Process and system

Abstract

A process for producing a supplementary cementitious material (SCM), comprising the steps of (i) providing a calciferous feedstock, (ii) subjecting the feedstock to size reduction under phase transition conditions 102 to produce a particulate material, (iii) reacting the material 109 to produce a crude product, and (iv) processing the crude product 111 to give SCM 114. Step (ii) may comprise atomisation or granulation, (iii) may comprise carbonation and (iv) may comprise thickening, dewatering, and / or drying. A system for carrying out the process, and a SCM produced by the process are defined. An atomisation process wherein molten calciferous feedstock is atomised and rapidly quenched to provide a particulate material, and the particulate product produced by the process are defined. A process for carbonising a calciferous feedstock slurry, wherein the slurry is treated using counter-current flow of CO2 rich gas through multiple parallel reactor tanks, and the system for carrying out the process are defined. A process for drying a product using heat recovery from an atomisation process, and a process for producing a SCM comprising carbonating molten slag calciferous feedstock, wherein machine learning is applied with sample analysis to determine the SCM composition and to control the reaction conditions are specified.

Description

TECHNICAL FIELD The present invention concerns processes for producing a supplementary cementitious material, and associated systems and process therefor. BACKGROUND Carbon capture is the process by which carbon dioxide gas (COj) from a range of sources, whether it be industry or the atmosphere is separated, treated, and transported to a long-term storage location. The aim of carbon capture technology is to reduce greenhouse gas emissions and thus mitigate climate change and its effects. CO? captured can be stored in different ways, for example in deep geological formations or as mineral carbonates. Carbon capture has the potential to achieve 14% of the global greenhouse gas emissions reductions needed by 2050 and is widely viewed as the only practical way to achieve decarbonization in the industrial sector, particularly in heavy industry. Amidst a global drive to reduce carbon emissions, heavy industries, such as steelmaking and cement production, aim to decarbonise as fast as possible. Concurrently, the demand for products of such industries, such as steel and cement, is expected to increase. Thus, methods for decarbonising such heavy industry are urgently needed. According to the World Steel Association, every tonne of steel produced emits on average 1.85 tonnes of CO?, equating overaii to about 8% of global CO? emissions. The transition to net-zero production methods in this highly carbon intensive industry requires large capital Investment. Additionally, waste materials, such as slag, produced from steel production, in themselves pose significant environmental challenges. Currently, low carbon steel is produced by methods that alter the steelmaking process itself. Steel can be produced via two main processes: either using an integrated blast furnace (BF) / basic oxygen furnace (BOF) or an electric arc furnace (EAF). Efforts to decarbonise the industry largely seek to improve the efficiency of these processes, or to use alternate fuel sources, such as biomass or hydrogen, rather than the conventional coal. For example, current efforts include using hydrogen in the direct reduction of iron (DR!) arid increasing the amount of steel recycling using electric arc furnaces. However, these approaches are also challenging. For example, DRI requires orders of magnitude more green hydrogen than is currently produced worldwide, as well as large capital investment. Furthermore, only 2,5% of current, iron ore production is suitable for DRI. Electric arc furnaces may be used for steel recycling, but if the electricity used to power such furnaces is not in itself carbon neutral, no ultimate reduction of the carbon footprint results. The use of EAF for recycling uses less energy than BF-BOF processes because it is not a primary steelmaking process. Despite its advantages, EAF still has a considerable carbon footprint, mainly because they often uses some fossil fuels, such as oxy-fuels, in their heating processes. Additionally, since EAF steelmaking mainly uses recycled materials such as scrap iron and scrap steel, the resulting EAF slag and dust can be toxic. EAF dust frequently contains toxic elements, persistent organic pollutants or dioxins, and is categorized as a hazardous industrial waste. Supplementary cementitious material (SCM) is a material that can be added to concrete mixtures in addition to, or as a partial replacement of, traditional Portland cement or blended cements to improve both fresh and hardened concrete properties. SCMs may be added to alter properties of the overall cement blend, including durability, permeability, pumpability and finishability, mitigating alkali reactivity and the overall hardened properties of concrete through hydraulic or pozzolanic activity (or both). Cement clinker is a solid material produced in the manufacture of Portland cement as an intermediary product. The production of Portland cement clinker is estimated to account for about 5% of the total man-made CO2-emissions. Production of composite cements containing supplementary cementitious materials (SCMs) is seen as a solution for reducing the carbon emissions impact in cement production. However, the cost and availability of high quality SCMs such as granulated blast furnace slag or fly ash are limited. An affordable and reliable replacement of these materials by other cementitious materials is needed. BS EN 197-1 categorises cements into five types based on their composition, these are: CEM I, II, ill, IV and V. Typically in general construction, CEM I, which is pure (100%) Portland cement, and CEM II, which is a mixture of Portland cement and SCMs such as fly ash, ground granulated blast furnace slag (GGBFS) or limestone, up to a maximum additive content of 35% by weight, are mostly used. Ground granulated blast furnace slag (GGBFS) is a cementitious material produced as a by-product from blast-furnaces used to make iron, and is already widely used as a 'green' cement replacement in CEM II, Hi and V cements, but demand for this material far outstrips supply. GGBFS is currently used as a type of SCM to reduce the embedded emissions of a given cement blend. CEM HI cements are specifically focused on mixtures of Portland cement and GGBFS and is further divided into three sub-types; A, B and C, depending on the amount of slag contained within. For example, A contains the least slag at 40% by weight, and C contains the most at 90% by weight. However, in the art, the maximum feasible substitution of Portland cement by steel slag is approximately 20% by weight due to stability challenges observed when higher proportions are used. The heat of hydration is the heat generated when water and Portland cement react. The heat of hydration is most influenced by the proportion of C3S and C2S in the cement, but is also influenced by the water-cement ratio, fineness and curing temperature. As each one of these factors is increased, heat of hydration increases. In large mass concrete structures such as gravity dams, hydration heat is produced significantly faster than it can be dissipated, which can create nigh temperatures in the centre of these large concrete masses that, in turn, may cause undesirable stresses as the concrete cools to ambient temperature. The use of GGBFSs is advantageous due to the lower heat of hydration of these materials, which is favourable in large infrastructure projects. In contrast, normal cement, which has a higher heat of hydration, can result in the internal temperature of the concrete reaching high temperatures. In the future, changes in steel making technique’s are predicted to decrease; the supply of GGBFS, whereas cement demand is predicted to grow. The shift in steel manufacture from blast furnaces and blast oxygen furnaces to direct iron reduction and electric arc furnaces will also contribute to this predicted reduction in GGBFS supply. Under the current EU Emissions Trading System (ETS) allowance, steel producers have a carbon allowance, and their taxes are calculated accordingly. The ETS definition now allows storage of CO2 in existing minerals to count as ETS-compliant. Therefore, storing carbon in ex-situ cement has potential positive tax implications. Whilst it is known that steel slag may be used to produce materials for cement production, these methods are limited to the addition of small quantities of steel slag. These methods also teach that using a higher steel slag proportion in a cement mix results in soundness issues owing to the free lime content. Examples of current processes provided in the art are given below: CN1486951 describes a steel slag cement produced with limestone, clay, sandstone, and steel slag. The steel slag is used as an additive alongside GGBFS in the production of a cement mix, using a maximum of 17% steel slag. KR20110050611 describes an admixture composition for cement to reduce the generation of carbon dioxide. The steel slag is similarly used as an additive alongside GGBFS in the production of a cement mix, using a maximum of 10% steel slag. The physical properties of steel slag may be altered to improve the cementitious nature of the slag and improve the suitability of the material for cement applications. Whilst it is known that the properties of steel slag may be altered through chemical reaction, such as calcination, challenges concerning the free lime content in the slag are the cause of volume instabilities. Examples of current processes provided in the art are given below: CN104556754 describes a method for preparing a low-cost steel slag cement, comprising 5-20% steel slag, using a calcination process to activate the cementitious properties of the slag. EP4157795 describes