NZ623179B2

NZ623179B2 - Electrolytic production of powder

Info

Publication number: NZ623179B2
Application number: NZ623179A
Authority: NZ
Inventors: John Clifford; James Collins; Melchiorre Conti; James Deane; Lucy Grainger; Kartik Rao
Original assignee: Metalysis Limited
Priority date: 2011-10-04
Filing date: 2012-10-04
Publication date: 2016-08-30

Abstract

method of producing metallic powder comprises steps of arranging a volume of feedstock comprising a plurality of non-metallic particles within an electrolysis cell, causing a molten salt to flow through the volume of feedstock, and applying a potential between a cathode and an anode such that the feedstock is reduced to metal. In preferred embodiments the feedstock is a plurality of discrete powder particles and these particles are reduced to a corresponding plurality of discrete metallic particles. The particles of the feedstock and metallic particles have an average diameter less than 5mm and a D90 size no greater than twice the D10 size. In advantageous embodiments the feedstock may be sand. feedstock is reduced to metal. In preferred embodiments the feedstock is a plurality of discrete powder particles and these particles are reduced to a corresponding plurality of discrete metallic particles. The particles of the feedstock and metallic particles have an average diameter less than 5mm and a D90 size no greater than twice the D10 size. In advantageous embodiments the feedstock may be sand.

Description

Electrolytic production of powder The invention relates to a method for producing metallic powder using electrolysis reduction processes such as electro-decomposition. ound The present invention concerns a method for the reduction of a feedstock comprising a metal compound or compounds, such as a metal oxide, to form a reduced product. As is known from the prior art, electrolytic processes may be used, for example, to reduce metal compounds or semi-metal compounds to metals, semi-metals, or partially reduced compounds, or to reduce mixtures of metal nds to form alloys. In order to avoid tion, the term metal will be used in this document to encompass all such products, such as metals, semi-metals, alloys, intermetallics, and partially reduced products.

In recent years, there has been great interest in the direct production of metal by direct ion of a solid feedstock, for example, a metal-oxide feedstock. One such direct reduction process is the Cambridge FFC® electro-decomposition s (as described in WO 99/64638). In the FFC process, a solid compound, for example a metal oxide, is arranged in contact with a cathode in an electrolysis cell comprising a fused salt. A potential is applied between the cathode and an anode of the cell such that the nd is reduced. In the FFC process, the potential that produces the solid compound is lower than a deposition potential for a cation from the fused salt.

Other reduction processes for reducing feedstock in the form of a cathodically connected solid metal compound have been proposed, such as the Polar® process described in WO 03/076690 and the process described in WO 03/048399.

Conventional implementations of the FFC process and other solid-state electrolytic reduction processes typically involve the tion of a ock in the form of a porous preform or precursor, fabricated from a sintered powder of the solid compound to be reduced. This porous m is then painstakingly coupled to a cathode to enable the reduction to take place. Once a number of preforms have been coupled to the cathode, then the e can be lowered into the molten salt and the preforms can be reduced.

During reduction of many metal oxides, for example titanium dioxide,, the individual particles making up the m undergo further sintering forming a solid mass of metal, which may have entrapped salt.

It may sometimes be desirable to produce ic powder, for example powder for subsequent processing using various known powder urgy techniques. Powder has 6287717_4.docx previously been produced by a processing route involving direct reduction of solid preforms, such as pellets, to form solid pellets of reduced metal. After ion, these reduced pellets may be crushed or ground to form powder of a desired particle size.

Some metals such as titanium are difficult to comminute to powder without undergoing additional steps such as hydrogen deprecation.

Summary of the Invention The invention provides a method for producing metallic powder as defined in the appended independent claim, to which reference should now be made. Preferred or advantageous features of the invention are set out in various dependent sub-claims.

Thus, in a first aspect a method for producing metallic powder may comprise the steps of arranging a cathode and an anode in contact with a molten salt within an electrolysis cell, arranging a volume of feedstock comprising a plurality of non-metallic particles within the electrolysis cell, g a molten salt to flow h the volume of ock, and applying a potential between the cathode and the anode such that the feedstock is reduced to metal in which the feedstock has a particle size distribution defined by a D10 particle size and a D90 particle size, in which the D90 particle size is no more than 100% greater than the D10 particle size, and in which the les making up the feedstock have an average particle diameter of less than 5 mm.

In a second aspect, a method for producing metallic powder may comprise the steps of arranging a cathode and an anode in contact with a molten salt within an olysis cell, an upper surface of the cathode supporting a feedstock sing a plurality of nonmetallic particles, and a lower surface of the anode being vertically spaced from the feedstock and the cathode, and applying a potential between the cathode and the anode such that the feedstock is reduced to metal.

In a third , a method for producing ic powder may comprise the steps of arranging a cathode and an anode in contact with a molten salt within an electrolysis cell, an upper e of the cathode supporting a free-flowing feedstock sing a plurality of discrete non-metallic particles, and a lower surface of the anode being vertically spaced from the feedstock and the cathode, and applying a potential between the cathode and the anode such that the feedstock is reduced to a plurality of discrete metal particles.

A method for producing metallic powder may involve a combination of the es set out in two or more of these s. The following preferred or advantageous features may 6287717_4.docx be used in conjunction with any aspect described above. red and advantageous features may be combined in any permutation or combination.

It is preferred that the feedstock is a free-flowing powder comprising a plurality of separate discrete particles of feedstock al. The use of lowing particles, for example free-flowing powder particles, as a feedstock may provide considerable advantage over prior art electro-decomposition methods that have required a powdered non-metallic feedstock to be formed into a porous perform or precursor prior to reduction.

Preferably, individual particles in the feedstock are reduced to individual les of metal. Preferably, there is substantially no ng between separate particles.

Preferably, there is substantially no sintering between adjacent ock particles during reduction.

