WO2025000050A1 - Ore processing method for metal recovery - Google Patents

Abstract

The invention relates to a method of separating metal from ore comprising the steps of: (a) optionally pre-processing the ore, (b) mixing the ore with a caustic medium such as one or more alkali metals or alkaline earth bases at elevated temperature above 160°C, preferably 200°C to 350°C, or more preferably 250°C to 350°C and (c) subjecting the mixture to electrolysis to deposit at least one metal at a cathode and evolve oxygen at an anode. In one embodiment, the caustic medium at elevated temperature dissolves at least one metal species from the ore. While the invention is applicable to a wide range of ores, typically the ore is an iron ore, mineral sand or nickel ore.

Description

ORE PROCESSING METHOD FOR METAL RECOVERY

FIELD OF INVENTION

[0001] The present invention relates to the field of ore processing.

[0002] In one form, the invention relates to processing ores to provide valuable metal products.

[0003] In one particular aspect the present invention is suitable for recovery of metal from ores by chemical conversion, dissolution and electrodeposition.

[0004] It will be convenient to hereinafter describe the invention in relation to iron ore, particularly the reduction of iron from haematite ore however it should be appreciated that the present invention is not so limited but extends to a wide range of ores, and a wide range of metals.

BACKGROUND ART

[0005] It is to be appreciated that any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the present invention. Further, the discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related art problems by the inventor. Moreover, any discussion of material such as documents, devices, acts or knowledge in this specification is included to explain the context of the invention in terms of the inventor’s knowledge and experience and, accordingly, any such discussion should not be taken as an admission that any of the material forms part of the prior art base or the common general knowledge in the relevant art in Australia, or elsewhere, on or before the priority date of the disclosure and claims herein.

[0006] Traditionally, reduction of metals such as iron from ore, particularly haematite ore, is done in a pyrometallurgical process which produces significant greenhouse gases, particularly carbon dioxide. Carbon Is alloyed with iron to make steel as part of this process (normally to excessive levels when first reduced in a blast furnace) to produce pig iron and then reduced by oxidation in a basic oxygen steelmaking furnace. More recently, a direct reduced iron (DRI) process has been progressively displacing blast furnace capacity. While this pathway is offers reduced carbon dioxide emissions, it is far from being carbon neutral. The DRI process uses high operating temperatures and has high inefficiencies. In addition, the process also does not work well with low grade ores (i.e., below 65 wt% Fe).

[0007] The alternative treatment methods typically include extractive metallurgy to remove metals from natural mineral deposits. Extractive metallurgy techniques are commonly grouped into three categories: hydrometallurgy, pyrometallurgy and electrometallurgy including electrorefining and electrowinning. Many of these processes also use high operating temperatures and have high inefficiencies.

SUMMARY OF INVENTION

[0008] An object of the present invention is to provide an improved process for extraction of metal from ore.

[0009] It is a further object of the embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of related art systems or to at least provide a useful alternative to related art systems.

[0010] In a first aspect of embodiments described herein there is provided a method of separating metal from ore comprising the steps of:

(a) optionally pre-processing the ore,

(b) mixing the ore with a molten caustic medium to dissolve at least one metal species from the ore, and

(c) subjecting the molten mixture to electrolysis to deposit at least one metal on a cathode and evolve oxygen at an anode.

[0011] The caustic medium may be circulated in the process, with a small bleed required to remove impurities. [0012] The molten caustic medium preferably comprises one or more alkali metal or alkaline earth bases. Alkali metal or alkaline earth bases suitable for use in the present invention are preferably hydroxides, although other bases such as metal oxides or metal ammonium species may also be used. In one particularly preferred embodiment, the molten caustic medium is sodium hydroxide (NaOH).

[0013] The ore fed into the process of the present invention is typically subjected to pre-processing steps including crushing and drying to remove moisture as well as water bound in the lattice structure. In a second aspect of embodiments described herein there is provided a method for the separating metal from ore comprising the steps of:

(a)(i) crushing the ore to a desired particle size;

(a)(ii) drying the crushed ore;

(b) mixing the crushed, dried ore with a caustic medium at elevated temperature, preferably molten caustic medium;

(c) passing the mixture through electrolysis cells to collect metal on a cathode and release oxygen at an anode;

(d) removing the collected metal from the cathodes or using a cathode (initially in the form of a starter-sheet) that is of the same material as the metal collected.

[0014] It will be apparent to the person skilled in the art that a very wide range of ores can be processed according to the present invention. Preferably, ore for use in the present invention is chosen from the group comprising one or more of the following: iron ore including hematite, goethite, magnetite, titanomagnetite and pisolitic ironstone; aluminium containing ores including bauxite, cryolite and corundum; gold ores including gold-polysulfide, gold-quartz, gold-telluride, gold-tetradymite, gold-antimony, gold-bismuth-sulfosalt, gold-pyrrhotite, and gold-fahlore; manganese containing ores such as romanechite, manganite hausmannite and rhodochrosite; lead ores including galena, cerussite and anglesite; zinc ores including calamine and smithsonite; cobalt containing ores; uranium containing ores; copper containing ores including copper pyrite, malachite, cuprite and copper glance; nickel containing ores such as laterites and magmatic sulphide deposits; titanium containing ores; tungsten containing ores; silicon containing ores; rare earth containing ores; chromium containing ores; silver containing ores such as argentite; tin containing ores such as cassiterite, tinstone, stannite or cylindrite; heavy sands and quartz.

[0015] In a particularly preferred embodiment the ore is iron ore, which is particularly rich in iron oxides, particularly in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH) n(H2O)) or siderite (FeCO3). In another preferred embodiment the ore is a silicon containing ore which is particularly rich in sodium silicate.

[0016] Where used herein the term ‘ore’ is used broadly to include any naturally occurring mineral or solid material from which a metal or valuable mineral can be extracted profitably. These include mineral sands. For example, the present invention includes mixing mineral sands with a molten caustic medium to dissolve at least one metal species such as a metalloid from the ore, then subjecting the molten mixture to electrolysis to deposit at least one metal on a cathode and evolve oxygen at an anode.

[0017] The molten metal base or bases at elevated temperature may comprise a super-alkaline media. Upon contact with the metal base, metal containing moieties are chemically converted to solvable species and/or the resulting species are fully or partially dissolved in the molten metal base electrolyte. Without wishing to be bound by theory it is believed that sulphide ores, for example, are converted to oxides.

[0018] Additional compounds may facilitate the dissolution or chemical conversion of the ore. In particular, the addition of silicates may promote dissolution or chemical conversion of the ore.

[0019] The process of the present invention may include one or more bleed streams. Some steps of the process will build up materials such as solid fines, slimes, or breakdown products from chemicals. Their presence can lead to degradation of the overall performance of the process. Having a bleed from the relevant step removes these products and helps to maintains process performance.

[0020] Optimally, the bleed flow will be sufficient to prevent major build-up of the aforementioned material, yet not so large as to waste useful material.

[0021] The bleed from the electrolysis step may be further processed and recirculated to the process of the present invention. For example, the bleed may be further processed to remove impurities so that the caustic medium can be returned to the leach. Alternatively, after further processing the bleed can be fed back between the dissolution step and the electrolysis step.

[0022] Removal of impurities from the bleed may be carried out, for example, using a gravimetric approach to separate species having different densities.