a process for synthesizing high purity calcium carbonate precipitate from waste or byproducts bearing calcium compounds, including steel slags. The method utilises an extraction solvent to produce a calcium rich solution from the slag calciferous feedstock to which it carries out carbonation to produce the precipitate product. Atomisation is a process for breaking a bulk material in the fluid state down into smaller particles. Whilst it is known that methods of atomisation may be used with slag for the purposes of metal recovery or slag granulation, it is not known to use the process of atomisation to enhance a process including carbon capture or the production of a SCM. Examples of current atomisation processes provided in the art are given below: WO2016197244 describes a process for upgrading titania-rich slags using gas atomisation of a liquid siag to decrease particle size, and processing post atomisation to produce relevant products. AU2015367203 describes a process of atomisation utilising oxygen to atomise liquid slag, to increase the magnetic iron content for the purpose of enhanced metal recovery. None of the above noted prior art provides a process in which waste material from heavy industries, such as steelmaking and cement production, can be upcycled into a supplementary cementitious material, nor a process in which CO? can be captured and removed from the atmosphere in the process. Thus, new carbon capture and storage solutions are needed for the steel and cement industries, preferably those that would allow use of significant quantities of industrial waste from steel and cement production for CO? capture. SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a process for producing a supplementary cementitious material, comprising the steps; i. providing a calciferous feedstock, ii. subjecting the calciferous feedstock to size reduction under phase transition conditions effective to produce a particulate material, ill. reacting the particulate material to produce a crude product, and iv. processing the crude reaction product to give the supplementary cementitious material. The calciferous feedstock used in the process may be a steel slag. Advantageously, a process using such calciferous feedstocks aids in the reduction of carbon emissions. This may be achieved by upcycling waste that otherwise is difficult to recycle, which in turn results in lower handling costs. Particularly, steel slags, which previously could only be recycled as aggregates in road construction or sent to landfill, may now be able to generate revenue and contribute to the circular economy. In preferred embodiments the steel slag calciferous feedstock may be molten slag or remeited air-cooled slag. The steel slag calciferous feedstock may be obtained from an electric arc furnace, a basic oxygen furnace, a blast furnace, or any other conventional steelmaking facility. The use of steel slag calciferous feedstocks from steelmaking facilities in the process is able significantly to reduce the emissions of the steelmaking process. Using molten slag as opposed to solid slag also requires less energy. in embodiments where the calciferous feedstock is a molten steel slag, or rernelted air-cooled slag, the slag temperature may be from about 1000°C to about 2000“C, about 1200°C to about 1800°C, about 1300°C to about 1700°C, about 1400°C to about 1600°C or about 1400’C to about 1500°C. in a preferred embodiment, the temperature of the molten siag may be about 1500°C. The calciferous feedstock is subjected to size reduction to produce a paniculate material. Size reduction may be achieved by atomisation or granulation. In embodiments when size reduction is carried out by atomisation, the process may be carried out by direct mechanical means, or by contacting with a high velocity fluid. Direct mechanical means may be selected from centrifugal atomisation, mechanical disintegration, impact atomisation, or any other conventional direct mechanical atomisation process. In embodiments where the atomisation is carried out by contacting with a high velocity fluid, the high velocity fluid may be selected from water, oil, or a gas, or any compatible mixture thereof. In a preferred embodiment, at least part of the high velocity fluid may be recycled from downstream in the process. For example the fluid may comprise a gas stream, such as recycled off-gas from a downstream carbonation reactor. Consequently, the invention provides a process wherein size reduction is effected by fluid atomisation. In this case the calciferous feedstock is contacted with a fluid, preferably a fluid provided at least in part by a recyclate from the process downstream of the size reduction stage, under conditions effective to comminute; the feedstock. Preferably size reduction may be carried out by atomisation, and the atomisation process may comprise rapidly cooling the calciferous feedstock and concurrently removing heat. Heat may be removed by a working fluid, optionally wherein the working fluid is a processed flue gas recycled from downstream in the process. The heat removed from the cooling of the calciferous feedstock may be recycled and used downstream in the process, for example in drying the supplementary cementitious material product. In such an embodiment, where heat is extracted from the atomiser by using the flue gas flow in the system as a heat transfer fluid, overall process energy efficiency is greatly increased. Alternatively heat extraction or recovery may be achieved using gas, water, or thermal photovoltaics (PV). in preferred embodiments, the particulate material produced by the size reduction step may have increased amorphous content, and / or reduced crystal size. In conventional technology slag is tipped and / or tapped off the furnace and left to cool on the ground, and the resulting mineralogy is not particularly cementitious. In contrast, we find that when quenched rapidly the material undergoes a phase transition and the resulting metastable structure has improved reactivity during the subsequent process steps, in particular step iii). Advantageously, using a size reduction step, such as atomisation, can reduce the energy consumption by up to 94% versus traditional comminution techniques and size reduction of calciferous feedstock slag increases surface area and creates highly reactive minerals. Additionally, rapid quenching of the calciferous feedstock in this manner is able to generate a highly amorphous, hydraulic material, which is more suitable for mineralisation processes than known processes in the art. For example, dry granulation is a known atomisation technique using centrifugal / mechanical atomisation to atomise blast furnace slag, and the size of the resuiting granules is typically 1-2mm. In contrast, the process according to the invention produces particles at least an order of magnitude smaller, thus increasing the reactive surface area and therefore leading to more reactive crystal structures. The size reduction process, such as atomisation, is therefore highly advantageous as it may provide significant energy savings and accelerate chemical processes. The particulate material may comprise particles from about 20 pm to about 3000 pm, from about 20 pm to about 1000 pm, from about 20 pm to about 500 pm, from about 20 pm to about 200 pm, from about 20 pm to about 100 pm, from about 50 pm to about 200 pm, from about 50 pm to about ISO pm, from about 50 pm to about 100 pm, or from about 80 pm to about 100 pm in diameter, in a preferred embodiment, the particulate material may comprise particles of about 100 pm or less in diameter. The person skilled in the art will appreciate that there may be a trade-off between processing a high feedstock throughput and providing a relatively small particle size {which will aid subsequent processing / reaction of the particulate; material). The specific preferred particle size will therefore depend to some extent on the; end application. The process may further comprise an additional step of grinding the particulate material to reduce the average particle size as required, and the additional grinding step may be included at any point after atomisation, such as directly after the atomisation step, or alternatively as a final processing step of the supplementary cementitious material. In some embodiments of the present invention at least one additional grinding step may be included. The particles produced may be fine particles. The particles produced by an additional grinding step may be from about 2 pm to about 20 pm, from about 5 pm to about 10 pm, from about 5 pm to about 15 um, from about 5 pm to about 20 pm, from about 10 pm to about 20 pm or from about 15 pm to about 20 pm in diameter. In a preferred embodiment the particles produced by an additional grinding step may be about 20 pm in diameter, in the form of a fine powder. In preferred embodiments of the present invention, the process may further comprise an additional step of hydrating the particulate material to produce a slurry, and this step may follow the atomisation step ii) and precede the reaction step iii). The slurry produced from the hydration of the particulate material may comprise from about 10% by weight to about 80% by weight, 20% by weight to about 80% by weight, about 30% by weight to about 80% by weight, about 40% by weight to about 80% by weight, about 50% by weight to about 80% by weight, about 60% by weight to about 80% by weight or about 70% by weight to about 80% by weight particulate material, wherein the particulate material is atomised calciferous feedstock (e.g. slag), in a preferred embodiment of the invention, the slurry may comprise greater than about 10% by weight atomised calciferous feedstock. In preferred embodiments of the present invention, in step iii), where the particulate material is reacted to produce a crude product, the particulate material may be subjected to a carbonation reaction under carbonation conditions. In the carbonation reaction, which may also be referred to as