In the prior art, powder has been formed by reducing pellets of oxide material (each pellet formed by consolidation of thousands of individual oxide particles) into pellets of metal. These metal pellets have then been crushed to form metal powder. The inventors have determined that, contrary to us understanding, it is possible to reduce a ock comprising discrete particles of feedstock material into a powder comprising discrete particles of metal material. Not only is the step of ing feedstock preforms eliminated (which was previously understood to be essential), but there is no need to crush reduced s to form a commercially usable metallic powder.

Advantageously, the feedstock may be a naturally occurring sand or fine gravel or may comprise lowing particles d from a naturally occurring sand or very fine gravel.

The sand or gravel may be a beneficiated sand or gravel. Sands and gravels may contain one or more metallic ore minerals, either as whole particles or as crystallites within particles. Such minerals may be reduced using a s according to the invention to extract the metallic component. For example, the feedstock may derive from a naturally occurring rutile sand. Rutile is the most common naturally occurring titanium dioxide polymorph.

The feedstock may comprise particles derived from crushed rock, for example a crushed ore. The feedstock may comprise particles derived from a crushed slag, for example a slag formed by heating a mineral sand or ore.

Advantageously, the feedstock may se a naturally occurring mineral. For example, the feedstock may comprise a naturally occurring sand such as rutile or ilmenite. Such natural sands comprise many particles, each of which may have a different ition.

Such sands may also comprise multiple grains of different l types. 6287717_4.docx ageously, the feedstock may comprise a first non-metallic particle having a first composition and a second non-metallic le having a second composition. The feedstock may then be reduced under conditions such that the first non-metallic particle is reduced to a first metallic particle having a first metallic composition and the second non- metallic particle is reduced to a second ic particle having a second metallic composition. In the prior art, experiments are bed in which metal oxide particles of different compositions are blended, formed into a preform, and reduced. The resulting metal product is an alloy. Thus, it would be expected that the result of reducing a particulate feedstock sing particles of different compositions would be an alloy. singly, it has proved possible to reduce a feedstock sing multiple particles having different compositions to a metallic powder comprising multiple particles of different compositions, with apparently no alloying n separate individual particles.

There may be significant benefits in being able to reduce a free-flowing feedstock in this way. For example, the invention may make the production of metal by direct reduction of naturally occurring minerals as found in ores and sands both practically and economically viable.

As sands are likely to consist of more than two particles having a different composition, the ion may occur such that each different particle is individually reduced to metal.

Thus, in an advantageous embodiment it may be said that the feedstock further comprises an nth non-metallic particle having an nth composition, the nth non-metallic particle being reduced to an nth metallic particle having an nth metallic ition. The term “n” may be any whole number.

Titanium is an t that occurs in many naturally occurring minerals. Thus, the feedstock may advantageously comprise a high proportion of titanium, and the resulting reduced metal may then se a high proportion of titanium.

There are a number of ent scales for classifying particulate materials according to particle size. On the Wentworth scale, for example, sand is classified as ranging from 62.5 microns to 125 microns in diameter (very fine sand), 125 microns to 250 microns in diameter (fine sand), 250 microns to 500 microns in diameter (medium sand), 500 s to 1 mm in diameter (coarse sand) and 1 mm to 2 mm in diameter (very coarse sand). Very fine gravel is d as particles ranging from 2 mm in diameter to 4 mm in diameter. Particles of material, and ularly particles of sand, are rarely perfect spheres. In ce individual particles may have different lengths, widths, and breadths.

For convenience, however, particle sizes are usually stated as a single diameter, which is approximately correct providing the particles do not have an excessively high aspect 6287717_4.docx ratio. Sands and s may be described by a single average particle size for the purposes of this invention.

Preferably, a feedstock suitable for use in an embodiment of the invention substantially comprises free-flowing les of between 62.5 microns and 4 mm in diameter.

Particularly preferably, the feedstock comprises free-flowing particles of a size that would be classed as sand on the Wentworth scale. Particularly preferably the feedstock comprises free-flowing particles of a size that would be classed as fine sand or medium sand on the Wentworth scale.

Average particle size may be ined by a number of ent techniques, for example by sieving, laser diffraction, dynamic light ring, or image analysis. While the exact value of the average particle size of a sample of sand may differ slightly depending on the measurement technique used to ine the average value, in practice the values will be of the same order providing the les do not have an excessively high aspect ratio. For example, the skilled person will appreciate that the same sand may be found to have an average particle diameter of perhaps 1.9 mm if analysed by sieving, but 2.1 mm if analysed by a different technique, such as image analysis.

The particles making up the feedstock preferably have an average particle diameter of between 10 microns and 5 mm, more preferably n 20 microns and 4 mm, or between 60 microns and 3 mm. A particularly red feedstock may have an average particle diameter of between 60 microns and 2 mm, preferably between 100 microns and 1.75 mm, for example between 250 microns and 1.5 mm.

It is preferred that the average particle diameter is determined by laser diffraction. For example, the average particle size could be determined by an analyser such as the n Mastersizer Hydro 2000MU.

It may be desirable to specify the range of particle size in a feedstock. A feedstock containing particles that vary in diameter over a wide range may pack more densely than a feedstock in which the majority of the particles are of substantially the same particle size. This may be due to smaller particles filling interstices between adjacent larger particles. It may be desirable that a volume of a feedstock has sufficient open space or voidage for a molten salt to flow freely h a bed formed by the feedstock. If the feedstock packs too y, then the molten salt flow-path h the feedstock may be inhibited. 6287717_4.docx Particle size range may be determined by laser diffraction. For example, the le size range could be determined by an er such as the Malvern sizer Hydro 2000MU.

It may be convenient to select a feedstock size range by a process of g. The selection of size ranges or size fractions of particles by g is well known. It is preferred that the feedstock comprises free-flowing particles within a size range of 63 microns to 1 mm as determined by sieving. It may be particularly preferred that the feedstock comprises free-flowing particles within a size range of 150 microns to 212 microns as determined by sieving.