[0023] In another aspect of embodiments described herein there is provided a method for separating metal from ore comprising the steps of:

(a)(i) crushing the ore to a desired particle size;

(a)(ii) drying the crushed ore;

(b) mixing the crushed, dried ore with a caustic medium at elevated temperature, preferably molten;

(c) passing the mixture through electrolysis cells to collect metal on a cathode and evolve oxygen at an anode, and spent caustic liquor;

(d) removing the collected metal;

(e) bleeding and cooling spent liquor from the electrolysis cells;

(f) separating the spent liquor into a crud comprising impurities and a cleaned caustic medium; and

(g) returning the cleaned caustic medium to the mixing step. [0024] The metal that collects on the cathode may be removed from the cathodes or starter sheets. Starter sheets are cathodes made of metals such as iron or steel, that are removed from the process and may be sold in combination with the deposited metal.

[0025] As the spent liquor cools, impurities coalesce and solidify in the upper level, leaving the relatively clean caustic medium in the lower levels. The process may include the further steps of;

(h) crushing any solid crud,

(I) milling the crud in liquid to form a suspension;

(j) thickening the suspension of crud; and

(k) drying, preferably spray drying, the thickened suspension.

[0026] The present invention further includes a metal separated from an ore according to the method of the invention.

[0027] Other aspects and preferred forms are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.

[0028] In essence, embodiments of the present invention stem from the realization that a caustic medium can be used to convert ore to a liquid that can be electrochemically treated to deposit valuable metals onto a cathode. More particularly, the realisation extends to the fact that no carbon needs to be used in the process. When renewable energy is applied, no carbon dioxide is released to the atmosphere in any direct or supporting step.

[0029] Advantages provided by the present invention comprise the following:

• can be carried out at ambient pressure;

• low electrowinning potential leading to low energy consumption; • recycling of processing media and by-products leading to reduced waste;

• low emission;

• low operating temperature leading to the ability to easily follow intermittent renewable energy loads;

• low capital and operating costs;

• can be used to process a broad range of ores ranging from very low to very high metal content;

• includes a highly selective electrochemical process; and

• provides high purity products including high purity metal (>98 wt% purity).

[0030] Further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further disclosure, objects, advantages, and aspects of preferred and other embodiments of the present application may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which:

FIG 1 illustrates the steps of the process of the current invention;

FIG 2 illustrates in more detail, suitable apparatus and plant configurations for use in the process of the present invention; FIG 3 is a plot of iron ore solution concentration (wt%) against iron content in the dried iron ore;

FIG 4 is a plot of current vs voltage for electrodeposition of iron from a hydroxide eutectic to illustrate energy consumption of the present invention;

FIG 5 is a plot of x-ray diffraction measurements for iron ore sourced from the Pilbara region of Western Australia; and

FIG 6 is a plot of silica input and sodium hydroxide consumption against the generation of sodium silicate, and water according to the present invention.

[0032] List of Parts

DETAILED DESCRIPTION

[0033] It is to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. Additionally, unless otherwise specified, it is to be understood that discussion of a particular feature of component extending in or along a given direction or the like does not mean that the feature or component follows a straight line or axis in such a direction or that it only extends in such direction or on such a plane without other directional components or deviations, unless otherwise specified.

Process Overview

[0034] FIG 1 is a diagram illustrating the following process steps of the present invention:

• ore reclaiming step (1) - Ore is reclaimed from an ore stockpile and conveyed or otherwise transported to a mill for dry crushing.

• ore grinding step (2) - The ore is ground in a mill.

• ore drying step (3) - Ground ore from the mill is subjected to a drying step, which may include for example, passing through a dry cyclone. Oversize material may be returned to the mill for regrinding until it reaches the desired target size.

• chemical conversion step (4) - The dry product is mixed into a caustic medium, such as a molten alkali metal or alkali earth at a volume flow rate that will allow proper mixing. Apparatus such as a series of cascade mixing tanks may be used to ensure a controlled chemical conversion followed by dissolution of solids. • electrowinning step (5) - The molten product is subjected to electrowinning. For example, the molten product may be passed through electrowinning cells where the metal product is collected on nickel or mild steel cathodes. The cathode material may be chosen to optimise efficiency of removal of the metal.

• isolation of final product (6) - The metal product is then removed from the cathodes and suitably packaged for transport by road or water.

[0035] Optionally the spent caustic media is bled from the electrowinning step, the impurities are removed, and the remaining cleaned caustic material is returned for use or as a ‘top up’ reagent at a convenient point in the process such as the chemical conversion step or the dissolution step, or after the electrowinning step. Separation of the impurities as a crud from the caustic material is preferably carried out according to the following steps:

• bleed electrowinning step (7) - The spent caustic medium that is left when metal and oxygen have been removed during electrowinning may be bled and replaced with fresh caustic medium to avoid build-up of impurities.

• bleed cooling (8) - The bleed stream is cooled, and impurities form on the upper level of the cooling liquid. This may, for example, be carried out in “crud” baths. The relatively clean, solid, caustic forming the bottom layer is remelted and returned to the chemical conversion step with “top- up” reagent.

• crud crushing (9) - The upper layer of crud comprising impurities is crushed.

• crud milling (10) - The crushed crud is then milled in water before the resultant stream is thickened.

• crud drying (11) - The thickened crud stream is dried, for example, by spray drying methods. The dried impurities may then be used for other purposes such as downstream processes. For example, they may be used as feedstock for creating value-added products such as geopolymers or zeolites. They may alternatively be subjected to further processing such as electroreduction to recover other valuable metals (such as aluminium or silicon) or metalloids. [0036] The steps of the present invention are now described in greater detail with reference to the embodiment of the process that is illustrated in FIG 2.

[0037] Step 1 - Ore Reclaim

[0038] The object of ore reclaim is to deliver ore fines at a controlled rate to a crusher.

For example, fines may be delivered by trucks to a stockpile on a prepared pad situated close to the crushing facility and stockpiled adjacent a feed bin. Ore fines can be loaded into the feed bin by a front-end loader or by direct tipping or other suitable means.

[0039] Loading of fines to the feed bin can be controlled by any convenient means, such as a crusher operator who activates tipping from a suitable location such as a central control room. Typically, a feeder, such as an apron feeder under the feed bin discharges to a sacrificial conveyer which then discharges to an enclosed belt conveyer.

[0040] The primary crusher discharge conveyor may include a tramp metal detection and a belt magnet to remove extraneous metal from potentially damaging downstream equipment.

[0041] Preferably, dust emission control in the ore reclaim area is provided by an extraction system within the reclaim structure. The dust emission control system may for example, consist of a single dry bag house and the dust can be discharged back to the enclosed conveyor belt. A sump pump may be provided in the basement level of the fines reclaim building to remove dust collected by washdown of the primary crushing area.

[0042] Step 2 - Ore Grinding

[0043] In a preferred embodiment belt feeders are installed beneath the fine ore bin and discharge to respective high pressure grinding roll (HPGR) crushers. A variable speed drive in each feeder may be used to maintain the level in the HPGR feed chute which ensures that the HPGR remains choke fed in normal operation [0044] Tramp metal, if detected by a dedicated metal detector on each feeder, may actuate a flop gate in the HPGR belt feeder discharge chute. A metal detection can lead to diversion of the individual feeder discharge to a HPGR bypass conveyor. The stream containing the metal can then pass under a bypass magnet that removes the metal and the conveyor discharge can gravitate back to the HPGR discharge conveyor. This system is designed to allow the crushers to remain online in the event of a metal detection event.

