Metal oxide reduction

Abstract

The present invention relates to a method for preparing a metal or an alloy comprising the metal from a metal precursor. The method includes reacting said metal precursor with a reducing agent in a self-sustaining exothermic reaction, and separating the metal or alloy comprising the metal from a slag produced during said reacting. The present invention also relates use of an intermetallic compound defined by the chemical formula Ca8(Al3-xMx) as a reducing agent in the reduction of a metal precursor to prepare a metal or metal alloy.

Description

[0001] METAL OXIDE REDUCTION

[0002] Technical field

[0003] The present invention relates to a method for preparing a metal or metal alloy from a metal precursor comprising an oxide of the metal, and to a use of an intermetallic compound for the reduction of a metal precursor. Background

[0004] Metals such as titanium and zirconium, as well as refractory metals, actinides and rare earth metals, for example neodymium, are today essential in many fields of technology. These elements are extracted from refined ores using various processes. Titanium is commercially extracted from refined ores using the Kroll process wherein liquid titanium chloride (TiCL) is derived from refined ores and later reduced using magnesium.

[0005] Other reduction processes are also known in the art for extracting these elements from refined ores. However, these processes are expensive, as they require special reaction conditions and strong reductants. Aluminothermic reduction processes for example, uses Aluminium as an active metal mixed with metal oxides from refined ores to achieve a reaction wherein oxygen is removed from the metal oxide. However, aluminothermic reduction of refractory and rare earth metal oxides suffers from that the extracted metal, although reduced from oxygen, typically is left alloyed with the aluminium. Aluminothermic reduction of Titanium for example, results in the obtained titanium being alloyed with aluminium as well as the formation of intermetallic Titanium Aluminides. This is of course undesirable if one aims for producing pure Titanium. Hence, when aiming for preparing pure metals, the aluminothermic reduction may be performed using an active metal mixture further including metal calcium. Such active metal mixtures limit the amount of aluminium left in the obtained metal. The prior art gives some examples of such active metal mixtures comprising even further metals such as magnesium, sodium, or barium. For example, US 2006 / 0107788 discloses a method for preparing refractory or rare earth metals from metal compounds by reducing them using a reducing agent comprising at least one of calcium, magnesium, sodium, barium, or potassium. Similarly, US 7,354,472 discloses a method for preparing a refractory metal from refractory metal oxides, or refractory metal alloys from mixtures of refractory metal oxides, by reducing them using magnesium, calcium, aluminium, or mixtures thereof. Also, US Pat. 4,373,947 discloses a process for the preparation of refractory metal alloy powders comprising the steps of mixing of precursor metal oxides and an alkaline oxide or carbonates, calcinating said mixture, and then reducing the mixture using metal calcium.

[0006] The active metal mixture used in the reduction should preferably not only contribute to the reduction of the metal oxides during the reduction process. Further key aspects of the reaction mixture are that it should achieve an exothermic reaction which is stable, self-sustaining or at the most only require a moderate heat input for starting and thereafter sustaining the reaction. Some of these aspects are facilitated by having the reaction mixture in the powdered form. Hence, it is desirable that the reaction mixture can be prepared using metals in the powdered form. However, alkali or alkali earth metals such as calcium are notoriously volatile and require careful handling and storage conditions, particularly when in the powdered form. Further to this, metallic calcium in the powdered form reduces the stability of the reaction which is undesirable. Therefore, metal calcium in reaction processes disclosed in the prior art is often added as larger pieces or chunks.

[0007] Provided the above, it is an aim of the present invention to provide an improved method for the reduction of metal oxides which overcomes or at least alleviates some of the shortcomings of the prior art.

[0008] Summary

[0009] The invention is set out in the appended set of claims. This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. It is an object of the present invention to provide a solution to at least some of the problems associated with reduction processes using calcium metal, i.e. , calciothermic reduction processes.