The particle density or true density of a particulate solid or powder is an intrinsic physical property of a material. It is the density (mass per unit volume) of the dual particles that make up the powder. In contrast, bulk density is a e of the average density of a large volume of the powder in a ic medium (usually air).

The measurement of particle density can be done in a number of standard ways - most commonly based on the edes’ principle. The most widely used method entails the powder being placed inside a container (a pycnometer) of known volume, and weighed.

The pycnometer is then filled with a fluid of known density, in which the powder is not soluble. The volume of the powder is determined by the difference between the volume as shown by the pycnometer, and the volume of liquid added (i.e. the volume of air displaced).

Bulk density is not an intrinsic property of a powdered or particulate material; it is a property that can change depending on how the material is handled.

It is defined as the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume and internal pore volume.

Dry bulk density = mass of powder / volume as a whole The bulk density of a mineral sand or ore concentrate depends greatly on the mineral make up of the sand and the degree of compaction. The bulk density has ent values depending on whether it is measured in the as-poured, freely settled, condition, or in a compacted state (known as a settled or tapped condition). 6287717_4.docx For example, a powder poured in to a container will have a particular bulk density; if the container is disturbed, the powder les will move and usually settle closer together, resulting in a higher bulk density. For this reason, the bulk y of powders is y reported both as "freely settled" (or "as-poured" density) and "tapped" density (where the tapped density refers to the bulk density of the powder after a specified compaction s, usually involving vibration of the container.) As used herein, a volume of bulk feedstock refers to a volume of particulate feedstock in the as-poured condition. For example, a volume of ock may be a volume of a sand ock that is in the as-poured condition and has not been compressed or rately agitated. The volume of the feedstock includes the volumes of each individual particle making up the feedstock and the voids or interstices between those particles.

As used herein, bulk density of a feedstock refers to the density calculated by dividing the total mass of feedstock by its volume. Bulk density may be determined, for e, by pouring the feedstock into a receptacle of known volume until that receptacle is filled, determining the mass of the particles within the volume, and calculating the density.

As used herein, a tapped feedstock is a volume of ulate feedstock that has been poured and then compressed, agitated or tapped to induce settling of the feedstock. A volume of a tapped feedstock would be referred to as a tapped volume. A tapped density would be calculated using the mass of a powder and a tapped volume.

As used herein, the voidage of a feedstock (as-poured or tapped) refers to the proportion of the feedstock that is free space between particles making up the feedstock, and is expressed as a percentage of the bulk volume. The voidage can be determined by comparing the density of the feedstock with the theoretical density of particles of the feedstock al. The skilled person will be aware of methods for determining voidage of different ocks.

The inventors have noted that the voidage of a feedstock may contribute to the y of the feedstock to reduce as individual particles. For example, an experimental reduction was carried out involving a rutile ock having a le size distribution of between 150 microns and 212 microns (determined by sieving) and a bulk density of 2.22 gcm-3 (the rutile density was assumed to be 4.23 gcm-3, which is the theoretical density of titanium dioxide). Therefore, in the as-poured condition this feedstock had a voidage of 47%. A portion of this ock, when arranged in a suitable electrolysis tus in an as-poured condition, reduced to individual particles of Ti-based metal. By contrast, the same rutile feedstock, when settled by tapping, had a tapped density of 2.44 gcm-3 and a 6287717_4.docx tapped voidage of 42%. A portion of this feedstock, when arranged in the electrolysis apparatus, settled, and reduced under the same conditions as the as-poured feedstock, formed a sintered mass of Ti-based metal.

Thus, for use in any aspect of the t ion it is preferred that the feedstock is a volume of bulk feedstock (i.e. in the as-poured or freely d condition) and not a tapped feedstock. It is preferred that the volume of bulk feedstock has a voidage of greater than 43% to facilitate flow of molten salt through the feedstock. It may be preferred that a volume of bulk feedstock has a voidage of between 44% and 54%.

Preferably the voidage is between 45% and 50% for example n 46% and 49% or between 47% and 48%.

One standard way of defining the particle size distribution in a sample of les is to refer to D10, D50 and D90 values. D10 is the particle size value that 10% of the population of particles lies below. D50 is the particle size value that 50 % of the population lies below and 50% of the tion lies above. D50 is also known as the median value. D90 is the particle size value that 90 % of the population lies below. A feedstock sample that has a wide particle size distribution will have a large difference between D10 and D90 values. Likewise, a feedstock sample that has a narrow particle size distribution will have a small difference n D10 and D90.

Particle size distribution may be determined by laser diffraction. For example, the particle size distribution, ing D10, D50 and D90 values, could be determined by an analyser such as the Malvern Mastersizer Hydro 2000MU.

It may be preferable that D10 for any feedstock is greater than 60 microns and D90 is lower than 3 mm. It may be beneficial if the feedstock has a size distribution in which D90 is no more than 75% greater than D10 or no more than 50% greater than D10.

D10 is ably between 0.25 and 1 mm. D90 is preferably between 0.5 mm and 3 mm.

One embodiment of a feedstock may have a population of particles in which D10 is 1 mm and D90 is 3 mm. Another embodiment of a feedstock may have a population of particles in which D10 is 1.5 mm and D90 is 2.5 mm. Another embodiment of a feedstock may have a population in which D10 is 250 microns and D90 is 400 microns. r embodiment may have a population in which D10 is 0.5 mm and D90 is 0.75 mm.

In addition to allowing a more open bed of feedstock to form, the particles in a feedstock which has a narrow particle size bution may also all reduce at approximately the 6287717_4.docx same rate. It may advantageously help prevent ing of individual particles if the ion for the particles in the feedstock finishes at approximately the same time.