[0045] An HPGR typically has two rolls driven by synchronised variable speed drives which control the HPGR crusher throughput. The crusher gap is typically controlled by hydraulic pressure on the movable rolls. Tertiary crushed ore can gravitate directly to an HPGR discharge conveyor which conveys the crushed product to a two-stage air classification circuit.

[0046] Preferably, oversize particles are removed from the ground ore. For example, ground ore from mill may be passed through a dry cyclone and oversize particle can be returned to mill for regrinding to target size.

[0047] Step 3 - Ore Drying

[0048] The crushed ore may be passed through a dryer to remove water of crystallisation before the ore is fed to the chemical conversion step. The leach feed is typically dried at elevated temperature and the off gas from the dryer can be used in part in the crushing circuit for heating and product transport, and in part in the spray dryer to evaporate water from the caustic waste solutions.

[0049] The dry product is collected and conveyed in part to the chemical conversion step and in part to the bleed.

[0050] Step 4 - Chemical conversion

[0051] In a preferred embodiment, dried and crushed iron ore may be fed from the dryer to a leach feed box by screw feeders which mix all feed streams to the fines leach circuit through operation of dart valves. The dry product may be mixed into molten caustic medium at elevated temperature and at a volume flow rate that will allow proper mixing.

[0052] Chemical conversion may be carried out by many means. In a preferred embodiment a series of cascade mixing tanks ensures a controlled dilution of solids. Agitated atmospheric leach tanks, with leach agitators may provide the necessary mixing and solids suspension for optimum reaction kinetics. The last tank in the train may discharge to a pump box from where the leach discharge is pumped by the duty leach discharge pump to an electrowinning circuit.

[0053] Typically, the caustic medium is a metal base chosen from alkali metal bases such as lithium, sodium, potassium, rubidium or caesium hydroxide, or alkaline earth bases such as calcium, barium, or strontium metal hydroxides. In a particularly preferred embodiment, the metal base is chosen from lithium hydroxide, sodium hydroxide, potassium hydroxide or calcium hydroxide. In a particularly preferred embodiment, the caustic medium comprises 45 wt% to 100 wt% sodium hydroxide and/or potassium hydroxide.

[0054] One or more metal bases may be contacted with the ore, and combinations of metal bases may be in the form of a eutectic mixture. Eutectic mixtures of sodium, potassium and/or lithium hydroxide is particularly preferred. In some embodiments, for economic reasons NaOH is preferred. Compared to KOH and LIOH, NaOH is also more potent when it comes to its chemical reactivity with metal oxides, but pure NaOH may not be as efficient as the combination of NaOH with KOH to form a eutectic system, which allows for lower operating temperature.

[0055] The caustic media comprising alkali metal or alkaline earth bases are contacted with the ore at elevated temperature, preferably a temperature above 160 °C, or above 200 °C, preferably above 250 °C, more preferably above 300 °C. In a particularly preferred embodiment, the alkali metal or alkaline earth bases are contacted with the ore at a temperature of 160 °C to 400 °C, preferably 200 °C to 350 °C, more preferably 250 °C to 350 °C. [0056] For example, with reference to eutectics, most mixtures of NaOH and KOH have lower melting points than the constituent compounds. For a 1 :1 molar ratio of NaOH:KOH, the eutectic forms at 170 °C. If adsorbed water is present, such as in a 1 :1 :1 ratio of NaOH:KOH:H2O, the temperature of formation of the eutectic can be below 100 °C. However, water is undesired due to possible parasitic reactions during electroreduction process. In addition, water diluted eutectic mixtures do not have the same ability to chemically convert and dissolve metal oxides.

[0057] Molten metal bases, particularly hydroxides often include impurities such as water. Preferably metal bases incorporated in the super-alkaline media of the present invention will include water in amounts of no more than one mole of water per mole of hydroxide. It is also possible to drive off water from the super-alkaline media by short term heating of the super-alkaline media to higher temperatures (i.e., > 500 °C). A shield of inert gas over the super-alkaline media can then be used to restrict or prevent reabsorption of water.

[0058] The metal bases used in the present invention may include small amounts of chemical impurities. For example, sodium hydroxide may form, or include small amounts of sodium carbonate (Na2(CO3)).

[0059] Step 5 - Electrowinning

[0060] Preferably, the metal is recovered by passing the molten product through electrowinning cells where the metal is collected on a cathode. In the electrowinning cell or cells, the anode is preferably positioned higher than cathode. Separation efficiency of deposited solid-state iron product from cathode will determine the best cathode material to use.

[0061] Preferably, multiple identical tank houses are used to strip metal from the molten caustic slurry. Each tank house may comprise multiple banks of electrowinning cells. The molten slurry within each cell can be distributed via an individual manifold located at the base of each cell. [0062] As the metal is electroplated, sodium and potassium hydroxide are regenerated however several side reactions may consume additional reagent.

[0063] Plating takes place over a cycle time that depends on the desired thickness of metal on the cathode.

[0064] The unavoidable evolution of oxygen at the anodes would tend to give rise to an effervescent bubbling effect at the electrolyte surface. This potentially causes a “caustic mist” which is preferably removed by a ventilation system, which covers the cells to prevent lead aerosols in the immediate area.

[0065] A critical operation impacting on the current efficiency of an electrowinning cell house is that of detecting and correcting short circuits (“shorts”) between anode / cathode pairs and poor contacts. Shorts and poor contacts can be individually identified, allowing the operator to take remedial action. Alternatively, hand-held gauss meters can be employed.

[0066] Step 6 - Final Product Removal

[0067] Cathode handling typically involves lifting a proportion of the plated cathodes from each cell at a time, such as by using an overhead cathode stripping crane and lifting cradle and then transporting them to cathode storage conveyers.

[0068] In one embodiment of the present invention, the metal deposit is removed from the cathode so that the cathodes can optionally be reused.

[0069] Alternatively, the cathodes may be sacrificial and remain combined with the deposited metal. The cathodes can be cleaned of molten caustic media with hot water sprays and the washed cathodes stacked. The hanger bars may be automatically stripped from the cathodes and passed to the starter sheet package bin for reuse. Starter sheets that have previously been prepared can be used to replace the cathodes removed.

[0070] The cathodes can then be weighed and bundled for shipment. [0071] Step 7 - Bleed Electrowinning

[0072] A bleed stream may be taken from the main electrowinning circulating flow and is subjected to electrowinning to remove most of the leached iron in this stream. As the metal is plated, sodium and potassium hydroxide are regenerated in the bleed flow.

[0073] Most of the water generated in electrowinning would be consumed in regenerating sodium and potassium hydroxide. Optimally, the bleed electrolyte is stripped to the minimum level possible consistent with the number of electrowinning cells used and current efficiency.

