Method for refining metal

Abstract

A method for refining metal and processing slag to obtain a low content of impurities, reduce iron loss and increase productivity. In the method, a first furnace creates an initial slag with a low basicity and a high metal oxide content. The initial slag is heated and the metal oxide content of the initial slag is reduced to produce a resulting slag product with a low iron oxide content. The method produces more steel and a slag product having less iron oxide than is possible with conventional processes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing of U.S. Provisional Patent Application No. 63 / 763,732, entitled “Method for Refining Metal”, filed on Feb. 26, 2025, and the specification thereof is incorporated herein by reference.BACKGROUND OF THE INVENTIONField of the Invention (Technical Field)

[0002] Embodiments of the present invention relate to a method for producing steel, and more specifically, a method for producing steel from direct reduced iron and / or scrap, which can include lower grade ores.BACKGROUND

[0003] Direct reduced iron (“DRI”) is produced by the direct reduction of iron ore into iron by a reducing gas, which traditionally includes a mixture of hydrogen and carbon monoxide, so that less carbon dioxide is produced, thus mitigating the problem of the production of greenhouse gases. DRI systems need not be part of an integrated steel plant, so the initial capital investment and operating costs of direct reduction systems are lower than those of integrated steel plants.

[0004] Electric arc furnaces (“EAFs”) are a leading technology in the steelmaking industry, renowned for their versatility and efficiency in steel production. Unlike traditional blast furnace methods, which rely on the combustion of coke, EAFs use electrical energy to melt scrap steel or DRI. The process involves passing an electric current through graphite electrodes, creating an arc that generates intense heat. The ability to precisely control the temperature and chemical composition of the molten steel makes EAFs ideal for the production of specialty steels and alloys. EAF technology is highly valued for its flexibility and environmental benefits. It can operate with a variety of raw materials, including steel scrap, DRI, and pig iron, making it a versatile choice for steelmakers.

[0005] Direct reduction (“DR”) operators, EAF operators, and / or cement companies benefit from the present innovation. Such benefits include: substantial earnings before interest, taxes, depreciation, and amortization (“EBITDA”) improvement through the use of less expensive, low-quality ore and upcycling of slag to valuable supplementary cementitious material; long-term supply security of iron ore (as low-quality ore is abundant); essentially limitless sink of slag (for example (“e.g.”), cement plants next to steel plants) instead of putting it in a landfill; and substantial carbon dioxide (“CO2”) savings and EBITDA improvements for cement companies. Coal-based blast furnaces are responsible for up to 10% of all global CO2 emissions. There is a present need for a direct reduction system that is less expensive and scalable to compete with coal-based blast furnaces and reduce CO2 emissions.

[0006] The concentration of detrimental elements in crude steel needs to be minimized, and the loss of iron needs to be as small as possible. DRI can be processed to remove gangue and undesirable substances in a converter or in an electric arc furnace. However, it is difficult to achieve a reduction in detrimental elements while processing DRI if the amount of gangue is too high.

[0007] The use of high-quality DRI in EAFs presents challenges, particularly in terms of cost and resource availability. The availability of high-quality DRI can be limited by geographical location and the production capacity of DRI plants, affecting the overall feasibility of steel producers. Another drawback is the composition of the slag produced. Unlike blast furnace slag, typical EAF slag cannot be used in cement production and is often relegated to road construction or landfill, the latter of which is not environmentally friendly. Thus, there is a present need for a system that allows the use of lower-quality materials or ores while producing high-quality slag that can be used in the cement, fertilizer, and road construction material industries.

[0008] Significant challenges, including a shortage of suitable DR-grade iron ore and excessive gangue content in the available ores hamper steel production from DRI. Traditional production methods frequently contend with impurities or detrimental elements in the final steel product. To mitigate this issue, traditional methods generally necessitate maintaining a high basicity level in the slag, leading to increased slag volumes and subsequent disposal challenges as well as required high energy input. Typically, a compromise between these goals can be achieved by adjusting the basicity to a value in the range of about 2.5 or more. This high basicity also results in more significant iron losses in the slag, compelling producers to rely exclusively on high-grade DRI. There is a present need for a process that optimizes material use and enhances environmental sustainability in steel production by facilitating more effective slag reuse. Currently, approximately only 3% of iron ores are DR grade ores. Such a process opens up DR systems beyond ores that are only DR grade specific.BRIEF SUMMARY OF EMBODIMENTS OF THE PRESENT INVENTION

[0009] Embodiments of the present invention relate to a method for refining metal and processing slag, the method including: processing a feed material with a melting process, where the melting process includes conveying the feed material into a first furnace; heating the feed material inside the first furnace to a first temperature to produce a crude steel and an initial slag; introducing one or more oxidizing agents into the first furnace; introducing a slag forming agent into the first furnace; allowing the one or more oxidizing agents and the slag forming agent to react with the feed material within the first furnace at least until the initial slag has a basicity of below 1.5 and an iron oxide (“FeO”) content of at least 35%, where the basicity is a binary basicity of the ratio of calcium oxide (“CaO”) to silicon dioxide (“SiO2”); processing the initial slag with a slag post-treatment process, where the slag post treatment process includes providing one or more post-treatment reducing agents, and producing a slag treatment metal and a slag product by allowing the one or more post-treatment reducing agents to react with the heated initial slag.