[0010] According to a first aspect, the present invention relates to a method for preparing a metal or an alloy comprising the metal from a metal precursor, the method comprising: obtaining a reaction mixture by mixing said metal precursor with a reducing agent; reacting said metal precursor with the reducing agent in an self-sustaining exothermic reaction; and separating the metal or alloy comprising the metal from a slag produced during said reacting, wherein the metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta, and the metal precursor comprises an oxide of the metal, and reducing agent comprises an intermetallic compound Ca8(Al3-xMx), wherein 0<x<1 .5, wherein element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si.

[0011] According to a second aspect, the present invention relates to a use of an intermetallic compound defined by the chemical formula Cas(Al3-xMx) as a reducing agent in the reduction of a metal precursor to prepare a metal or metal alloy, wherein the metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta, and the metal precursor comprises an oxide of the metal, and 0<x<1.5, and element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si.

[0012] Because the reduction agent in the invention comprises mostly calcium while at the same time being stable at atmospheric conditions, a calciothermic reduction process can now be performed much more easily and safely compared to the prior art.

[0013] The method and use may further be used to prepare other metal(s) or alloys comprising such metal(s) than those listed above.

[0014] A further scope of applicability will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples are given by way of illustration only. Brief description of the drawings

[0015] The above and other aspects will now be described in more detail, with reference to appended figures. The figures should not be considered limiting; instead, they are used for explaining and understanding.

[0016] As illustrated in the figures, the certain aspects of the depicted elements may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general. Like reference numerals refer to like elements throughout.

[0017] Figure 1 is a schematic flow diagram of the steps of a method for preparing a metal or an alloy comprising the method according to aspects of the present invention.

[0018] Figure 2 is a schematic illustration of the triclinic crystal structure of CasAh, according to embodiments of the present invention.

[0019] Figure 3 is an XRD pattern of produced CasAh, according to embodiments of the present invention.

[0020] Figure 4 is an XRD pattern of produced titanium metal after leaching, according to embodiments of the present invention.

[0021] Figure 5 is a micrograph of cross-sectioned titanium metal particles embedded in CaO-A^Os slag, produced according to aspects of the present invention.

[0022] Figure 6 is a micrograph of cross-sectioned titanium-niobium TisoNbso particles embedded in a leachable slag matrix of CaO-A^Os slag, produced according to aspects of the present invention.

[0023] Figure 7 is an XRD pattern of produced titanium-niobium TisoNbso alloy after leaching, according to embodiments of the present invention.

[0024] Detailed description

[0025] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It must be noted that, as used in the specification and the appended claim, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", “including”, “containing” and similar wordings does not exclude other elements or steps.

[0026] Calciothermic reduction processes known in the art suffer from problems not only related to the handling of metallic calcium but also the balancing of reaction rates in order to ensure a stable but still self-propagating reaction. A too volatile reaction will create excess gasses which is hazardous in a closed reaction vessel. Such excessive gas generation is negative, also regarding the yield of the reduction process as a whole.

[0027] Therefore, as shown in Fig.1 , the present invention relates to a method for preparing a metal or an alloy comprising the metal from a metal precursor. The method comprising the steps of: reacting S1 said metal precursor with a reducing agent in a self-sustaining exothermic reaction. Self-sustaining in this regard means a reaction which, once the reaction has been activated, produces enough heat during said reacting such that the reaction propagates without the need of addition of further heat from an external source, for example a furnace.

[0028] After said step of reacting S1 , the method comprises a further step of separating S2 the metal or alloy comprising the metal from a slag produced during said reacting. The metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta, and consequently, the metal precursor comprises an oxide of the same metal. The metal precursor is not limited to comprise the oxide from one metal, as metal precursor may comprise a plurality of metal oxides, and optionally also additions of pure metal for the purpose of alloying.

[0029] The metal oxide may be selected from TiCh, TiFeOs, ZrCh, HfCh Nd20s, Nb20s Ta2Os, V2O5, SC2O3, UO2, ThCh, and combinations thereof. Depending on the respective composition of elements present in the reducing agent and / or the metal precursor, the method may be used to produce pure metal. Alternatively, the method may be used to produce an alloy of the metal, such as an alloy selected from ThsZr?, Ti22V4, Ti23Fe4, and TisoNbso.

