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 (ii) comprises up to 10 wt% metal oxide(s). It may be that the metal or alloy produced during step (ii) comprises up to 15 wt% metal oxide(s). It may be that the metal or alloy produced during step (ii) comprises up to 20 wt% metal oxide(s).

[0066] The metal or alloy produced during step (ii) may be 100 wt% metal(s), i.e. the metal or metal alloy may comprise no metal oxide(s). The metal or alloy produced in step (ii) may be 90% wt% metal(s). The metal or alloy produced in step (ii) may be 85% wt% metal(s). The metal or alloy produced in step (ii) may be 80% wt% metal(s). The wt% of metal(s) may be determined by SEM-EDX analysis.

[0067] Where the metal or alloy produced during step (ii) 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 (ii) comprises up to 10 wt% oxygen. It may be that the product of step (ii) comprises up to 15 wt% oxygen. It may be that the product of step (ii) comprises up to 20 wt% oxygen. The wt% of oxygen may be determined by SEM-EDX analysis.

[0068] It may be that at least 90% by weight of the total mass of material added in step (ii) is the second component. It may be that at least 95% by weight of the total mass of material added in step (ii) is the second component. It may be that at least 99% by weight of the total mass of material added in step (ii) is the second component.

[0069] For the avoidance of doubt, where at least 90%, 95%, or 99% by weight of the total mass of material added in step (ii) is the second component, it is not intended to exclude thepresence of additional components described herein. For example, where the metal produced by the method of the invention is an alloy, and the second component is the metal oxide, one or more additional metals and / or metal oxides may be present in step (ii).

[0070] It may be that at least 90% by weight of the total mass of material added in step (ii) is a metal oxide or metal oxide mixture. It may be that at least 95% by weight of the total mass of material added in step (ii) is a metal oxide or metal oxide mixture. It may be that at least 99% by weight of the total mass of material added in step (ii) is a metal oxide or metal oxide mixture. The metal oxide mixture may comprise the metal oxide of the second component and one or more additional metals and / or metal oxides.

[0071] It may be that less than 10% by total weight of the material present in step (ii) is a metal halide salt, e.g. CaCl2. It may be that less than 5% by total weight of the material present in step (ii) is a metal halide salt, e.g. CaCl2. It may be that less than 1% by total weight of the material present in step (ii) is a metal halide salt, e.g. CaCl2. It may be that step (ii) is performed in the absence of a metal halide salt, e.g. CaCl2.

[0072] It may be that the metal halide salt is CaCh. It may be that the metal halide salt is CaF2. It may be that the metal halide salt is CaCl2 and CaF2.

[0073] The method is typically carried out in the absence of a molten salt bath. The method is typically carried out in the absence of zinc.

[0074] The method may further comprise repeating steps (i) and (ii). In particular, when the metal or metal alloy produced in step (ii) comprises metal oxides that have not been fully reduced to their respective metal form, steps (i) and (ii) may be repeated. Thus, it may be that the product of step (ii) (including any product having gone through any washing, leaching, and / or post-production steps detailed herein) is used as the ‘metal oxide’ of either the first or second component of the method.

[0075] The method may further comprise the step of washing the metal oxide with water and / or an organic solvent prior to step (i), when the first component is the metal oxide. Where the method further comprises the step of washing the metal oxide with water and / or an organic solvent prior to step (i), when the first component is the metal oxide, the step of washing the metal oxide with water and / or an organic solvent is performed between steps (ia) and (i).

[0076] The method may further comprise the step of washing the metal oxide with water and / or an organic solvent prior to it being added in step (ii), when the second component is the metal oxide.

[0077] Any organic solvent may be used for the purpose of mixing including, for example, alcohols, aldehydes, ketones, ethers, esters, alkanes or cycloalkanes. Specific examplesof 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.Post production

[0078] The method may further comprise the step of removing impurities from the metal formed during step (ii). Thus, the method may further comprise the step of cooling the product of step (ii). The cooled product of step (ii) may subsequently be leached and / or washed. The method my comprise the step (step (iii)) of leaching the product of step (ii). The product of step (ii) may be leached with water. The method my comprise the step (step (iv)) of washing the product of step (ii) and / or washing the product of step (iv). The product of step (ii) or step (iii) may be washed with dilute aqueous acid.

[0079] The leaching / washing step(s) may conveniently be performed at a temperature in the range of from 15 to 100°C. The leaching / washing step(s) may be performed for a duration in the range of from 30 minutes to 3 hours. This leaching / washing step(s) may be repeated until substantially no impurities are present.

[0080] Dilute aqueous mineral acids, including inorganic acids such as hydrochloric, sulphuric, phosphoric or nitric acid may be used in the washing step. 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 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.

[0081] The acid may be hydrochloric acid. In particular, the hydrochloric acid may be used at a concentration of 0.4M.

[0082] Leaching / washing of the metal obtained from step (ii) with acid results in the removal of oxides formed from the reducing agent used in the reaction. For example, washing with acid may remove CaO and / or MgO, where Ca and / or Mg, or their respective hydrides are the reducing agent.