As the flow of molten salt through the bed may be important it may be desirable to specify a voidage for a bed formed from a volume of the ock. For example, it may be desirable to specify that the bed has greater than 40% voidage or greater than 45% voidage.

Preferably the volume of feedstock is located on a mesh, which is preferably oned substantially horizontally, h which molten salt may flow. For e, the upper surface of a cathode that retains the volume of feedstock may be in the form of, or comprise, a mesh. Preferably, the feedstock is retained by such a mesh having a mesh size smaller than an average particle size of the feedstock. Particularly preferably, the mesh has a mesh size equal to or smaller than the D10 value for the feedstock population. The mesh size may be smaller than D5. The ulate feedstock may be supported on the surface of the mesh and molten salt may then be able to flow through the mesh and the bed of feedstock. Movement of salt through a mesh may, advantageously, gently agitate the particles and help prevent individual particles from ing together. It is not desirable, however, for the movement of salt to cause the feedstock to become sed, or to carry individual particles away from the mesh.

Preferably, the volume of feedstock is retained at its edges by a suitable retaining barrier.

For example, a cathode used to t a feedstock may comprise a retaining barrier ng ock to be ted on its upper surface. It is preferable that the feedstock is loaded onto the cathode to a depth of greater than 5 mm, preferably greater than 1 cm or greater than 2 cm. The depth of the feedstock may depend to a great degree on the size of the particles to be reduced. However, in a batch process in which feedstock loaded onto a e is reduced, the lower the feedstock depth the lower the yield of metal in any particular run or batch.

Examples of minerals capable of yielding high value metals that may be found in naturally occurring sands and oxide ores include, rutile, ilmenite, anatase, and leucoxene (for titanium), scheelite (tungsten), cassiterite (tin), monazite (cerium, lanthanum, thorium), zircon (zirconium hafnium and silicon), cobaltite (cobalt), chromite (chromium), bertrandite and beryl (beryllium, aluminium, silicon), uranite and pitchblende (uranium), quartz (silicon), molybdenite (molybdenum and rhenium) and stibnite (antimony). One or more of these ls may be suitable as a component of a feedstock for use in the present invention. This list of minerals is not exclusive. The invention may be used to 6287717_4.docx reduce particles of material, for example sands or crushed ores, that contain one or more minerals not listed above.

Advantageously, the particles making up the feedstock may be substantially free from porosity. The prior art electro-decomposition methods have used porous feedstock.

Substantially all of the grains or particles making up many powder feedstocks may be fully dense, for example powdered feedstocks derived from most naturally occurring sands or from crushed ore. As used herein, the term fully dense means substantially free from porosity.

The les making up the feedstock may have an absolute density of n 3.5 g/cm3 and 7.5 g/cm3, preferably between 3.75 g/cm3 and 7.0 g/cm3, for example between 4.0 g/cm3 and 6.5 g/cm3, or between 4.2 g/cm3 and 6.0 g/cm3. Many minerals and oxides of metals, ularly the heavy metals have a high density. Many naturally occurring minerals containing titanium, zirconium, and iron fall into this category.

Minerals containing some of the heavy elements, for example U, Th, or Ta, may have a density that is greater than 7.5 g/cm3. For example, pitchblende and uranite may have densities of up to 11 g/cm3. Embodiments of the t invention may be used to reduce particles containing such high density ls. Likewise, ls containing lighter elements, for example Si, may have a density that is lower than 3.5 g/cm3. For example, silica may have a density that is about 2.6 g/cm3. Embodiments of the present invention may be used to reduce particles containing such low density minerals.

The feedstock may comprise a synthetic mineral or a treated mineral. For example, in order to produce a titanium powder the feedstock may be formed entirely or in part from a synthetic rutile al. One method of forming a synthetic rutile may be by treatment of Ilmenite is a mineral having a nominal composition of FeTiO3. Reduction of natural ilmenite particles may yield a titanium alloy powder. However, it is known that ilmenite can be treated to form a synthetic rutile of nominal ition TiO2 by removing the iron tuent. Such synthetic rutiles are produced for use in the pigment industry.

Methods of treating te to produce synthetic rutile generally involve leaching in an acid or alkali to remove impurities and unwanted elements such as iron. Such methods of producing synthetic rutile are well known in the art. In practice, the most common commercial processes for treating ilmenite to e synthetic rutile are the Becher process, te process, Austpac process, and Ishihara process. 6287717_4.docx Synthetic rutile is a porous particle produced by chemical leaching. This may be particularly advantageous in facilitating control over the porosity of the d metallic le. Synthetic rutile is used to form titanium. Other synthetically produced materials may be used to form other metallic powders.

The feedstock may comprise porous particles. Some natural sands and ores are porous, as are some synthetic ls. The degree of porosity in the reduced les may be influenced by the degree of porosity in the feedstock. It may be advantageous to form a powder comprising or consisting of porous metallic particles. dual crystals that form part of a polycrystalline solid are often termed crystallites or grains. Within each crystallite, atoms are arranged in a regular ordered pattern.

Boundaries n adjacent crystallites (crystallite boundaries or grain boundaries) are disordered. Preferably, the particles making up a feedstock are crystalline and have an average llite size of greater than 10 micrometres, and more ably greater than micrometres. Many chemical compounds, such as chemically purified “synthetic” oxides, are formed by processes such as al precipitation or condensation.

Although particles formed may be many hundreds of micrometres in diameter, the crystallite size of such synthetic materials is typically of the order of a few tens of nanometres. It may be advantageous, r, for the crystallite size to be significantly higher, for example of the order of tens, or hundreds, of micrometres.