[0074] Water balance in the process is principally affected by three different steps which are explained as follows, using iron ore as the exemplary ore. When iron ore is processed according to the present invention there are three main products (silica, iron(ll) and iron(lll)) in the dissolution process which have four different chemical “routes” that affect water balance:

1) The silica “route" releases water all the way through the process according to the following equations:

Dissolution: 2 Fe₂O₃ + 4 Na₂SiO₃ + 4 H₂O 4 FeSiO₃ + 8 NaOH + O₂

4 SiO₂ + 8 NaOH -> 4 Na₂SiO₃ + 4 H₂O

Overall: 2 Fe₂O₃ + 4 SiO₂ —> 4 FeSiO₃ + O₂

Deposition: 4 FeSIO₃ + 8-NaOH —> 4-Fe + 4-Na₂SiO₃ + 4 H₂O + 2 O₂

2) The iron(ll) “route” which is water neutral overall:

Dissolution: 2 Fe₂O₃ + 4 NaOH 4 NaHFeO₂ + O₂

Deposition: 4 NaHFeO₂ — > 4 Fe + 4 NaOH + 2 O₂

Overall: 2 Fe₂O₃ — > 4-Fe + 3 O₂

3) The iron(lll) “route” which requires water during dissolution, but which is water neutral overall:

Dissolution: 2 Fe₂O₃ + 4 NaOH + 2 H₂O —> 4-NaH₂FeO₃

Deposition: 4 NaH₂FeO₃ —> 4 Fe + 4 NaOH + 2 H₂O + 3 O₂ Overall: 2 Fe2O3 — » 4 Fe + 3 02

4) The iron(lll) (sodium ferrite) “route” which does not require water for dissolution, but which is water neutral overall:

Dissolution: 2 Fe2Os + 4 NaOH -> 4 NaFeO2 + 2 H2O

Deposition: 4 NaFeO2 — >■ 4 Fe + 2 Na2O + 3 02

Overall: 2 Fe20s — > 4 Fe + 3 02

2-Na₂O + 2-H₂O -» 4-NaOH

[0075] The route four (4) is the most likely route. In addition, to the above and depending on the water balance in the system, the following reactions may occur:

2 NaFeO2 + H2O -> Fe20a + 2 NaOH (Reverse reaction to dissolution in “route” 4.)

NaFeO2 + 2 H2O -> Fe(OH)s + NaOH (Further chemical conversion of sodium ferrite to iron(lll) hydroxide.)

[0076] Support for this contention is illustrated in FIG 5 which is a plot of x-ray diffraction measurements on iron ore from the Pilbara region of Western Australia. Hematite (58% Fe) was treated for 1 hour in 50:50 NaOH:KOH eutectic at 350 °C resulting in complete conversion of hematite into sodium ferrite and potassium ferrite. The ratio of iron ore to eutectic mixture was 10 wt%. Iron ore was dried at 200 °C for 2 hours before introducing dried ore to eutectic. Due to high concentrations of potassium hydroxide, sodium hydroxide, sodium ferrite and potassium ferrite, x-ray diffraction did not detect impurities in the iron ore.

[0077] FIG 5 should be read in conjunction with the following TABLE 1

[0078] Water balance in the process is also affected by chemical conversion of impurities contained in the iron ore described by the following reactions, broadly deployed in the Bayer process, which introduce addition water into the process:

SiO₂ + 2-NaOH -> Na₂SiO₃ + H₂O

AI₂O₃ + 2 NaOH -> 2 NaAIO₂ + H₂O

[0079] As well as chemical conversion of titania described by the following reaction which introduces water into the process:

TIO2 + 2 NaOH Na2TiO3 + H2O

[0080] The above equations are true for other alkali metal or alkaline earth bases, and their hydroxides (i.e., KOH, LIOH, RbOH, CsOH, FrOH).

[0081] Other sources of water that may affect water balance include: i. Humidity, ii. Residual water in iron ore, and iii. Residual water in hydroxides.

[0082] Measurements showed that even at 350 °C there is about 4 wt% of water in molten sodium hydroxide. The residual water contained in sodium hydroxide at 350 °C has a very low activity, meaning that vapor pressure is very low, and it is difficult to remove water from sodium hydroxide by heating.

Bleed Treatment [0083] Step 8 - Bleed Cooling

The bleed electrowinning discharge can be treated with ground ore to react the sodium and/or potassium silicates (which are water soluble) to iron silicate which is not water soluble. Sodium and potassium oxides can also react which further improves sodium and potassium hydroxide recovery. Reaction of residual hydroxide with ore is one possible way to neutralise the ‘waste’ stream.

[0084] The slurry is then cooled, such as in a jacketed agitated tank in closed circuit with a cooling tower. Cooling a molten slurry causes the multiple phases in solution in the molten caustic to separate out. Once separation is complete molten caustic medium is pumped from the bottom of the kettle. Molten crud is pumped from the top of the kettle and allowed to solidify.

Crud Treatment

[0085] Step 9 - Crud Crushing

[0086] The crud produced by cooling of the electrowinning bleed stream can be recovered, stockpiled, and loaded into a crud crushing feed bin. Loading of crud into the feed bin may be controlled by the crusher operator from the central control room.

[0087] An apron feeder or similar under the feed bin may discharge to the crud crusher to produce a product suitable to feed the semi-autogenous grinding (SAG) mill.

[0088] Step 10 - Crud Milling

[0089] The solidified crud can be milled in a mill to allow the sodium and potassium oxides in the crud to be dissolved for recovery. The mill discharge can be cycloned to impart particle size classification.

[0090] Cyclone underflow can be recycled to a mill feed chute. Cyclone overflow will gravitate to a crud thickener where the undissolved solids can be recovered to the thickener underflow. Thickener overflow is pumped to a spray dryer.

[0091] Thickener underflow can be pumped to a filter surge tank to provide a buffer between the milling and filtration circuits. The thickener underflow can be filtered and washed with wash liquor and filtrate is recycled to the crud thickener. Washed filter cake should be suitable for disposal.

[0092] Step 11 - Spray Drying

[0093] The combined liquor streams from the crud milling and cathode washing can be treated in a spray dryer to recover the sodium and potassium hydroxide as a solid product for recycle to the leach. Waste heat from the ore dryer may be used in the spray dryer to evaporate the water.

[0094] EXAMPLES

[0095] The present invention will be further described with reference to the following non-limiting examples.

[0096] EXAMPLE 1 - Processing of Iron Ore

[0097] The present invention will be further explained with reference to the following example in which iron was recovered from Marra Mamba style fine ores (-6 mm) that are found in the Pilbara, Western Australia, using a 5 Mtpa modular process plant. Marra Mamba ore has about 58% iron content and less than 1 % moisture when particle size is less than 6 mm. Impurities include silica, alumina, and magnesia as well as trace content of phosphorus and titania.

[0098] Step 1 - Ore reclaim

[0099] Marra Mamba type -6 mm iron fine ore stockpile was conveyed by trucks to a mill and stockpiled. Front end loaders loaded fines to a feed bin. An ore reclaim conveyor discharged into an 1850 tonne live capacity fine ore bin providing approximately one (1) hour live capacity ahead of the crushing circuit. Withdrawal rate from the fine ore bin was matched to the crushing circuit availability of 87.4% corresponding to an average feed rate of 653 dry metric tonnes per hour in normal operation. Live capacity of the feed bin was about 650 tonnes giving approximately 1 hour surge capacity at design reclaim throughput.

[00100] Belt feed conveyer belts were installed beneath the fine ore bin for discharge to respective high pressure grinding roll (HPGR) (1200 CRR-0001, 0002) crushers. A variable speed drive on each feeder was used to maintain the level in the HPGR feed chute to ensure that the HPGR remained choke fed in normal operation.

[00101] Step 2 - Ore grinding

[00102] The -6 mm iron or was crushed to 1 mm average particle size. Ground ore from crusher was passed through a dry cyclone and +1 mm oversize was returned to crusher for regrinding to target size.