[0010] The method for refining metal and processing slag can include heating the initial slag. The method can include providing one or more post-treatment reducing agents including providing at least one of hydrogen, carbon, hydrocarbon, silicon, aluminum, or other metallothermic reduction agents or electricity. The method can include introducing one or more oxidizing agents and the slag forming agent including introducing a metal oxide. The method can include transferring the initial slag to a second furnace and performing the slag post treatment process therein. The method can include applying the second furnace as a retrofit unit such that an existing production furnace becomes the first furnace described herein. The method can include conveying the feed material into the first furnace including conveying hot briquetted iron into the first furnace. Conveying the feed material into the first furnace can include conveying direct reduced iron into the first furnace. Conveying the feed material into the first furnace can include conveying iron scrap into the first furnace. Conveying the feed material into a first furnace can include conveying the feed material into an electric arc furnace. Conveying the feed material into a first furnace can include conveying the feed material into a basic oxygen furnace.

[0011] In one embodiment, the method can be performed in batches and not a continuous flow. In one embodiment, the method can be performed as a continuous flow and not in batches. Heating the initial slag can include heating the initial slag with an electric furnace (e.g., an electric arc furnace, submerged arc furnace, or others) and where producing a slag treatment metal and a slag product includes producing a slag product with an FeO concentration of less than 5%. Producing a slag treatment metal and a slag product can include producing a slag product with an FeO concentration of less than 1%. Heating the initial slag can include heating the initial slag with a blast furnace, and producing a slag treatment metal and a slag product can include producing a slag product with an FeO concentration of less than 5%. Producing a slag treatment metal and a slag product can include producing a slag product with an FeO concentration of less than 1%. Heating the initial slag can include heating the initial slag with a top blown rotary converter, and producing a slag treatment metal and a slag product can include producing a slag product with an FeO concentration of less than 5%. Heating the initial slag can include heating the initial slag having an FeO concentration of at least 40%. The method can include heating the feed material in a preheating chamber. Processing the initial slag with a slag post-treatment process can include producing one or more grades of slag treatment metal using a step process with controllable reduction of the initial slag. Producing one or more grades of slag treatment metal using a step process with controllable reduction of the initial slag can include a full reduction of the initial slag and further metal treatment with an oxidizing agent. The method can include heating the initial slag at a second temperature, where the second temperature is lower than the first temperature. The method can include performing at least one of a desulphurization process and a dephosphorization process by adding at least one reagent. The reagent can include at least one of oxygen, lime, calcium carbide, other reagents, a combination thereof, and one or more slags.

[0012] Embodiments of the present invention also relate to a method for processing metallurgical slag to recover differentiated metallic fractions, the method including: receiving a slag into a slag treatment reactor; refining the slag by introducing a reducing agent in at least one step including: reducing an iron oxide (“FeO”) content of the slag to a predetermined concentration lower than a previous concentration and separating at least one metallic fraction. The method can include performing an impurity removal step on at least one of the separated at least one metallic fractions, the impurity removal step including introducing an oxidizing agent to the separated at least one metallic fraction to selectively oxidize trace impurities and transferring the oxidized impurities back into a slag phase. The oxidizing agent can include at least one of mill scale, iron ore, or an iron oxide containing material. Refining the slag by introducing a reducing agent in at least one step can include refining the slag by introducing a reducing agent in a plurality of sequential reduction stages. The method can include a final reduction stage that reduces the FeO content to a final concentration of less than 5% and produces a residual slag phase with a final binary basicity (CaO / SiO2) of less than 1.5.

[0013] The slag can be mixed with a metallurgical by-product with an initial FeO content of at least 35% in an initial mix. The metallurgical byproduct can be a mill scale. The plurality of sequential reduction stages can include at least three stages including: a first stage of reducing the FeO content to a first concentration of below 25% and separating a first metallic fraction; a second stage of reducing the FeO content to a second concentration of below 15% and separating a second metallic fraction; and a third stage of reducing the FeO content such that the final concentration is achieved and separating a third metallic fraction. The plurality of sequential reduction stages can include at least two stages including: a first stage of reducing the FeO content to a first concentration of between 15% and 25% and separating a first metallic fraction; and a second stage of reducing the FeO content such that the final concentration is achieved and separating a second metallic fraction. The method can include performing an impurity removal step on at least one of the separated metallic fractions, the impurity removal step including: introducing an oxidizing agent to the separated metallic fraction to selectively oxidize trace impurities, including manganese or chromium, and transferring said oxidized impurities back into a slag phase. The oxidizing agent can include at least one of mill scale, iron ore, other iron oxide containing residues, or an iron oxide containing material (e.g., EAF dust). The residual slag phase produced after the final reduction stage can be discharged and solidified to form a product with a binary basicity below 1.5 and a residual FeO content of less than 1%. The method can include performing at least one of a desulphurization process and a dephosphorization process by adding at least one reagent. The reagent can include at least one of oxygen, lime, calcium carbide, other reagents, a combination thereof, and one or more slags.