Because boundaries between crystallites have a highly defective structure, diffusion occurs more y at these boundaries. If a ock particle has a fine crystallite structure then the volume of crystallite boundaries within that particle will be greater than if the particle had a coarser crystallite structure. Diffusion is one of the factors that controls the degree of sintering between adjacent particles in a feedstock, for example during electro-reduction. An electro-reduction reaction involving powdered material with a large crystallite size may, therefore, be more controllable than if the ock has a fine crystallite size. Individual particles of a feedstock may be less prone to sintering together (so as to produce a free-flowing metal powder product) if the crystallite size is of, or tends towards, a similar magnitude to the particle size, such as being on average greater than a tenth, a quarter or half of the particle size.

Advantageously, the feedstock may comprise a first set of particles having a composition in which a first metallic element forms the greater proportion by mass, and a second set of particles in which a second metallic element forms the greater proportion by mass.

Preferably, the feedstock is reduced using a method embodying the ion such that there is no alloying between the first set of particles and the second set of particles. 6287717_4.docx ters such as temperature of the molten salt, and reduction time may be controlled in order to reduce the feedstock such that individual grains of the d material do not irreversibly bond together.

Prior art electro-decomposition methods teach the use of preforms moulded and sintered from particulate feedstock and individually coupled to a e. Where a powdered ock is used in its unprocessed form, it would not be practical to ensure that each powder particle could contact a portion of a cathode. In embodiments of the t invention, it is preferred that the feedstock particles, which have an average diameter, are loaded onto a surface or into a fine-mesh basket to a depth of between 10 and 500 times the average particle diameter of the feedstock. For example, feedstock may be loaded onto the upper surface of a cathode to a depth of between 10 and 500 times the average feedstock particle diameter.

The reduction time is advantageously as low as possible, to limit or prevent sintering of individual particles of the metal product. Advantageously, the ion time may be lower than 100 hours, preferably lower than 60 hours or lower than 50 hours. Particularly preferably the reduction time is lower than 40 hours.

The salt temperature is advantageously as low as possible, to limit or prevent ing of individual particles of the metal product. Preferably, the molten salt temperature during reduction is maintained to be lower than 1100°C, for example lower than 1000°C, or lower than 950°C, or lower than 900°C.

Advantageously, the feedstock may be reduced with substantially no sintering between individual particles such that a metallic powder can be recovered having an e diameter of slightly lower than an average diameter of the particles making up the feedstock. The reason that the metallic les are typically slightly smaller than the feedstock particles is that the ock particles tend to have a ceramic structure that includes a non-metallic element such as oxygen or sulphur, whereas the reduced les have a ic structure from which much of this non-metallic element has been removed.

The reduced feedstock may form a e mass of individual metallic particles.

Advantageously, such a friable mass may be easily broken up to form a free-flowing metallic powder. Preferably, substantially every particle forming the metallic powder corresponds to a non-metallic particle from the feedstock. 6287717_4.docx The methods according to various embodiments of the invention described above may be particularly suitable for the production of metal powder by the reduction of a solid feedstock comprising particles of metal oxide or metal oxides. Pure metal powders may be formed by reducing pure metal oxides, and alloy powders and intermetallics may be formed by reducing ocks comprising particles of mixed metal oxides. Preferably metal powders formed by processes embodying the invention have an oxygen content of lower than 5000 ppm, preferably lower than 4000 ppm, or lower than 3,500 ppm.

Some reduction processes may only operate when the molten salt or electrolyte used in the s comprises a ic species (a reactive metal) that forms a more stable oxide than the metallic oxide or compound being reduced. Such information is readily available in the form of dynamic data, specifically Gibbs free energy data, and may be conveniently determined from a standard Ellingham diagram or predominance diagram or Gibbs free energy m. Thermodynamic data on oxide stability and Ellingham diagrams are available to, and understood by, electrochemists and extractive metallurgists (the skilled person in this case would be well aware of such data and information).

Thus, a preferred electrolyte for an electrolytic ion process may comprise a calcium salt. Calcium forms a more stable oxide than most other metals and may therefore act to facilitate reduction of any metal oxide that is less stable than calcium oxide. In other cases, salts ning other reactive metals may be used. For example, a reduction process according to any aspect of the invention described herein may be performed using a salt comprising lithium, sodium, potassium, rubidium, caesium, ium, calcium, strontium, barium, or yttrium. Chlorides or other salts may be used, including mixture of chlorides or other salts.

By selecting an appropriate electrolyte, almost any metal oxide les may be capable of reduction using the methods and apparatuses described . lly occurring minerals containing one or more such oxides may also be reduced. In particular, oxides of beryllium, boron, magnesium, aluminium, silicon, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, ium, m, molybdenum, hafnium, tantalum, tungsten, and the lanthanides including lanthanum, , praseodymium, neodymium, samarium, may be reduced, preferably using a molten salt comprising calcium chloride.

The d person would be capable of selecting an appropriate electrolyte in which to reduce a particular metal oxide, and in the majority of cases an electrolyte comprising calcium chloride will be suitable. 6287717_4.docx Preferably, the reduction occurs by an electro-decomposition or electro-deoxidation s such as the FFC Cambridge process or the BHP Polar process and the s described in WO03/048399.

In a still further aspect, a metallic powder may comprise a plurality of discrete metallic particles, formed by the direct reduction of a feedstock comprising a plurality of nonmetallic particles, the ock having a particle size distribution defined by a D10 particle size and a D90 particle size, in which the D90 particle size is no more than 100% greater than the D10 particle size, each of the metallic particles being formed by the direct reduction of a discrete non-metallic le.

The term ‘comprising’ as used in this specification and claims means ‘consisting at least in part of’. When interpreting statements in this specification and claims which include the term ‘comprising’, other features besides the features prefaced by this term in each statement can also be present. Related terms such as ‘comprise’ and ‘comprised’ are to be interpreted in similar manner.

In the description in this specification reference may be made to subject matter which is not within the scope of the ed . That subject matter should be readily identifiable by a person skilled in the art and may assist in g into practice the invention as d in the presently appended claims.

