A novel SLAG valorisation and modification process

Abstract

The present invention relates to a novel slag valorisation and modification process, more particularly a novel slag valorisation and modification process capable of valorising slag and modifying slag for use in downstream cement and concrete processes.

Description

[0001] A NOVEL SLAG VALORISATION AND MODIFICATION PROCESS

[0002] FIELD OF APPLICATION OF THE INVENTION

[0003] The present invention relates to a novel slag valorisation and modification process, more particularly a novel slag valorisation and modification process capable of valorising slag and modifying slag for use in downstream cement and concrete processes.

[0004] BACKGROUND TO THE INVENTION

[0005] The steel industry is undergoing a transformative shift towards more environmentally acceptable and sustainable production methods, including the adoption of novel routes such as Direct Reduced Iron (DRI) combined with Electric Arc Furnaces (EAF) or Open Bath Furnaces (OBF). While these processes offer environmental benefits and reduce carbon emissions, they also introduce significant challenges associated with the generation and management of the slags from such green processes. These slags, characterised by unique chemical compositions, physical properties, and slag / metal ratios, present both opportunities and obstacles.

[0006] Valorisation of slag refers to the process of converting slag from metallurgical processes, into valuable products rather than treating it as waste. This approach helps in both reducing environmental impact and creating economic benefits. Currently, the valorisation of these new slags remains unexplored and is presently commerciallyunderdeveloped. In general, the smelting industry’s focus has primarily been on slag cleaning furnaces, which are used to recover high-value metal elements from slag. However, this narrow approach fails to address the broader potential of slag, particularly for cementitious applications, where slags could serve as valuable substitutes for traditional materials like clinker in cement production.

[0007] In the current state of the art, the leading green steel decarburising pathways, such as the DRI-EAF and -OBF processes, involve efforts to modify slag compositions directly within the primary production units. This approach, while reducing upfront capital expenditure, introduces several operational drawbacks. For instance, in Open Bath Furnaces (OBF), modifications to slag compositions to attain properties for value addition can adversely affect furnace operation by increasing electrical conductivity, reducing thermal conductivity, and accelerating refractory wear. These issues result in narrow operating envelopes, higher maintenance costs and reduced furnace lifespans.

[0008] Similarly, in EAFs, slag modification within the furnace often complicates operations. The high iron oxide content in EAF slag from operating in a low reducing environment to produce steel leads to the slag being unsuitable for cementations applications. Moreover, the need for operational adjustments, such as changes in temperature control and slag management, adds complexity and reduces furnace efficiency. Existing EAF infrastructure, not initially designed for such modifications, struggles to handle the varying chemical compositions without compromising product quality and operational performance.Environmental concerns further complicate the situation. While steel slags are generally not classified as hazardous, the leaching of heavy metals remains a significant issue, particularly in regions with strict regulatory limits. The reliance on solid-based assessments rather than leachate-based evaluations restricts the use of steel slags, even when their environmental impact is comparable to that of natural minerals. These regulatory challenges, combined with the technical difficulties of reducing heavy metal content in liquid steel slags, limit the potential for these slags to be fully utilised in high-value applications such as cement and concrete production.

[0009] Whilst EP 4417713 A1 addresses the treatment of steel slags through a two-step continuous electric furnace (CEF) process, it primarily focuses on the recovery of iron from slag and the optimisation of energy use within continuous steel production. However, this process fails to describe the potential for valorisation of slag into commercially viable products. In particular, EP 4417713 A1 lacks specific post-taphole slag modification processes, such as the integration of a dedicated slag valorisation furnace, that is designed to handle a diverse range of feed materials, including molten, semi-molten, and solid slags, as well as fine waste streams and sludges.

[0010] Moreover, EP 4417713 A1 does not address the complexities of modem steel production slag compositions, particularly those generated from environmentally acceptable production routes such as DRI-EAF or OBF. EP 4417713 A1 in fact overlooks the operational challenges introduced by attempting to modify slag withinprimary furnaces, such as electrical and thermal conductivity issues and accelerated refractory wear.

[0011] In view of the foregoing, it is clear that the current state of the art in slag management faces significant limitations, including the absence of commercially viable slag valorisation processes, operational challenges in modifying slags within existing furnace infrastructure, and environmental and regulatory barriers. There is a clear and pressing need in the art for a process that can overcome, at least partially, these disadvantages and enable the effective and sustainable use of new steel slags in high-value applications.

[0012] Given the above, it is clear that there exists a present need for a robust, economical, and environmentally acceptable process to valorise slags generated from evolving steel production routes, particularly those slags generated in electric smelting furnaces and other modern steelmaking processes.

[0013] OBJECT OF THE INVENTION

[0014] Accordingly, it is an object of the present invention to provide a process for the valorisation of slag generated by modem steel production processes, particularly slag generated in electric smelting furnaces, by decoupling slag modification from steelmaking and optimising slag for cementitious and other high-value applications.It will be appreciated that reference to “LOI” in the context of the present invention refers to loss on ignition.

[0015] It will be appreciated that reference to “LSF” in the context of the present invention refers to lime saturation factor.

[0016] For purposes of the present invention, the term “iron oxide” denotes any chemical compound composed of iron and oxygen. It will be appreciated that iron oxide covers all forms of iron oxides, including FeO and hematite (Fe2Os).

[0017] SUMMARY OF THE INVENTION

[0018] According to a first aspect of the invention, there is provided a novel slag valorisation and modification process, the process including the steps of:

[0019] i) feeding a feed mixture to a slag valorisation furnace to form a metal product, a conditioned slag with varying composition and off-gas, according to an adjustable feed recipe, wherein the feed mixture includes components selected from the group consisting of molten slag; semi-molten slag; solid raw material feed; and a combination thereof; and

[0020] ii) transferring the conditioned slag to at least one of a granulation system to form a cement replacement product that has a glass content of at least 60% wt., and a clinkering system to form clinker, wherein the clinkering system cools the conditioned slag at a pre-determined cooling rate from 2.5 degrees Celsius perminute up to and including 30 degrees Celsius per minute utilising at least one of heat from the off gas and air, or a combination thereof;

[0021] wherein the adjustable feed recipe comprises controlling (a) the chemical composition of the feed mixture; (b) the temperature of the slag valorisation furnace to be above the liquidus temperature of the conditioned slag up to and including 1850 degrees Celsius; and (c) the residence time of the feed mixture in the slag valorisation furnace from 2 hours up to and including 12 hours;

[0022] to optimise any one or more of the degree of reduction of metal oxides in the feed mixture, metal droplet formation and settling, homogenisation and tapping temperature of the conditioned slag;

[0023] in order to ensure a metal oxide content in the conditioned slag of less than 2% wt.; wherein the conditioned slag has a composition of CaO (25-57% wt.), SiO2 (23-45% wt.), AI2O3 (1-24% wt.) and MgO (1-26% wt.); and

[0024] wherein the CaO, MgO, and SiO2 content in the conditioned slag comprises at least 60% wt. of the sum of CaO, MgO and SiO2 contained in the feed mixture, prior to being transferred to at least one of the granulation system and the clinkering system.

