pellet

Abstract

A method of producing a pellet, the method comprising the steps of: a.providing a particulate substrate at a temperature in the range 30°C - 90°C, wherein the particulate substrate is selected from a metal ore, metal ore-containing waste, metal fines, iron residue, iron filings, mineral waste, carbonaceous material, arc furnace waste or combinations thereof; _ b. mixing the particulate substrate with a binder and water to form a gelled substrate mixture; c. forming a pellet from the gelled substrate mixture; and d. curing the pellet. Pellets obtained by this method.

Description

[0001] P608393PC00

[0002] Pellet

[0003] The invention relates to methods of producing pellets from a particulate substrate and a binder, in particular where the method includes forming a gelled substrate mixture, and to pellets obtained using this method.

[0004] Though abundant in the Earth's core, the amount of carbon, and various metals and metal ores available is finite. There are environmental costs associated with mining metal ores and metals, such as iron, and smelting activities, particularly in terms of pollution. As a result, it is desirable to maximise the recycling of waste materials, which in turn reduces the waste that must be handled and stored, for instance, in the case of iron waste, typically by long term storage in heaps or ponds.

[0005] The production of pellets from carbonaceous materials, particulate metals and metal ores is generally known in the art. Often, the particles are bound together using a binder to form a pellet. In pelleting processes, binders are typically added as powders. However, powders can be difficult to process into pellets which are stable and sufficiently strong to be transported not only to the site of use, but within the large processing plants at their destination. Powder binders can also explode or easily escape into the atmosphere. This can be disadvantageous financially due to loss of material, gives rise to a risk of direct human injury and can create an inhalation hazard with either short term toxic effects or causing longer term disease.

[0006] In addition, pelleting processes using powders often give inconsistent results and can be problematic when production is upscaled due to difficulties in efficient powder dispersion in industrial scale mixers. There may also be interference between the binder components, as a result of temperature and pressure effects. The use of powders can also impact solubilization differentials in unpredictable ways. This means that significant testing is required before industrial scale use, making the transition from formulation to industrial pelleting more difficult and expensive.

[0007] The provision of binders in gel form has been described in the Applicant's earlier publication WO 2024 / 023517. This document describes the chemical gelation of a binder, either prior to mixing with a particulate substrate, or post-mixing but prior to pellet formation. This provides for a method in which the binder is efficiently dispersed through the particulate substrate in the final pellet product, improving the processing of the pellet, leading to consistently strong pellets.P608393PC00

[0008] However, it would be desirable to develop a process for pelleting in which ease of manufacture is further improved, without loss of strength and pellet stability. The invention is intended to overcome or ameliorate at least some aspects of this problem.

[0009] Accordingly, in a first aspect of the invention there is provided a method of producing a pellet, the method comprising the steps of:

[0010] a. providing a particulate substrate at a temperature in the range 30°C - 90°C, wherein the particulate substrate is selected from a metal ore, metal ore- containing waste, metal fines, iron residue, iron filings, mineral waste, carbonaceous material, arc furnace waste or combinations thereof;

[0011] b. mixing the particulate substrate with a binder and water to form a gelled substrate mixture;

[0012] c. forming a pellet from the gelled substrate mixture; and

[0013] d. curing the pellet.

[0014] The formation of a gelled substrate mixture allows the binder to be more efficiently dispersed through the particulate substrate in the final pellet product. Without being bound by theory, it is believed that the formation of a gel (due to the presence of water this will be a hydrogel) not only binds the substrate particles together, enhancing the strength of the final pellet, but also acts as a processing aid because in the gel form, the binder is more dispersible and so can have lubricant effects. Overall, this improves the processing of the pellet, leading to more consistent results. Further, binding materials that can form gels are more easily dispersed than powder binders in industrial scale mixers. Furthermore, incorporating binding materials that can form gels allows for the easy dispersion of additional powder binders, thereby addressing the issues related to the exclusive use of powder binders. Accordingly, this leads to improved efficiency by reducing machine loading and overheating. Moreover, it has been noted that less of the binder is required to obtain comparative strengths to known binders because the gelation enhances the binding properties and enables any binding materials present that do not directly form part of the gel to reinforce the polymer bonds.

[0015] Further, the final pellets produced in the method of the invention have been surprisingly found to be stronger, with higher strength and rigidity relative to non-gelled pellets, which, whilst heat may be applied if desired, removes the need for high-temperature (above 150°C or 100°C) post-production heating (e.g., drying or curing processes) of the pellet to stabilize it for storage, transport, and use. This has noticeable environmental benefits, in that less energy is required for the creation of a pellet of sufficient strength from the particulate substrate. Further, pellets obtainable by methodsP608393PC00

[0016] according to the invention also generally exhibit high thermal stability, which means that the pellet reduces at a controlled rate and does not disintegrate in a blast furnace. As such, the provision of a "warmed" or "heated" particulate substrate is believed to contribute to the provision of a method for producing a pellet which does not require the application of significant heat at any stage of the production process, in that the process can be carried out at low temperatures, producing strong and robust pellets even where curing is below the temperatures (for instance temperatures of greater than 100°C) typically used. An advantage of forming the pellets at low temperature is a significant reduction in energy expenditure relative to the induration manufacture techniques commonly used. There is therefore also no need for high-temperature furnaces to produce the pellet, resulting in a simpler and more economically and environmentally beneficial manufacturing process. Further, the process of the invention provides for rapid pellet formation relative to non-temperature controlled gelation methods, without the need to apply pressure to induce gelation, such that throughput can be increased whilst providing pellets of high quality and strength. As a result, the process of the invention has an end-to-end lower carbon footprint than where gelation is pressure induced, yet remains significantly faster than where gels are formed at ambient temperature.

[0017] As used herein the terms "warmed" and "heated" or their derivatives are intended to be given their usual meaning in the art, in that energy is applied to the materials (be these the particulate substrate, the gelled substrate mixture, an agglomerate or pellet), in order to increase their thermal energy. Heating will typically be for the entire duration of a process step, although heating for limited time, or pulsing, is also envisaged providing that the external energy provided is sufficient to ensure that the material being heated is maintained at above ambient temperature, and where specified within the temperature range described for that process step. As used herein the term "ambient" is intended to refer to the temperature of the immediate surroundings, and will generally be considered to be 25°C or lower, often in the range 10 - 25°C, or 15 - 20°C.

[0018] It may be the case that the method will comprise the additional step of processing the gelled substrate mixture to form an agglomerate. As used herein the term "agglomerate" is intended to take its usual meaning in the art, referring to a particulate material formed from a collection of particles that are physically or chemically joined together.

[0019] The agglomerate may be formed by extrusion of the gelled substrate mixture, for instance through a roller press. Optionally, the pellet may then be formed by use of a second roller press including rollers with a series of evenly spaced recesses along their length. As such, the agglomerate and then the pellet may be formed by extrusion. The pellet may be formed by extrusion of the gelled substrate mixture, agglomerate orP608393PC00

[0020] granules formed from the agglomerate. The method may therefore comprise the step of forming the agglomerate and / or pellet by extrusion. Each extrusion process may independently take place at a temperature in the range of about 30°C to about 70°C, often in the range of about 35°C or 40°C to about 55°C. In some instances, alternative compressive techniques may be used, such as the screw extrusion, hammer mills, or pressure plates. The extrusion may be screw extrusion, for instance using a single or twin screw feeder, where the barrel of the extruder may optionally be vacuum vented. Screw extrusion is advantageous due to the continuous nature of the process and the ease of controlling the conditions (e.g. temperature, pressure) under which the gelled substrate mixture, or agglomerate, are placed. Alternatively, pan pelletisation may be used.