Specific embodiment of the invention A specific embodiment of the invention will now be described with reference the accompanying drawings, in which; Figure 1 is a schematic diagram illustrating an electrolysis apparatus arranged for performing a method according to an embodiment of the invention, Figure 2A is a schematic sectional view rating additional detail of the cathode structure of the electrolysis apparatus of figure 1, Figure 2B is a plan view of the cathode rated in figure 2A, Figures 3 and 4 are SEM ing electron micrography) micrographs illustrating particles of a rutile sand feedstock, Figures 5 and 6 are SEM micrographs illustrating metallic powder particles resulting from the reduction of a rutile sand feedstock using a method according to an embodiment of the invention, 6287717_4.docx Figure 7 is a SEM micrograph illustrating particles of a synthetic rutile feedstock, and Figure 8 is an SEM micrograph illustrating titanium particles resulting from the reduction of a tic rutile feedstock.

Figure 1 illustrates an electrolysis tus 10 configured for use in performing a reduction method embodying the invention. The apparatus comprises a stainless steel cathode 20 and a carbon anode 30 situated within a housing 40 of an electrolysis cell.

The anode 30 is disposed above, and spatially separated from, the cathode 20. The housing 40 contains 500 kg of a m de based molten salt electrolyte 50, the electrolyte comprising CaCl2 and 0.4 wt % CaO, and both the anode 30 and the cathode 20 are arranged in contact with the molten salt 50. Both the anode 30 and the cathode 40 are coupled to a power supply 60 so that a potential can be applied between the cathode and the anode.

The cathode 20 and the anode 30 are both substantially ntally oriented, with an upper e of the cathode 20 facing s a lower surface of the anode 30.

The e 20 incorporates a rim 70 that extends upwards from a perimeter of the cathode and acts as a retaining barrier for a feedstock 90 supported on an upper surface of the cathode. The rim 70 is integral with, and formed from the same material as, the cathode. In other embodiments, the rim may be formed from a different al to the cathode, for example from an electrically insulating material.

The structure of the cathode may be seen in more detail in Figure 2A and Figure 2B. The rim 70 is in the form of a hoop having a diameter of 30 cm. A first supporting ember 75 extends across a diameter of the rim. The cathode also comprises a meshsupporting member 71, which is in the form of a hoop having the same diameter as the rim 70. The mesh-supporting member has a second supporting cross-member 76 of the same dimensions as the supporting cross-member 75 on the rim 70. A mesh 80 is supported by being sandwiched between the rim 70 and the mesh-supporting member 71 (the mesh 80 is shown as the dotted line in Figure 2A). The mesh 80 comprises a stainless steel cloth of mesh-size 100 that is held in tension by the rim 70 and the meshsupporting member. The cross-member 75 is disposed t a lower surface of the mesh 80 and acts to support the mesh. An upper surface of the mesh 80 acts as the upper surface of the cathode.

The stainless steel cloth forming the mesh 80 is fabricated from 30 micrometre thick wires of 304 grade stainless steel that have been woven to form a cloth having square holes 6287717_4.docx with a 150 micrometre opening. The mesh 80, cross-member 75 and rim 70 that form the e are all electrically conductive. In other embodiments, the mesh may be the only electrically conductive component of the cathode.

Example 1 A method embodying the ion will be illustrated with an example in which the feedstock to be reduced is a natural conventionally beneficiated rutile sand. Rutile is a naturally occurring mineral ning a high proportion (perhaps 94-96 wt %) of TiO2.

Rutile sand also contains many other elements and particles or grains of other non-rutile minerals. The skilled person will be aware of the compositions of typical rutile sands.

The rutile sand used in this specific example comprises grains of material having an average particle diameter as measured by laser diffraction (using a Malvern Mastersizer Hydro 2000MU) of about 200 micrometres and a bulk density of about 2.3 g/cm3. The density of individual grains forming the sand may be in the range from about 4 g/cm3 to about 7 g/cm3, depending on the composition and crystal structure of each individual grain. Figure 3 is a SEM micrograph illustrating the individual particles in the feedstock.

The particles are mainly angular and predominantly TiO2.

The SEM micrograph of Figure 4 illustrates a polished section of some of the individual grains. The majority of the particles are imaged having a light grey colour 400 and are grains that are substantially TiO2 (although there will be many impurity elements and each grain will have a slightly different ition). One of the grains is imaged as a lighter grey 410. This is a particle of zircon. Another grain has a darker grey colouring 420 and this is a grain with a high concentration of n indicating it is probably quartz.

About 3 kg of the ock 90, consisting of l rutile sand, was ed on the upper surface of the cathode 20 and in contact with the molten salt 50 (which consisted of CaCl2 and 0.4 wt % CaO). Thus, the rutile sand 90 was supported by the mesh 80 of the cathode and retained at a depth of approximately 2 cm by the cathode-rim 70. The bed depth of the rutile is imately 100 times the average particle diameter of the rutile sand les.

The molten salt was maintained at a temperature of about 1000 °C and a potential was applied between the anode and the cathode. Thermal currents and gas lift effect generated by the buoyancy of the gases (which are predominantly CO and CO2) generated at the anode cause the molten salt to circulate within the cell and generate flow through the bed of rutile supported on the cathode. The cell was operated in nt 6287717_4.docx current mode, at a current of 400 A, for 52 hours. After this time, the cell was cooled and the e removed and washed to free salt from the reduced feedstock.

The reduced feedstock was removed from the cathode as a friable lump or cake of metallic powder particles that could be ted using light manual pressure. The lumps of material were tumbled in a barrelling tumbler containing alumina balls, and the material separated out into individual powder les. These powder particles were then dried.