[0030] The reducing agent comprises the single-phase intermetallic compound Ca8(Al3-xMx), where 0<x<1.5, and element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si. This compound can also be described as CasAh, with an optional substitution of up to half of the aluminium by the element M.

[0031] CasAh has a triclinic crystal structure and belongs to a family of phases known as the Zintl phases, characterized by intermediate metallic-ionic bonding. The inventors have found that up to half of the aluminium in the triclinic single-phase intermetallic CasAh can be substituted by an element M selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si. The atomic radii of these elements make them suitable for substitution of aluminium in the CasAh compound.

[0032] A calcium-aluminium phase diagram indicating a CasAh compound has been shown in Figure 3 in reference

[0001] ,

[0033] Figure 2 schematically illustrates the triclinic crystal structure of CasAh, with aluminium atoms in light grey and calcium atoms in dark grey. The molar mass of CasAh is 401 .57 g / mol.

[0034] Ca8(Al3-xMx) is brittle and therefore easy to comminute into powder form, which is a preferred form for the reducing agent of the present invention. The brittleness may be attributed to the low Poisson’s ratio (<0.25) of the intermetallic compound. Preferably, the reducing agent is provided in a powdered form, more preferably in a powder having a particle size in the range of 1-1000 microns, preferably 10-100 microns, as determined by e.g. sieving. The reducing agent may be provided in a powdered form in which at least 95 % by weight of the particles in said powder have a particle size in the range of 1-1000 microns, preferably 10-100 microns.

[0035] It has also been found to be substantially inert at normal atmospheric conditions. This is attributed to the formation thin of a thin AI2O3 nano-layer that protects the powder particle surfaces against hydrolysis and pyrophoricity in air. Air stability is critical for industrial applications and scale-up.

[0036] Ca8(Al3-xMx) has been found by the surprising discovery of the inventors to be an excellent compound for reduction processes for a number of reasons.

[0037] Firstly, CasAh has a low congruent meting point of 575 °C. Compared to metal calcium, which has a melting point of 850 °C, CasAh requires a lower ignition energy to start a therm itic self-sustaining reaction with the metal precursor.

[0038] Further, the reaction is more stable compared to the use of metal calcium. Ca8(Al3-xMx) does not vaporize at high temperatures and evacuated conditions, which results in a more stable, more efficient, and less explosive thermitic reaction. This is important from a health and safety perspective.

[0039] Still further, Ca8(Al3-xMx) has improved wetting properties in the molten state compared to metal calcium. Furthermore, the chemistry of Ca8(Al3-xMx) can be tailored according to the need. Such tailoring may be used for determining the composition of the prepared alloy as will be described later.

[0040] As an example, in the case that x=0, Ca8(Al3-xMx) can be expressed as CasAh. CasAh may be referred to as the undoped compound and comprises Ca and Al as the two main constituents. In this case, the compound substantially consists of Ca and Al.

[0041] In the case that x>0, the compound may be referred to as the doped compound, comprising calcium, aluminium and the third metal element M, wherein the third metal element M substitutes aluminium in Ca8(Al3-xMx). x in Ca8(Al3-xMx) may be 0<x<1.0, preferably 0<x<0.6, or even more preferably 0<x<0.3. x in Ca8(Al3-xMx) may be 0.1 <x<1.0, preferably 0.1 <x<0.6, or even more preferably 0.1 <x<0.3.

[0042] The reducing agent may comprise at least 95 % of single-phase Ca8(Al3-xMx) by weight of the reducing agent, such as at least 96 % by weight of the reducing agent, such as at least 97 % by weight of the reducing agent, such as at least 98 % by weight of the reducing agent, such as at least 99 % by weight of the reducing agent, such as at least 99.5 % by weight of the reducing agent. The reducing agent may substantially consist of single-phase Ca8(Al3-xMx).

[0043] An optional remainder in the reducing agent may preferably comprise or consist of a naturally formed aluminium oxide layer and / or unavoidable impurities.

[0044] The unavoidable impurities may be present in an amount of up to 1 .0 % percent by weight of the reducing agent, such as in an amount of up to 0.5 % percent by weight of the reducing agent, such as in an amount of up to 0.1 % percent by weight of the reducing agent.