[0014] Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or can be learned by practice of the invention. The objects and advantages of the invention can be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

[0016] FIG. 1 is a diagram that illustrates a metallurgical method for the production of steel, according to an embodiment of the present invention:

[0017] FIG. 2 is a diagram that illustrates a main melting process, according to an embodiment of the present invention; and

[0018] FIG. 3 is a diagram that illustrates a slag post-treatment process, according to an embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention is directed to enhancing the treatment of DRI, scrap, and / or metal to obtain a low content of impurities and to reduce iron loss and to increase productivity in the main melting process. Embodiments of the present invention also relate to a system for producing steel.

[0020] Embodiments of the present invention also relate to a method of refining metal where a first furnace separates slag with a low basicity and a high metal oxide content and a second furnace reduces the metal oxide content.

[0021] Embodiments of the present invention relate to a method for producing steel from a main melting process and a slag post-treatment process, where the main melting process comprises a first furnace, and the slag post-treatment process comprises a second furnace.

[0022] Embodiments of the present invention also relate to a system for producing steel, including the following: a source of direct reduced iron or scrap; a first furnace in which a main melting process is conducted in order to obtain crude steel; a second furnace in which a slag post-treatment is conducted; and feeding the metal phase tapped from the second furnace to the first furnace. Various melting furnaces which are suitable can be utilized in accordance with the invention.

[0023] Embodiments of the present invention also relate to a system for granulating slag after a furnace using well-known water or air granulation units; and grinding the granulated slag to a desired fineness so that it can be used as slag cement using well-known grinding technologies (such as vertical grinding mills, cement roller press, or ball mills).

[0024] The term “basicity” is defined as a ratio of calcium oxide (CaO) to silicon dioxide (SiO2). Basicity can be adjusted by adding and / or removing CaO and / or SiO2.

[0025] Referring now to the figures, FIG. 1 illustrates one embodiment of system 100. System 100 includes feed material 105, first furnace 110, initial slag 115, crude steel 120, second furnace 125, slag treatment metal 130, and slag product 135. Slag treatment metal 130 can be deposited directly into crude steel 120 instead of entering first furnace 110.

[0026] System 100 for producing steel can include two processes—melting process 140 (illustrated in FIG. 2) and slag post-treatment process 145 (illustrated in FIG. 3). Melting process 140 involves first furnace 110. Slag post-treatment process 145 involves second furnace 125.

[0027] FIG. 2 illustrates melting process 140. Melting process 140 can be used for gangue separation and removing impurities. Impurities can include, but are not limited to, sulfur (“S”), titanium (“Ti”), vanadium (“V”), chromium (“Cr”), zinc (“Zn”), copper (“Cu”), manganese (“Mn”), silicon (“Si”), tin (“Sn”), phosphorous (“P”), lead (“Pb”), or a combination thereof. Melting process 140 can also be applied, in one embodiment, to an existing system of scrap or DRI melting with a melting furnace. Melting process 140 optionally begins with source material 205 and scrap material 210 entering preheating chamber 215. Slag treatment off gas 220 and / or melting off gas 290 can be used to heat preheating chamber 215. Hot gas 225 can exit preheating chamber 215 in batches and / or a continuous stream. Accordingly, in one embodiment, the process is performed in batches and not continuously. In another embodiment, the process is performed continuously and not in batches. Feed material 105 then exits preheating chamber 215. The use of preheating chamber 215 is optional, and melting process 140 can occur with feed material 105 or source material 205 entering first furnace 110 directly, without preheating chamber 215. In granulation and grinding operations, hot gas streams from hot gas 225 can be used to dry slag product 135 during the granulation and / or grinding operations. Although first furnace 110 is referred to herein as a “first” furnace, such terminology is merely to distinguish it from the “second” furnace (although optionally a second furnace need not be provided—as described further below). To be clear, preheating chamber 215, which can optionally be a furnace, and / or any other furnace can optionally be used to process feed material 105 before feed material 105 encounters first furnace 110.