Figures 5 and 6 are SEM micrographs illustrating individual powder grains from the reduced sand. It can be seen that the metallic particles of the powder correspond in size and shape to the grains that formed the sand (the average particle size of the reduced material is slightly lower than the e particle size of the ock). Analysis revealed that the compositional differences between individual grains forming the feedstock were maintained in the individual grains forming the reduced powder. This suggests that each individual grain has been reduced individually to metal within the bed and that alloying n grains of different composition has not occurred.

Example 2 Figure 7 is an SEM image showing synthetic rutile particles formed by treating ilmenite (by leaching as described above) to remove unwanted elements. The particles are slightly porous when compared with l rutile. A feedstock was prepared by sieving synthetic rutile particles and selecting the fraction falling n meshes of 63 s and 212 microns. 1129 grams of the synthetic rutile feedstock was loaded onto the upper surface of a cathode and reduced as described above in relation to Example 1, except that the temperature of the salt was maintained at 980 degrees centigrade and the reduction proceeded for 50 hours. After reduction a powder was extracted and washed as described above.

Figure 8 illustrates a titanium powder particle from the resulting powder. It can be seen that the general size and shape of the metallic le is of the same order as the feedstock particles, but the metallic particle is more porous and has a slightly r shape.

Example 3 The following ments were carried out to igate the effect of different particle size ranges on progress of reduction. A rutile sand material was sourced from ABSCO 6287717_4.docx Materials that comprised r than 95 % TiO2 and had a particle size range defined as a m of 4% of material retained on a 180 micron sieve. This material was taken by the applicant and sieved (using Retch brand sieves) into three ons. The fractions were (1) particles having diameter less than 150 s (i.e. particles that passed through a sieve having a mesh size of 150 microns), (2) particles having a diameter between 150 microns and 212 microns (i.e. particles that pass through a sieve of 212 micron mesh size but are retained by a sieve having 150 micron mesh size), and (3) particles having a diameter greater than 212 microns (i.e. particles that are retained by a sieve having a mesh size of 212 microns). Each of these three size fractions was used as a free-flowing particulate ock for reduction to metal. Particle size distribution was measured for each on using laser ction (Malvern Mastersizer Hydro 4000MU).

These results are shown in table 1 below.

The reduction of each feedstock was carried out substantially as described above in relation to Example 1. Reduction was performed in a molten salt consisting of CaCl2 with 0.6 wt % CaO held at a temperature of 950°C. Reduction was performed at a nt current of 400 A for a period of 68 hours. The distance between the cathode and the anode was set as 5 cm.

The bulk density and bed porosity for each feedstock were calculated, and the results are given in table 1 below. For these calculations it was assumed that the grains had the same density as TiO2.

Sieve Bulk Bed Feedstock fraction D10 (µm) D50 (µm) D90 (µm) density porosity (µm) (g/cm3) (%) (1) <150 108 156 225 2.30 45.6 (2) 150-212 121 180 267 2.38 43.7 (3) >212 205 280 382 2.44 42.3 Table 1: Parameters of three rutile feedstocks having different particle sizes.

After reduction for 68 hours, feedstock number 2 (150-212 micron size fraction) and feedstock number 3 (>212 micron size fraction) had reduced to discrete particles of titanium. Oxygen analysis on the titanium powder t of these reductions (using Eltra ON-900) showed that oxygen had been reduced to levels of between 3000 and 4500 ppm.

Feedstock number 1 (size fraction <150 micron), however, did not fully reduce, and did not form discrete les of titanium. A metallic crust had formed on the top and bottom 6287717_4.docx of the feedstock bed and the centre of the bed had converted to m titanates. This suggests that there was insufficient salt flow through the bed of feedstock 1. This may be attributable to the small size of the interstices n particles in feedstock 1, as compared with relatively larger interstices between particles in feedstock number 2 and number 3. 6287717_4.docx

Claims

1. A method for producing metallic powder comprising the steps of: arranging a e and an anode in contact with a molten salt within an electrolysis cell, 5 arranging a volume of feedstock comprising a ity of non-metallic particles within the electrolysis cell, causing a molten salt to flow through the volume of feedstock, and applying a potential between the cathode and the anode such that the ock is reduced to metal in which the feedstock has a particle size distribution defined by a D10 10 particle size and a D90 particle size, in which the D90 particle size is no more than 100% greater than the D10 particle size, and in which the particles making up the feedstock have an average particle diameter of less than 5 mm.

2. A method for producing metallic powder according to claim 1 in which the volume 15 of feedstock is arranged on an upper surface of the cathode and a lower surface of the anode is ally spaced from the feedstock and the upper surface of the cathode.

3. A method according to claim 1, in which the particles making up the ock have an average particle diameter between 60 microns and 3 mm.

4. A method according to claim 3, in which the les making up the feedstock have an average particle diameter between 250 microns and 2.5 mm.

5. A method ing to claim 4, in which the particles making up the feedstock 25 have an average particle er between 500 microns and 2 mm.

6. A method according to any preceding claim in which the D10 particle size for the feedstock is greater than 60 microns and the D90 particle size for the feedstock is lower than 3 mm.

7. A method according to any preceding claim in which the feedstock is a bulk feedstock that has not been settled or compacted.

8. A method according to any preceding claim in which the feedstock has a voidage 35 of greater than 43%. 6287717_4.docx

9. A method according to claim 8 in which the feedstock has a voidage of between 44% and 54%.

10. A method according to any preceding claim, in which the particles making up the 5 feedstock are substantially free from porosity.

11. A method according to claim 10, in which the particles making up the feedstock are greater than 90% dense. 10

12. A method according to claim 11, in which the particles making up the feedstock are greater than 95% dense.

13. A method ing to any one of claims 1 to 6 in which the les making up the feedstock are porous.

14. A method according to claim 13 in which the particles making up the feedstock have a porosity of between 10% and 50%.

15. A method according to any preceding claim in which the particles making up the 20 feedstock have a y of between 3.5 g/cm3 and 7.5 g/cm3.