a mineralisation reaction, the particulate material may be contacted with a COz-rich gas stream. in some embodiments, the particulate material may only be partially carbonated. Partial carbonation may be favourable in order to achieve optimum SCM performance by leaving some reactive oxides still present in the material. The COz-rich gas stream may be obtained from exhaust gases from the steelmaking process (such as EAF), combustion gases from mill burners, or a high COz-concentration gas source obtained for example from a carbon capture system, or from another industrial process. Preferably, the COz-rich gas stream comprises flue gas from industrial processes, for example flue gas from a steelmaking or milling processes. Additionally, the COz-rich gas stream may include COz-rich off-gas recycled from downstream in the process, for example from a product drying stage. The COz-rich gas stream may comprise from about 5% by weight to about 100% by weight, about 20% by weight to about 80% by weight, about 20% by weight to about 70% by weight, about 30% by weight to about 60% by weight, about 30% by weight to about 50% by weight or about 40'% by weight to about 50% by weight CO?. In a preferred embodiment of the invention, the COz-rich gas stream may comprise’ greater than about 25% by weight COj. In an embodiment where the COz-rich gas stream is from EAF exhaust gas, the stream may comprise about 30% et. COz. In an embodiment where the COz-rich gas stream is from the combustion gases of mill burners, the stream may comprise about 8% by weight CO,-. In an embodiment where the COz-rich gas stream is from pure COz obtained from a carbon capture system, the stream may comprise about 99% by weight COz. In some embodiments, the C02-rich gas stream may be pressurised. In such embodiments the gas stream pressure may be about 2 bar, about 3 bar, about 4 bar, about 5 bar, about 6 bar, about 7 bar, about 10 bar, about 50 bar, or about 100 bar. in a preferred embodiment of the invention, the COj-rich gas stream may be about 5 bar. The reaction in step iii) may be carried out under maintained or enhanced pressure. The reaction pressure may be from about 1 to about 100 bar, from about 1 to about 50 bar, from about 1 to about 10 bar, from about 1 to about 5 bar, from about 2 to about 5 bar, from about 2 to about 4 bar, from about 3 to about 4 bar, or from about 3 to about 5 bar. Upon completion of the reaction, the pressure may be released to initiate product precipitation. The use of a pressure change to facilitate precipitation of carbonate-containing products back into the slag slurry is able to reduce the amount of limestone addition required in a cement biend. The reaction in step iii) may be enhanced through the addition of one or more catalysts. Exemplary catalysts may include biocatalysts such as enzymes. In some embodiments, product precipitation may be enhanced further. Product precipitation may be enhanced by adding calcium to increase the precipitation of carbonates, particularly CaCOj, or by heating the reaction mixture. Advantageously, using a CO2-rich gas stream to effect conversion of the particulate material to produce a crude product is able to facilitate the carbonation of free lime in the calciferous feedstock. Free lime can be a problem when calciferous feedstock such as slag is added directly to cement blends in aggregate form, as it can result in volume instabilities overtime, in turn, by altering the mineralogy of the calciferous feedstock, the process of the invention greatly increases the quantity of calciferous feedstock, such as steel slags, that may be added to a cement mix, including up to levels comparable with GGBFS. Additionally, conventional processes in the art make no use of the high-pressure gas, nor of its potential energy after use, wasting significant amounts of energy. In contrast, in the present invention, the pressurised CO? from the carbonation reaction, vented from the reactor, may be used as a working fluid in the heat recovery process, providing greater energy efficiency to the overall process. In preferred embodiments, in step iii), the reaction of the particulate matter may take place in at least one reactor tank, or in at least two reactor tanks, in parallel or in series. In a most preferred embodiment, the reaction of the particulate matter may take place in six reactor tanks in parallel or in series, and provided with a gas contraflow system. Use of multiple batch reactors connected together in this manner may allow for continuous processing of calciferous feedstocks, such as slags, and CO2 containing gas. Advantageously, the use of multiple batch reactors achieves high CO3 capture efficiencies from industrial flue gases. In preferred embodiments of the present invention, the step comprising processing the crude reaction product to give the supplementary cementitious material (step iv) may comprise the following steps; a) thickening b) dewatering, and / or c) drying. in the thickening process, the water content may be reduced using a settling tank. The water removed in the thickening step may be recycled to the particulate hydration step (when present). In the thickening step, the water content may be reduced from at least about 90% by weight to about 50% by weight or less, for example from at least about 90% by weight to about 40% by weight or less. Advantageously, a thickening step increases the amount of time available for carbonate precipitation to occur, increasing the amount of carbon-containing product obtained, and thus contributing to carbon capture. In the dewatering process, the water removed in the dewatering step may be recycled to the particulate hydration step (when present). In the dewatering step, the water content may be reduced from at least about 90% by weight to about 60% by weight or less, from at least about 90% by weight to about 50% by weight or less, from at least about 90% by weight to about 40% by weight or less, from at least about 90% by weight to about 30% by weight or less, or from at least about 90% by weight to about 20% by weight or less. In a preferred embodiment, the water content may be reduced to at least about 30% wt or less. In the drying process, the drying may be supplemented by heat recovered from the atomisation process, in such embodiments, the hot air and flue gas stream from the atomiser may provide from about 0% to about 100%, from about 10% to about 100%, from about 20% to about 80%, from about 30% to about 70%, from about 40% to about 70%, from about 40% to about 60% of the energy required for the drying process. In a preferred embodiment, the recycled heat provides a t least about 50% of the energy required for the drying process. The heat may be recovered from the atomisation process in the form of a high temperature air stream. The temperature of the high temperature airstream may be from about 200°C to about 500°C, from about 250°C to about 400°C, from about 275°C to about 400°C, from about 250°C to about 300X, from about 300X to about 400°C or from about 350”C to about 400°C. In some embodiments the temperature may be at least 250°C, at least 275°C, at least 300%, at least 350°C or at least 400°C. In the drying step, when present, the amount of water in the processed material may be further reduced by at least about 60% by weight, by at least about 50% by weight, by at least about 40% by weight, by at least about 30% by weight, by at least about 20% by weight, by at least about 10% by weight, by at least about 5% by weight, by at least about 2% by weight, by at least about 1% wt As a result, the amount of water present in the processed material after the drying step may be up to about 2% by weight or less, up to about 1.5% by weight or less, up to about 0.75% by weight or less, up to about 0.5% by weight or less, up to about 0.25% by weight or less, for example up to about 0% by weight. In a preferred embodiment of the present invention the moisture content of the processed material may be reduced to less than about 1% by weight water. Advantageously, the drying step results in additional precipitation of carbonates, increasing the amount of carbon-containing product obtained, and thus contributing to carbon capture. The reaction of the particulate matter in step iii) may be monitored and controlled by a reaction monitoring system and said system may collect data, such as spectroscopic, micrographic, thermal or diffractive data. The composition of the calciferous feedstock, and in particular steel slag when such is used as the feedstock or as part of it, can vary significantly (e.g., from steelworks to steelworks), so the reaction conditions need to be adaptable. Therefore, in some embodiments of the present invention, the data collected from the reaction monitoring system may be analysed by machine learning techniques to control the reaction conditions. The machine learning techniques may be applied in combination with sample analysis, such as X-ray diffraction and X-ray fluorescence. Advantageously, by monitoring and controlling the calciferous feedstock, atomisation process, reaction conditions, and further processing steps, a more consistent supplementary cementitious product can be produced, with properties tailored to the desired end application. In some embodiments according to the first aspect, the process may be powered using renewable energy. According to a second aspect of the present invention, there is provided a system for carrying out the process according to the first aspect of the invention, comprising an atomiser, and at least one reactor tank. The system may further comprise a slag crucible, a grinding mill, a compressor, a reaction monitoring system, a settling tank, dewatering press, and / or a dryer. The system may comprise multiple reactor tanks in parallel or in series with one another. The tanks may be configured to enable contraflow contacting of the COz-rich gas with the particulate material. The reaction monitoring system (when present) may use machine learning to