[0045] The step of reacting may be preceded by a step of preparing the reducing agent CasAh-xMx by melting calcium metal and aluminium metal in a crucible, such as a stainless steel crucible. The relative amount of calcium metal and aluminium metal is selected such that the stochiometric relationship between Ca and Al in the Ca8(Al3-xMx) single-phase compound is facilitated. In the case that x=0, when preparing the undoped compound, the relative amounts of Ca and Al in said crucible during said preparing would be 72.73 atom-% and 27.27 atom-% for calcium metal and aluminium metal respectively. In the case that a doped compound is prepared, wherein x>0, the step of preparing the reducing agent Ca8(Al3-xMx) comprises melting calcium metal, aluminium metal and the third metal element M in a crucible. The relative amount of calcium metal, aluminium metal and the third metal element M is selected such that the stochiometric relationship between Ca, Al and M in the Ca8(Al3-xMx) single-phase compound is facilitated. For example, if x=1 , the relative amounts of Ca, Al and the third element M in said crucible during said preparing would be 72.73 atom-%, 18,18 atom-% and 9.09 atom- % for calcium metal, aluminium metal and third metal element M respectively. The step of obtaining the reducing agent Ca8(Al3-xMx), may be succeeded by a further step of comminution of the Ca8(Al3-xMx) compound to a powder. The particle size of the achieved powder may be determined by sieving, resulting in powder particles in the range of 1-1000 microns, preferably 10-100 microns.

[0046] In a preferred embodiment of the method, the reducing agent is provided in a powdered form. Hence, as stated earlier, the step of preparing the reducing agent Ca8(Al3-xMx), may be succeeded by a further step of comminution of the Ca8(Al3-xMx) to a powder having a particle size in the range of 1-1000 microns, preferably 10-100 microns.

[0047] The metal precursor may also be provided in the powdered form. It may either be obtained off-the-shelf in the powdered form, or it may be subject to comminution prior to said reacting.

[0048] The metal precursor is preferably provided as a powder having a particle size in the range of 1-1000 microns, preferably 10-100 microns, as determined by sieving. The improved wetting of the Ca8(Al3-xMx) in the molten state, as compared to molten calcium metal, allows for the Ca8(Al3-xMx) to wet a larger proportion of the surface of the particles. Consequently, the metal oxide particles can be provided in micron-size and still be properly wetted by molten Ca8(Al3-xMx).

[0049] In some embodiments, both the reduction agent and the metal precursor are provided in the powdered form. In such embodiments wherein both the reduction agent and the metal precursor are provided in the powdered form, the step of reacting may be preceded by a step of obtaining a reaction mixture by mixing powders of said metal precursor with powders of said reducing agent by means known to the person skilled in the art. Said means of mixing may include but is not limited to the use of a ball mill, tumbler or a mortar and pestle. Generally, mixing of metal precursor and reducing agent is beneficial for achieving a complete and uniform reaction between the reducing agent and the metal precursor. Said step of obtaining a reaction mixture may also be performed when only one of, or none of the reducing agent or metal precursor are provided in the powdered form. In other embodiments, the crushing and pulverizing of metal precursor and / or the reduction agent may be achieved during the step of achieving the reaction mixture, when using for example a ball mill as means for mixing. Unlike when using pure calcium metal, the preparation of the reaction mixture can be performed at ambient conditions having atmospheric levels of oxygen present when using the reduction agent disclosed in the present invention. This is a significant advantage compared to the prior art. Further to the above, the reducing agent Ca8(Al3-xMx) has surprisingly been found to have a self commutating property whilst exposed to normal ambient conditions. Accordingly, the powdered form of the reducing agent may be acquired without the need for commutating processing steps.

[0050] In some embodiments, the step of reacting is preceded by a step of compressing or briquetting the reaction mixture into a compact. Said step of compressing or briquetting the reaction mixture may be achieved by any means known to the person skilled in the art including but not limited to the use of a die and a plunger together with an hydraulic press for applying an appropriate amount of force. The term “appropriate force” in this regard means a force which achieves a compact of powders which stays together after being removed from for example a die.