[0025] In an embodiment of the invention, particularly when clinker is to be formed, step (ii) may be preceded by modifying the composition of the conditioned slag by at least one of adding solid raw material feed and further reductant to form a slag product suitable for use as the cement replacement product.

[0026] In terms of the invention, the metal oxide in the conditioned slag of less than 2% wt is FeO.In an embodiment of the invention, the conditioned slag may comprise a composition of CaO (>45% wt.), SiO2(<40% wt.), AI2O3 (<10% wt.), FeO (<7.0% wt.), MgO (<1.5% wt.), SO3 (<1.0% wt.), Na2O (<0.75% wt.), K2O (<1.75% wt.), Cl (<0.05% wt.), and LOI (<0.1% wt.), prior to being transferred to the clinkering system.

[0027] In an embodiment of the invention, the clinker may comprise a composition of CaO (>57% wt.), SiO2(16%<SiO2<30% wt.), AI2O3(3<AI2O3<10% wt.), FeO (<5.0% wt.), MgO (<5% wt.), SO3 (<1.5% wt.), Na2O (<0.4% wt.), K2O (<1.75% wt.), Cl (<0.05% wt.), LOI (<1.0 % wt.), C3S>55%, C2S<20%, C3A>5, C4AF < 15%, and LSF > 90%.

[0028] In an embodiment of the invention, when clinker is formed, at least one of the slag modification step and the addition of further raw material feed in the clinkering system is performed to increase the CaO content of the material entering the clinkering system to a level suitable for clinker production, preferably greater than 57% wt. CaO.

[0029] In an embodiment of the invention, the molten slag originates from a primary reduction process furnace that produces molten iron or steel plant slag. Preferably, the primary reduction process furnace may be an EAF or an OBF.

[0030] It is to be appreciated that the composition of the molten slag and semi-molten slag in the feed mixture is dependent on the variation of the chemical composition of DRI, notably the extent of direct reduction of the DRI, carbon content from the products ofthe EAF or OBF, and the gangue composition fed to the EAF or OBF that produces the molten slag and semi-molten slag.

[0031] It is further to be understood that silicon and / or iron reduction has an effect on SiO2 and FeO concentrations in the molten slag as the EAF or OBF is optimised for a low slag-to-metal ratio. Fluctuations in the carbon balance of the EAF or OBF will inadvertently affect the carbon content of the molten slag, which influences overall process stability and quality.

[0032] Yet, it is further to be understood that by virtue of introducing the novel slag valorisation and modification process into the overall steel-making process, the EAF or OBF can be charged with feed material of lower quality that may comprise one or more low-grade iron-containing materials selected from the group consisting of taconite ores having an Fe content of 20-40% wt.; siderite (FeCO3) ores having an Fe content of 40-58% wt.; limonite (FeO(OH) nH2O) ores having an Fe content of 50-60% wt.; goethite (FeO(OH)) ores having an Fe content of 50-60% wt.; clay-bound hematite ores; pisolitic ironstone ores; bog iron ores; lateritic iron ores; jarosite residues; red mud (bauxite residue) containing residual iron; iron ore tailings and rejects; blast-furnace flue dust; converter and electric-arc-furnace dust; steel-mill sludge and mill scale; pellet-plant return fines; manganese-bearing tailings; siliceous banded iron formations with less than 55% wt. Fe; ferruginous quartzites; ferruginous lateritic saprolites; iron-rich chlorite schists; serpentinised peridotites containing disseminated magnetite; ferruginous kaolinite clays; iron sands with less than 45 % wt. Fe; iron-bearing slags from pyrometallurgical processes; electric-arc furnace slag; moltenslag originating from a primary reduction process furnace producing molten iron or steel-plant slag.

[0033] In an embodiment of the invention, the composition of the conditioned slag or the slag product may be dependent on composition requirements of the at least one of the cement replacement product produced by the granulation system and the clinker produced by the clinkering system, respectively.

[0034] In an embodiment of the invention, the composition of the conditioned slag may be influenced by variation of the composition of the DRI, the extent of direct reduction, carbon content, and gangue composition fed to the EAF or the OBF, wherein the DRI gangue composition can vary between from 40% wt. up to and including 80% wt. SiO2, from 5% wt. up to and including 30% wt. MgO, from 5% wt. up to and including 40% wt. CaO, and from 5% wt. up to and including 25% wt. AI2O3.

[0035] In an embodiment of the invention, prior to feeding the feed mixture to the slag valorisation furnace, supplementary molten slag originating from steel plant converters may be added to the feed mixture to optimise a feed-solid ratio to yield the slag product at a reduced cost.

[0036] A carbonaceous reducing agent is added in the slag valorisation furnace to at least one of the modified slag and the slag product to increase the metallic units recoverable in order to recover alloys of higher value when the at least one of the modified slag and the slag product is recycled back to the slag valorisation furnace.In an embodiment of the invention, the molten slag may be transferred to the slag valorisation furnace using a means selected from the group consisting of slag pots, overhead cranes, or directly via slag launders.

[0037] Preferably, the molten slag is transferred to the slag valorisation furnace using slag pots or slag launders.

[0038] In an embodiment of the invention, prior to feeding the feed mixture to the slag valorisation furnace, the solid raw material feed is stored in a storage system, whereafter it is transferred to a proportioning plant, wherein the proportioning plant is used to mix the solid raw material feed according to the adjustable feed recipe to condition and modify the slag to form the metal product and conditioned slag.