control the conditions of the reactor tank. Advantageously, the system of multiple batch reactors may achieve highetr CO2 capture efficiencies from industrial flue gases than conventional systems. This is partly as a result of the ability to use the reactors in contraflow, whereby the CO2-rich gas is flowed from one reactor tank to the next, ensuring a high reaction rate in each reactor tank. Additionally, the use of high-pressure carbonation exhaust gas in each reactor tank improves energy efficiency of the overall process. The system is able to facilitate the capture of a significant amount of CO2 through the carbonation of calciferous feedstocks, such as slag, and the amount of CO2 captured can be monetised which favourably helps offset the overall processing costs, allowing for similar margins to GGBFS production. According to a third aspect of the present invention, there is provided a supplementary cementitious material produced according to the process according to the first aspect of the invention. Preferably, the supplementary cementitious material product may have a fret; lime content of about 6% by weight or less, about 5% by weight or less, about 4% by weight or less, about 3% by weight or less, about 2% by weight or less, or about 1% by weight or less. In a most preferred embodiment, the supplementary cementitious material product may have a free lime content of less than about 4% by weight Advantageously a material in which the free lime content is reduced to these levels does not exhibit latent soundness issues. The supplementary cementitious material may be used to produce a blend with cement, which may be used in the production of concrete. Advantageously, the supplementary cementitious material product significantly reduces the embedded emissions of cement production, by removing CO2 from the atmosphere through the storage of carbon in the form of a useful end product, and a reduction in the amount of emissions produced in other industry,, such as the amount of emissions produced during the clinkering of Portland cement. According to a fourth aspect of the present invention, there is provided an atomisation process for converting a calciferous feedstock to a particulate material, wherein the calciferous feedstock is atomised and rapidly quenched to provide the particulate material. By "rapidly quenched", we mean for preference that the calciferous feedstock is simultaneously cooled and comminuted under conditions effective to generate an at least partly amorphous, preferably at least 50% by weight amorphous, particulate material. The calciferous feedstock used in the atomisation process, may be a molten calciferous feedstock, as previously described. In preferred embodiments according to this aspect, the calciferous feedstock may be steel slag. The atomisation process may use an atomiser. The atomiser may be a rotary disk or cup atomiser, an electrostatic atomiser, an ultrasonic atomiser, or any other conventional atomiser known in the art. Preferably, the atomiser may be a rotary disk atomiser. The atomised calciferous feedstock may be rapidly quenched with a stream of air. The stream of air may be a high energy air, which preferably may comprise; recycled flue gas. An off-gas may be produced from the atomisation process. The off-gas may be a high-temperature off-gas, and this may be used in a heat recovery process. Recovering energy in this manner is advantageous as it greatly improves the overall process energy efficiency. Alternatively, heat extraction or recovery may be achieved using other working fluids, or by thermal photovoltaics (PV). The atomisation process may be preferably integrated into a process of carbon capture. According to a fifth aspect of the present invention, there is provided a particulate product produced according to the atomisation process according to the fourth aspect of the invention. The particulate material may comprise particles from about 20 pm to about 3000 pm, from about 20 pm to about 1000 pm, from about 20 pm to about 500 pm, from about 20 pm to about 200 pm, from about 20 pm to about 100 pm, from about 50 pm to about 200 pm, from about 50 pm to about 150 pm, from about 50 pm to about 100 pm, or from about 80 pm to about 100 pm in diameter. In a preferred embodiment, the particulate material may comprise particles of about 100 pm or less in diameter. The particulate material may be amorphous, in a preferred embodiment, the particulate matter will be greater than 50% by weight amorphous. According to a sixth aspect of the present invention, there is provided a process for the carbonation of a calciferous feedstock slurry, wherein the slurry is treated using counter current flow of a COj-rich gas stream through multipie parallel or connected-in-series reactor tanks. The reactor tanks may be batch reactor tanks. The counter current flow of a CO?-rich gas stream through multiple reactor tanks is preferable as it allows for continuous processing of the calciferous feedstock slurry using the gas stream, which achieves high CO?-capture efficiencies and also improves the reaction yields. In some embodiments, the carbon capture efficiency can be even more greatly enhanced, where the CO2-rich gas stream may be flue gas from industrial processes. For example, the flue gas may be from the steelmaking or milling processes. The C02-rich gas stream may also include COj-rich off-gas recycled from downstream in the process, such as the gas vented from the reactor tanks at completion of the reaction. The CO2 rich gas may be first introduced into the reactor tank that is most near to completion and may be sequentially flowed through each subsequent reactor tank, ending in the reactor that is furthest from completion. The calciferous feedstock slurry may be produced from the hydration of particulate matter, for example, the particulate matter may be produced by the atomisation of steel slag. As referenced above, the calciferous feedstock slurry may be partially carbonated, meaning that the carbonation reaction does not proceed to completion. In such embodiments, the calciferous feedstock slurry may be up to about 20% by weight, up to about 30% by weight, up to about 40% by weight, up to about 50% by weight, up to about 60% by weight, up to about 70% by weight, up to about 80% by weight, or up to about 90% by weight carbonated with respect to the total amount of carbonatabie reactants within the material. Upon completion of the reaction, the COj-rich gas stream may be removed, and the pressure may be released to initiate product precipitation. The use of a pressure change to facilitate precipitation of the carbonatecontaining products back into the slag slurry is able to reduce the amount of limestone addition required in a cement blend. Residual CO2 may be vented from the reactor, in the form of an off-gas, and recycled in other processes, and preferably it may be vented from the final reactor in the contraflow system. The slurry in each reactor tank may be recirculated by a slurry pump. According to a seventh aspect of the present invention, there is provided a reactor system for carrying out the process according to the sixth aspect of the invention. The reactor system according to this aspect may comprise multiple parallel or connected-in-series reactor tanks, a gas compressor, and a contraflow system. Each reactor tank may be fitted with a pump to circulate the contents of the tank. The reactor system may also comprise a reaction monitoring system, which may use machine learning to control the conditions of the multiple reactor tanks. According to an eighth aspect of the present invention, there is provided a process for drying a product, wherein the process comprises using heat recovery from an atomisation process. The process may use a high temperature air stream from an atomisation process to dry the product. The high temperature airstream may comprise a mixture of air and flue gas. The high temperature air stream from an atomisation process may provide from about 0% to about 100%, from about 10% to about 100%, from about 20% to about 80%, from about 30% to about 70%, from about 40% to about 70%, from about 40% to about 60% of energy required for the drying process. In a preferred embodiment, the recycled heat provides at least about 50% of the energy required for the drying process. In a preferred embodiment of this aspect, the product may be a supplementary cementitious material. According to a ninth aspect of the present invention, there is provided a process for producing a supplementary cementitious material, the process comprising treating a molten slag calciferous feedstock through a carbonation reaction, wherein machine learning is applied in combination with sample analysis to determine the supplementary cementitious material composition and to control the reaction conditions. For the avoidance of doubt, ail features relating to the first aspect of the present invention may apply, where appropriate, to any of the other aspects of the present invention and vice versa. it will also be apparent to the skilled addressee that the respective steps of providing the calciferous feedstock, subjecting the calciferous feedstock to size reduction, reacting the particulate material, and processing the crude reaction may each be conducted at independently remote locations. It should be apparent that each of the latter aspects of the invention, and each or any of their described variants, may be provided in combination with the first aspect of the invention and each or any of its described variants and / or in combination with any one or more of each other. DETAILED DESCRIPTION Slag is a by-product formed in smelting, welding, and other metallurgical and combustion processes from impurities in the metals or ores being treated. Slag predominantly comprises mixed oxides of elements such as silicon, sulphur, phosphorus, and aluminium; ash; and products formed in their reactions with furnace linings and fluxing substances such as limestone. In