16. A method according to claim 15 in which the particles making up the feedstock have a density of between 3.75 g/cm3 and 7.0 g/cm3. 25

17. A method according to claim 16 in which the particles making up the feedstock have a density of between 4.0 g/cm3 and 6.5 g/cm3.

18. A method according to claim 17 in which the particles making up the ock have a density of n 4.2 g/cm3 and 6.0 g/cm3.

19. A method according to any preceding claim, in which the particles making up the feedstock are lline and have an average crystallite size of greater than 10 micrometres. 35

20. A method according to claim 19, in which the particles making up the feedstock have an average crystallite size of greater than 50 micrometres. 6287717_4.docx

21. A method according to claim 20, in which the particles making up the feedstock have an average crystallite size of greater than 100 micrometres.

22. A method according to any preceding claim in which the feedstock has an 5 average crystallite size that is greater than 10% of the average particle size.

23. A method according to claim 22 in which the ock has an average crystallite size that is greater than 20% of the average particle size. 10

24. A method according to claim 23 in which the feedstock has an average crystallite size that is greater than 30% of the average particle size.

25. A method according to claim 24 in which the feedstock has an average crystallite size that is greater than 50% of the average le size.

26. A method ing to any preceding claim in which the feedstock comprises a first set of particles having a composition in which a first metallic element forms the greater proportion by mass, and a second set of particles in which a second metallic element forms the greater tion by mass, the feedstock being reduced under 20 conditions such that there is no alloying between the first set of particles and the second set of particles.

27. A method according to any preceding claim in which the feedstock ses one or more lly occurring minerals.

28. A method according to claim 27 in which the feedstock ses one or more minerals selected from the list consisting of rutile, ilmenite, anatase, leucoxene, scheelite, cassiterite, monazite, lanthanum, zircon, cobaltite, chromite, bertrandite, beryl, uranite, pitchblende, quartz, molybdenite and stibnite.

29. A method ing to any ing claim in which the feedstock comprises rutile, anatase, leucoxene or ilmenite.

30. A method according to any preceding claim in which the feedstock comprises a 35 synthetic mineral.

31. A method according to claim 30 in which the feedstock ses synthetic rutile. 6287717_4.docx

32. A method according to any ing claim in which the feedstock comprises a first tallic particle having a first composition and a second non-metallic particle having a second composition, in which the feedstock is reduced under conditions such 5 that the first non-metallic particle is d to a first metallic particle having a first metallic composition and the second non-metallic particle is reduced to a second ic particle having a second ic composition.

33. A method according to claim 32 further comprising an nth non-metallic particle 10 having an nth composition, the nth non-metallic particle being reduced to an nth metallic particle having an nth metallic composition, in which n is any whole number greater than

34. A method according to any preceding claim in which the feedstock ses a 15 high proportion (>94 wt %) of titanium, and the resulting reduced metal comprises a high proportion (>94 wt %) of titanium.

35. A method ing to any preceding claim in which the feedstock particles have an average diameter and the feedstock is loaded onto the upper surface of the cathode to 20 a feedstock depth of between 10 and 500 times the average diameter of the feedstock les.

36. A method according to any preceding claim in which the feedstock particles comprise crystallites having an average crystallite diameter and the feedstock is loaded 25 onto the upper surface of the cathode to a feedstock depth of between 10 and 500 times the average diameter of the feedstock llites.

37. A method according to any preceding claim in which the upper surface of the cathode comprises a mesh having a mesh size smaller than the D10 particle size of the 30 feedstock.

38. A method according to any preceding claim in which the cathode comprises a retaining barrier allowing feedstock to be supported on its upper surface to a depth of greater than 5 mm.

39. A method according to claim 38 in which the retaining r allows feedstock to be supported on its upper surface to a depth of greater than 1 cm. 6287717_4.docx

40. A method according to claim 39 in which the retaining barrier allows feedstock to be supported on its upper e to a depth of greater than 2 cm. 5

41. A method according to any one of claims 38 to 40 in which the retaining barrier is a peripheral barrier.

42. A method ing to any preceding claim in which the molten salt temperature during reduction is maintained at less than 1100°C.

43. A method ing to any preceding claim in which the reduction is an electrolytic reduction.

44. A method according to claim 43 in which the reduction occurs by an electro- 15 decomposition according to the FFC dge process or the BHP Polar process.

45. A method according to any preceding claim in which the feedstock is reduced with substantially no sintering between particles such that a powder can be recovered having an average diameter of slightly lower than an average diameter of the particles making up 20 the feedstock.

46. A method according to any preceding claim in which the reduced feedstock forms a friable mass of metallic particles that may be broken up to form the metallic powder, substantially each of the particles forming the metallic powder corresponding to one non- 25 metallic particle in the feedstock.

47. A method according to any preceding claim in which the feedstock consists of free-flowing discrete particles of non-metallic material. 30

48. A method according to claim 26 in which the discrete particles of tallic material have an average particle size (D50) of between 100 and 250 microns as measured by laser diffraction.

49. A metallic powder formed using a method ing to any preceding claim.

50. A metallic powder comprising a ity of te metallic particles, formed by the direct reduction of a feedstock comprising a plurality of non-metallic particles, the 6287717_4.docx feedstock having a particle size bution d by a D10 particle size and a D90 particle size, in which the D90 particle size is no more than 100% greater than the D10 particle size, each of the metallic particles being formed by the direct reduction of a discrete non-metallic particle.

51. A method for producing ic powder according to claim 1, the method being substantially as herein described with reference to any embodiment disclosed.

52. A metallic powder according to claim 49 or claim 50, the metallic powder being 10 substantially as herein described with reference to any embodiment disclosed. 6287717_4.docx WO 50772 FIGWLE 2.8 WO 50772 ‘\\_ "gt-‘3; " FIGUAE 3 y:\§ PCT/G