[0039] The solid raw material feed may further include additives selected from the group consisting of modifying fluxes; argillaceous materials such as quartzite (silica), bauxite (alumina), burnt and unburnt limestone, dolomite and magnesite (CaO and MgO), Fluorspar (calcium fluoride), iron ore (iron oxide), soda ash (sodium carbonate), natural pozzolans, shales and clays; reductants such as coke, anthracite, char, coal or a biocarbon source, coal fines and wastes; industrial wastes and byproducts such as agricultural wastes, construction wastes (cement pastes), slag residues such as copper slags, bauxite residues / redmud, fly ash, silica fumes, recycled glass, municipal waste such as incinerator bottom ash, sewage sludge; and a combination of thereof.It is to be appreciated that the feed recipe that comprises the ratio in which the solid raw material feed is fed to the slag valorisation furnace is dependent on the amount and composition of the conditioned slag, slag product, cement replacement product, and clinker to be produced.

[0040] In an embodiment of the invention, the feed mixture includes dry fine materials and wet fine materials to be fed to the slag valorisation furnace.

[0041] In an embodiment of the invention, dry fine materials may be selected from the group consisting of dust, dried sludge, fine fly ash, clay, and a combination thereof. The dry materials may be injected into a slag bath of the slag valorisation furnace with a pneumatic transport system and a lance.

[0042] In an embodiment of the invention, the wet fine materials may be pelletised or briquetted and fed to the slag valorisation furnace and fed to the proportioning plant to allow for proportioning according to the feed recipe prior to being fed as part of the feed mixture.

[0043] In an alternative embodiment of the invention, the wet fine material may be dried to form dry fine materials.

[0044] In an embodiment of the invention, the slag valorisation furnace may provide an offgas duct that allows for the off-gas to be conducted to a downstream gas facility.In an embodiment of the invention, the downstream gas facility may include a waste heat recovery unit for combusting the off gas to generate heat that can be repurposed for the process. Preferably, the heat recovered from the waste heat recovery unit may be utilised in the rotary kiln to regulate and maintain the set cooling rate of the conditioned slag or the slag product to form the clinker.

[0045] In an embodiment of the invention, the feed mixture may be fed to the slag valorisation as pre-mixed, or the components of the feed mixture may be fed to the slag valorisation furnace as separate material batches that are delivered via a furnace charging system above the slag valorisation furnace that feeds the components of the feed mixture into designated bins.

[0046] In an embodiment of the invention, a pre-heater may be provided to heat the feed mixture or the separate material batches. Preferably, the feed mixture may be heated to a temperature from 400 degrees Celsius up to and including 800 degrees Celsius.

[0047] In an embodiment of the invention, the slag valorisation furnace may further provide at least one feeding chute. Preferably, more than one feeding chute may be provided by the slag valorisation furnace.

[0048] In an embodiment of the invention, the feed mixture may be fed continuously into the slag valorisation furnace using a loss-in-weight system that accurately controls a feed-to-power ratio of the slag valorisation furnace.It is to be appreciated that the loss-in-weight system accounts for fluctuations in the weight of the feed mixture to calculate the amount of power that must be fed to the furnace. In doing so, power wastage is mitigated, and the process efficiency is increased.

[0049] In an embodiment of the invention, the slag valorisation furnace may comprise a steel vessel.

[0050] In an embodiment of the invention, the steel vessel may be lined with refractory materials.

[0051] In an embodiment of the invention, the steel vessel may be rectangular or circular shaped.

[0052] In an embodiment of the invention, the steel vessel may be configured to be a semiclosed furnace.

[0053] It is to be appreciated that a semi-closed slag valorisation furnace is impervious to external elements, save for the ingress of air into the inside of the steel vessel during the feeding of the feed mixture via at least one of a side wall of the slag valorisation furnace, and a roof charging door of the slag valorisation furnace.In an alternative embodiment of the invention, the slag valorisation furnace, as embodied by the steel vessel, may be an open furnace that is open to external elements.

[0054] In an embodiment of the invention, the steel vessel may be water-cooled steel or may have copper with water cooling that is lined with refractory material on a hot face thereof.

[0055] In an alternative embodiment of the invention, the steel vessel may provide a suspended refractory roof, wherein the suspended refractory roof includes suitable anchors, protection against over-heating, enhanced brick design and thermal spall resistant characteristics.

[0056] In an embodiment of the invention, the slag valorisation furnace may be operated as an OBF. Therefore, the feed mixture is fed into the slag valorisation furnace to an active energy zone thereof, where the energy is transferred to the furnace bath and the peripheral regions against the furnace side walls.

[0057] In an embodiment of the invention, a portion of the feed mixture may be fed to form a thin solid layer on top of the open bath to decrease radiation heat loss from the slag valorisation furnace roof and a freeboard of the slag valorisation furnace.

[0058] In an embodiment of the invention, the feed mixture that is fed to the slag valorisation furnace is smelted in a zone below the electrical arc of the slag valorisation furnace.In an embodiment of the invention, the molten slag, semi-molten slag, or combination thereof in the feed mixture, is melted to form the conditioned slag according to the feed recipe.

[0059] In an embodiment of the invention, melting of the molten slag, semi-molten slag, or combination thereof in the slag valorisation furnace may reduce metal oxides such as iron oxide to a desired extent using the reductant to form the metal product whilst allowing for other metal oxides to report to the conditioned slag according to the adjustable feed recipe and desired compositions of both the metal product and conditioned slag.

[0060] It is to be appreciated that a difference in density between the metal product and the conditioned slag causes the conditioned slag to lie above the metal product.

[0061] In an embodiment of the invention, the metal product as it forms may accumulate in a bath at the bottom of the slag valorisation furnace.

[0062] In an embodiment of the invention, the metal product may be tapped intermittently from the slag valorisation furnace via at least one of a single tap hole or a multi-taphole system.

[0063] In an embodiment of the invention, the metal product may be transferred to the steelmaking process.In an embodiment of the invention, akin to the metal product, the modified slag will accumulate in a bulk slag bath inside the slag valorisation furnace.

[0064] The modified slag may be tapped intermittently from the slag valorisation furnace via at least one of a single tap hole or a multi-taphole system.