[00103] Step 3 - Ore drying

[00104] Marra Mamba ore typically has less than about 1% moisture. The crushed ore was passed through a dryer to remove water of crystallisation before the ore was fed to the chemical conversion step. The leach feed was dried at a temperature of 700 °C.

[00105] Step 4 - Chemical Conversion

[00106] The dry product was mixed at <18% solids to melted NaOH (325 °C to 350 °C) at a volume flow rate that allowed proper mixing. The consumption rate of sodium hydroxide was approximately 90 kg/tonne of ore. The caustic NaOH media was required to be heated to processing temperature prior to adding ore, because the mixture tends to solidify quickly. The proportion of solids added into the mixture had a maximum of 18 wt% at 58% iron ore grade. This maximum would be reduced if lower grade feed was used. The output concentration of the processing circuit was approximately 5 wt% dissolved ore.

[00107] A series of four cascade mixing tanks ensured a controlled dilution of solids down to approximately 5% solids. Nickel lined vessels were appropriate for this chemistry and temperature. It will be readily apparent to the person skilled in the art that the vessels can be made of any convenient material, such as nickel 200, stainless steel with metal lining, Hastelloy® such as Hastelloy® C-276, Inconel alloy such as Inconel 625 or single crystal corundum. Other materials such as zinc oxide, cerium(IV) oxide, magnesium oxide and nickel oxide may be suitable materials for manufacture of vessels, but their suitability depends on their mechanical properties. Mixing efficiency was important along with maintaining heat in the leach tanks and leach agitators provided the necessary mixing. The last tank in the cascade discharged to a pump box from where the leach discharge was pumped by the duty leach discharge pump to a distribution circuit which split the leach discharge equally between five electrowinning circuits.

[00108] Without wishing to be bound by theory, it is believed that the chemistry occurring during the chemical conversion followed by dissolution step comprised the following major reactions:

Fe₂O₃ + 2-NaOH -> 2-NaFeO₂ + H₂O

Fe₂O₃ + 2-KOH -> 2 KFeO₂ + H₂O

2 Fe₂O₃ + 4 NaOH -> 4-NaHFeO₂ + O₂

2 Fe₂O₃ + 4 KOH -> 4 KHFeO₂ + O₂

Fe₂O₃ + 4-NaOH 2-NaH₂FeO₃ + Na₂O

Fe₂O₃ + 4 KOH -> 2 KH₂FeO₃ + K₂O

2 Fe₂O₃ + 4 Na₂SIO₃ — > 4 FeSiO₃ + 4 Na₂O + O₂

2 Fe₂O₃ + 4-K₂SiO₃ —> 4-FeSiO₃ + 4 K₂O + O₂

SiO₂ + 2 NaOH -> Na₂SiO₃ + H₂O

SiO₂ + 2 KOH K₂SiO₃ + H₂O

AI₂O₃ + 2-NaOH 2-NaAIO₂ + H₂O

AI₂O₃ + 2 KOH -> 2 KAIO₂ + H₂O

Na₂O + H₂O — > 2 NaOH

K2O + H₂O -> 2 KOH

[00109] The above reactions have been derived for systems with sodium hydroxide, potassium hydroxide or eutectic mixtures of sodium and potassium hydroxide. Similar reactions are true for other alkali metal or alkaline earth bases, and their hydroxides. [00110] Step 5 - Electrowinning

[00111] Recovery of deposited solid-state iron was via electrowinning onto a cathode. The molten product was passed through electrowinning cells where the product is collected on nickel or mild steel cathodes.

[00112] Five (5) identical tank houses were provided to strip iron from molten caustic slurry. Each tank house comprised four banks of electrowinning cells of 69 cathodes and 70 anodes each. It will be readily apparent to the person skilled in the art that the electrowinning tanks can be made of any convenient material, such as nickel 200, stainless steel with metal lining, Hastelloy® such as Hastelloy® C-276, Inconel alloy such as Inconel 625 or single crystal corundum. Other materials such as zinc oxide, cerium(IV) oxide, magnesium oxide and nickel oxide may be suitable materials for manufacture of vessels, but their suitability depends on their mechanical properties. Each cathode had 2 m² of plating area. The overall electro-winning cell houses were designed for an iron cathode production of 2,870,000 tpa, plus the additional iron electrowon in the bleed electrowinning circuit used for the impurity removal circuit. Each bank had a dedicated rectifier operating at a voltage of 204 V and a current of 276,000 A. The molten slurry within each cell was distributed via an individual manifold located at the base of each cell at a flow rate of between 1.80 l/min/m² based on a current density of 1000 A/m².

[00113] As the metal was plated, sodium and potassium hydroxide were regenerated however several side reactions consumed additional reagent.

[00114] Solution from the cell overflows into a common pipe header by which the molten slurry gravitates to a heated circulation tank.

[00115] Plating took place over a cycle time that was dictated by the desired cathode thickness of approximately 12 mm, which resulted in a maximum cathode weight of 425 kg.

[00116] Without wishing to be bound by theory it is believed that the relevant chemistry comprises the following major reactions: 4 NaFeO2 — > 4 Fe + 2 Na2O + 3 02

4 KFeO₂ -> 4-Fe + 2 K₂O + 3 O₂

2 NaHFeO₂ 2-Fe + 2-NaOH + 0₂

2 KHFeO₂ -+ 2 Fe + 2 K0H + O2

4 NaH₂FeO₃ -> 4 Fe + 4 Na0H + 2 H₂O + 3 O₂

4 KH₂FeO₃ -► 4-Fe + 4 K0H + 2 H₂O + 3 O₂

2 FeSiO₃ + 4 Na0H 2 Fe + 2 Na₂SiO₃ + 2 H₂O + 0₂

2 FeSiO₃ + 4 K0H -> 2 Fe + 2 K₂SiO₃ + 2-H₂O + O2

[00117] The regeneration of hydroxides occurs by reacting alkali metal oxides or alkaline earth metal oxides with residual water in the system, resulting in the following reactions:

Na₂O + H2O — > 2 NaOH

K2O + H2O -> 2 KOH

[00118] The above reactions have been derived for systems with sodium hydroxide, potassium hydroxide or eutectic mixtures of sodium and potassium hydroxide. Similar reactions are true for other alkali metal or alkaline earth bases, and their hydroxides.

[00119] Step 6 - Final Product Removal

[00120] A thin sheet of steel was guillotined to produce starter sheets of suitable size for cathodes. A handing bar was automatically fitted to the starter sheet before the prepared cathodes were stacked on a rack for use in the five tank houses. As electrowinning cells were stripped of loaded cathodes, a set of starter sheets is replaced in individual electrowinning cells as required.

[00121] Cathode handling involved lifting one third (15) of the plated cathodes from each cell at a time with an overhead cathode stripping crane and lifting cradle and then transporting them to a cathode storage conveyer. There they were cleaned of molten caustic with hot water sprays and the washed cathodes were transferred to conveyors feeding a stacking machine. The hanger bars were stripped from the cathodes and passed to the starter sheet package bin for reuse.

[00122] The cathodes of “green” iron (>98%) are then ready for storage, shipment or further processing to produce various steel grades.