pyrometailurgical processes, such as those carried out in the steelmaking process, slag floats on the surface of the molten metal. Variants of siag are often further defined by reference to the type of precursor and / or processing conditions used to produce them, such as blast furnace (BF) slags basic oxygen furnace (BOF) slag, and electric arc furnace (EAF) slag. Lime is an inorganic material composed primarily of calcium oxides and hydroxides, usually calcium oxide and / or calcium hydroxide. In steel slags, a portion of the CaO found in the material may reside as free lime, as opposed to in a crystal phase, such as Ca-silicate. Free lime poses problems for upcycling steel slag waste into concretes, as it causes volume instabilities. This is because the expansion of residual CaO when hydrated results in cracking of the concrete, which can sometimes occur years after pouring and setting. Free lime can act as a useful activator of cementitious phases, but in excess causes the soundness issues mentioned above. Typically, GGBFS will have no more than 4% free lime content. Supplementary cementitious material (SCM) is a material that can be added to concrete mixtures in addition to, or as a partial replacement of, traditional Portland cement or blended cements to improve both fresh and hardened concrete properties. SCMs may be added to alter properties of the overall cement blend, including durability, permeability, pumpability and finishability, mitigating alkali reactivity and the overall hardened properties of concrete through hydraulic or pozzolanic activity (or both). Currently, SCMs have a great variability in their physicochemical properties, which presents a distinct challenge for their application in cement production as this introduces uncertainty in end product strength. Therefore, provision of a consistent SCM, whose production is controllable would be greatly advantageous and would enable increased use of SCMs in cement mixes. Cementitious, or hydraulic, materials such as Portland cement set and harden when they come into contact with water through hydration reaction. Cement hydration is an irreversible chemical reaction resulting in hydrated cement paste, a strong, stiff material. The primary hydration products are calcium silicate hydrate, which provides strength and performance properties in concrete, and calcium hydroxide, which does not contribute to performance and is prone to chemical attack. SCMs may be designed to increase long term strength, as well as increase durability, by reducing permeability. Increased SCM content may also delay set time by slowing the rate of hydration. This is helpful during hot weather but may not be in cooler weather. SCM addition also reduces risk of thermal cracking by lowering peak hydration temperatures. Metal cations may be leached from steel slags, whilst also storing CO2 through the following reactions: CaSiO3 + CO2 ■■> CaCO3 + SiO2 C3(OH)2 + CO2 -» CaCOa + H2O These two carbonation reactions are both naturally occurring in weathering, in processes such as the carbonatesilicate cycle. Carbon mineralization is a versatile and thermodynamically downhill process that can be harnessed for capturing, storing, and utilizing COz to synthesize products with enhanced properties. In a carbonation process, which may also be referred to as a mineralisation process owing to the fact that the metal ions are converted into carbonate minerals, there are usually three distinct reactions necessary. First, the caicium / magnesium-silicates and calciurn / magnesium hydroxides found in the slag need to be dissolved into water. Secondly, CO? is contacted with the water. Thirdly, the products are extracted out of the process to precipitate the calcium and magnesium carbonates. The overall process may be accelerated by increasing the acidity of the water solution. However, a highly acidic environment does not induce precipitation of carbonate minerals which means the equilibrium needs to be adjusted to induce the precipitation. To this end, the CO?, which may be introduced in the form of flue gas, may be introduced at high pressure, preferably in a contraflow manner. Achieving contraflow is more difficult with a slurry, and hence mechanical assistance using a slurry pump may be required to ensure constant movement of the slurry. A number of tanks may be used, for instance four tanks, each at a different state of reaction. The amount of CO? may vary in each tank and the CO? reactant will be moved through the tanks in a continuous system, starting in the reactor tank that is closest to completion, flowing through each tank in order, ending in the reactor tank that is furthest from completion. The compressed CO?-rich gas flows through the reaction tanks sequentially to achieve contraflow contacting. The pressurised gas dissolves CO? into the slurry, leaching the metal cations from the slag and forming carbonates within solution. The tank containing the most reacted slurry is contacted with the most concentrated flue gas to improve reaction rates. Once the contents of a tank has fully leached all of its calcium and magnesium, it is disconnected from the flue gas stream. The fully reacted tank is then depressurised, or placed under vacuum, to initiate, and enhance, the precipitation of carbonates out of solution. The remaining CO? may be subsequently taken out, and recycled to other processes, and the reactor tank may then be depressurised. The pressure change can induce precipitation, which therefore is a batch precipitation process. At the beginning of the; reaction the solution pH may for example be at least approximately neutral. The addition of a calciferous feedstock, such as steel slag, or any other feedstock containing free lime, will increase the pH of the solution. The increase of pH is a result of the hydration of the free lime (CaO), which forms Ca(OH)? and, subsequently, a saturated 'lime solution' comprising Caseations and hydroxyl ions (OH). The pH of the reaction mixture after steel slag addition may be about pH 11, or more, if the reaction mixture is saturated the pH will be approximately 12. (Knapp et al., Environ. Sei. Techno!., 2023, 57, 26, 9854-9864). The high concentrations of hydroxyl ions in the reaction mixture aids the dissolution of CO? into the solution due to the formation of bicarbonate (HCO.f) and carbonate (CO?2-) ions. The availability of hydroxyl ions in pure water is very small as only a small amount of water is dissociated, therefore, the generation of a lime solution from a calciferous feedstock can produce an effective solvent to increase the rate of dissolution and the quantity of CO? that may be dissolved. As a result of the dissolution of CO? and Ca2+, in the reaction mixture, the saturation state of CaCO? (at a given set of reaction conditions) may be increased. CaCO?, which is poorly water soluble, exhibits retrograde solubility and therefore depressurising and heating of the reaction chamber also increases the saturation state of the solution, enabling more metal carbonates to precipitate and significantly increasing the levels of CO2 capture. Additional calcium may then be introduced to increase the solubility of the calcium carbonate products while keeping the pH constant. As used herein, the term "contraflow" is used to refer to a direction which is generally opposite to the direction in which a mixture circulates in a general direction. Thus, a gas introduced in a contraflow manner will flow against the direction of the circulating reaction mixture. Advantageously, a continuous, contraflow capture system for flue gases into a siag slurry as described herein additionally allows for the batch removal of volumes of slag that have fully reacted with CO2 and then accelerates the precipitation of carbonates from solution. The system enables a carbon capture efficiency of greater than 95% from flue gases from steel production. The invention will now be more particularly described with reference to the following examples and figures, iri which; Figure 1 iiiustrat.es a simplified flow diagram of the process according to the present invention. Figure 2 illustrates a detailed process flow diagram of the process in accordance with an embodiment the present invention. Figure 3 illustrates a contraflow contacting reactor system in accordance with an embodiment of the present invention. Figure 4 shows an X-ray diffraction spectra comparing pre- and post-carbonated slag. Referring to Figure 1, there is shown a simplified flow diagram which describes the process according to an embodiment of the present invention, industrial waste material (101), in the form of steel slags is provided to an atomiser (102). The waste material may also be supplemented by additional materials (103), such as silica, metal oxide powders, reductants (such as aluminum or graphite) or oxygen, added to alter and improve the atomisability of the waste material and cementitious properties. The atomization process is rapidly quenched by a stream of air (104) provided to the atomiser. The stream of air may comprise pressurized off-gas from downstream in the process. The particulate product is passed to a grinder (105), with the residual gas stream (106) being removed. The particles subsequently pass from the grinder (105) to a hydration chamber (107), in which they are mixed with water (108) to provide a slurry. The resultant slurry is then passed to mineralization reactor (109), In the mineralization reactor, the slurry is contacted with carbon dioxide (110), which may be in the form of a flue gas. This reaction may be carried out under pressure and produces carbonate products in a carbonation reaction. The reaction may be a fuH carbonation reaction or a partiai carbonation reaction. The off-gas (104) is removed from the reactor and may be recycled to the atomization stage. The resultant slurry is de-watered (ill), with the water effluent (112) being removed. The water effluent (112) may be reused within the process, particularly in the hydration stage. The