[0065] It is to be appreciated that the molten slag and / or the semi-molten slag forming part of the feed mixture contributes a significant amount of sensible energy to the process. Accordingly, to power the slag valorisation furnace, it is only necessary to utilise electrical energy to the extent required to melt solids and / or semi-molten material and to account for the thermal losses from the process.

[0066] In an embodiment of the invention, the slag valorisation furnace may provide either a single electrode or multiple electrodes capable of being operated in at least one of the following configurations: (i) direct current (DC) configuration providing a single electrode, acting as a cathode, with a bottom -located anode, the anode can be a pintype, billet type, or conductive hearth type; (ii) DC configuration providing twin electrodes, functioning as dual cathodes, with a bottom -located anode, the anode can also be a pin-type, billet type, or conductive hearth type; (iii) DC configuration providing dual electrodes, where one electrode serves as the cathode and the other as the anode; (iii) DC configuration providing multiple dual electrodes positioned as pairs within the slag valorisation furnace; (iv) alternating current (AC) configuration providing three electrodes, arranged in a delta knapsack connection; (v) AC configurationproviding a six-in-line positioned electrode furnace; and (vi) AC configuration providing multiple delta knapsack-connected electrode arrangements.

[0067] In an embodiment of the invention, the slag valorisation furnace may provide a power supply capable of being operated in an arrangement selected from the group consisting of (i) a DC mode, wherein at least one rectifying unit receives AC input to produce a DC output; (ii) a DC mode, wherein a single 3-phase transformer transforms and transfers the power to a single 3-electrode delta knapsack connection; (iii) an AC mode, wherein three single-phase transformers transform and transfer the power to a single 3-electrode delta knapsack connection; (iv) an AC mode, wherein three singlephase transformers transform and transfer the power to 3 electrode pairs; and (v) an AC mode, wherein multiple 3-phase transformers transform and transfer the power to multiple electrode delta knapsack connections.

[0068] In an embodiment of the invention, the electrodes may be Soderberg electrodes that are of the pre-baked carbon type electrodes or pre-baked graphite type electrodes.

[0069] In an embodiment of the invention, the solid raw feed material may be introduced as fine materials via injection or in a lumpy form in various locations during the transfer of the modifying slag.

[0070] In an embodiment of the invention, the modified slag or slag product may be transferred to a granulation system.In an embodiment of the invention, the granulation system may quench the modified slag or the slag product to form the cement replacement product that has a glass content of at least 60% wt.

[0071] In an embodiment of the invention, the modified slag may be transferred to the rotary kiln, wherein the rotary kiln comprises an elongate refractory brick-lined metal tube that allows for the modified slag or slag product to cool down at a set rate to produce the clinker.

[0072] In an embodiment of the invention, the rotary kiln may be rotatable to prevent a buildup of materials therein.

[0073] In an embodiment of the invention, the heat recovered from the waste heat recovery unit may be utilised to ensure that the modified slag or slag product is cooled down at a set rate to produce the clinker.

[0074] According to a second aspect of the invention, there is provided a slag product having cementitious properties produced by the novel slag valorisation and modification process according to the first aspect of the invention.

[0075] According to a third aspect of the invention, there is provided a slag product to produce hot clinker produced by the novel slag valorisation and modification process according to the first aspect of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Preferred embodiments of the invention are described below with reference to the accompanying figures, wherein:

[0077] Figure 1 depicts a block diagram of the novel slag valorisation and modification process according to the first aspect of the invention;

[0078] Figure 2 depicts a block diagram of the novel slag valorisation and modification process, wherein conditioned slag is further modified to produce a slag product utilising the optional slag modification step prior to being fed to the at least one of the granulation system and the clinkering system;

[0079] Figure 3 depicts a ternary diagram of the varying composition of the DRI gangue material contained in the feed mixture according the first aspect of the invention;

[0080] Figure 4 depicts the connection between a slag valorisation furnace and the overall steel production process, including the steps of a slag modification and post-processing;

[0081] Figure 5 depicts the structural design of the slag valorisation furnace according to Figure 2, including its refractory lining and cooling systems;Figure 6 exemplifies a typical rectangular slag valorisation furnace with six in-line electrodes, including a single DC configuration adapted for molten charge, demonstrating the configuration for optimal slag processing;

[0082] Figure 7 depicts a DC slag valorisation furnace design showcasing its internal components and electrode arrangement;

[0083] Figure 8 depicts the slag valorisation furnace feed system layout, showcasing the equipment and processes involved in feeding both solid and molten materials into the furnace;

[0084] Figure 9 depicts the layout of a pneumatic injection system for a slag valorisation furnace, showing how fine materials, such as dust and sludges, are injected into the slag bath; and

[0085] Figure 10 depicts the post-slag-valorisation slag modification, showcasing the steps employed to further modify slag after it exits the slag valorisation furnace to prepare the slag for cementitious products and the like.

[0086] The presently disclosed subject matter will now be described more fully hereinafter with reference to the accompanying examples, in which representative embodiments are shown. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will bethorough and complete and will fully convey the scope of the embodiments to those skilled in the art.

[0087] DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0088] A non-limiting example of a preferred embodiment of the invention is described in more detail below, with reference to Figures 1 to 10.

[0089] With reference to Figure 1 , a process is initiated by feeding a feed mixture into a slag valorisation furnace to form a metal product, a conditioned slag, and an off-gas. The feed mixture includes molten slag, semi-molten slag, solid raw materials, reductants, conditioning agents, and steel plant waste, as defined by an adjustable feed recipe. The adjustable feed recipe is crucial for determining appropriate component ratios and operating parameters that permit the optimal treatment of the feed mixture, particularly molten slag and semi-molten slag, to form the conditioned slag.

[0090] Referring to Figure 2, a block diagram illustrates how the novel slag valorisation and modification process can optionally include a slag modification step. In this step, the conditioned slag is further modified by adding suitable raw material feed and / or reductants to produce a slag product before being transferred to at least one of a granulation system or a clinkering system. Where this optional step is exercised, additional raw material feed or reductants can adjust the chemistry of the conditioned slag, especially if a specific downstream application, such as cementitious material, requires more precise compositions. This may include ensuring the conditioned slagmeets particular oxide requirements, such as CaO (>45% wt.), SiO2(<40% wt.), AI2O3(<10% wt.), FeO (<7.0% wt.), MgO (<1.5% wt.), SO3(<1.0% wt.), Na2O (<0.75% wt.), K20 (<1.75% wt.), Cl (<0.05% wt.), and LOI (<0.1% wt.) before being transferred to the clinkering system.