[0051] The step of reacting is achieved by heating. In some embodiments said heating may be uniform, such that the entire reaction mixture or compact is uniformly heated in order to instigate said reacting. However, the heating can also be local, such that only a portion of the reaction mixture or compact is heated. In the case of local heating, the reaction will propagate throughout the reaction mixture or compact, i.e. self-propagating reaction, due to the exothermic nature of the reaction. Heating may for example be achieved by Vacuum Induction Melting (VIM). In a preferred embodiment, said step of reacting is achieved by heating said reaction mixture in an inert atmosphere, thereby igniting said self-sustaining exothermic reaction. Heating in an inert atmosphere may for example be achieved by Vacuum Induction Melting (VIM).

[0052] In some embodiments, the metal precursor may comprise a further oxide, wherein the further oxide is selected from the list consisting of: TiCh, TiFeOs, ZrO2, HfO2, NCI2O3, Nb20s, Ta2Os, V2O5, SC2O3, UO2, ThO2 and combinations thereof. For example, the metal precursor may comprise both TiO2 and V2O5. The metal precursor may also comprise three or more oxides, for example TiCh, V2O5 and ZrO8. These two examples are provided as examples only and should not be considered limiting as any combination of the previously listed oxides are possible. The metal precursor may further comprise a pure metal, i.e. a metal not in an oxidated state, selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si, in an amount of less than 10 % of the total weight of the metal precursor. By combining different oxides and pure metals in the metal precursor, the alloying of said prepared alloy may be determined by the molar ratio between metals and / or metal oxides present in the metal precursor used in said reacting.

[0053] In other embodiment, the alloying of said prepared alloy may be determined by the element M in the reducing agent Ca8(Al3-xMx), wherein M are metal atoms from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si, which substitute Al in the intermetallic Ca8AI8phase.

[0054] Further to this, in yet another embodiment of the method, the alloying of the prepared alloy may be determined by the combination of oxides and metals included in the metal precursor, and by the metal(s) substituted into the reducing agent.

[0055] The relative amounts of metal precursor and reducing agent in the reaction is balanced such that the molar ratios of reaction are matched, as exemplified in the following balanced reactions:

[0056] Hence, as exemplified by balanced reaction (I), the molar ratio between the metal precursor (TiO2) and the reducing agent (Ca8AI3) is at least 25 : 4. In a preferred embodiment, the amount of reducing agent may be higher than the ratio suggested by the balanced reaction, to ensure a complete reduction of the precursor metal.

[0057] In some embodiments, the step of separating the metal or alloy comprising the metal from slag produced during said reacting comprises leaching in a dilute acid or alkali solution.

[0058] According to the second aspect of the invention, there is also provided a use of an intermetallic compound defined by the chemical formula Ca8(AI3.xMx) as a reducing agent in the reduction of a metal precursor to prepare a metal or metal alloy, wherein the metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta, and the metal precursor comprises an oxide of the metal, and 0<x<1 .5, and element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si. In the case that x=0, the intermetallic compound may be referred to as undoped wherein the Ca8(AI3-xMx) is Ca8AI3. Alternatively, in some embodiments x in Ca8(AI3-xMx) is 0<x<1.0, preferably 0<x<0.6, or even more preferably 0<x<0.3.

[0059] Embodiments described in relation to the first aspect are also applicable as embodiments of the second aspect.

[0060] Elements may be denoted interchangeably by their elemental name and by their symbols in the periodic table.

[0061] EXAMPLES In the following, examples of the invention are provided, the examples should be interpreted as examples only and not limiting of the scope of the invention in any way.

[0062] Example 1 : Preparing undoped reducing agent

[0063] Preparing of the undoped reducing agent, CasAI3was achieved by melting 72.73 atom-% calcium metal and 27.27 atom-% aluminium in a crucible. An XRD pattern of the achieved undoped reducing agent is provided in Fig. 3.

[0064] Example 2: Preparing doped reducing agent comprising vanadium

[0065] Preparing a doped reducing agent comprising vanadium was achieved by melting 72.73 atom-% metal calcium, 18,18 atom-% metal aluminium and 9.09 atom-% vanadium metal in a crucible.