[00123] Bleed Treatment

[00124] The molten caustic electrowinning/chemical conversion media was bled to remove build-up of impurities. The bleed stream was cooled in “crud” baths. The impurities formed on the upper level of the “crud” baths. The relatively clean, now solid, caustic at the bottom was remelted and returned to the circuit with “top-up” (replenishing) reagent and the other caustic recovered in the aqueous circuit. The upper layer of crud was crushed and then milled in water before the resultant stream was thickened and sent for disposal. The thickener overflow was sent to a spray dryer to recover itinerant caustic soda, with the resultant solids being returned to the process.

[00125] Step 7 - Bleed Electrowinning

[00126] A bleed stream was taken from the main electrowinning circulating flow and subjected to electrostripping to remove most of the leached iron in the stream. As the metal is plated, sodium and potassium hydroxide are regenerated in the bleed flow.

[00127] Without wishing to be bound by theory it is believed that the relevant reactions are as follows:

4 NaFeO₂ 4 Fe + 2 Na₂O + 3 02

4 KFeO₂ -> 4 Fe + 2 K₂O + 3 O₂

2 NaHFeO₂ -> 2-Fe + 2-NaOH + O₂

2 KHFeO₂ -> 2 Fe + 2 KOH + O₂

4 NaH₂FeO₃ -> 4 Fe + 4 NaOH + 2 H₂O + 3 O₂

4 KH₂FeO₃ -> 4Te + 4 KOH + 2 H₂O + 3 O₂

2 FeSiO₃ + 4 NaOH -> 2 Fe + 2 Na₂SiO₃ + 2-H₂O + O₂ [00128] The regeneration of hydroxides occurs by reacting alkali metal oxides or alkaline earth metal oxides with residual water in the system, resulting in the following reactions:

Na₂O + H₂O — > 2 NaOH

K₂O + H₂O — > 2 KOH

[00129] The above reactions have been derived for systems with sodium hydroxide, potassium hydroxide or eutectic mixtures of sodium and potassium hydroxide. Similar reactions are true for other alkali metal or alkaline earth bases, and their hydroxides.

[00130] Step 8 - Bleed Cooling

[00131] The bleed electrowinning discharge is treated with ground ore to react the sodium and potassium silicates which are water soluble to iron silicate which is not water soluble. Sodium and potassium oxides are also reacted which further improves sodium and potassium hydroxide recovery.

[00132] Without wishing to be bound by theory it is believed that the relevant reactions are as follows:

2 Fe₂O3 + 4 Na₂SiO3 — > 4 FeSiO3 + 4 Na₂O + O₂

2 Fe₂O3 + 4-K₂SiO3 —* 4-FeSiO3 + 4-K3O + O₂

[00133] The regeneration of hydroxides occurs by reacting alkali metal oxides or alkaline earth metal oxides with residual water in the system, resulting in the following reactions:

Na₂O + H₂O -> 2 NaOH

K₂O + H2O -> 2 KOH

[00134] The above reactions have been derived for systems with sodium hydroxide, potassium hydroxide or eutectic mixtures of sodium and potassium hydroxide. Similar reactions are true for other alkali metal or alkaline earth bases, and their hydroxides. [00135] The slurry was then cooled to about 300 °C in a jacketed agitated tank in closed circuit with a cooling tower. Cooling the molten slurry to 300 °C caused the multiple phases in solution in the molten caustic to separate out. Several cooling kettles were provided to allow the separation to occur batchwise. Once separation was complete molten sodium and potassium hydroxide was pumped from the bottom of the kettle. Molten crud was pumped from the top of the kettle and allowed to solidify.

[00136] Step 9 - Crud Crushing

[00137] The crud produced by cooling of the electrowinning bleed stream was recovered and stockpiled. Lump crud was loaded into the crud crushing feed bin by a front-end loader, under the control of a crusher operator from a central control room. Live capacity of the crud crusher feed bin was 100 tonnes giving approximately 1 hour surge capacity at design reclaim throughput.

[00138] An apron feeder under the feed bin discharges to the crud crusher to produce a product suitable to feed a semi-autogenous grinding (SAG) mill.

[00139] Step 10 - Crud Milling

[00140] The solidified crud was milled in a single stage SAG mill to allow the sodium and potassium oxides in the crud to be dissolved for recovery. The SAG mill discharge was cycloned to impart classification.

[00141] Cyclone underflow was recycled to the SAG mill feed chute. Cyclone overflow gravitated to the crud thickener where the undissolved solids were recovered to the thickener underflow. Thickener overflow was pumped to a spray dryer circuit.

[00142] Thickener underflow was pumped to a filter surge tank to provide a buffer between the milling and filtration circuits. The thickener underflow was filtered and washed on two belt filters. Wash liquor and filtrate was recycled to the crud thickener. The washed filter cake was suitable for disposal.

[00143] Step 11 - Spray Dryer [00144] The combined liquor streams from the crud milling and cathode washing were treated in a spray dryer to recover the sodium and potassium hydroxide as a solid product for recycle to the leach.

[00145] EXAMPLE 2 - Bench Scale Optimisation of Chemical Conversion of Iron

[00146] Initial test work was carried out to optimise the dissolution of the iron ore used in Example 1. Test results suggested that the dissolution of ore occurs within a few minutes for dried (200 °C) ore with a particle size of 130 microns.

[00147] The maximum concentration of ore that could be dissolved in the molten caustic (the saturation point) has been measured at 300 °C for different ore qualities after one- and four-hours’ exposure to the hydroxide. There was no appreciable difference in the amount of ore dissolved after one and four hours. The saturation point is dependent on the ore quality.

[00148] The more impure ore (with higher amount of silica and alumina) has higher saturation point. This is illustrated by the plot of FIG 3 which shows that the maximum concentration of ore in solution (i.e., saturation) increases with decreasing ore purity.

[00149] Control experiments were performed using pure silica and alumina dissolved in molten hydroxide. The saturation points for both were above 30% wt. This indicates that all silica and alumina in the ore samples is dissolved in molten hydroxide. However, the increase in saturation point with silica and alumina rich ore is significantly higher than the additional silica and alumina, so it appears that there is a synergistic effect from additional silica and alumina which is presumed to be linked to the formation of iron silicates and iron aluminates.

[00150] Other minerals present such as iron oxides or aluminium oxides may also react with NaOH to form additional salts in solution.

[00151] EXAMPLE 3 - Bench Scale Electrowinning Optimisation [00152] Initial bench scale electrowinning test work was based on a cathode area of 8 cm² operating at 310 °C. A caustic medium of NaOH and KOH (5:1 mix ratio) was used to lower the melting point of the hydroxide.

[00153] It is anticipated that using NaOH as the sole component of the caustic medium is feasible and may offer advantages. In this case, the operating temperature would need to be increased to ~350 °C.

[00154] The test work found that ore loading in the 2 to 6 wt% range is provided a sufficiently low viscosity and at the same time provided enough iron in solution to maintain a current density in the 500 to 1000 A/m² range with cell voltages ranging from 1.6 V to 1 .9 V. The spacing between cathode and anode was 2.5 cm.

[00155] FIG 4 is a plot of current vs voltage for electrodeposition of iron from hydroxide eutectic to illustrate energy consumption of the present invention. The eutectic was at 310 °C with 7 wt% dried Pilbara ore (55 wt% Fe) in solution.

[00156] The plot illustrates the energy consumption per ton of iron produced as a function of cell potential (upper trace) including 90% estimated Faradaic (current) efficiency. The lower trace represents the current density.