[0028] Feed material 105 and slag treatment metal 130 preferably then enters first furnace 110. In one embodiment, slag treatment metal 130 can enter preheating chamber 215 before entering first furnace 110. In one embodiment, feed material 105, slag treatment metal 130, lime and / or dolomite, oxygen, and air can be combined in first furnace 110 to produce crude steel 120 and initial slag 115. First furnace 110 can comprise electrodes and refractories, which are consumed over time and therefore need to be changed regularly. First furnace 110 can also produce melting heat loss 285 and melting off gas 290. Melting off gas 290 exits first furnace 110 through outlet 292 in batches and / or a continuous stream. Melting off gas 290 can be used to heat preheating chamber 215.

[0029] FIG. 3 illustrates slag post-treatment process 145. Slag post-treatment process 145 can be used for resource recovery, lowering iron losses, and / or upcycling the slag to supplementary cementitious materials, which can be a major driver of EBITDA improvement, and which can eliminate the problem of unrecycled slag not being used. Slag post-treatment process 145 preferably begins with initial slag 115 entering second furnace 125. Initial slag 115, lime and / or dolomite, carbon, hydrogen, and air can be combined within second furnace 125 to produce slag treatment metal 130 and slag product 135. Second furnace 125 can comprise electrodes and refractories, which are consumed over time and therefore need to be changed regularly. Second furnace 125 can also produce slag treatment heat loss 350 and slag treatment off gas 220. Slag treatment off gas 220 exits second furnace 125 through outlet 357. Slag treatment off gas 220 can be used to heat preheating chamber 215. In granulation and grinding operations, hot gas streams can be used to dry slag product 135.

[0030] In one embodiment, slag post treatment process 145 can be added to an existing system that already has an existing first furnace. In this embodiment, the chemistry of slag in the existing first furnace can optionally be altered or kept the same from the existing system.First Multi-Step Variant:

[0031] In one embodiment, the slag post-treatment process can be configured as a multi-stage or stepwise reduction process. Unlike a single-step reduction that targets the recovery of all metals from the metal oxides simultaneously, a stepwise approach allows for the selective reduction of specific metal oxides. By controlling the reduction potential (e.g., by adjusting the amount of reducing agents such as carbon and / or hydrogen, and controlling temperature), the system can produce distinct metal streams of different qualities and / or compositions.

[0032] In one step, the thermodynamic conditions can be adjusted to reduce iron oxides while leaving other oxides in the slag phase. This yields a metal product with high iron purity and low alloy content, which can be tapped to separate it before another step.

[0033] In another step, after the thermodynamic conditions have been adjusted to reduce mostly iron oxides, but also some of the contaminating oxides. This yields iron with medium purity and low to medium alloy content, which can be tapped to separate it before another step.

[0034] The control variable for a reduction process can be an FeO concentration or Oxygen concentration in the slag phase. For example, a first reduction can be from about 30-45% in initial slag to about 15-20% in a first step, then to about 5-10% in another reduction step, and to below about 1% in another reduction step. FeO concentration or Oxygen concentration values can be indicative and are preferably chosen for a desired slag chemical composition. During the method, the chemistry composition of the steel and slag phases can be controlled and corrected as needed by defining the tapping time.

[0035] In another step, after the reducing potential has been increased, the reducing potential can be increased further (e.g., higher reducing agent addition) to reduce the remaining metal oxides. This yields a “scrap grade” iron product or ferro-alloy product rich in valuable alloying elements such as vanadium (V). In addition, it yields a slag product, which after granulation has the same properties as granulated blast furnace slag (“GBFS”). The target control value for the final reduction is preferably a FeO concentration suitable for normal GBFS. For GBFS as a final slag product, the composition and binary basicity ratio are adjusted to meet standardized slag properties. The binary basicity can include the ratio of calcium oxide (“CaO”) to silicon dioxide (“SiO2”).

[0036] The above-described multi-step slag post treatment can be carried out with including but not limited to, carbon, hydrogen, hydrocarbons, biochar, or a combination thereof (or any other reduction medium). In addition, it can be followed by varying post-treatment of the metal fractions (if necessary, depending on feedstock quality and product specifications of the iron products) in a separate vessel or tapping ladle (e.g., desulfurization, dephosphorization, carburization, decarburization, alloying, degassing etc.).

[0037] The above-described multi-step slag post treatment processes can be used if the chemical composition of the steel phase does not fulfill the criteria for a certain grade of pig iron (steel making grade, foundry grade or nodular grade). For a desulfurization process, the tapped metal in a furnace can be treated with standard additives to remove the sulfur from the steel phase as stable sulfide components.

[0038] The dephosphorization process can remove phosphorous from the steel through the addition of standard additives.

[0039] The carburization process can be used to increase the final carbon content in pig iron to a value of about 3.5-4.5%. During the tapping of a metal phase, the desired amount of carbon containing reagents can be added directly to a furnace (for example, a ladle furnace).