dewatered slurry passes to a drier (113), in which it is dried to produce the supplementary cementitious material product (114). In the drying stage, heat may be recovered from earlier in the process, such as from the residual gas stream (106) from the atomization process. Referring to Figure 2, there is shown a detailed process flow diagram of the process in accordance with an embodiment the present invention. Molten slag ¢201) is poured into a slag crucible (202), where it is doped with additional material (1), such as silica, metal oxide powders , reductants (such as aluminium or graphite) or oxygen, to improve its cementitious behaviour and atomisability. Doped molten slag (2) is transferred to an atomiser (203), where it is atomized to an atomized powder (4). The atomization process may convert the slag into particles of sizes of approximately 100 pm. The atomised molten liquid is then rapidly quenched by a stream of air (3). The stream of air (3) may comprise recycled flue gas from downstream processes. The hot off-gas (5) from the atomization process is vented and may be used in a downstream heat recovery process. Atomised powder (4) Is transferred to a grinding mill (204) in which it may be ground down to a particle size of approximately 20 pm. The powder is then mixed with water (6) to produce a slurry (7). The slurry (7) may have a weight content of at least 10% slag. The slag slurry (7) is pumped into one of a number of reaction tanks (205). For simplicity, only one is shown here (see Figure 3 for an example of the multi-tank set-up). The slurry (7) contained in the tank is recirculated by a pump (8) and the reaction conditions are monitored by a reaction monitoring system (206). Flue gas (9), comprising CO2, is provided to a gas mixing chamber (207), where it may be mixed with CO2 rich gases from downstream in the process. The mixed flue gas (10) is compressed by a compressor (208) to produce a compressed flue gas (10), which may be at 5 bar. The compressed flue gas (10) is flowed into the reaction tank. In some cases, the compressed flue gas (10) is flowed through multiple reaction tanks sequentially to achieve contraflow contacting, starting with the tank containing the most reacted slurry, and ending in the least. in the reaction tank (205), the pressurised gas dissolves CO2 into the slurry, leaching the metal cations from the slag and forming carbonates within solution, with the reaction progression monitored by the reaction monitoring system (206). Once the contents of a tank have fully leached all of its calcium and magnesium, the tank may be disconnected from the flue gas stream, and the fully reacted tank is then de-pressurised to initiate the precipitation of carbonates out of solution. The vented fluegas (13) that exits the tank is stiii under significant pressure, and to maximise the use of the energy in this pressurised gas stream, it is passed through a venturi (209) that entrains approximately three times as much air (14) into the gas stream while reducing the stream pressure to approximately 1.4 bar. This high mass flow rate of air and flue gas may be used as the stream of air (3) used in the atomiser to quench the molten slag, in doing so this air stream can heating up the process to approximately 350"C. Once fully precipitated, the carbonate slurry (15) is pumped out of the reaction tank (205) and into a settling tank (210), where the water content is reduced to produce a concentrated carbonate slurry (16), for example from approximately 90% by weight to 50% by weight The water extracted from the settling tank (17) is transferred to a water tank (211), from where it can be recycled to the grinding mill (204). The concentrated carbonate slurry (16) is passed to a dewatering press (212), such as a filter press, where the water content is reduced to produce a dewatered carbonate slurry (18), for example from approximately 50% by weight to 25% by weight The water extracted from the press (19) is transferred to a water tank (211), from where it can also be recycled to the grinding mill (204). The dewatered carbonate slurry (18) is then passed into a dryer (213), where the moisture content is reduced to <1% by weight water, to produce the end product of a dry SCM (214). The hot air and flue gas stream (5) from the atomiser can provide, for example 50% of, the energy required for the drying process. Steam (20) produced from the drying process is transferred to a condenser (215) which is cooled by external water-cooling loop (21) and the resuitant condensed water (22) is transferred to water tank (211) from where it can be recycled back into the atomiser. Cleaned flue gas (23), which may comprise unreacted CO2, may also be collected and transferred to gas mixing chamber (207) to be further recycled in the process. The end product of a dry SCM (214) is outputted from the system. Referring to Figure 3, there is shown a contraflow contacting reactor system in accordance with an embodiment of the present invention. The contraflow contacting reactor system comprises a number of different reaction tanks (301-306). Each reaction tank (301-306) is fitted with reaction monitoring equipment (307), which monitor the pressure, pH, temperature and alkalinity conditions of each reactor, and a slurry pump (308), which recirculates the slurry held in each reaction tank. The slag slurry (31) is pumped, by a slurry pump (308) into one of the reaction tanks (301). The other reaction tanks contain a fixed amount of slurry at different levels of progression through the mineralization reaction. CO?-rich flue gas (32) is passed into a compressor (309), where it is compressed to produce a pressurized flue gas stream (33), which may for example be at 5 bar pressure. The compressed flue gas (33) flows through four of the reaction tanks sequentially to achieve contraflow contacting, starting with the most reacted tank (305) and ending at the least reacted tank (302), passing through lines (34, 35 and 36), The vented flue gas (37) that exits the final tank is still under significant pressure and may be used in other processes such as the quenching of molten slag in an atomiser. The pressurized gas dissolves CO? into the slurry, leaching the metal cations from the slag and forming carbonates within solution. By contacting the most reacted slurry with the most concentrated flue gas, reaction rates may be improved. Once the contents of a tank have fully reacted, and has leached all of its calcium and magnesium, for example tank (306), it is disconnected from the flue gas stream, and the tank that is full of fresh slag slurry, for example tank (301), may be connected at the end of the tank cascade. The pressurized flue gas stream (33) supply may then be reconnected to the tank that was next furthest through reacting. The fully reacted tank (306) is then depressurized, initiating the precipitation of carbonates from solution. The product stream (38) is then pumped by a slurry pump (308) to downstream processes, such as a dewatering step (310). Referring to Figure 4, there is shown an X-ray diffraction spectra comparing pre- and post-carbonated slag. Powder X-ray Diffraction (XRD) was conducted prior to the carbonation process and post the carbonation process. The carbonation process alters the slag mineralogy, removing CO? and forming stable CaCOj minerals, permanently locking up CO?. This is demonstrated by the spectrum for the material post-carbonation, which has a clear calcite (CaCOj) peak, in contrast to the pre-carbonation sample, where it is not present. This provides clear evidence that the material has captured CO? in the reaction chamber and has stored it as a stable carbonate mineral. Both materials showed typical peaks for wustite solid solution, derived from the high iron (Fe) content in the slag sample, and also p-C?S, a calcium silicate mineral that has favourable cementitious properties. EXAMPLES Exampie 1 A sample of electric arc furnace (EAF) slag was obtained and analysed to quantify the carbon capture potential of the material and potential of the slag to be upcycled into a valuable supplementary cementitious material (SCM). The sample provided was powdered in a ball mill and melted via alkali fusion with a lithium metaborate and lithium tetraborate flux. The cooled sample formed a metal oxide glass, which was dissolved in a 2.5 % HNO3 solution. Bulk chemistry was then measured by inductively-coupled-plasma mass spectrometry with internal standards. Reproducibility of standards and repeat measurements of the sample was <5%. Powder X-ray Diffraction (XRD) was conducted prior to carbonation experiments and post carbonation experiments (Fig. 4) to assess the mineralogy. Bulk chemistry was also assessed by inductively-coupled-plasma mass spectrometry. Critically, the material post carbonation had a clear calcite (CaCOs) peak, in comparison to the pre-carbonation sample. This provides clear evidence that the material captured CO? in the reaction chamber and stored it as a stable carbonate mineral. Both materials showed typical peaks for wustite solid solution, derived from the high Fe content in the sample, and also P-C2S, a calcium silicate mineral that has cementitious properties. Post carbonation a clear CaCO?, peak was observed in the XRD spectra, proving the material is capable of being used as a calciferous feedstock in mineral carbonation reactions, which capture CO2. Analysis showed that per kg of slag generated, 100g of CO? could be captured and stored in a stable mineral form. Additionally, by converting excess free lime (CaO) in the slag to stable CaCOa via the carbonation process, the material may be sold as SCM. The combined value of the slags use in carbon capture and as an SCM was assessed in a techno-economic assessment and this showed that the slag produced could generate a profit of $56 per tonne processed from tax credits awarded from the inflation reduction act to industrial carbon capture and storage facilities and the sale of an SCM into the cement industry.