[0083] In preferred embodiments, the method comprises both steps (iii) and (iv), i.e. the method comprises steps (i), (ii), (iii), and (iv).

[0084] The leaching / washing 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 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.

[0085] The metal or alloy produced may be a powder.

[0086] 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 product of step (iv) and casting the molten metal or alloy in to a desired shape / form.

[0087] It may be that the metal or metal alloy is used in additive manufacture techniques, such as laser, electron beam, or other powder bed additive manufacture processes.

[0088] 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.

[0089] 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.

[0090] The metal or alloy may be subjected to a hydride-dehydride process. Such processes may result in the production of an angular I 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.Determination of Ti

[0091] It may be that the method comprises the step of determining the temperature at which an exotherm occurs.

[0092] It may be that the method for the production of a metal from a metal oxide comprises the steps of:(ia) determining the temperature at which an exotherm occurs, (T ia);(i) heating a first component to a temperature, Ti;(ii) adding a second component to the first component to form a mixture of the first and second component, wherein the second component is added to the first component at a rate sufficient to maintain a reaction temperature that is at or above Ti, to form the metal; wherein:one of the first and second components is the metal oxide and the other of the first and second components is a reducing agent comprising a Group II metal or a hydride thereof;Tia is a temperature at which an exotherm occurs when the first and second components react;Ti is a temperature at or above which an exotherm occurs when the first and second components react.

[0093] It may be that step (ia) comprises the steps of: a) mixing the first and second components at specific ratio to form a mixture of the first and second components; b) heating the mixture of the first and second components in a receptacle; c) monitoring the temperature of the receptacle containing the mixture of the first and second components; and d) recording the temperature at which a spike in the exotherm occurs.

[0094] It may be that step (ia) comprises the steps of: a) mixing the first and second components at specific ratio to form a mixture of the first and second components; b) washing the mixture from step a) with a solvent, preferably acetone, to form a washed mixture; c) drying the washed mixture from step b); d) heating the mixture from step c) in a receptacle; e) monitoring the temperature of the receptacle containing the mixture of the first and second components; f) recording the temperature at which a spike in the exotherm occurs.

[0095] It may be that step (ia) comprises the steps described in any of the methods described in the examples described herein for determining Ti.BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:Figure 1 is a graph showing spikes in the exotherm of the reaction between titanium dioxide and calcium to determine Ti.Figure 2 is a graph showing the temperature profile of the reaction between TiC>2 and Ca, as set out in Comparative Example 1.Figure 3 is a graph showing the temperature profile of the reaction between TiC>2 and Ca, as set out in Example 1.DETAILED DESCRIPTION

[0097] The terms ‘metal oxide’ and ‘oxide of the metal’ are used interchangeably throughout this specification.

[0098] It is to be understood that the term ‘metal’, as used throughout this specification, may be considered to encompass semi-metals and metal alloys. For example, the term ‘metal’ may be considered to encompass silicon. The term ‘metal’ may also be understood to refer only to metals or alloys thereof. 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, or alloys thereof. The term ‘metal’ may also be understood to refer only to metals. In these embodiments, the term metal may only refer to transition metals and rare earth metals.

[0099] In this specification, the term ‘solid state’ is intended to mean a method in which the two components are added to the reactor as solids. One of the components (e.g. calcium) may melt during the process to form a liquid. In particular, in a solid state method, the metal oxide remains in the solid state throughout the process. Typically, the term ‘solid state’ excludes methods in which the components are heated in a molten salt bath.

[0100] 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.

[0101] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the inventionare 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.

[0102] 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.METHODS AND EXAMPLESMethodsDetermination of Ti

[0103] The temperature at which an exotherm occurs when the first and second components react may be determined by mixing specified quantities of the first and second components in small scale experiments and plotting the temperature at which an exotherm occurs.

[0104] Small scale experiments are performed with masses of first and second components that are large enough to observe the exotherm, whilst being small enough to avoid damage to the reaction vessel. Typically, small scale experiments relate to reactions where the total mass of metal oxide is in the range of from 100g to 300g.

[0105] Small scale experiments were performed according to the following procedure:1. Weigh first and second components at specific ratio2. Mix the first and second components with acetone and soak for 1 hour3. Vacuum dry mixture for 24 hours4. Load dried mixture of first and second components into crucible and load the crucible in the furnace6. Place the mixture under vacuum for several hours, typically overnight7. Following vacuum step, heat the furnace at a rate of ~ 4.5 °C per minute8. Observe temperature of crucible9. Record the temperature at which a spike in the exotherm occurs.

[0106] The above process is repeated across a number of different metal oxide : reducing agent mass ratios in the range 0.05:1 to 1:0.01, e.g. 2.1 to 1:5. The highest temperature at which a spike in the exotherm occurs is determined to be Ti.