[0040] The above-described multi-step slag post treatment processes can be performed in a furnace or directly during the tapping using well-known metallurgical procedures.Second Multi-Step Variant:

[0041] In one embodiment of the present invention, the slag post-treatment process can be configured as another multi-stage process. In this embodiment, a first “strong” reduction can be used to preferably recover all or at least substantially all, metals simultaneously into a metal alloy phase and leave a slag product—which after tapping and granulation has the same previously-noted properties as GBFS (the metal phase stays in the furnace or tapped as well). Several portions of the initial slag can be treated one by one without metal tapping. The metal phase can be collected in the furnace and used as a hot heel for the next treatment.

[0042] In one embodiment, a slag forming agent can be added to the first furnace and / or second furnace. The slag forming agent can include, but is not limited to, flux, lime (CaO), calcium carbide (CaC2), oxidative reagents basic slags, or a combination thereof. The slag forming agents can be charged with the main material or initial slag.

[0043] The metal phase can then be treated in the same furnace or a subsequent vessel. If a desulphurization is desired (depending on feedstock quality and product specifications of the metal), it can be executed according to standard and well-known processes. A dephosphorization can also be executed according to standard and well-known processes. Iron oxide carriers, mill scales, iron ore, and / or oxygen can be used as an oxidizing agent. Direct oxygen blowing can be used as an oxygen source to improve dephosphorization conditions as well as selectively remove trace metals. The steel can be “killed” (e.g., lower oxygen activity) in a furnace or tapping ladle with carbon or another medium (e.g., aluminum). The steel can be carburized and alloyed. Other post-treatment, including for example degassing, can follow.

[0044] Another step can be used for treatment, particularly if using silicon and / or other highly reactive metals as they do not allow to selectively reduce iron as described above. However, silicon and other highly reactive metals have other advantages—for example providing an exothermic reduction to manage system temperature for subsequent processes. In the case of metallothermic reduction, the temperature in the reduction step can be well managed (by for example adding cold iron oxide carriers or scrap) but can also be adjusted in a way (e.g., overheating) that there is enough energy left in the system for subsequent endothermic processes (such as alloying).

[0045] While embodiments described herein illustrate the second furnace integrated with a first furnace, the slag post-treatment system can be configured to operate as an independent, standalone unit. In this decoupled configuration, the second furnace functions as a dedicated slag valorization unit that is not temporally or geographically bound to the operation of the first furnace.

[0046] In one embodiment, the systems described herein can include a flexible feedstock intake system capable of processing slag in various thermal states: hot slag, cold slag, and / or a mixture of both. Slags can be from electric arc furnace production sites, basic oxygen furnaces, or other metallurgical operations. Copper rich slags and vanadium rich slags can be used.

[0047] When processing cold slag, the system can use the preheating chamber or dedicated burners within the second furnace to bring the material to the a molten state for reduction. This flexibility allows the system to serve as a centralized recycling hub for multiple steelmaking facilities.

[0048] The metal phase recovered from the slag post-treatment process (the slag treatment metal) can be treated with specific chemical adjustments to meet final product specifications. In one embodiment, the system includes a secondary refining step performed on the recovered metal phase. Depending on the chemical requirements of the final steel product, the recovered metal phase can undergo dephosphorization to remove excess phosphorus, which may have reverted to the metal phase during the reduction of the slag, or desulfurization to lower sulfur content to acceptable limits.

[0049] In one embodiment, the refining steps described herein can be integrated into the second furnace operation or conducted in a separate vessel (e.g., a ladle furnace or converter) immediately following the tapping of the slag treatment metal.

[0050] First furnace 110 can comprise, but is not limited to: a refractory-lined furnace shell that can withstand high temperatures and mechanical stresses; an electrode assembly with one or more adjustable graphite, or other material, electrodes for generating an electric arc; a power supply system including a transformer for delivering electricity; a raw material charging system, for example a top-loading or conveyor mechanism for introducing scrap metal, DRI, or other feedstock; one or more burners, using natural gas or other industrial gases, positioned strategically within first furnace 110 for supplemental heating and improved energy efficiency during the melting process; an oxygen charge system with one or more injectors inside first furnace 110 for adjusting oxygen content during the melting process; a carbon charge system with one or more injectors inside the furnace for adjusting the slag foaming; a cooling system, which can be water-cooled or air-cooled, to dissipate heat from critical components; a fume extraction and pollution control system including hoods, dust collectors, and filters to manage emissions; a tilting mechanism for pouring molten metal and removing slag; a refractory lining made from heat-resistant materials to protect against thermal and chemical wear; a control system, for example a programmable logic controller (“PLC”), for regulating key operational parameters; and temperature monitoring and sampling probes for real-time metallurgical control.