[0091] Referring to Figure 3, a ternary diagram highlights the varying composition of DRI gangue material contained in the feed mixture. It illustrates how fluctuations in gangue composition, particularly in SiO2, MgO, CaO, and AI2O3, can shift the chemistry of the conditioned slag, impacting operational stability and final product quality. The composition of the molten slag or semi-molten slag in the feed mixture is also dependent on the extent of direct reduction of the DRI, the carbon content in an EAF or OBF, and the gangue composition fed to the primary reduction process furnace. Silicon and / or iron reduction in the EAF or OBF influences SiO2and FeO concentrations when a low slag-to-metal ratio is sought. Any fluctuations in the carbon balance consequently alter the molten slag composition, affecting overall process stability and slag quality.

[0092] By virtue of positioning the slag valorisation furnace downstream of the EAF or OBF, the process acquires a previously unattainable capability of using low grade iron bearing feed materials in those furnaces. The downstream slag valorisation process purifies and reconditions the molten slag from the primary reduction furnace to allow the EAF or OBF to tolerate feed stocks well below the high purity direct reduced iron or blast-furnace-grade pellets normally required. Prior to this downstream slag valorisation process, conventional steel making using an EAF or OBF demandedhigh quality feed stocks to maintain acceptable slag chemistry, low slag-to-metal ratios and stable operation. The present invention obviates those strict feed-purity requirements and thereby enables direct introduction of low-grade ores, process residues and tailings into the furnace circuit, representing a clear inventive advance over the prior art.

[0093] Figure 6 provides an overview of how the feed mixture, once prepped according to the adjustable feed recipe, undergoes high-temperature treatment in the slag valorisation furnace. This furnace is generally a steel vessel, equipped with six-in-line electrodes and a single DC power configuration adapted for molten slag. Optimal slag-metal separation occurs here, generating the metal product and the conditioned slag. The feed mixture is smelted under carefully managed conditions, allowing molten or semimolten slag to mix homogeneously with the solid constituents. Control of chemical composition, temperature, and residence time, as determined by the adjustable feed recipe, ensures sufficient reduction of iron oxide (target FeO < 2% wt.), while the conditioned slag achieves a composition of CaO (25-57% wt.), SiO2(23-45% wt.), AI2O3(1-24% wt.), and MgO (1-26% wt.). Moreover, the CaO, MgO, and SiO2content in the conditioned slag comprises at least 60% wt. of the sum of these components contained in the feed mixture.

[0094] Referring to Figures 3 and 5, the molten slag commonly originates from a primary reduction process furnace, such as an electric arc furnace (EAF) or an open bath furnace (OBF). Transfer methods like slag pots, overhead cranes, or direct slag launders enhance the feed-solid ratio, a critical factor for recovering valuable metallicunits and reducing operational costs. Once the feed mixture enters the slag valorisation furnace, it experiences a residence time of 2 to 12 hours, managed by an intermittent tapping frequency that allows metal oxide reduction, droplet coalescence, temperature homogenisation, and a controlled tapping temperature of the conditioned slag. The operating temperature is kept above a liquidus temperature of the targeted slag product, up to and including 1850°C, ensuring a molten state conducive to metallurgical reactions. The degree of metallisation of metal elements in the feed mixture is also targeted to maximise iron recovery, keeping FeO in the final slag below 2% wt.

[0095] It is to be appreciated that adjusting the ratio of components in the feed mixture is critical for achieving a desired slag product. This adjustment depends on natural variability in the DRI’s chemical composition (extent of direct reduction, carbon content, gangue composition), silicon and iron reduction dynamics that affect SiO2and FeO levels, and a low yield ratio of slag to metal. Even small changes in the reductants or the DRI can significantly affect the slag chemistry. Figure 3 illustrates how the DRI gangue composition can shift between 40% - 80% wt. SiO2, 5% wt. - 30% wt. MgO, 5% wt. - 40% wt. CaO, and 5% wt. - 25% wt. AI2O3, all of which ultimately influence the composition of the conditioned slag.

[0096] Where there is a need to produce a clinker rather than a cement replacement, the conditioned slag or the slag product may be transferred to the clinkering system (as part of the optional step shown in Figure 2). This system methodically cools the conditioned slag in a rotary kiln at a controlled rate from 2.5 up to and including 30degrees Celsius per minute. By carefully regulating temperature, oxygen levels, and residence time, the clinker can attain a composition with CaO (>57% wt.), SiO2(16% < SiO2< 30% wt.), AI2O3(3% < AI2O3< 10% wt.), FeO (<5.0% wt.), MgO (<5% wt.), SO3(<1.5% wt.), Na2O (<0.4% wt.), K2O (<1.75% wt.), Cl (<0.05% wt.), LOI (<1.0% wt.), C3S > 55%, C2S < 20%, C3A > 5, C4AF < 15%, and LSF > 90%. This composition is particularly desirable for cement production, with stable and reactive phases meeting or exceeding conventional industry standards.

[0097] Figures 1 , 2, and 8 show how the slag product may then be routed to a granulation system for rapid quenching, forming a high-glass-content cement substitute, or to the clinkering system for methodical cooling in a rotary kiln. A waste heat recovery system can be employed to harness thermal energy from furnace off-gases, thereby improving overall energy efficiency. The molten slag may also be supplemented by molten slag originating from steel plant converters before feeding to the slag valorisation furnace, optimising a feed-solid ratio to produce the slag product more economically. Additional converter components such as a carbonaceous reducing agent may be introduced in the slag valorisation furnace to increase metallic units recovered, allowing higher-value alloys to be recycled back into the slag valorisation furnace.

[0098] The molten slag is transferred to the slag valorisation furnace using means selected from slag pots, overhead cranes, or direct slag launders. Preferably, the molten slag is moved via slag pots or slag launders. Prior to this, the solid raw material feed may be stored in a dedicated storage system, after which it is conveyed to a proportioning plant for mixing. This mixing step ensures that the solid raw material feed isincorporated in the proper ratios prescribed by the adjustable feed recipe so that slag conditioning is precise, whilst the metal product and the conditioned slag achieve optimal characteristics.