[00157] The coating deposited under these conditions on nickel or iron cathodes had an iron content between 95 wt% and 98 wt% depending on the ore quality. In these tests the dissolved silica and alumina was not removed from the molten hydroxide prior to the electrowinning and the applied voltage/current, where lower voltage/current always gave higher iron content. However, the impurity in the deposited iron was oxygen, not silica (or silicon) or alumina (or aluminium).

[00158] EXAMPLE 4 - Bench Scale Optimisation of Metallurgical Grade Silicon Production

[00159] Laboratory-scale attempts to produce high purity silicon using the above- mentioned process relied on two different sources of feedstock including quartz (>98% SiO2) and beach sand. However, other sources of silica feedstock can be used including silica sand (>95% SI02, <0.6% Fe2O3), or silica (sodium silicate) rich waste from iron ore processing described in previous examples presented in this patent specification.

[00160] The first step in the electrochemical production of metallurgical grade silicon is pre-processing of silicon feedstock. This step may vary depending on the purity of silicon feedstock. In particular, lower silica content beach sand contains organic and inorganic impurities which must be removed before electroreduction to limit or eliminate the amount of impurities transferred into the final product Australian beach sand was tested, the sand having a silica content of 69.8% and 73.4% SiO2). However, the processable range is higher allowing production of metallurgical grade silicon from higher and lower grade silica sources. Preprocessing of lower grade silica feedstocks is described below (under the heading ‘Preparation of silica from beach sand’.)

[00161] Higher grade silica feedstocks are commonly subjected to intense chemical processing to remove impurities, including washing and desiccation, among other methods. Instead of intense chemical methods, it is also a common practice in the industry when silicon precursors are present (e.g., fluorosilicate or fluoride systems), to remove impurities with reduction potentials lower than silicon by setting a preelectrolysis potential. However, impurities with a reduction potential higher than the pre-electrolysis potential remain in the electrolyte. For this pre-electrolysis impurity removal step an additional set of electrodes is generally required. In certain cases, the anode may remain the same whereas the cathode is replaced to attract impurities with the lower silica (sodium silicate) potential. Once impurities are removed and silicon (sodium silicate) feedstock is purified, the cathode is changed for electroreduction and deposition of metallurgical grade silicon.

[00162] Preparation of silica from beach sand

[00163] The objective of this experiment was two-fold: i. To explore the viability of processing beach sand with molten hydroxide in order to obtain high purity silica as a feedstock for zero carbon metallurgical-grade silicon production via electrowinning in molten hydroxides, and ii. To create a baseline and methodology for spodumene processing in molten hydroxides.

[00164] Methodology and observations

[00165] The experiment included the following steps:

1. The sand was washed a couple of times with deionised water to remove any salt and other water-soluble impurities;

2. After the washing step, the sand was filtered through a filter paper;

3. The sand was dried in the lab at 200 °C for a period of 2 hours in air;

4. Once dried, larger impurities were removed using a sieve with the mesh size of 1 mm. The process was repeated 5 times to ensure removal of all large particles,

5. Removal of larger particles was followed by magnetic removal of magnetite (Fe₃O4) particles. This was done by placing a strong neodymium magnet in a plastic bag and screening the sand evenly distributed on the tray. The magnetic removal was repeated a couple of times, by shaking the tray in between to expose magnetic particles that might have been on the bottom of the tray;

6. The sand was then exposed to concentrated hydrochloric acid (32% HCI) to remove any organic particles including seashells (calcium carbonate). Hydrochloric bathing was performed over a period of 4 hours, followed by several water rinses. The calcium carbonate reacted with hydrochloric acid forming water soluble calcium chloride (CaCb) and releasing carbon dioxide (CO2) which created foam, according to the following equation:

CaCO₃ + 2 -HCI CaCI₂ + CO2 + H2O

The HCI wash was performed until no further sign of foam or bubbles was noticed, indicating that organic impurities had been removed; The hydrochloric acid treatment was followed by washing with deionised water; The wet sand was distributed on a tray and dried in an oven at 200 °C for 4 hours; The dried sand was placed in a sodium hydroxide bath at 350 °C for 2 hours to form sodium silicate (Na2SiO3), in accordance with the following equation;

SiO₂ + 2-NaOH Na₂SiO₃ + H₂O Upon formation of sodium silicate and water, the water was removed from the electrolyte via evaporation at an operating temperature of 350 °C; The sodium silicate and sodium hydroxide were cooled down to room temperature and leached with water. The leaching process was relatively slow and may benefit from elevated temperature and agitation. The leaching reaction was exothermic due to reaction of water with remaining sodium hydroxide; The leached aqueous solution of sodium silicate, sodium hydroxide and other impurities present in the processed beach sand were treated with dilute hydrochloric acid (32% HCI) to precipitate silica according to the following equation;

Na₂SiO3 + 2 HCI -> SiO₂ + 2-NaCI +H2O

Treatment of remaining sodium hydroxide with hydrochloric acid results in a reaction according to the following reaction:

NaOH + HCI -> NaCI + H2O The content of the beaker was filtered using standard vacuum filtration methodologies and rinsed; 14. The silica was collected and dried in an oven at 120 °C overnight and formed a solid white product; and

15. The dried silica was ground to produce fine powder.

[00166] It will be appreciated by the person skilled in the art that extraction of silica from other natural sources such as soil is possible. However, sources such as soil are not desirable feedstocks due to the extensive purification required.

[00167] Preparation of sodium silicate and electrochemical production of metallurgical grade silicon

[00168] The objective of this experiment was two-fold: i. To explore the viability of processing beach sand with molten hydroxide in order to obtain high purity silica as a feedstock for zero carbon metallurgical-grade silicon production via electrowinning in molten hydroxides, and ii. To create a baseline and methodology for spodumene processing in molten hydroxides.

[00169] Methodology and observations

[00170] The experiment included the following steps:

1. 50 grams of anhydrous sodium hydroxide (NaOH) was measured and melted in nickel 200 crucible at 400 °C;

2. Once the sodium hydroxide was molten and had turned from opaque to transparent liquid, 10 grams of quartz (SiO2) was added into the crucible. Quartz grain size varied from roughly 4 to 8 mm in size;

3. The quartz grains instantaneously reacted with sodium hydroxide forming sodium silicate and water according to the following equation:

SiO₂ + 2-NaOH Na₂SiO₃ + H₂O 4. As the chemical conversion proceeded, water was produced and diluted the sodium hydroxide, causing it to appear slightly opaque. Leaching became visibly slower due to dilution of the hydroxide with water;

5. Some quartz crystals floated on the surface of molten hydroxide, and while reacting and dissolving in the hydroxide, visible piezoelectric charge was produced due to pressure forced on the quartz crystal during to dissolution;

6. Within about 40 minutes from the start of addition of the quartz crystals, the solution turned white and became very dense (gluey) and resembled a clay-like material. This might be caused by the melting point of produced sodium silicate (Na2SiO3), which is 1 ,088 °C.

7. To dilute the resulting solution and to be able to attempt electrowinning, another 50 grams of sodium hydroxide was added into the nickel crucible. Once added, the sodium hydroxide melted and the solution turned opaque again with a degree of transparency. It is believed that further water was generated through conversion of silica into sodium silicate as per equation above. The solution was left overnight at 400 °C to evaporate the water produced;

8. Next day, precipitate was observed at the bottom of the crucible. The precipitate was easily solubilised upon stirring. It is believed that that precipitate was an early stage of formation of a sodium silicate-based geopolymer. This may indicate that either a more dilute solution or a higher temperature is required to prevent the polymerisation.