[0051] Second furnace 125 can comprise, but is not limited to: a refractory-lined furnace shell that can withstand high temperatures and mechanical stresses; an electrode assembly with one or more adjustable graphite, or other material, electrodes for generating an electric arc; a power supply system including a transformer for delivering electricity; a raw material charging system, for example a top-loading mechanism for introducing liquid or solid slags; one or more burners, using natural gas or other industrial gases, positioned strategically within first furnace 110 for supplemental heating and improved energy efficiency during the melting process; a reduction agent charge system with one or more injectors inside first furnace 110 for adjusting iron oxide content during the melting process; a cooling system, either water-cooled or air-cooled, to dissipate heat from critical components; a fume extraction and pollution control system including hoods, dust collectors, and filters to manage emissions; a tilting mechanism for pouring molten metal and removing slag; a refractory lining made from heat-resistant materials to protect against thermal and chemical wear; a control system, for example a PLC, for regulating key operational parameters; temperature monitoring and sampling probes for real-time metallurgical control; and a slag removal system for separating and discharging slag efficiently.

[0052] Melting process 140 and slag post-treatment process 145 can be done in one EAF. Melting iron carriers (such as hot briquetted iron (“HBI”), DRI, or scrap) in EAFs is preferably done in batches under oxidizing conditions. At the end of the batch, the slag treatment is initiated by first tapping most of the liquid crude steel. Then the slag treatment is initiated by introducing carbon-carriers, hydrogen, or hydrocarbon. Once the slag is tapped, other subsequent steps as described herein can follow (e.g., granulation and grinding after tapping) and the next batch of melting iron carriers can start.

[0053] The invention can use EAFs but is not limited to this type of melting furnace. A top blown rotary converter can be used. To the extent that the description herein is directed to an EAF, a person skilled in the art will recognize that other furnaces can be used. For example, for the first stage, a basic oxygen furnace (“BOF”) can also be used to benefit from the new slag chemistry described herein. For the second stage, a submerged arc furnace or similar concepts can be used. Although the invention can use EAFs or other furnaces located on one industrial site, the benefits also occur if they are placed in different locations.

[0054] As used herein and throughout, gangue separation is the process of removing non-valuable substances, or gangue, from valuable minerals in DRI. Melting process 140 can achieve general gangue separation and liquid steel with a phosphorus concentration below at least 250 parts-per-million (“ppm”), below about 100 ppm to about 400 ppm, or below about 200 ppm to about 300 ppm; and a carbon content below at least 0.3%, below about 0.1% to about 0.5%, or below about 0.2% to about 0.4%.

[0055] Melting process 140 can use electrodes comprising, e.g., graphite or other materials, to transfer heat, supplemented by oxygen, natural gas burners, and carbon injectors for temperature and chemical composition control. The electrodes can be solid, hollow, or another configuration.

[0056] Gangue separation in melting process 140 can be achieved through density and surface tension differences between crude steel 120 and initial slag 115. As the temperature increases, the metallic iron melts and separates from the less dense initial slag 115. The denser molten iron settles at the bottom of first furnace 110, while the lighter slag floats on top. This density-driven stratification is enhanced by surface tension differences that prevents extensive mixing of the two phases (i.e., crude steel 120 and initial slag 115). These differences facilitate the collection and removal of slag from the surface of the molten metal, thereby yielding a higher-purity metallic iron.

[0057] Melting process 140 can be conducted as a batch process. Melting process 140 can be conducted as a continuous process.

[0058] First furnace 110 produces iron at a recovery rate of about 90% to about 99%, about 95% to about 99%, or about 97% to about 99%. First furnace 110 has a higher throughput of iron than traditional furnaces because iron is recycled in second furnace 125.

[0059] Second furnace 125 can upcycle initial slag 115 by reducing iron content to about 1% to about 30%, about 5% to about 20%, or about 10% to about 15%, and adding additional components in slag product 135. For example, if a system has a capacity of one million tons annually, then second furnace 125 can upcycle initial slag 115 into slag treatment metal 130 in a stream of about 110,000 tons to about 140,000 tons, about 115,000 tons to about 135,000 tons, or about 120,000 tons to about 130,000 tons. By upcycling slag, system 100 provides greater EBITDA and carbon dioxide savings. Initial slag 115 can be in hot and liquid state or a cold and solid state. Furthermore, initial slag 115 can be pre-processed before going into second furnace 125. Such pre-processing can include crushing, shredding, and iron separation via magnetic or other separation technologies.

[0060] Slag post-treatment process 145 can be optimized for iron recirculation and reusage of slag product 135 in production of other materials, e.g., granulated blast furnace slag, fertilizer, road construction material, or ground granulated blast furnace slag (“GGBFS”). The production of GGBFS or other products can use additional treatment such as water / air granulation and grinding. Granulation leads to a product called granulated blast furnace slag, which can be sold to cement producers or grinding mills. Further grinding this granulated slag leads to ground granulated blast furnace slag (or slag cement), which can be used directly for concrete production.