[0099] The solid raw material feed may include additives selected from modifying fluxes; argillaceous materials such as quartzite, bauxite, limestone, dolomite, magnesite, fluorspar, iron ore, soda ash, natural pozzolans, shales, and clays; reductants like coke, anthracite, char, coal, or biocarbon sources; industrial wastes and byproducts (including agricultural wastes, construction wastes, copper slags, bauxite residues, fly ash, silica fume, recycled glass, municipal waste incinerator bottom ash, and sewage sludge); or any combination thereof. The ratio of these added materials depends on the compositions required for the conditioned slag, the slag product, the cement replacement product, or the clinker.

[0100] Referring to Figure 6, the proportioning plant is shown feeding both dry and wet fine materials to the slag valorisation furnace, ensuring the required number of fluxes, reductants, and filler materials. Figure 7 illustrates how pneumatic injection can introduce fine particulate matter directly into the slag bath, improving energy efficiency and minimising dust. When composition adjustments remain necessary, Figure 2 indicates that another optional modification step can be undertaken to align the slag with downstream requirements. This ensures the final composition is suitable for applications such as construction aggregates or specialised cement.The solid raw material feed, as depicted in Table 1, typically comprises calcareous and argillaceous materials, as well as other potential additives such as ashes, dust, and slag:

[0101] Table 1: Typical raw material feed

[0102] Calcareous Argillaceous Material

[0103] Material

[0104] Calcium Silicon Aluminium Iron Limestone Clay Clay Clay

[0105] Marl Marl Shale Iron Ore Calcite Sand Fly Ash Mill Scale Aragonite Shale Aluminium Ore Shale Refuse

[0106] Shale Fly Ash Blast Furnace Dust Sea Shells Rice hull

[0107] Ash

[0108] Cement Kiln Dust Slag

[0109]

[0110] Each feed component is stored and proportioned to meet specific composition targets, supporting stable furnace operation, minimising waste, and securing consistent quality in the conditioned slag or the slag product.

[0111] Disadvantages of the current state of the art

[0112] Disadvantages of the current state of the art in steel manufacturing, particularly regarding slag processing, primarily revolve around slag cleaning furnaces designedonly to recover high-value metal elements from slag. These processes are typically integrated within primary metal production units such as an EAF or OBF, aiming to handle slag modification simultaneously with metal production. While this approach reduces initial capital expenditure, it imposes complexities and inefficiencies that the novel slag valorisation process of the present invention intends to surmount.

[0113] Producing slag products in EAFs and OBFs demands alterations to standard steelmaking operations, which complicates furnace management, increases maintenance frequency, and elevates operating costs. The chemical composition of slag, especially in an OBF, also predisposes the furnace to accelerated refractory wear, resulting in frequent relines. Many facilities lack infrastructure specifically designed for slag products, creating mismatches in operating conditions and degraded product quality. High iron oxide content in EAF slags similarly leads to suboptimal slagbased materials relative to traditional counterparts, requiring extra processing and inflating the environmental footprint.

[0114] Advantages afforded by the present invention over the current state of the art

[0115] The novel slag valorisation and modification process of the present invention addresses these operational and economic hurdles by decoupling slag processing from primary metal production and employing modem, high-temperature techniques: I. Independent Operation: The process of the present invention allows a slag valorisation furnace to function as an autonomous unit, granting greater flexibility for charging regimes, temperature control, and feed ratio adjustments. With theslag modification process of the present invention operating independently, primary steel production remains uninterrupted, minimising production losses during furnace maintenance or downtime;

[0116] II. Optimised Slag Composition & Refractory Compatibility: The slag valorisation furnace of the present process adjusts slag compositions to be optimal for heat transfer, which extends the life of standard, cost-effective refractories. This specialised design lowers overall material costs and reduces the frequency of relining;

[0117] III. Reduced Operational Disruptions: By detaching the slag processing from primary metalmaking, maintenance or downtime on the valorisation furnace no longer constrains iron or steel production. Plants benefit from smoother operations, lower overhead, and increased overall uptime;

[0118] IV. Maximised Metal Recovery & Waste Reduction: The process of the present invention recovers valuable metallic units more effectively, converting slag into commercially viable by-products rather than discarding it as waste. This minimises the environmental footprint of steel production and extracts more economic value from each tonne of raw material;

[0119] V. Use of Modem Technologies: The slag valorisation and modification process of the present invention harnesses approaches like dust injection and advanced high-temperature smelting. These methods accommodate a wider range of feedmaterials, including fine particulates that can be challenging in traditional furnace setups, offering further flexibility and processing efficiency; and

[0120] VI. Integrated Heat Recovery: By capturing thermal energy in an off-gas stream, the present process significantly reduces energy consumption. A heat recovery system can repurpose this energy to power ancillary steps (e.g., slag granulation, clinkering), thus bolstering energy efficiency and promoting a more sustainable metallurgical cycle overall.

[0121] Accordingly, the Applicant believes that the novel slag valorisation and modification process of the present invention provides significant technological and operational advancements over the current state of the art in slag processing within the steel industry. By addressing the inherent limitations of existing methods and introducing a more flexible, efficient, and environmentally friendly approach, the present process sets a new standard in slag valorisation and management, aiming to transform slag waste into valuable resources effectively.

Claims

AMENDED CLAIMSreceived by the International Bureau on 30 April 2026 (30.04.2026)1. A novel slag valorisation and modification process, the process including the steps of:i) feeding a feed mixture to a slag valorisation furnace to form a metal product, a conditioned slag with varying composition and off-gas, according to an adjustable feed recipe, wherein the feed mixture includes components selected from the group consisting of molten slag; semi-molten slag; solid raw material feed; and a combination thereof; andii) transferring the conditioned slag to at least one of a granulation system to form a cement replacement product that has a glass content of at least 60% wt., and a clinkering system to form clinker, wherein the clinkering system cools the conditioned slag at a pre-determined cooling rate from 2.5 degrees Celsius per minute up to and including 30 degrees Celsius per minute utilising at least one of heat from the offgas and air, ora combination thereof; andwherein the adjustable feed recipe comprises controlling (a) the chemical composition of the feed mixture; (b) the temperature of the slag valorisation furnace to be above the liquidus temperature of the conditioned slag up to and including 1850 degrees Celsius; and (c) the residence time of the feed mixture in the slag valorisation furnace from 2 hours up to and including 12 hours;to optimise any one or more of the degree of reduction of metal oxides in the feed mixture, metal droplet formation and settling, homogenisation, and AMENDED SHEET (ARTICLE 19)tapping temperature of the conditioned slag; in order to ensure a FeO content in the conditioned slag of less than 2% wt., wherein the conditioned slag has a composition of CaO (25-57% wt.), SiO2 (23-45% wt.), AI2O3 (1-24% wt.) and MgO (1-26% wt.), andwherein the CaO, MgO, and SiO2 content in the conditioned slag comprises at least 60% wt. of the sum of CaO, MgO and SiO2 contained in the feed mixture, prior to being transferred to at least one of the granulation system and the clinkering system.