[0021] The agglomerate and / or the pellet may be formed at low temperature, for instance in the range 30°C - 200°C. The term "formed at low temperature" means, for example, without curing, sintering, or heating to above about 200°C, or above about 150°C, or above about 120°C, or about 90°C. It is generally desirable for the upper limit of the "low temperature" range to be as low as possible, and less than 200°C, as this reduces the energy used in the pellet formation process, reducing costs and (dependent on the source of energy used) potentially also the carbon footprint of the process. However, it is envisaged that during the method of the invention heat will be applied such that the pellet is not "cold-formed", because the particulate substrate is heated to in the range 30°C - 90°C prior to mixing with the binder and water. Therefore, it will be the case that there is an application of heat during pellet production, but that only low levels of heat will be applied.

[0022] As such, it may be the case that the particulate substrate is provided at a temperature in the range 30°C - 90°C, often 40°C - 80°C or 40°C - 75°C, often the particulate substrate will be provided at a temperature of 60°C or less, or in the range 45°C - 70°C or 50°C - 60°C. It will be understood that, given the nature of the technology, the cited temperature ranges (for instance 30°C - 90°C) will be variable within limits within the particulate substrate, in that the particulate substrate may not be heated uniformly, leading to regions of slightly higher, or slightly lower temperature than the bulk. Where a temperature is provided for the bulk particulate substrate, it is to be interpreted as ±2°C; with an understanding that temperatures will be controlled within the range 30°C - 90°C. This means that a reference to 30°C can be interpreted as the bulk material being 30°C (+2°C) because the coolest regions of the particulate substrate will be controlled such that they are at or above 30°C, and a reference to 90°C can be interpreted as 90°C (-2°C), because temperatures will be controlled such that the warmest regions of the particulate substrate are at 90°C or less. However, a referenceP608393PC00

[0023] to, for instance 60°C, can be interpreted as 60±2°C. In other words, the heating will be configured to ensure that all of the material falls within the temperature range 30°C -90°C, but it is acknowledged that within that range there may be non-uniform heating and so pockets of particulate which fall within the ±2°C variance.

[0024] It has surprisingly been found that by providing the particulate substrate in a "warm" form (i.e. in the temperature ranges above) prior to mixing and subsequent processing as described above, gelation of the substrate mixture can be induced rapidly, such that the pellets can be produced quickly, with strength, yet without the need to apply more than "warming" heat at any point in the pelletisation process, or the need for the application of pressure to induce gel formation.

[0025] As noted above, the particulate substrate is provided warm, and this may be through the application of a substrate heating step, wherein particulate substrate at ambient temperature is heated to a temperature in the range 30°C - 90°C prior to mixing step b. This may be the case where, for instance, the method is a batch process, and the particulate material has been stored ready for pelletisation. For instance, the particulate material may have been pre-processed by drying and / or milling and then placed into storage. It may further be the case that the particulate substrate may be heated to a temperature above the temperature at which it will be provided, and allowed to cool to that temperature (for instance in the range 30°C - 90°C from above 100°C) as this allows accurate control of the temperature of the particulate substrate when it is provided for mixing. There may, therefore, optionally be a substrate heating step before mixing, wherein the particulate substrate is heated to a temperature in the range 30°C -90°C, or optionally 40°C - 80°C or 40°C - 75°C, often the particulate substrate will be heated to a temperature of 60°C or less, or in the range 45°C - 70°C or 50°C - 60°C.

[0026] Heating may be via any known non-destructive method of heating the substrate, such that it has a broadly consistent temperature range throughout the bulk of the substrate. For instance, by using jacket mixers, rotary dryers and / or or oven technology (for instance an air convection oven which is set to a temperature in the range 100°C -200°C, often 100°C - 150°C). Additionally or alternatively, the particulate substrate may be provided on a heated belt, and / or heated using IR or microwave radiation.

[0027] Alternatively, the particulate substrate may already be warm, for instance, it may have been heated for drying, and provided to the method of making a pellet before the residual heat has entirely dissipated, such that it can be provided at in the range 30°C -90°C without specific heating. This could be the case where the method is a continuous process, and drying of the particulate occurs directly before provision of the substrateP608393PC00

[0028] and mixing. As above, it may be that the particulate substrate be heated to a temperature above the temperature at which it will be provided, and allowed to cool to that temperature (for instance in the range 30°C - 90°C from above 100°C) as this allows accurate control of the temperature of the particulate substrate when it is provided for mixing.

[0029] Additionally, it may be the case that further steps of the method comprise heating. For instance, the curing of the pellet may comprise heating (step d.), optionally wherein heating is to a temperature in the range 30°C - 200°C. It has been found that by curing the pellets in this "warmed" temperature range, which is low temperature but where some heat is applied, curing occurs more quickly. This provides pellets that are stronger than in the absence of heating at this stage, or where heating is above this temperature range, and pellets that are ready for transport sooner than in the absence of the heating at the curing stage. Alternatively, heating may be to a temperature in the range 40°C -150°C, or 40°C - 70°C, or 50°C - 60°C. It has been found that pellets of excellent strength can be formed quickly at lower temperatures, such that heating to, at most, 150°C, 70°C or 60°C retains pellet strength, with improved environmental benefits as less energy is required to heat the pellets during curing.

[0030] However, the skilled person would understand and appreciate that factors such as the external ambient temperature, nature of the components in the formulation, and the desired properties of the pellets to be produced (e.g., a low water content) would impact whether external heat is recommended, the level of heat that is then applied and for what period of time. Therefore, the skilled person would consider such factors when determining if an optional further heating step using low level heat is to be used in the process, and the period of time and level of heat to apply in the process.

[0031] It will often be the case that curing of the pellet comprises heating, wherein the pellet is heated during curing to a temperature greater than the temperature at which the particulate substrate is provided. In other words, it has been found to be advantageous for the curing temperature to be greater than the temperature at which the particulate substrate is provided, and therefore, the temperature of the substrate to which the binder and water are added for mixing. This provides stronger pellets than where the curing temperature is lower than that at which the particulate substrate is provided. Without being bound by theory, this is believed to be because the additional heat during curing causes the chemical reactions between the binder and the particulate substrate to move closer to completion.P608393PC00

[0032] It may be the case that curing of the pellet comprises curing for a time period in the range 0.25 - 24 hours, often 0.5 - 6 hours, 0.5 - 4 hours, 1 - 2 hours or around 1 hour. Reducing curing time, reduces manufacture time and energy usage.

[0033] As noted above, it may be the case that more than one step within the method comprises heating. This may be steps a. and d. (the provision of warmed substrate and the curing of the pellet) as described above; and / or additionally steps b. and / or c. (mixing the particulate substrate with a binder and water, and pellet formation). If an agglomerate is formed, the agglomeration step may also be heated. Often, however, steps a. and d. will comprise heating, optionally with the addition of step b. (mixing the particulate substrate), as it has been found to be beneficial to maintain the components of the pellet at a temperature above ambient during the entire pellet production process to maximise the strength of the pellets. In many method configurations, for instance where the method of forming the pellets is configured as a continuous process, the heat provided by the particulate substrate in step a. will be sufficient to maintain the temperature of the components (particulate substrate, binder and water) at a temperature above 30°C (or higher temperature as desired) for the duration of the mixing and any subsequent steps prior to curing. Further, it has generally been found that the gelled substrate from mixing step b. retains heat for a sufficient period of time to allow agglomeration and pellet formation without the application of heat during these stages. This can be beneficial as, if no heat is applied during agglomeration or pellet formation, less heat needs to be applied across the entire process, and the environmental benefits of the method are maximised. None-the-less, formation of the pellet (step c.) and the optional agglomerate formation may also comprise heating.