[0061] Slag post-treatment process 145 of system 100 can be used for processing initial slag 115 in second furnace 125 for the purpose of recirculating iron and obtaining slag product 135. Slag product 135 can be a final slag, ready for a final product, e.g., cement, fertilizer, road construction material, or GGBFS. Slag post-treatment process 145 can be done by adding carbon and / or hydrogen-containing agents (including but not limited to biochar, hydrogen, or hydrocarbon). Slag post-treatment process 145 can be conducted using mill scale, iron ore, scrap, or other iron-containing materials (e.g., EAF) in addition to the initial slag 115.

[0062] Slag post-treatment process 145 can be distinguished from melting process 140 by its flexibility in using carbon and hydrogen-containing reducing agents (e.g., biochar or hydrocarbon) for the reduction process. Slag post-treatment process 145 treats slag to produce slag treatment metal 130 (which can be iron) and slag product 135 (which can be, e.g., a cement-ready material). Slag treatment metal 130 can be treated separately as a pig iron of different qualities, ferro-alloys, or other iron-bearing products, or can be recycled to melting process 140 in a hot or cold state. First furnace 110 can facilitate melting process 140 in oxidation conditions with the addition of oxygen. Second furnace 125 can facilitate slag post-treatment process 145, melting slag with carbon / hydrogen to reduce the iron oxide to iron.

[0063] Melting process 140 can comprise impurity and carbon optimization that specifies control measures to maintain impurity and carbon content at low levels in the final steel product, enhancing material properties and market value. Low impurity and carbon contents can be achieved by obtaining low basicity slag (slag with basicity less than at least 1.5, less than about 0.5 to about 3, or less than about 1 to about 2) with high FeO content (above at least 30%, above about 20% to about 50%, or above about 30% to about 40%).

[0064] Slag post-treatment process 145 not only recovers iron but also prepares slag for direct use in cement production, significantly reducing waste and promoting sustainability, as a clinker substitute product (e.g., supplementary cementitious material). Slag with high FeO content (above at least 30%, above about 10% to about 50%, or above about 30% to about 40%) can be treated to minimize the FeO content to a concentration lower than at least 15%, lower than about 0.5% to about 8%, or lower than about 3% to about 5%. Managing SiO2, CaO, Al2O3, and MgO levels in the slag reduction process can make slag as a partial replacement of cement source materials due to its similar chemical composition.

[0065] Slag post-treatment process 145 can be conducted as a batch process. Slag post-treatment process 145 can be conducted as a continuous process.

[0066] Feed material 105 can comprise direct reduced iron (“DRI”), steel scrap, or other iron carriers (for example pig iron or hot metal). Feed material 105 can comprise direct reduced iron made from iron ore with an iron content above at least 30%, above about 40% to about 90%, or above about 60% to about 70%. Feed material 105 can comprise any type of iron ore or other iron-containing material.

[0067] Feed material 105 can comprise DRI with an iron content above at least 70%, above about 70% to about 100%, or above about 80% to about 90%. Feed material 105 comprised of DRI can be obtained from low-grade iron ore with iron content at least above 50%, and a carbon content that is added during the reduction phase ranging from about 0% to about 5%, about 1% to about 4%, or about 2% to about 3%. The DRI can be in any form and can include, but is not limited to, HBI, cold briquetted iron (“CBI”), DRI fines, or other forms.

[0068] Feed material 105 can comprise an oxide compound and / or element. The element can include, but is not limited to, iron (Fe). The oxide compound or oxidizing agent can include a metal oxide including, but not limited to, iron(III) oxide (Fe2O3); iron(II) oxide (FeO); aluminum oxide (Al2O3); calcium oxide (CaO); magnesium oxide (MgO); or a combination thereof. The oxide compound can include, but is not limited to, silicon dioxide (SiO2), phosphorus pentoxide (P2O5), or a combination thereof. The oxidizing agent can include various forms, for example, ore and / or pre-reduced materials such as DRI.

[0069] Feed material 105 can comprise source material 205 that is heated from preheating chamber 215 or another furnace, e.g., a shaft furnace. The exhaust gases from first furnace 110 and second furnace 125 can be used to preheat feed material 105 in an additional furnace or furnaces, for example, rotary kilns.

[0070] Source material 205 can enter preheating chamber 215 at a rate that is determined by the mass flow of the steel production plant.

[0071] Feed material 105 can comprise hot DRI. Feed material 105 can be a temperature in a range from about 300° C. to about 600° C., about 350° C. to about 550° C., or about 400° C. to about 500° C.

[0072] First furnace 110 can alter the chemistry of feed material 105 and / or source material 205 by changing the basicity of the resulting slag. First furnace 110 can adjust the basicity of the resulting slag to a range from about 0.5 to about 3, about 1.0 to about 2.5, or about 1.0 to about 1.5.

[0073] First furnace 110 can alter the chemistry of feed material 105 and / or source material 205 by changing the iron oxide content of the resulting slag. First furnace 110 can adjust the iron oxide content of the resulting slag to a range from about 20% to about 70%, about 35% to about 65%, or about 35% to about 45%.