Claims

1. A process for producing a supplementary cementitious material, comprising the steps;i. providing a calciferous feedstock,ii. subjecting the calciferous feedstock to size reduction under phase transition conditions to produce a particulate material,iii. reacting the particulate material to produce a crude product, andiv. processing the crude reaction product to give the supplementary cementitious material.

2. The process according Claim 1, wherein the calciferous feedstock comprises slag, optionally steel slag, optionally molten slag or remelted air-cooled slag, optionally obtained from an electric arc furnace, a basic oxygen furnace, and / or a blast furnace.

3. The process according either one of Claims 1 or 2, wherein size reduction of the calciferous feedstock is achieved by atomisation or granulation.4, The process according to Claim 3, wherein the calciferous feedstock atomisation process is carried out by direct mechanical means, or by contacting with a high velocity fluid, optionally wherein the direct mechanical means is selected from centrifugal atomisation, mechanical disintegration, or impact atomisation, or the high velocity fluid is selected from water, oil, or a gas.

5. The process according to Claim 4, wherein the high velocity fluid comprises material recycled from downstream in the process.

6. The process according to either one of Claims 4 or 5, wherein the atomisation process comprises rapidly cooling the calciferous feedstock and concurrently removing heat, optionally wherein the heat is removed by a working fluid, optionally wherein the working fluid is a processed flue gas recycled from downstream in the process, and / or wherein the heat removed from the cooling of the calciferous feedstock is recycled and used downstream in the process.

7. The process according to any one of Claims 1 to 6, wherein the particulate material has increased amorphous content, and / or reduced crystal size.

8. The process according to any one of Claims 1 to 7, wherein the particulate material comprises particles from about 20 pm to about 3000 pm, from about 20 pm to about 1000 pm, from about 20 pm to about 500 pm, from about 20 pm to about 200 pm, from about 20 pm to about 100 pm, from about 50 pm to about 200 pm, from about 50 pm to about 150 pm, from about 50 pm to about 100 pm, or from about 80 pm to about 100 pm in diameter.

9. The process according to any one of Claims 1 to 8, wherein the process further comprises an additional step of grinding the particulate material to reduce the average particle size, wherein the additional grinding step is included at any point after atomisation, optionally wherein at least one additional grinding step is included, optionally wherein the particles produced are fine particles, optionally wherein the particles are from about 2 pm to about 20 pm, from about 5 pm to about 10 pm,, from about 5 pm to about 15 pm, from about 5 pm to about 20 pm, from about 10 pm to about 20 pm, or from about 15 pm to about 20 pm in diameter.

10. The process according to any one of Claims 1 to 9, wherein the process further comprises an additional step of hydrating the particulate material to produce a slurry, wherein this step follows the atomisation step ii) and preceding the reaction step iii).

11. The process according to anyone of Claims 1 to 10, wherein in step iii), the particulate material is subjected to a carbonation reaction, optionally wherein the particulate material is contacted with a COj-rich gas stream, optionally wherein the CO2-rich gas is obtained from exhaust gases from the steelmaking process, combustion gases from mill burners, or pure CO2 obtained from industrial processes such as a carbon capture system, optionally wherein the CO2-rich gas stream includes CO2-rich off-gas recycled from downstream in the process.

12. The process according to Claim 11, wherein the particulate material is only partially carbonated during step iii), and / or wherein the CO2-rich gas stream is pressurised, optionally wherein the CO2 partial pressure is at least about 0.1 bar, at least about 1 bar, at least about 2 bar, at least about 3 bar, at least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 50 bar, or at least about 100 bar.

13. The process according to any one of Claims 1 to 12, wherein the reaction in step iii) is carriedout under pressure, optionally wherein the reaction pressure is from about 1 to about 100 bar, from about 1 to about 50 bar, from about 1 to about 10 bar, from about 1 to about 5 bar, from about 2 to about 5 bar, from about 2 to about 4 bar, from about 3 to about 4 bar, or from about 3 to about 5 bar, optionally wherein upon completion of the reaction, the pressure is released to initiate product precipitation, and / or heated.

14. The process according to anyone of Claims Ito 13, wherein in step iv), processing the reaction product comprises the following steps;a) thickening,b) dewatering, and / or c) drying.

15. The process according to Claim 14 wherein In the thickening step, the water content is reduced from about 90% by weight to about 40% by weight, or from about 90% by weight to about 50% by weight, and / or wherein the water removed in the dewatering step is recycled to the particulate hydration step (when present], optionally wherein the water content is reduced from about 905¾ by weight to about 20% by weight, from about 90% by weight to about 30% by weight, from about 90% by weight to about 40% by weight, from about 90% by weight to about 50% by weight, or from about 90% by weight to about 60% by weight, and / or wherein in the drying step the amount of water is reduced from about 60% by weight to about 0% by weight, from about 50% by weight to about 0% by weight, from about 40% by weight to about 0% by weight, from about 30% by weight to about 0% by weight, from about 20% by weight to about 0% by weight, from about 10% by weight to about 0% by weight, from about 5% by weight to about 0% by weight, from about 2% by weight to about 0% by weight, or from about 1% by weight to about 0% by weight16. The process according to any one of Claims 1 to 15, wherein in step iii) the reaction of the particulate matter takes place in at least one reactor tank, optionally at least two reactor tanks in parallel or in series, and / or wherein the reaction of the particulate matter in step iii) is monitored and controlled by a reaction monitoring system, wherein the system collects data, optionally wherein the data collected from the reaction monitoring system is analysed by machine learning techniques to control the reaction conditions, optionally wherein the machine learning is applied in combination with sample analysis.