2. The process as claimed in claim 1 , wherein when clinker is to be formed, step (ii) is preceded by modifying the composition of the conditioned slag by at least one of adding solid raw material feed and further reductant to form a slag product, suitable for use as the cement replacement product.

3. The process as claimed in claim 1, wherein the conditioned slag comprises a composition of CaO (>45% wt.), SiO2 (<40% wt.), AI2O3 (<10% wt.), FeO (<7.0% wt.), MgO (<1.5% wt.), SO3 (<1.0% wt.), Na2O (<0.75% wt.), K2O (<1.75% wt.), Cl (<0.05% wt.), and LOI (<0.1% wt.), prior to being transferred to the clinkering system.

4. The process as claimed in claim 1 , wherein the clinker comprises a composition of CaO (>57% wt.), SiO2(16%<SiO2<30% wt.), AI2O3 (3<AI2O3<10% wt.), FeO (<5.0% wt.), MgO (<5% wt.), SO3 (<1.5% wt.), Na2O (<0.4% wt.), K2O (<1.75%AMENDED SHEET (ARTICLE 19)wt.), Cl (<0.05% wt.), LOI (<1.0 % wt.), C3S>55%, C2S<20%, C3A>5, C4AF < 15%, and LSF > 90%.

5. The process as claimed in any one of the preceding claims, wherein the composition of the at least one of the conditioned slag and the slag product depends on composition requirements of the at least one of the cement replacement product produced by the granulation system and the clinker produced by the clinkering system, respectively.

6. The process as claimed in claim 1 or claim 3, wherein the composition of the conditioned slag is influenced by variation of the composition of the DRI, the extent of direct reduction, carbon content, and gangue composition fed to the EAF or the OBF, wherein the DRI gangue composition can vary from 40% wt. up to and including 80% wt. SiO2, from 5% wt. up to and including 30% wt. MgO, from 5% wt. up to and including 40% wt. CaO, and from 5% wt. up to and including 25% wt. AI2O3.

7. The process as claimed in claim 1 or claim 2, wherein feeding the feed mixture to the slag valorisation furnace is preceded by adding supplementary molten slag, originating from steel plant converters, to the feed mixture to optimise a feed-solid ratio to yield the slag product at a reduced cost.<IMG file=null he=null id=imgf000044_0001 img-content=null img-format=null inline=null orientation=null wi=null>

8. The process as claimed in any one of claims 1 , 2, and 7, wherein a carbonaceous reducing agent is added in the slag valorisation furnace to at least one of the modified slag and the slag product to increase the metallic units recoverable in order to recover alloys of higher value when the at least one of the modified slag and the slag product is recycled back to the slag valorisation furnace.

9. The process as claimed in claim 1 , wherein the molten slag is transferred to the slag valorisation furnace using a means selected from the group consisting of slag pots, overhead cranes, or directly via slag launders.

10. The process as claimed in claim 1, wherein prior to feeding the feed mixture to the slag valorisation furnace, the solid raw material feed is stored in a storage system, whereafter it is transferred to a proportioning plant, wherein the proportioning plant is used to mix the solid raw material feed according to the adjustable feed recipe to condition and modify the slag to form the metal product and conditioned slag.

11. The process as claimed in claim 1 or claim 10, wherein the solid raw material feed may further include additives selected from the group consisting of modifying fluxes; argillaceous materials such as quartzite (silica), bauxite (alumina), burnt and unburnt limestone, dolomite and magnesite (CaO and MgO), Fluorspar (calcium fluoride), iron ore, iron oxide, iron ore green pellets, mill scale, EAF slag, soda ash (sodium carbonate), natural pozzolans, shales AMENDED SHEET (ARTICLE 19)and clays; reductants such as coke, anthracite, char, coal or a biocarbon source, coal fines and wastes; industrial wastes and byproducts such as agricultural wastes, construction wastes (cement pastes), slag residues such as copper slags, bauxite residues / redmud, fly ash, silica fumes, recycled glass, municipal waste such as incinerator bottom ash, sewage sludge; and a combination thereof.

12. The process as claimed in any one of claims 1 to 11, wherein the solid raw material feed comprises one or more low-grade iron-containing materials selected from the group consisting of taconite ores having an Fe content of 20- 40% wt.; siderite (FeCO3) ores having an Fe content of 40-58% wt.; limonite (FeO(OH) nH2O) ores having an Fe content of 50-60% wt.; goethite (FeO(OH)) ores having an Fe content of 50-60% wt.; clay-bound hematite ores; pisolitic ironstone ores; bog iron ores; lateritic iron ores; jarosite residues; red mud (bauxite residue) containing residual iron; iron ore tailings and rejects; blastfurnace flue dust; converter and electric-arc-furnace dust; steel-mill sludge and mill scale; pellet-plant return fines; manganese-bearing tailings; siliceous banded iron formations with less than 55% wt. Fe; ferruginous quartzites; ferruginous lateritic saprolites; iron-rich chlorite schists; serpentinised peridotites containing disseminated magnetite; ferruginous kaolinite clays; iron sands with less than 45% wt. Fe; iron-bearing slags from pyrometallurgical processes; electric-arc- furnace slag; and molten slag originating from a primary reduction process furnace producing molten iron or steel-plant slag.AMENDED SHEET (ARTICLE 19)13. The process as claimed in claim 1, wherein the feed mixture includes dry fine materials and wet fine materials to be fed to the slag valorisation furnace, wherein the dry fine materials are selected from the group consisting of dust, dried sludge, fine fly ash, clay, and a combination thereof and are injected into a slag bath of the slag valorisation furnace with a pneumatic transport system and a lance, and wherein the wet fine materials are pelletised or briquetted and fed to the slag valorisation furnace and fed to the proportioning plant to allow for proportioning according to the adjustable feed recipe prior to being fed to the slag valorisation furnace as part of the feed mixture.