[0107] A plot of the reaction of calcium and titanium dioxide, as determined by the above method and using metal oxide : reducing agent mass ratios in the range of 2:1 to 1:5, can be seen in Figure 1. Figure 1 shows that for titanium dioxide : calcium, Ti is 715°C (this occurs at a titanium dioxide : calcium mass ratio of 4:1).Comparative Example 1

[0108] TiC>2 (1.2413 kg) was loaded into a reactor and washed with acetone for 1 hour before being dried under vacuum for 24 hours. Ca (0.494 kg) was loaded into the reactor. The reactor was heated at ~20°C / min from 0°C to 580°C, followed by heating at ~4°C / min from 580°C to 700°C. It was noted that a spike in the exotherm was observed at 622°C, where the temperature within the furnace reached in excess of 1200°C.

[0109] After the temperature within the furnace had returned to approximately 640°C, heating was continued at ~4°C I min from to 700°C. Ca (0.902 kg) was fed into the furnace with a screw feeder and the furnace heated further, up to 900°C, for approximately 5 hours.

[0110] Figure 2 plots the temperature profile of the above process.Example 1

[0111] TiC>2 (1.376 kg) was loaded into a reactor and washed with acetone for 1 hour before being dried under vacuum for 24 hours. The reactor was heated to 480°C, followed by heating at ~2.6°C I min from 480°C to 760°C. Ca (1.514 kg) was fed into the furnace with a screw feeder and the furnace heated further, up to 900°C, at ~2.0°C I min. The furnace was held at 900°C for approximately 5 hours before being allowed to cool to room temperature. Titanium dioxide was reduced to titanium metal, as shown by the SEM-EDX analysis of the material obtained. This is shown in Table 1.Table 1:

[0112] It was noted that an exothermic spike was observed at 840°C. Without wishing to be bound by theory, it is believed that this temperature spike resulted from the rapid addition of calcium that had accumulated on the screw feeder, as this is the approximate melting point of calcium.

[0113] Figure 3 plots the temperature profile of the above process.

Claims

CLAIMS1. A solid state method for the production of a metal from a metal oxide, said method comprising the steps of:(i) heating a first component to a temperature, Ti;(i) adding a second component to the first component to form a mixture of the first and second component, wherein the second component is added to the first component at a rate sufficient to maintain a reaction temperature that is at or above Ti, to form the metal; wherein: one of the first and second components is the metal oxide and the other of the first and second components is a reducing agent comprising a Group II metal or a hydride thereof; andTi is a temperature at or above which an exotherm occurs when the first and second components react.

2. The method of claim 1 , wherein the second component is added to the first component at a rate sufficient to maintain a reaction temperature that is below a temperature, T2, wherein T2 is the maximum temperature at which the reactor in which the reaction takes place can operate without damage.

3. The method of claim 2, wherein T2 is 1200°C.

4. The method of claim 2, wherein Ti is a temperature from 500°C to 750°C.

5. The method of any of claims 1 to 4, wherein the molar ratio of the metal oxide to the reducing agent is from 1 :0.5 to 1 :4, by total amount of the metal oxide and reducing agent.

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

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

8. The method of any preceding claim, wherein said metal is a transition metal or a rare earth metal and said metal oxide is an oxide of the transition or rare earth metal, wherein, optionally, said transition metal is titanium, tantalum, niobium, hafnium or zirconium and said oxide of the transition metal is titanium dioxide, tantalum pentoxide, niobium pentoxide, hafnium dioxide or zirconium dioxide.

9. The method of any preceding claim, wherein the metal oxide is titanium dioxide and the metal produced is titanium.

10. The method of any preceding claim, wherein the first component is the metal oxide and the second component is the reducing agent.

11. The method of claim 10, wherein no reducing agent is present in step (i).

12. The method of claim 10, wherein the reducing agent is present in an amount of less than 5 mol% of the metal oxide in step (i).

13. The method of any of claims 1 to 9, wherein the first component is the reducing agent and the second component is the metal oxide.

14. The method of claim 13, wherein no metal oxide is present in step (i).

15. The method of claim 13, wherein the metal oxide is present in an amount of less than 5 mol% of the reducing agent in step (i).

16. The method of any preceding claim, wherein the metal is an alloy.

17. The method of claim 16, wherein the first component is the metal oxide and one or more additional metal and / or metal oxide is present in step (i).

18. The method of claim 16 or claim 17, wherein one or more additional metal and / or metal oxide is added in step (ii).

19. The method of claim 17 or claim 18, wherein the one or more additional metal or metal oxide is selected from aluminium, titanium, molybdenum, zirconium, tin, silicon, niobium, iron, and chromium, or an oxide thereof.

20. The method of any preceding claim, further comprising the step of mixing the components of the reaction.

21. The method of claim 20, wherein the mechanical mixing is performed by a fluidised bed reactor.

22. The method of claim 20, wherein the mechanical mixing is performed by a rotary kiln.

23. The method of any preceding claim, further comprising the step of washing the metal oxide with water and / or an organic solvent prior to step (i), when the first component is the metal oxide, or prior to being added in step (ii), when the second component is the metal oxide.

24. The method of any preceding claim, further comprising the steps of:(iii) leaching the product of step (ii) with water; and(iv) washing the product of step (iii) with a dilute aqueous acid.

25. The method of any preceding claim, wherein the method is configured to produce the metal in an amount of at least 500g.

26. A metal formed by the method of any of claims of 1 to 25.

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