[0066] In examples 3-11 below, all metal precursors and reducing agents were provided in powdered form. The “parts” are molar parts.

[0067] Example 3: Pure titanium metal

[0068] Preparing of pure Ti metal was achieved by mixing 25 parts TiO2(metal precursor) with 4 parts CasAh (reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a Vacuum Induced Melting (VIM) furnace to start the self-propagating reaction according to:

[0069] The reacted material was then crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in a powder. Subseguent XRF-analysis indicate that the powder comprises 99.17 weight-% titanium as well as 0.58 weight-% iron and 0.25 weight-% nickel which are both ascribed to pick-up from the stainless steel reaction vessel. An XRD pattern of the achieved hexagonal close packed (hep) titanium metal is provided in Fig. 4. A Cross-sectional micrograph is shown in Fig. 5, showing pure Ti powder particles embedded in a leachable slag matrix of 32CaO- 6AI2O3, prior to acid leaching.

[0070] Examples 4: Ti-Zr alloy

[0071] Preparing of Ti-Zr alloy was achieved by mixing 18 parts TiO2(metal precursor), 7 parts ZrO2(metal precursor) and 4 parts Ca8AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to:

[0072] 18TiO2+ 7ZrO2+ 4Ca8AI3Tii8Zr7+ 32CaO-6AI2O3(ll)

[0073] The reacted material was then crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in a powder. Subsequent XRF-analysis indicate that the powder comprises 56.4weight-% titanium, 42.3 weight-% zirconium, as well as 1.2 weight-% hafnium provided as an impurity in the ZrO2.

[0074] Example 5: Ti-V alloy

[0075] Preparing of Ti-V alloy was achieved by mixing 22 parts TiO2(metal precursor), 4 parts Ca8AI2V (reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to:

[0076] 22TiO2+ 4Ca8AI2V Ti22V4+ 32CaO-4AI2O3(III) The reacted material was then crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in a Ti-V alloy powder.

[0077] Example 6: Ti-Fe alloy

[0078] Preparing of Ti-Fe alloy was achieved by mixing 19 parts TiO2(metal precursor), 4 parts TiFeO3(metal precursor), 4 parts Ca8AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to:

[0079] The reacted material was then crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in a Ti-Fe alloy powder.

[0080] Example 7: Nd metal

[0081] Preparing of Nd metal was achieved by mixing 25 parts Nd2O3(metal precursor), 6 parts Ca8AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to:

[0082] The reacted material was then crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in Nd metal powder.

[0083] Example 8: TiNb superconductor alloy

[0084] Preparing of TiNb superconductor alloy was achieved by mixing 50 parts TiO2 (metal precursor), 25 parts Nb20s (metal precursor), and 18 parts CasAh (reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to: TisoNbso + 144CaO-26AI2O3(VI)

[0085] The reacted material was then crushed and CaO-Al2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in a powder. Subsequent XRF-analysis indicate that the powder comprises 70.9 weight-% Nb, 29.0 weight-% titanium, which is approximately equivalent to the equiatomic TiNb composition.

[0086] A cross-sectional micrograph is shown in Fig. 6, showing TisoNbso powder particles embedded in a leachable slag matrix of 144CaO-26Al2O3, prior to acid leaching.

[0087] An XRD pattern of the achieved body-centred cubic (bcc) titaniumniobium metal is provided in Fig. 7.

[0088] Hypothetical example 9: Uranium metal

[0089] Preparing of Uranium metal will be achieved by mixing 25 parts UO2 (metal precursor), and 4 parts Ca3AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture will be then pressed into pellets (compacts). The pellets will be heated in a VIM furnace to start the selfpropagating reaction according to:

[0090] The reacted material will then be crushed and CaO-AI2O3slag was removed by leaching in 3M HCI solution for 6 hours. The material will then be washed and filtered in a Buchner filter, and air-dried, resulting in a uranium metal powder.