14. The process as claimed in claim 1 or claim 13, wherein the wet fine material is dried to form dry fine materials.

15. The process as claimed in claim 1 , wherein the slag valorisation furnace provides an off-gas duct that allows for the off-gas to be conducted to a downstream gas facility.

16. The process as claimed in claim 1 or claim 15, wherein the downstream gas facility includes a waste heat recovery unit for combusting the off-gas to generate heat to be utilised in the rotary kiln to regulate and maintain the pre-determined cooling rate from 2.5 degrees Celsius per minute up to and including 30 degrees Celsius per minute of the conditioned slag or the slag product to form the clinker.AMENDED SHEET (ARTICLE 19)17. The process as claimed in claim 1, wherein the feed mixture is fed to the slag valorisation furnace as pre-mixed or the components of the feed mixture are fed to the slag valorisation furnace as separate material batches that are delivered via a furnace charging system above the slag valorisation furnace that feeds the components of the feed mixture into designated bins.

18. The process as claimed in any one of claims 1 to 17, wherein the feed mixture is fed continuously into the slag valorisation furnace using a loss-in-weight system that accurately controls a feed-to-power ratio of the slag valorisation furnace.

19. The process as claimed in any one of the preceding claims, wherein the slag valorisation furnace comprises a steel vessel configured to be a semi-closed furnace that is impervious to external elements, save for the ingress of air into the inside of the steel vessel during the feeding of the feed mixture via at least one of a side wall of the slag valorisation furnace and a roof charging door of the slag valorisation furnace.

20. The process as claimed in any one of the preceding claims, wherein the slag valorisation furnace is configured to be an open bath furnace that is open to the external elements.

21. The process as claimed in any one of the preceding claims, wherein the slag valorisation furnace is operated as an OBF, wherein the feed mixture is fed into AMENDED SHEET (ARTICLE 19)the slag valorisation furnace into an active energy zone thereof, and wherein the energy is transferred to a furnace bath and against at least one peripheral region of a side wall of the slag valorisation furnace.

22. The process as claimed in claim 21 , wherein a portion of the feed mixture is fed to form a thin solid layer on top of the open bath to decrease radiation heat loss from the slag valorisation furnace roof and a freeboard of the slag valorisation furnace.

23. The process as claimed in claim 1 , wherein the feed mixture is smelted in a zone below the electrical arc of the slag valorisation furnace.

24. The process as claimed in any one of the preceding claims, wherein the metal product accumulates in a bath at a bottom region of the slag valorisation furnace, and wherein the modified slag accumulates in a bulk slag bath inside the slag valorisation furnace.

25. The process as claimed in any one of the preceding claims, wherein at least one of the metal product and the modified slag is tapped intermittently from the slag valorisation furnace via at least one of a single tap hole or a multi-taphole system.

26. The process as claimed in claim 1 , wherein the slag valorisation furnace provides one of a single electrode and multiple electrodes capable of being operated in at AMENDED SHEET (ARTICLE 19)least one of the following configurations (i) direct current (DC) configuration providing a single electrode, acting as a cathode, with a bottom -located anode, the anode can be a pin-type, billet type, or conductive hearth type; (ii) DC configuration providing twin electrodes, functioning as dual cathodes, with a bottom -located anode, the anode can also be a pin-type, billet type, or conductive hearth type; (iii) DC configuration providing dual electrodes, where one electrode serves as the cathode and the other as the anode; (iii) DC configuration providing multiple dual electrodes positioned as pairs within the slag valorisation furnace; (iv) alternating current (AC) configuration providing three electrodes, arranged in a delta knapsack connection; (v) AC configuration providing a six-in-line positioned electrode furnace; and (vi) AC configuration providing multiple delta knapsack-connected electrode arrangements.

27. The process as claimed in claim 1 , wherein the clinkering system is a rotary kiln, wherein the rotary kiln comprises an elongate refractory brick-lined metal tube that allows for the modified slag or slag product transferred thereto to cool down the conditioned slag at the pre-determined cooling rate from 2.5 degrees Celsius per minute up to and including 30 degrees Celsius per minute to produce the clinker.

28. The process as claimed in claim 27, wherein the rotary kiln is utilised to prevent a build-up of materials therein.AMENDED SHEET (ARTICLE 19)29. A cementitious slag product comprising a glass content of at least 60% wt., a FeO content of less than 2% wt., and a composition comprising CaO in the range from 25 up to and including 57% wt., SiO2in the range from 23 up to and including 45% wt., AI2O3in the range from 1 up to and including 24% wt., and MgO in the range from 1 up to and including 26% wt.

30. A clinker product produced by the process according to any one of claims 1 to 28, the clinker product comprising a composition of:CaO (>57% wt.);SiO2(16% < SiO2 < 30% wt.);- AI2O3 (3 < AI2O3 < 10% wt.);FeO (<5.0% wt.);MgO (<5% wt.);SO3 (<1.5% wt.);Na2O (<0.4% wt.);K2O (<1.75% wt.);Cl (<0.05% wt.);LOI (<1.0% wt.);C3S > 55%;C2S < 20%;C3A > 5;C4AF < 15%, andLSF > 90%.AMENDED SHEET (ARTICLE 19)31. A slag product having cementitious properties produced by the novel slag valorisation and modification process according to any one of claims 1 to 28.

32. A slag product to produce hot clinker produced by the novel slag valorisation and modification process according to any one of claims 1 to 28.

33. Use of the cementitious slag product according to claim 29 or the slag product having cementitious properties according to claim 31 as a cement replacement product in at least one of cement and concrete.

34. Use of the clinker product according to claim 30 in the production of cement.

35. Use of the cementitious slag product according to claim 29 or the slag product to produce hot clinker according to claim 32 as a precursor for clinker production.<IMG file=null he=null id=imgf000052_0001 img-content=null img-format=null inline=null orientation=null wi=null>

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