[0034] It has therefore been found to be advantageous to provide a method of producing a pellet wherein more than one step in the method occurs at a temperature of 30°C or greater, optionally in the range 30°C - 200°C, or in the range 40°C - 150°C, or 40°C -70°C, or 50°C - 60°C. By operating in these temperature windows, the temperature of the components of the pellet are maintained at above ambient temperature, which has surprisingly been found to provide strong pellets with rapid formation. This has been found to be the case, in particular where steps a. to d. all occur at a temperature of 30°C or greater, such as within the ranges defined above. In particular, heat may be directly applied in one or more of steps a., b. and d.; optionally in all of these steps. Where heat is not directly applied in a step, for instance in step c., prompt completion of the step, before the materials cool to ambient temperature, ensures that the components of the pellet can be maintained at above ambient temperature, or above 30°C (for instance, in the range 30°C - 200°C, or in the range 40°C - 150°C, or 40°C -70°C, or 50°C - 60°C) for the duration of the pellet production process.P608393PC00

[0035] Further, during agglomeration the forming of the pellet, frictional heat may be generated by any pressing and / or extrusion processes used, and the binder may undergo exothermic reactions in situ, thereby providing additional sources of heat within the production process which do not require the application of external heat to the materials in the pellet.

[0036] In view of the desire, in some instances, to promptly complete unheated steps, it may be the case that mixing of the particulate substrate with the binder and water to form the gelled substrate mixture occurs for a time period in the range 1 - 5 minutes, often 2 - 4 or 3 - 4 minutes, often around 3 minutes. As used herein, reference to "prompt completion" of steps and similar concepts is intended to be interpreted as, in a continuous process, such that the materials and pellets move from one step to the next directly after the previous step in the method is completed (without intervening storage). Whether the method is configured in a batch or continuous process, in order to ensure that the materials or pellets do not cool to ambient temperature, or to less than 30°C or less than the temperatures described above, it will generally be the case that formation of the pellet occurs in the range 1 - 15 minutes, often 1 - 10 or 1 - 5 minutes of mixing of the particulate substrate, binder and water to form the gelled substrate mixture.

[0037] Traditionally, pellets were formed using heat processes producing so-called, hot bonded (indurated) briquettes. In induration techniques, initially, a "green" pellet is formed from the combination of particulate substrate and a binder, which is then shaped into a pellet (often using a pelletiser). As used herein, the term "green pellet" takes its usual meaning in the art and refers to a pellet that does not yet have the required strength for its end use and requires further treatment or processing. The green pellets are hardened via a series of steps including drying, pre-heating, firing, and cooling of the green pellets. The primary purpose of the drying stage is the removal of moisture from the pellets, making them more stable and easier to handle. Removal of water in a controlled manner prevents crack formation and maintains the structural integrity of the pellet. The temperature range of the drying stage is dependent on the chemical and physical properties of the green pellet; however, it is likely to be in the range of 100°C - 250°C for 5 - 10 minutes. The pre-heating stage usually takes place using a ramped heating process from around 300°C - 350°C for 10 to 15 minutes, to up to around 1250°C -1350°C. The pre-heating stage ensures that any metal hydrates or metal carbonates present decompose to their anhydrous forms. Decomposition of these types of compounds helps to improve the structural integrity of the resultant pellet by removing water and / or gas which can react causing overpressure and cracking of the pellet during firing. The firing stage will often take place at temperatures greater than 1350°C forP608393PC00

[0038] roughly 10 - 20 minutes (for typical capacities such as 250 - 500 tph) and will result in the sintering of the pellet, providing the strength needed to render it suitable for its end use. During the sintering process, the bonds within the pellet are formed by recrystallisation and bridging, creating ceramic bonds and the formation of macro voids which allow for some expansion and stress relief. As used herein, the term "macro void" relates to voids within the pellet that have a size ranging from about 50 pm to about 1 mm in diameter. The void formation is particularly important where the briquette is a metal ore briquette, as reduction of the metal (for instance the hematite to magnetite conversion in iron ore) causes volume changes and stresses on the briquette. As macro void formation does not occur without firing, alternative methods are needed to prevent disintegration of the pellet when placed under internal stress. The gelation techniques described herein provide such an alternative by offering rapidly induced improved chemical bonding strength.

[0039] Further, relative to the processes of the invention, induration processes are uneconomical as they are complex, must be executed with care and require the application of significant heat. For instance, the raw material preparation is critical. The components of the green pellet must be of an appropriate size range, surface area, and moisture content in order to withstand the process, as surface chemistry plays a significant role. Moreover, as the process involves multiple heating stages, it requires a great deal of energy. As such, there is a need for a pellet production process that is less energy intensive and more cost effective. Moreover, there is a need for a process where there is more flexibility in the physical state of the particulate substrate used, and which results in the generation of pellets having comparable or even superior physical properties to those generated using an induration process. The methods of the invention, through their use of gel formation with controlled low temperature conditions help to offer a solution to this problem.

[0040] As suggested above, it may be the case that the method comprise an additional step of milling the particulate substrate prior to provision for pelletisation. Additionally, or alternatively, there may also be provided a step of drying the particulate substrate prior to provision for pelletisation. The step of drying the particulate substrate may comprise heating the particulate substrate to a temperature sufficient to drive off water present in the substrate. This may involve heating to temperatures in the range 50°C - 150°C, often in the range 80°C - 120°C. Often the particulate substrate will be dried to constant mass.

[0041] Typically, the particulate substrate is selected from a metal ore, metal ore-containing waste, metal fines, iron residue, iron filings, mineral waste, carbonaceous material, arcP608393PC00

[0042] furnace waste or combinations thereof. The particulate substrate is often sourced from the waste products of other industrial processes. The particulate substrate may comprise waste products from a single waste stream (in which variation will be in particle size only) or waste products from a combination of waste streams (in which mixed waste of different compositions will be present). This is environmentally beneficial as the recycling and reuse of such materials reduces the amount of finite resources that may otherwise go to waste, introducing a desirable circularity into these industrial processes.

[0043] Without being bound by theory, it is believed that, whether the particulate substrate comprises a single waste type or a combination of different waste types, the formation of a gel aids distribution of the wastes in a pseudomatrix before the pellet is formed.

[0044] The carbonaceous material may be coke, coke breeze, graphite, carbon black, peat or coal. Often the carbonaceous material will comprise coke and / or coal. As used herein, the term "coal" is intended to include lignites, sub-bituminous coal, bituminous coal, steam coal and anthracite. Cokes have been found to be particularly problematic at forming pellets and so the invention offers a particular benefit in the provision of stronger coke pellets.

[0045] Mineral wastes may include mill scale, mill sludges, fines from ores and / or metalcontaining wastes.

[0046] The metal, metal ore, or the metal ore mineral waste may contain; iron, zinc, nickel, copper, chromium, manganese, gold, platinum, silver, titanium, tin, lead, vanadium, cadmium, beryllium, molybdenum, uranium, aluminium, or mixtures thereof; for instance, as elemental metal or in the form of, for example, oxides or silicates.