[0091] Hypothetical Example 10: Thorium metal

[0092] Preparing of Thorium metal will be achieved by mixing 25 parts ThO2(metal precursor), and 4 parts Ca8AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture will then be pressed into pellets (compacts). The pellets will be heated in a VIM furnace to start the selfpropagating reaction according to:

[0093] 25ThO2+ 4Ca8AI325Th+ 32CaO-6AI2O3(VIII)

[0094] The reacted material will then be crushed and CaO-AI2O3slag will be removed by leaching in 3M HCI solution for 6 hours. The material will then be washed and filtered in a Buchner filter, and air-dried, resulting in a thorium metal powder.

[0095] Example 11. Scandium metal

[0096] Preparing of Sc metal was achieved by mixing 25 parts Sc2O3(metal precursor), 6 parts Ca8AI3(reducing agent), thereby achieving a reaction mixture. The reaction mixture was then pressed into pellets (compacts). The pellets were heated in a VIM furnace to start the self-propagating reaction according to: The reacted material was then crushed and CaO-A^Osslag was removed by leaching in 3M HCI solution for 6 hours. The material was then washed and filtered in a Buchner filter, and air-dried, resulting in Sc metal powder.

[0097] References

[0098] [1] Ozturk, K., Zhong, Y., Chen, LQ. Et al. Linking first-principles energetics to CALPHAD: An application to thermodynamic 1 Sodelling of the Al-Ca binary system. Metall Mater Trans A 36, 5-13 (2005).

Claims

CLAIMS1 . A method for preparing a metal or an alloy comprising the metal from a metal precursor, the method comprising:- obtaining a reaction mixture by mixing said metal precursor with a reducing agent;- reacting said metal precursor with said reducing agent in a self- sustaining exothermic reaction; and- separating the metal or alloy comprising the metal from a slag produced during said reacting; wherein: the metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta; the metal precursor comprises an oxide of the metal; and the reducing agent comprises an intermetallic compound Ca8(Al3-xMx), wherein 0<x<1.5, wherein element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si.

2. The method according to claim 1 , wherein the reducing agent is provided in a powdered form.

3. The method according to claim 1 or 2, wherein the metal precursor is provided in a powdered form.

4. The method according to claim 3, wherein said step of obtaining the reaction mixture comprises mixing powder of said metal precursor with powder of said reducing agent.

5. The method according to claim 4, wherein said step of reacting is preceded by a step of compressing the reaction mixture into a compact.

6. The method according to any one of claims 1 to 5, wherein said step of reacting is achieved by heating said reaction mixture or compact, thereby igniting said self-sustaining exothermic reaction.

7. The method according to any one of claims 1 to 6, wherein the reducing agent is a single-phase chemical compound.

8. The method according to any one of claims 1 to 7, wherein the reducing agent is CasAh.

9. The method according to any one of claims 1 to 7, wherein x in Ca8(Al3-xMx) is 0<x<1.0.

10. The method according to any one of claims 1 to 9, wherein said metal precursor comprises a further oxide.11 . The method according to claim 10, wherein said further oxide is selected from the list consisting of: TiCh, TiFeOs, ZrCh, HfCh, Nd2Os, Nb2Os Ta20s, V2O5, SC2O3, UO2 and ThO2 and combinations thereof.

12. The method according to any one of claims 1 to 11 , wherein said metal precursor comprises a metal selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si, in an amount of less than 10 % of the total weight of the metal precursor.

13. The method according to any one of claims 1 to 12, wherein the step of separating the metal or alloy comprising the metal from slag produced during said reacting comprises leaching in a dilute acid or alkali solution.

14. The method according to any one of claims 1 to 13, wherein said step of reacting is preceded by a step of preparing Ca8(Al3-xMx) by melting calcium metal, aluminium metal and an optional third element M in a crucible.

15. Use of an intermetallic compound defined by the chemical formula Ca8(Al3-xMx) as a reducing agent in the reduction of a metal precursor to prepare a metal or metal alloy, wherein the metal is selected from the list consisting of Ti, Zr, Hf, V, Nd, Nb, Sc, U, Th and Ta; the metal precursor comprises an oxide of the metal; and0<x<1 .5, wherein element M is selected from the list consisting of Fe, Cu, Co, Ni, V, Mn, Mo, Nb, Ta, W, Cr, Sn and Si.

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