17. A system for carrying out the process according to any one of Claims 1 to 16, comprising: an atomiser, andat least one reactor tank.

18. The system according to Claim 17, further comprising;a siag crucible,a grinding mill,a compressor,a reaction monitoring system,a settling tank,a dewatering press, and / ora dryer; and / or whereinmultiple reactor tanks are provided in parallel or in series with one another, optionally wherein the tanks are linked to enable contraflow contacting of CO^-rich gas, and / or wherein the reaction monitoring system (when present) uses machine learning to control the conditions of the reactor tank.

19. A supplementary cementitious materia! produced according to the process of any one of Claims 1 to 16.

20. An atomisation process for converting a molten calciferous feedstock to a particulate material, wherein the calciferous feedstock is atomised and rapidly quenched to provide the particulate material.2.

1. A particulate product produced according to the atomisation process according to Claim 21.

22. A process for the carbonation of a calciferous feedstock slurry, wherein the slurry is treated using counter current flow of a CO2 rich gas stream through multiple parallel reactor tanks.2.

3. A reactor system for carrying out the process according to Claim 23.

24. A process for drying a product, wherein the process comprises using heat recovery from an atomisation process.

5. A process for producing a supplementary cementitious material, the process comprising treating a molten slag calciferous feedstock through a carbonation reaction, wherein machine learning is applied in combination with sample analysis to determine the supplementary cementitious material composition and to control the reaction conditions.08 11 24AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:-CLAIMS1. A process for producing a supplementary cementitious material, comprising the steps; i. providing a calciferous feedstock,ii. subjecting the calciferous feedstock to size reduction under phase transition conditions to produce a particulate material,iii. carbonating the particulate material to produce a crude product, andiv. processing the crude reaction product to give the supplementary cementitious material,wherein the calciferous feedstock comprises slag.

2. The process according Claim 1, wherein the calciferous feedstock comprises steel slag, optionally molten slag or remelted air-cooled slag, optionally obtained from an electric arc furnace, and / or a basic oxygen furnace.

3. The process according either one of Claims 1 or 2, wherein the calciferous feedstock is doped with additional material, optionally wherein the additional material is selected from silica, metal oxide powders, reductants or oxygen.

4. The process according to any one of Claims 1 to 3, wherein size reduction of the calciferous feedstock is achieved by atomisation or granulation.

5. The process according to Claim 4, wherein the calciferous feedstock atomisation process is carried out by direct mechanical means, or by contacting with a high velocity fluid, optionally wherein the direct mechanical means is selected from centrifugal atomisation, mechanical disintegration, or impact atomisation, or the high velocity fluid is selected from water, oil, or a gas.

6. The process according to Claim 5, wherein the high velocity fluid comprises material recycled from downstream in the process.

7. The process according to either one of Claims 5 or 6, wherein the atomisation process comprises rapidly cooling the calciferous feedstock and concurrently removing heat, optionally wherein the heat is removed by a working fluid, optionally wherein the working fluid is a processed flue gas recycled from downstream in the process, and / orwherein the heat removed from the cooling of the calciferous feedstock is recycled and used downstream in the process.

8. The process according to any one of Claims 1 to 7, wherein the particulate material has increased amorphous content, and / or reduced crystal size.9.The process according to any one of Claims 1 to 8, wherein the particulate materialcomprises particles from20 pm to50 pm to80 pm to500 pm, from200 pm, from20 pm to20 pm to50 pm to3000 pm, from200 pm, from150 pm, from20 pm to20 pm to50 pm to1000 pm, from100 pm, from100 pm, or from100 pm in diameter.08 11 2410. The process according to any one of Claims 1 to 9, wherein the process further comprises an additional step of grinding the particulate material to reduce the average particle size, wherein the additional grinding step is included at any point after atomisation, to produce fine particles.

11. The process according to Claim 10, wherein the fine particles are from 2 pm to 20 pm, from 5 pm to 10 pm, .from 5 pm to 15 pm, from 5 pm to 20 pm, from 10 pm to 20 pm, or from 15 pm to 20 pm in diameter.

12. The process according to any one of Claims 1 to 11, wherein the process further comprises an additional step of hydrating the particulate material to produce a slurry, wherein this step follows the atomisation step ii) and preceding the reaction step iii).

13. The process according to any one of Claims 1 to 12, wherein in step iii), the particulate material is contacted with a CO2-rich gas stream, optionally wherein the CO2-rich gas is obtained from exhaust gases from the steelmaking process, combustion gases from mill burners, or pure CO2 obtained from industrial processes such as a carbon capture system, optionally wherein the CO2-rich gas stream includes CO2-rich off-gas recycled from downstream in the process.

14. The process according to Claim 13, wherein the particulate material is only partially carbonated during step iii), and / or wherein the CO2-rich gas stream is pressurised, optionally wherein the CO2 partial pressure is at least 0.1 bar, at least 1 bar, at08 11 24least 2 bar, at least 3 bar, at least 4 bar, at least 5 bar, at least 10 bar, at least 50 bar, or at least 100 bar.

15. The process according to any one of Claims 1 to 14, wherein the reaction in step iii) is carried out under pressure, optionally wherein the reaction pressure is from 1 to100 bar, from 1 to 50 bar, from 1 to 10 bar, from 1 to 5 bar, from 2 to 5 bar, from 2 to 4 bar, from 3 to 4 bar, or from 3 to 5 bar, optionally wherein upon completion of the reaction, the pressure is released to initiate product precipitation, and / or heated.

16. The process according to any one of Claims 1 to 15, wherein in step iv), processing the reaction product comprises the following steps;a) thickening,b) dewatering, and / or c) drying.

17. The process according to Claim 16 wherein In the thickening step, the water content is reduced from 90% by weight to 40% by weight, or from 90% by weight to 50% by weight18. The process according to either Claim 16 or Claim 17, wherein the water removed in the dewatering step is recycled to the particulate hydration step (when present), optionally wherein the water content is reduced from 90% by weight to 20% by weight, from 90% by weight to 30% by weight, from 90% by weight to 40% by weight, from 90% by weight to 50% by weight, or from 90% by weight to 60% by weight.

19. The process according to any one of Claims 16 to 18, wherein in the drying step the amount of water is reduced from 60% by weight to 0% by weight, from 50% by weight to 0% by weight, from 40% by weight to 0% by weight, from 30% by weight to 0% by weight, from 20% by weight to 0% by weight, from 10% by weight to weight to 0% by weight, from 0% by weight, or from 5% by weight to 1% by weight to 0% by weight, from 0% by weight 2% by08 11 2420. The process according to any one of Claims 1 to 19, wherein in step iii) the reaction of the particulate matter takes place in at least one reactor tank, optionally at least two reactor tanks in parallel or in series,21. The process according to any one of Claims 1 to 20, wherein the reaction of the particulate matter in step iii) is monitored and controlled by a reaction monitoring system, wherein the system collects data, optionally wherein the data collected from the reaction monitoring system is analysed by machine learning techniques to control the reaction conditions, optionally wherein the machine learning is applied in combination with sample analysis.

22. A system for carrying out the process according to any one of Claims 1 to 21, comprising;an atomiser, andat least one reactor tank.

23. The system according to Claim 22, further comprising;a slag crucible, a grinding mill, a compressor, a reaction monitoring system, a settling tank,a dewatering press, and / or a dryer; and / or whereinmultiple reactor tanks are provided in parallel or in series with one another, optionally wherein the tanks are linked to enable contraflow contacting of CO2-rich gas, and / or wherein the reaction monitoring system (when present) uses machine learning to control the conditions of the reactor tank.

24. A supplementary cementitious material produced according to the process of any one of Claims 1 to 21.

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