[0047] Often, the particulate substrate comprises a metal, and more often the particulate substrate comprises iron. The use of iron is advantageous due to its ready availability and because it can be reused and recycled from the waste products of other processes to provide environmentally sustainable access to this material. Where the particulate substrate comprises a metal ore, often the ore will be an iron ore such as goethite, limonite, siderite, taconite, martite, hematite or magnetite. Often, where the particulate substrate is a metal ore, it will be an iron ore, such as hematite or magnetite, because of the ready availability of these materials and the need to utilise both the raw material and any waste containing iron ore efficiently.

[0048] The particulate substrate may be a powder or filings, the term "filings" being given its common meaning in the art. Often the particulate substrate has a particle diameter of 4 mm or less (broadest axis). Often the particle diameter will be in the range 0.1 mm to 4P608393PC00

[0049] mm. Often, at least 10 wt% of the particulate substrate is capable of passing through a 100 pm sieve prior to forming into a pellet. The ability to pelletise small particulate matter is excellent for the "recycling" of waste materials that, without pelletisation, would be extremely difficult to handle and reuse. Further, for virgin materials, such as ores, it ensures that a much higher percentage of the material is available at the point of end use, with less wastage arising from the loss of small particulates that have been, for instance, sheared off the surface of larger agglomerates during transport and handling. The presence of a range of particle sizes within the sample, improves the packing of the materials within the agglomerate during pellet formation, such as via extrusion or via a roller press including rollers with a series of evenly spaced recesses along their length. As noted above, the term agglomerate takes its usual meaning in the art, i.e., a particulate substrate formed from a collection of particles that are physically or chemically joined together.

[0050] The pellets comprise a binder, which is mixed with the particulate substrate and water to form a gelled substrate mixture. The binder may be a combination of binder materials, such that the binder comprises one or more binding materials. Given the presence of water, and the desire to produce a gelled substrate mixture, it will often be the case that the binder be hydrogel forming, such that at least one binding material is hydrogel forming. If there is only one binding material, such that the binder comprises or consists of a single binding material, then that binding material will generally be hydrogel forming. If there is more than one binding material, one or more than one may be hydrogel forming and may be accompanied by binding materials that do not form hydrogels. It is believed that the hydrogel forming binding material forms a hydrogel around the particulate substrate, providing the benefits described above.

[0051] As used herein, the terms "gel" and "hydrogel" refer to materials which are not a readily flowable liquid and not a solid but a gel which is comprised of a gel forming material, such as a hydrophilic polymer that does not dissolve in water. In other words, the gel or hydrogel may be a semi-solid substance. Typically, gels are formed through a gel forming material, such as a hydrophilic polymer forming an interconnected crosslinked network which can entrap, absorb and / or otherwise hold water thereby creating a gel. Some gels can be diluted with another liquid such as water, which disrupts the interconnected network, resulting in a solution, although typically the gels and hydrogels of the invention will be crosslinked gels that do not dissolve on dilution.

[0052] The water present in the mixing step will typically facilitate hydrogel formation. This may be moisture naturally present in the particulate substrate, water that is added specifically to enable hydrogel formation or a combination of the two. However, as theP608393PC00

[0053] particulate substrate is typically in dry form, such that it comprises less than 1 wt% water at the point of provision for pelletisation, most if not all of the water in the hydrogel will have been added during mixing to form the gelled substrate mixture. The amount of water in the hydrogel is generally adjusted to in the range of about 1 wt% to about 5 wt%, or about 2 wt% to about 4 wt%, or about 2.5 wt% to about 3.5 wt%, or about 3 wt% or in some instances about 4 wt%, for instance about 3.5 to about 4.5 wt%. At higher levels, the water has been found to dilute the systems too far, such that gel formation is less effective because the water reduces the viscosity of the system, providing less mechanical force for binding and less densification of the resulting pellet. Without being bound by theory, it is believed that not all of the water that is mixed with the binder is present in the final hydrogel. This is because small amounts act to ensure dissolution or mixing of other components.

[0054] It is generally known that gels generally require some time to form, this can be referred to as "resting" and is often for 1 to 2 hours. This can be undesirable as it delays the production process. Key to the invention is the warming of the substrate mixture, through the provision of a heated particulate substrate. It has been surprisingly found that this induces rapid gel formation, such that the gel forms almost instantly, and generally within a few seconds (for instance, 0 - 60 seconds, often 1 - 20 seconds or 2 -5 seconds). This has the advantage that the gelled substrate mixture is formed very quickly, and subsequent processing (for instance pelletisation and / or curing) can proceed without delay. As a result, the gel has been formed prior to any subsequent drying, granulation, agglomeration or pelletisation steps.

[0055] Typically, the particulate substrate is added in an amount of about 70 wt% to about 99.9 wt% of the pellet, often about 80 wt% to about 99 wt%, more often about 90 wt% to about 95 wt%. This maximises the substrate content in the pellet, whilst allowing for a sufficient amount of the binder to ensure stabilisation of the particulates. Typically, the ratio of the binder to the particulate substrate in the pellet is about 1.5 wt% to about 3.6 wt% binder to about 98.5 wt% to about 96.4 wt% particulate substrate, often about 2.5 wt% to about 3 wt% binder to about 97.5 wt% to about 97 wt% particulate substrate.

[0056] With regard to the binder, this will contain one or more binding materials, for instance there may be a single binding material, two, three or more as described below. Often, the binding material is selected from a natural polymer, a synthetic polymer (such as a synthetic organic resin), a cellulosic material, a glycerolipid, a polysaccharide, an inorganic binding material or combinations thereof. The binder may comprise at least one binding material selected from a synthetic polymer, a cellulosic material, a glycerolipid, an inorganic binding material, or combinations thereof.P608393PC00

[0057] As used herein, the term "cellulosic material" takes its usual meaning in the art and refers to any material derived from or containing cellulose. Cellulosic materials include natural materials primarily composed of cellulose as well as synthetic derivatives of cellulose. As used herein, the term "glycerolipid" takes its usual meaning in the art and refers to a type of lipid molecule that consists of a glycerol backbone esterified with one or more fatty acids or acyl groups.

[0058] An example of a natural polymer as used herein includes, but is not limited to, lignosulfonates. Examples of a synthetic polymer include, but are not limited to, polyvinyl alcohol, polyacrylics, styrene-acrylate copolymers, and synthetic organic resins, such as for example a polyacrylamide resin or a phenol-formaldehyde resin. As used herein, a phenol formaldehyde resin includes resole resin, which is a base catalysed phenol-formaldehyde resin with a formaldehyde to phenol ratio of greater than one, usually around 1.5, or Novolac resin, which has a formaldehyde to phenol molar ratio of less than one. As used herein, the term "polyacrylics" takes its usual meaning in the art and refers to a class of synthetic polymers derived from acrylic acid or its esters. Examples of polyacrylics include, but are not limited to, polyacrylic acid (PAA), poly(methyl methacrylate) (PMMA), and polyacrylamide (PAM). As used herein, the term "styrene-acrylate copolymer" takes its usual meaning in the art and relates to synthetic polymers formed by the copolymerization of styrene and acrylic acid or its derivatives. Examples of styrene-acrylate copolymers include, but are not limited to, 2-ethylhexyl acrylate styrene (2-EHA), ethyl acrylate styrene (EA), methyl methacrylate styrene (MMA), and butyl acrylate styrene (BA). Often, the styrene-acrylate copolymer will comprise ethyl acrylate styrene (EA). Examples of glycerolipids include mono-, di-, or tri-esters of glycerol, such as glyceryl acetate, glyceryl diacetate, and glyceryl triacetate. Examples of cellulosic materials include, but are not limited to cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), or a combination thereof. An example of a synthetic triglyceride includes, but is not limited to, glycerol triacetate. Examples of polysaccharides include, but are not limited to, wheat, maize, barley and potato starch or gum (e.g. gum Arabic, guar gum or xanthan gum). Examples of inorganic binding materials include, but are not limited to, silicates (e.g. a group I or group II metal silicate such as sodium silicate (NazSiCh), potassium silicate (KzSiCh), calcium silicate (CaSiCh), magnesium silicate (MgSiC ), alumina silicate, or combinations thereof) or refractory materials including, but not limited to, oxides, carbides, or nitrides of silicon, aluminium, magnesium, calcium, and zirconium (e.g. alumina, fireclays, bauxite, chromite, dolomite, magnesite, silicon carbide, zirconia, or combinations thereof). As used herein, the term "refractoryP608393PC00