[00171] The relationship between silica input the generation of sodium silicate, and water, as well as sodium hydroxide consumption is shown in FIG 6.

[00172] Electrodeposition of silicon

[00173] Attempts to electrodeposit the sodium silicate solution to produce metallurgical grade silicon (MG-Si) was made at -2.8 V using nickel 200 anode, and steel cathode. The resulting silicon was tested using XRF and XRD methodologies. The energy consumption of the electrowinning step was estimated to be in the range of 14.6 kWh/kg MG-Si.

[00174] Dissolution of silica to produce sodium silicate as well as subsequent electrowinning were performed in a nickel 200 container at 400 °C. However, depending on the ratio between silica and sodium hydroxide electrolyte, lower temperatures might be sufficient.

[00175] The above reactions have been exemplified for systems with sodium hydroxide. Similar reactions are true for other alkali metal or alkaline earth bases, and their hydroxides or eutectic mixtures.

[00176] During experimentation it was noticed that silica or sodium silicate have a negative impact on nickel 200 containment, wherein after a certain time some nickel is leached into the electrolyte resulting in nickel impurities in the silicon product. This nickel leaching is believed to be facilitated by silica or silicon and was not previously noticed for iron ore processing into iron, where silica levels are significantly lower than in the above-mentioned system. It would be beneficial to better understand the nickel dissolution mechanism in presence of silica or sodium silicate. Other potential vessel materials may be useable, such as, stainless steel, Hastelloy® such as Hastelloy® C- 276, Inconel alloy such as Inconel 625 or single crystal corundum. Other materials such as zinc oxide, cerium(IV) oxide, magnesium oxide and nickel oxide may be suitable materials for manufacture of vessels.

[00177] Post-processing of metallurgical grade silicon

[00178] Produced metallurgical grade silicon was washed in acidic water (pH 2 with HCI) under -2.0 V bias to prevent (or at least minimise) silicon dissolution in hydrochloric acid (HCI). Once dried under an inert atmosphere (i.e., argon, nitrogen) at 200 °C, XRF and XRD analyses were performed to measure purity of the resulting silicon.

[00179] Further post-processing of metallurgical grade silicon [00180] Metallurgical grade silicon (98% Si) is used extensively in the metallurgical industry, or as feedstock for higher purity silicon used mainly in the solar photovoltaics, and semiconductor industries.

[00181] Solar-grade polysilicon typically has purity levels of 6N (99.9999% Si) to 8N (99.999999% Si) and it is used to make solar cells. Some premium solar cells may use 9N (99.9999999% Si) polysilicon. The purity of electronic grade polysilicon generally ranges between 9N (99.9999999% Si) and 12N (99.9999999999% Si).

[00182] There are several processes that can be used to produce silicon with a purity of greater than 6N (99.9999% Si). The two most important and commonly used processes are the Siemens method and the fluidised bed reactor (FBR) method. Siemens and fluidised bed reactors are common in the industry and will be well known to those skilled in the art. There have also been multiple attempts to decarbonise Siemens and fluidised bed processes mainly through electrification of heating processes where used electricity was of low carbon footprint, i.e., renewable energy.

[00183] EXAMPLE 5 - Bench Scale Nickel Production

[00184] In another example nickel oxide concentrate (~1% Ni) was mixed with (i) sodium hydroxide, and separately (ii) a eutectic mixture of sodium and potassium hydroxide in a nickel 200 container at 350 and 250 °C, respectively. Dissolution was performed at atmospheric pressure. The species produced were soluble in the electrolyte indicating its suitability as a candidate for electrodeposition.

[00185] Having a high level of impurities introduced when adding low nickel concentrations is undesirable. It is assumed desirable to separate dissolved impurities from dissolved nickel oxide prior to electrodeposition taking place.

[00186] Upon passing an electric current through the solution, nickel was deposited onto the cathode in an electroplating process. Nickel concentrate often contains sizable volumes of iron oxide, in which case co-deposition and formation of nickel-iron alloys (also known as ferronickel) is possible. [00187] Other aspects, components and steps of the processing circuit remain the same or similar to those described earlier in this patent specification.

[00188] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[00189] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

[00190] Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures.

[00191] “Comprises/comprising” and “includes/including” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, ‘includes’, ‘including’ and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. [00192] When a Markush group or other grouping is used herein, all individual members of the group and all combinations and sub-combinations possible of the group members are intended to be individually included in the disclosure. Every combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.

[00193] Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition or concentration range, all intermediate ranges, and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[00194] One of ordinary skill in the art will appreciate that materials and methods, other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by examples, preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

[00195] Each references cited herein is incorporated by reference herein in their entirety. Such references may provide sources of materials, alternative materials, details of methods, as well as additional uses of the invention.

Claims

1 . A method of separating metal from ore comprising the steps of:

(a) optionally pre-processing the ore,

(b) mixing the ore with a caustic medium at elevated temperature above 160 °C, and

(c) subjecting the mixture to electrolysis to deposit at least one metal at a cathode and evolve oxygen at an anode.

2. A method according to claim 1 , wherein the elevated temperature is 160 °C to 400 °C, preferably 200 °C to 350 °C, more preferably 250 °C to 350 °C and the caustic medium is optionally a molten caustic medium.

3. A method according to claim 1 wherein the caustic medium at elevated temperature dissolves at least one metal species from the ore.

4. A method according to claim 1 , wherein the caustic medium comprises one or more alkali metal or alkaline earth bases.

5. A method according to claim 1 , wherein the ore is an iron ore chosen from hematite, goethite, limonite, siderite, magnetite, titanomagnetite, pisolitic ironstone and combinations thereof, and the metal deposited is from 95 wt% to 98 wt% iron.

6. A method according to claim 1 , wherein the ore is a mineral sand and the metal species is a metalloid.

7. A method according to claim 1 , wherein the ore is a nickel ore.

8. A method according to claim 1 , wherein the caustic medium is a metal base chosen from lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, caesium hydroxide, calcium hydroxide, barium hydroxide, or strontium hydroxide or combinations or eutectic mixtures thereof.

9. A method for separating metal from ore according to claim 1 , the method comprising the steps of:

(a) pre-processing the ore by,

(a)(i) crushing the ore to a desired particle size;

(a)(ii) drying the crushed ore;

(b) mixing the crushed, dried ore with a caustic medium at elevated temperature;

(c) passing the mixture through electrolysis cells to collect metal at a cathode and release oxygen at an anode; and

(d) removing the collected metal.

10. A method according to claim 9, wherein the collected metal is separated from the cathode.

11. A method according to claim 9, wherein the cathode and the metal collected are of the same material.

12. A method for separating metal from ore according to claim 2, wherein the method includes the further steps of:

(e) bleeding and cooling a spent caustic material from the electrolysis cells;

(f) separating the spent liquor into a solid crud comprising impurities and a cleaned caustic medium; and

(g) returning the cleaned caustic medium to the mixing step.

13. A method according to claim 12, which further includes the steps of:

(h) crushing any solid crud,

(i) milling the crud in liquid to form a suspension;

(j) thickening the suspension; and

(k) drying, preferably spray drying, the thickened suspension to create dried crud.

14. A method according to claim 13, wherein the dried crud is used as a feedstock for further processes.

15. A metal separated from an ore by a method according to any one of the preceding claims.

16. A system for carrying out the method of any one of claims 1 to 14.