[0059] material" refers to materials that are resistant to thermal stress, high pressure, or corrosion by chemical reagents.

[0060] These materials provide a combination of gel (often hydrogel) forming binding materials, and non-gel forming binding materials, providing flexibility of composition whilst offering the improved pellet strengths and ease of processability of the invention. These binding materials have the advantage that they can be used in a low concentration, and as such will not significantly affect the metallurgical or physical properties of the substrate mixture.

[0061] It will often be the case that the binder comprises at least one binding material selected from a cellulosic material, a synthetic polymer, a glycerolipid, one or more silicates, or combinations thereof. The binder may comprise at least one binding material selected from cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), a polyacrylamide resin, polyvinyl alcohol, a phenol formaldehyde resin, a polyacrylic, a styrene-acrylate copolymer, a glycerolipid, one or more silicates, or combinations thereof.

[0062] It will often be the case that the binder comprises at least one binding material selected from cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), a polyacrylamide resin, polyvinyl alcohol, polyacrylamide, one or more silicates, ethyl acrylate styrene (EA), glyceryl triacetate, glyceryl diacetate, a phenol-formaldehyde resin or combinations thereof. It will often be the case that the binder comprises at least one binding material selected from cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), a polyacrylamide resin, polyvinyl alcohol, polyacrylamide, one or more silicates, glyceryl triacetate, a phenol-formaldehyde resin or combinations thereof. The binder may comprise at least one binding material selected from carboxymethyl cellulose (CMC), a polyacrylamide resin, polyvinyl alcohol, a phenol formaldehyde resin, sodium silicate, magnesium silicate, glyceryl triacetate or combinations thereof. The binder may comprise at least one binding material selected from carboxymethyl cellulose (CMC), a polyacrylamide resin, polyvinyl alcohol, a phenol formaldehyde resin, sodium silicate, magnesium silicate or combinations thereof.

[0063] The synthetic polymer may be a polyacrylamide resin, polyvinyl alcohol, and / or a phenol-formaldehyde resin, such as resole resin or Novolac resin; the cellulosic material may be cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and / or hydroxyethyl methyl cellulose (MHEC); and / or the polysaccharide may be starch, for example, wheat, maize, barley and potato starch, gum Arabic, guar gum and / orP608393PC00

[0064] xanthan gum. These materials have been found to provide good gel formation and strengthening of the pellet relative to pellet strength in the absence of gel formation.

[0065] Where the binding material comprises a cellulosic material, it is often carboxymethyl cellulose (CMC), cellulosic fibres, hydroxyethyl methyl cellulose (MHEC), or a combination thereof. Where the binding material comprises a cellulosic material, it is often carboxymethyl cellulose (CMC) and / or hydroxyethyl methyl cellulose (MHEC). Where the binding material comprises a cellulosic material, it is often carboxymethyl cellulose (CMC). CMC is advantageous because it can be added in powder form which allows for control of the overall moisture content of the pellet. CMC also has a long shelflife in comparison to other plant derived binding materials. This is because other plant derived binding materials are often more susceptible to microbial attack and so break down more easily. Sometimes the binding material may be hydroxyethyl methyl cellulose (MHEC), which has been found to have particularly good adhesive qualities and helps to enhance the strength of the pellet. However, as MHEC is highly water soluble, this can affect the shelf life of the final pellet, reducing this in comparison to pellets containing CMC.

[0066] Generally, the binding material comprises at least one of CMC, a polysaccharide, polyvinyl alcohol and / or a polyacrylamide resin, as the hydrogel forming binding material. More than one of CMC, a polysaccharide, polyvinyl alcohol and a polyacrylamide resin may be present in combination with one another, or with other binding materials. Often a silicate (for instance a group I or group II silicate, such as sodium silicate), glycerolipids, cellulosic fibres, and / or a phenol formaldehyde resin will be present. Silicates, glycerolipids, cellulosic fibres, and phenol formaldehyde resins do not generally form hydrogels. The binder may therefore comprise a combination of a) one or more of CMC, a polysaccharide, polyvinyl alcohol and a polyacrylamide resin and b) one or more of a silicate (such as a group I or group II silicate), a glycerolipid, cellulosic fibres, and a phenol formaldehyde resin. The binder may comprise a combination of a) one or more of CMC, polyvinyl alcohol and a polyacrylamide resin and b) one or more of a silicate and a phenol formaldehyde resin. It may be that the binder consists essentially of the components listed in a) and b) above.

[0067] Often, CMC may be used as a binding material instead of, or in addition to, other binding materials, such that the binder may comprise about 10 wt% to about 100 wt%, often about 20 wt% to about 90 wt% or about 50 wt% to about 75 wt% CMC. Where the binder comprises CMC as a binding material, the binder is typically added in the range of about 0.01 wt% to about 3.5 wt% of the pellet, often about 0.1 wt% to about 3.0 wt%P608393PC00

[0068] of the pellet, often about 0.15 wt% to about 2.5 wt% of the pellet, often about 0.25 wt% to about 1 wt%. At these levels the binder offers good strengthening of the pellets.

[0069] Typically, the CMC has an active polymer content of about 40% to about 90% and a pH in the range of about 5 to about 9, or about 6 to about 8 when in solution. Further, the CMC will often be of molecular weight in the range of from about 3,000 to about 70,000. Optionally, the CMC will be of molecular weight in the range of from about 10,000 to about 50,000. Without being bound by theory, it is believed that, with lower molecular weights of CMC, for instance in the range about 10,000 to about 50,000, it is possible to prepare a binding material solution of high concentration, which in turn can improve the strength of the pellets.

[0070] Polyvinyl alcohol may be used as a binding material instead of or in addition to other binding materials. It may be the case that polyvinyl alcohol is used as a binding material together with a synthetic organic resin. The binder may comprise about 10 wt% to about 100 wt%, often about 20 wt% to about 90 wt% or about 50 wt% to about 75 wt% polyvinyl alcohol. Where the binder comprises polyvinyl alcohol as a binding material, the binder is typically present in the range of about 0.01 wt% to about 2.0 wt% of the pellet, often about 0.05 wt% to 1.5 wt% of the pellet, or about 0.07 wt% to about 1 wt% of the pellet. Without being bound by theory, the polyvinyl alcohol is believed to provide good mixing of components and high strength as the polymer network formed by polyvinyl alcohol is strong. Further, the process of pelleting with polyvinyl alcohol excludes air from the particulate substrate, which may reduce oxidation where the particulate substrate is metal. Metal oxidation is undesirable for the simple reason that it reduces the amount of the metal (e.g. metallic iron) available for processing by the end user.

[0071] Polyvinyl alcohol is typically commercially formed from polyvinyl acetate by replacing the acetic acid radical of an acetate with a hydroxyl radical by reacting the polyvinyl acetate with sodium hydroxide by saponification. Partially saponified means that some of the acetate groups have been replaced by hydroxyl groups thereby forming at least a partially saponified polyvinyl alcohol residue. Typically, the polyvinyl alcohol has a degree of saponification of at least about 80%, typically at least about 85%, at least about 90%, at least about 95%, at least about 99% or about 100% saponification. Typically, it is utilised as a solution in water. The polyvinyl alcohol may be modified to include, for example, a sodium hydroxide content. Typically, the polyvinyl alcohol binding material has an active polymer content of about 12% to about 13% and a pH in the range of about 4 to about 7 when in solution. Further, the polyvinyl alcohol will often be of molecular weight in the range of from about 15,000 to about 150,000. Optionally,P608393PC00

[0072] the polyvinyl alcohol will often be of molecular weight in the range of from about 30,000 to about 120,000. Without being bound by theory, it is believed that, with lower molecular weights, for instance in the range about 15,000 to about 60,000, it is possible to prepare a binding material solution of high concentration, which in turn can improve the strength of the pellets.

[0073] Where the binding material comprises a polyacrylamide resin, it will often be an anionic polyacrylamide resin of 100,000 to 10,000,000 Da molecular weight with a charge percentage of 25 - 50%. Where the binding material comprises a polyacrylamide resin, it may be added in the range about 0.05 wt% to 0.7 wt%, often about 0.1 wt% to about 0.3 wt%, often about 0.2 wt% to about 0.4 wt%.

[0074] Where the binding material comprises a polysaccharide, this may be starch or amylase starch. For instance, it may be pregelatinised potato starch. It may be added in the amount of about 0.8 wt% of the final pellet, often about 0.6 wt%. The use of a polysaccharide as a component of the binder may be desirable as polysaccharides often also function as thickening agents.

[0075] The inorganic binding material may comprise one or more silicates, (for example, a silicate in the form of its sodium salt), or refractory materials including, but not limited to, oxides, carbides, or nitrides of silicon, aluminium, magnesium, calcium, and zirconium and combinations thereof. For example, the refractory material may comprise alumina, fireclays, bauxite, chromite, dolomite, magnesite, silicon carbide, zirconia, or combinations thereof.

[0076] Often, the inorganic binding material comprises one or more silicates. The inorganic binding material may comprise two to four different silicates, for instance a combination of group I and group II silicates. The one or more silicates are often selected from sodium silicate (NazSiOs), magnesium silicate (MgSiO4), calcium silicate (CaSiOs), alumina silicate and combinations thereof. The one or more silicates may be in liquid form, powder form, or a combination thereof. It may be the case that the inorganic binding material is in powder form as the powder form of the silicate is more concentrated. It may be the case that the binding material comprises an inorganic binding material in combination with a synthetic polymer and / or a cellulosic material. Often, the inorganic binding material (whether alone or in combination with one or more other binding materials) is present in the pellet in the range of from about 0.5 wt% to about 2.5 wt%, often, in the range about 1 wt% to about 2.25 wt%, or about 1.5 wt% to about 2 wt%.P608393PC00

[0077] When silicates are present, and the one or more silicates is in liquid form, it will often be present in greater amounts because there is a lower level of active polymer content in liquid silicates than in powder silicates. Where the one or more silicates is in liquid form, it is often present in the pellet in the range of from about 0.5 wt% to about 6 wt%, often about 1 wt% to about 5 wt%, often 1.25 wt% to 3 wt%, often 1.5 wt% to 2 wt%.

[0078] Where the one or more silicates is in powder form, it is often present in the pellet in the range of from about 0.5 wt% to about 3.5 wt%, often, in the range about 1 wt% to about 3 wt%, or 1.5 wt% to about 2.5 wt%.

[0079] The binder (as used in this context to include the component binding materials) will generally be added in powder form, although pre-solubilised forms (e.g., bound in a liquid suspension) are envisaged. In examples where the binder is added as a powder, water will be present to promote gelation of the binder in situ. Provision of the binder as a powder allows for good control of the overall water content of the pellet relative to liquid addition. Warming the substrate mixture, improves cold strength of the pellet whilst reducing the time needed to achieve an acceptable cold strength, without the need to introduce high levels of heat to cure or dry the gelled substrate mixture. Such advantages may not be present if the binder does not form a hydrogel and instead, for example, takes the form of a film. An example of a situation in which the binder forms a film may be when the amount of water in the mixture is restricted, resulting in less dissolution of the binder in the water, preventing hydrogel formation.

[0080] As noted above, the binder comprises at least one binding material, which will often be hydrogel forming. However, it may be the case that the binder comprises two or more binding materials, one or more of which may be gel forming, although non-hydrogel forming binding materials may also be present. As such, the method of the invention may comprise a first binding material and a second binding material, wherein the first binding material and the second binding material are mixed with the particulate substrate to form the gelled substrate mixture. In this example, the first and second (and optionally further) binding materials are added during the step of mixing the particulate substrate with the binder (in this case comprising two or more binding materials) to form the substrate mixture. Alternatively, the binder may comprise a first binding material and a second binding material, wherein the first binding material is mixed with the particulate substrate and water to form a gelled substrate mixture, and a second binding material is subsequently mixed with the gelled substrate mixture. In this example, it may be the case that the first binding material is gel forming, and the second is non-hydrogel forming. Alternatively, the first binding material may be mixed with the particulate substrate in the absence of water, and a second binding material isP608393PC00

[0081] subsequently added to the mixture in the presence of water to form a gelled substrate mixture. In this example, it may be the case that the first binding material is nonhydrogel forming, and the second is gel forming. There may of course be more than one binding material mixed with the particulate substrate, and more than one binding material mixed with the gel once formed. Both methods have been found to offer strong pellets, obtainable through rapid production techniques.

[0082] It will often be the case that the total binder is added in the amount of about 0.05 wt% to about 7.0 wt% of the pellet. Often in the range about 0.3 wt% to about 6 wt%, often in the range about 0.4 wt% to about 5 wt%, often in the range about 0.8 wt% to about 4 wt%. It has been found that where less than about 0.05 wt% of the binder is present, the structural integrity of the agglomerate is low. Where one or more binding materials present are hydrogel forming, they will often be present (either alone, or in combination with one or more non-hydrogel forming binding materials) in the range about 0.05 wt% to about 1.5 wt% of the pellet. Often, in the range about 0.07 wt% to about 1.0 wt%, or about 0.1 wt% to about 0.9 wt%.

[0083] As described above, the gel may act as a processing aid. However, the method of the invention may optionally further comprise the step of adding a separate processing aid to the substrate mixture. This may be during the mixing of the particulate substrate with the binder and water, or mixing with the gelled substrate mixture (both step c.). The processing aid may include but is not limited to weak solutions of cationic, anionic, or non-ionic polymers, typically acrylic based flocculants, carbon (often in the form of graphite), lubricants, surfactants (such as sodium lauryl sulfate), stearates (such as calcium stearate or sodium stearate), stabilising fibres or combinations thereof. A processing aid can render the overall pelletisation process more efficient, which in turn saves both cost and energy.

[0084] The method of the invention may further comprise the step of adding one or more additional additives to the substrate mixture.

[0085] In a second aspect of the invention there is provided a pellet obtained by the method of the first aspect of the invention, the pellet comprising a particulate substrate selected from a metal ore, metal ore-containing waste, metal fines, iron residue, iron filings, mineral waste, carbonaceous material, arc furnace waste or combinations thereof and a binder.

[0086] Typically pellets according to the second aspect of the invention have an average volume in the range 2.5 cm3to 15 cm3, often in the range 3 cm3to 12 cm3, or 7 cm3to 11 cm3.P608393PC00

[0087] The pellets will generally be sized to minimise surface area, and will often be, for instance, roughly spherical, ovoid, cylindrical or cubic structures.

[0088] Unless otherwise stated, each of the integers described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art.

[0089] As used herein and in the accompanying claims, unless the context requires otherwise, "comprise" or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. The term "consist(s) / (ing) essentially of", with respect to the components of a composition or mixture, means the composition or mixture contains the indicated components and may contain minor additional components in an amount less than 1 wt% based on the total weight of the composition or mixture, provided that the additional components do not substantially alter the reactivity of the composition or mixture.

[0090] In addition, unless otherwise stated, all numerical values appearing in this application are to be understood as being modified by the term "about". As used herein, the term "about" means that the stated value can vary by ± 10%. For example, about 90 wt% means 90±9 wt%, and about 0.1 wt% means 0.1±0.01 wt%. When used with reference to a range, the term "about" applies to all values in the range.

[0091] Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said parameter, lying between the smaller and greater of the alternatives, is itself also disclosed as a possible value for the parameter.

[0092] In order that the invention may be more readily understood, it will be described further with reference to the specific examples hereinafter.

[0093] Examples

[0094] The examples described below illustrate how the use of thermally induced gelation (TIG) in the production of pellets improves the Tumble Index (TI), Abrasion Index (Al) and Reduction Disintegration Index (RDI) of the formed pellets.P608393PC00

[0095] Materials

[0096] The iron ore substrate used was a Scandinavian magnetite, comprising 99% w / w magnetite (FesC ) with a 71.5% w / w Fe content. The ore was dried completely before mixing with 4.0% w / w water and the binder.

[0097] The binder comprised two binding materials, 2.0% w / w sodium silicate (NazSiCh) and 0.5% w / w carboxy methyl cellulose (CMC). All percentages are by weight of the iron ore substrate.

[0098] Experimental Procedure

[0099] The dried iron ore substrate was heated to above the desired testing temperature and then allowed to cool to that temperature (i.e. 40°C or 60°C or 80°C or 100°C). This enabled the provision of the particulate substrate (the ore) at a controlled temperature. No additional heat or temperature regulation was applied, until the pellets were cured. Once the iron ore substrate achieved the desired testing temperature, it was placed in an Eirich ELIO Mixer, comprising a rotor and counter-rotating bowl. The binding materials and water were then added with mixing. Mixing was carried out with the rotor set to 300rpm and the counter-rotating bowl on setting 1. The mixing time was 3 minutes. Neither the water nor the binding materials were heated prior to mixing.

[0100] Once mixing was complete, the moisture content of the gelled substrate mixture was checked, and, if necessary, adjusted to be between 3.5 - 4.5 % w / w, just prior to feeding this mixture into a pocketed Sahut-Conreur 150 / 40 Lab Roller Press. The feed screw speed was maintained in the range of 20 - 50 rpm. The roller speed was maintained in the range of 2 - 5 rpm. The hydraulic pressure on the rollers was maintained at 180 bar; delivering 12.7 kN / cm of linear force.

[0101] Green pellets were collected, and gently hand screened on a 10 mm screen to remove compacted material at the edges of the pellets. After this the pellets were cured in a fan assisted oven at various temperatures and time intervals according to the examples given below.

[0102] Once cured, the pellets were tested for Tumble Index (TI), Abrasion Index (Al) and Reduction Disintegration Index (RDI) for selected runs.

[0103] Tumble Index (TI) and Abrasion Index (Al)

[0104] The Tumble Index (TI) and Abrasion Index (Al) were tested in accordance with ISO3271 (modified to use 500g of pellets), using an RB Automazion TB7000.P608393PC00

[0105] Reduction Disintegration Index Tests (RDI)

[0106] The thermal properties of pellets were tested by determining their reduction disintegration index (RDI) according to the standard ISO 4696-2:2015. In this test pellets were subjected to a reducing environment at 550°C, followed by a tumble test to measure the amount of disintegration following reduction. These conditions resemble those of the low-temperature reduction zone in an ironmaking blast furnace, used in the integrated route to steelmaking.

[0107] Test Data

[0108]

[0109] P608393PC00

[0110]

[0111] Effect of heating the particulate substrate

[0112] In Examples 1 and 14 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder as described above, formation of the gelled substrate mixture and curing. The pellet curing was for 2 hours at 60°C. Comparative Example 2 then replicates Examples 1 and 14, with the exception that the iron ore substrate is provided at ambient temperature.

[0113]

[0114] As can be seen from the data above, where the iron ore is not provided "warm", in this case at 60°C, the pellet performance decreases with the TI in Comparative Example 2 dropping to undesirable levels (less than 85%). Additionally, both the Al and RDI increased to greater than 15% which is also undesirable. The Al and RDI parameters are particularly indicative of pellet performance in a blast furnace, as they show the degree to which the pellet can remain intact both when tumbled cold (Al), and after 30 minutes under a reductive gas atmosphere at 550°C, being allowed to cool, and then tumbled cold (RDI). The lower these figures are the better the pellet quality.

[0115] In Example 8 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder as described above, formation of the gelled substrate mixture andP608393PC00

[0116] curing. The pellet curing was for 2 hours at 150°C. Comparative Example 13 then replicates Example 8, with the exception that the iron ore substrate is provided at ambient temperature.

[0117]

[0118] This comparison confirms the findings of the comparison with curing at 60°C above, illustrating that where the iron ore is not provided "warm", in this case at 60°C, the pellet performance decreases with the TI in Comparative Example 13 dropping to undesirable levels. Additionally, the Al increased to greater than 15% which is also undesirable.

[0119] Effect of substrate temperature

[0120] In Examples 1 and 14 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder and formation of the gelled substrate mixture. Subsequent pellet curing was for 2 hours at 60°C. In Example 3, the test of Examples 1 and 14 is repeated with the provision of the substrate at a test temperature of 80°C and in Example 4, the test of Examples 1 and 14 is repeated with the provision of the substrate at a test temperature of 100°C.

[0121]

[0122] P608393PC00

[0123]

[0124] As can be seen from the temperature comparisons above, the provision of the particulate substrate at temperatures of 60°C, 80°C or 100°C can provide for excellent quality pellets, fulfilling the requirements for each of TI (more than 85%,), Al (less than 15%) and (where measured) RDI (also less than 15%). However, Example 7 indicates that under curing conditions of 40°C over 24 hours, providing the particulate substrate at 100°C is detrimental to pellet strength, such that temperatures lower than 100°C may be more desirable.

[0125] Effect of curing temperature

[0126] In Examples 1 and 14 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder, formation of the gelled substrate mixture and curing. The pellet curing was for 2 hours at 60°C. In Example 8, the test of Examples 1 and 14 is repeated with pellet curing at 150°C.

[0127]

[0128] As can be seen from the data above, each of Examples 1, 14 and 8 provide pellets within desirable test parameters (TI more than 85%, and Al and RDI less than 15%). Without being constrained by theory, it is believed that heating during curing drives the binder reaction to further completion, improving pellet properties. Further, the comparison between Example 1 and Example 8 illustrates the benefits of curing at a temperature higher than the temperature at which the iron ore substrate was provided.

[0129] Effect of cooling between mixing and pellet formation

[0130] In Example 5 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder, formation of the gelled substrate mixture and pellet curing for 24 hours at 40°C. In Example 9, the test of Example 5 is repeated with cooling of the gelledP608393PC00

[0131] substrate mixture to ambient temperature after formation, and subsequent heating to the curing temperature of 40°C.

[0132]

[0133] It can be seen from a comparison of Examples 5 and 9 that allowing the gelled substrate mixture to cool prior to pelletisation, such that the temperature of the process is not maintained above ambient, produces pellets of a lower TI, higher Al and higher RDI than where pelletisation is carried out prior to cooling. Each of these test results fall outside of desired parameters for Example 9.

[0134] Effect of inducing gelation by heating the particulate substrate, relative to pressing or chemical gelation

[0135] In Examples 1 and 14 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder and formation of the gelled substrate mixture. Pellet curing was for 2 hours at 60°C.

[0136] This Example was compared with Comparative Example 10 and Comparative Example 11 which each relate to pellets produced by pellet formation methods which include a gel formation step, but not thermally induced gelation as a result of the provision of a warm particulate substrate. Specifically, Comparative Example 10 relates to an adaptation of the methodology of Examples 1 and 14 where instead of providing a warm particulate substrate, such that the particulate substrate is mixed with the binder and water at a temperature greater than 30°C, gelation is induced by mechanical pressure, achieved by compressing the particulate substrate, binder and water mixture between a pair of flat rather than pocketed wheels on the Sahut-Conreur 150 / 40 Lab Roller Press. Comparative Example 11 is an alternative adaptation of the methodology of Examples 1 and 14, where gelation is induced chemically by mixing the particulate substrate, binder and water together and then allowing that mixture to stand for a 60 minute period, and there is no warming of the substrate prior to mixing.P608393PC00

[0137]

[0138] As can be seen from the above, Comparative Examples 10 and 11, similarly to Examples 1 and 14, provide a pellet with excellent strength (TI, Al and RDI) properties. However, unlike Comparative Examples 10 and 11, the pellets could be formed quickly, as curing occurred at low temperatures for all three examples (60°C for Examples 1 and 14, and 40°C for Comparative Examples 10 and 11), yet after only two hours, the pellets of Examples 1 and 14 had attained the properties desired for transport and use. To achieve similar properties each of Comparative Examples 10 and 11 required curing for 24 hours, and it is noted that even after this time, Comparative Example 11 does not quite achieve the TI of greater than 85% and Al of less than 15% desired. As such, whilst being sufficiently strong and hardwearing for most applications, the pellets of Comparative Example 11, are slightly inferior to those of Example 1, despite the much longer curing (and so manufacture) time.

[0139] Effect of inducing gelation by combined methods

[0140] In Example 5 the iron ore substrate is provided at a test temperature of 60°C, prior to mixing with the binder and formation of the gelled substrate mixture. Pellet curing was for 24 hours at 40°C. Example 12 replicates Example 5, with the additional step of applying mechanical pressure by compressing the particulate substrate, binder and water mixture between a pair of flat rather than pocketed wheels on the Sahut-Conreur 150 / 40 Lab Roller Press.

[0141]

[0142] P608393PC00

[0143] As can be seen from a comparison of Example 5 and Example 12, both pellets meet the strength requirements for a pellet of this type, and as such the additional step of applying pressure to the pellets, as in Example 12, is arguably undesirable as it increased manufacturing complexity and machinery costs unnecessarily.

[0144] It would be appreciated that the method and pellet of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.

Claims

P608393PC00Claims1. A method of producing a pellet, the method comprising the steps of:a. providing a particulate substrate at a temperature in the range 30°C - 90°C, wherein the particulate substrate is selected from a metal ore, metal ore- containing waste, metal fines, iron residue, iron filings, mineral waste, carbonaceous material, arc furnace waste or combinations thereof;b. mixing the particulate substrate with a binder and water to form a gelled substrate mixture;c. forming a pellet from the gelled substrate mixture; andd. curing the pellet.

2. A method according to claim 1, wherein the particulate substrate is provided at a temperature in the range 40°C - 80°C.

3. A method according to claim 1 or claim 2, wherein the curing of the pellet comprises heating, wherein heating is to a temperature in the range 30°C - 200°C.

4. A method according to any preceding claim, wherein curing of the pellet comprises heating, wherein the pellet is heated during curing to a temperature greater than the temperature at which the particulate substrate is provided.

5. A method according to any preceding claim, wherein steps a. to d. all occur at a temperature of 30°C or greater.

6. A method according to claim 7, wherein heat is applied during each of steps a., c. and d.

7. A method according to claim 5 or claim 6, wherein the forming of the pellet is completed within 15 minutes of the mixing of the particulate substrate.

8. A method according to any preceding claim, wherein curing the pellet comprises curing for a time period in the range 0.25 - 4 hours.

9. A method according to any preceding claim, wherein the particulate substrate comprises a metal.

10. A method according to claim 9, wherein the particulate substrate comprises iron.

11. A method according to claim 9 or claim 10, wherein the particulate substrate comprises a metal ore.P608393PC0012. A method according to any preceding claim, wherein the binder comprises at least one binding material selected from a natural polymer, a synthetic polymer, a cellulosic material, a glycerolipid, a polysaccharide, an inorganic binding material or combinations thereof.

13. A method according to claim 12, wherein the binding material is selected from cellulosic fibres, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), polyvinyl alcohol, a polyacrylamide resin, a phenol formaldehyde resin, a glycerolipid, a polyacrylic, a styrene-acrylate copolymer, one or more silicates or combinations thereof.

14. A method according to claim 12 or claim 13, wherein the binding material is selected from polyvinyl alcohol, a polyacrylamide resin, a phenol formaldehyde resin, carboxymethyl cellulose (CMC), sodium silicate, magnesium silicate or combinations thereof.

15. A method according to any preceding claim, wherein the binder comprises two or more binding materials.

16. A method according to any of claims 12 to 15, wherein at least one binding material is hydrogel forming.

17. A method according to any of claims 12 to 16, wherein the binder comprises a combination of a) one or more of carboxymethyl cellulose, cellulosic fibres, polyvinyl alcohol and polyacrylamide resin and b) one or more of a silicate and phenol formaldehyde resin.

18. A method according to any of claims 12 to 17, wherein the binder comprises a first binding material and a second binding material, wherein the first binding material is mixed with the particulate substrate and water to form a gelled substrate mixture, and a second binding material is subsequently mixed with the gelled substrate mixture.

19. A method according to any preceding claim, wherein the binder is present in the amount of about 0.05 wt% to about 6.0 wt% of the pellet.

20. A method according to any preceding claim, further comprising the step of adding a separate processing aid to the substrate mixture.

21. A pellet obtained by the method of any preceding claim, comprising a particulate substrate selected from a metal ore, metal ore-containing waste, metal fines, ironP608393PC00residue, iron filings, mineral waste, carbonaceous material, arc furnace waste or combinations thereof and a binder.

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