[0074] The chemistry of initial slag 115 can determine the quality of crude steel 120. Three factors, namely, basicity, temperature, and oxygen potential / FeO concentration in initial slag 115 can influence operating parameters. High basicity can be used rather than high FeO concentration, as increasing FeO concentration leads to higher iron losses with initial slag 115 and can render initial slag 115 unusable in e.g., cement, fertilizer, road construction material, or GGBFS.

[0075] Operating with low-quality DRI can result in high amounts of initial slag 115 due to the high gangue content in feed material 105. In this embodiment, using high basicity can increase the amount of initial slag 115.

[0076] The basicity of initial slag 115 can range from about 0.5 to about 3, about 0.7 to about 1.7, or about 1.0 to about 1.3. The high oxidation potential of initial slag 115, which can be determined by a high iron oxide concentration above at least 30%, above about 10% to about 50%, or above about 20% to about 40%, achieves impurity distribution and trace elements reduction or removal.

[0077] Crude steel 120 can comprise crude steel. In melting process 140 of system 100, the general separation of gangue occurs, and crude steel 120 is tapped.

[0078] Crude steel 120 can comprise iron (Fe); carbon (C); manganese (Mn); silicon (Si); and / or phosphorus (P). The phosphorus (P) concentration can be in a range of about 50 ppm to about 1500 ppm, about 220 ppm to about 280 ppm, or about 240 ppm to about 260 ppm.

[0079] Scrap material 210 can be added to feed material 105. Scrap material 210 can comprise iron scrap. Feed material 105 can comprise entirely scrap material 210.

[0080] The temperature in melting process 140 can be about 1300° C. to about 1800° C., about 1400° C. to about 1700° C., or about 1500° C. to about 1600° C.

[0081] In melting process 140, the basicity of initial slag 115 can be regulated to about 0.5 to about 2.5, about 1.0 to about 2.0, or about 1.0 to about 1.5.

[0082] The basicity level in second furnace 125 can be between about 0.5 and about 2.5, about 0.7 and about 2, or about 1.0 and about 1.5.

[0083] The temperature in slag post-treatment process 145 can be about 1300° C. to about 1800° C., about 1400° C. to about 1700° C., or about 1500° C. to about 1600° C. The temperature in slag post-treatment process 145 can be lower than the temperature in melting process 140.

[0084] In slag post-treatment process 145, the basicity of slag product 135 can be regulated to about 0.5 to about 2.5, about 1.0 to about 2.0, or about 1.0 to about 1.5.

[0085] System 100 can comprise adjusting the basicity of initial slag 115 entering second furnace 125 to a target value. In slag post-treatment process 145, the basicity of initial slag 115 can be about 0.5 to about 2.5, about 1.0 to about 2.0, or about 1.0 to about 1.5.

[0086] Electrodes can be used to transfer heat to melting process 140 and slag post-treatment process 145 in system 100. Oxygen burners and other natural gas burners can also be used in system 100. The electrodes can comprise a graphite material or other suitable electrode materials. The electrodes can comprise solid or hollow electrodes, or other configurations.

[0087] System 100 provides an enhanced method for producing liquid steel. The production of liquid steel from DRI and scrap ensures low impurities, sulfur, trace elements, and carbon content in slag product 135.

[0088] Slag treatment metal 130 can comprise carbon (C) in a range of about 0% to about 2.5%, about 1% to about 2%, or about 1.5% to about 2%.

[0089] Slag treatment metal 130 can comprise silicon (Si) in a range of about 0% to about 1%, about 0.2% to about 0.8%, or about 0.4% to about 0.6%.

[0090] Slag product 135 can comprise iron(II) oxide (FeO); silicon dioxide (SiO2); aluminum oxide (Al2O3); calcium oxide (CaO); and magnesium oxide (MgO).

[0091] Slag product 135 can comprise phosphorus as phosphorus pentoxide (P2O5) in a range of about 0% to about 3%, about 0.5% to about 2%, or about 1% to about 2%.

[0092] Hot gas 225 can comprise carbon monoxide gas (CO(g)); carbon dioxide gas (CO2(g)); oxygen; nitrogen; water vapor; hydrogen; and argon, or a combination thereof.

[0093] Hot gas 225 can be a temperature in a range from about 500° C. to about 1000° C., about 625° C. to about 775° C., or about 675° C. to about 725° C.

[0094] Melting off gas 290 can comprise carbon monoxide, carbon dioxide, oxygen, nitrogen, hydrogen, and argon.

[0095] Slag treatment off gas 220 can comprise carbon monoxide, carbon dioxide, oxygen, nitrogen, hydrogen, and argon.

[0096] System 100 can comprise hydrogen, carbon, hydrocarbons, silicon, aluminum or other metallothermic reduction agents in slag post-treatment process 145.

[0097] Electrodes are consumed in first furnace 110 at a rate of about 0.5 kg / t steel to about 5 kg / t steel, about 1 kg / t steel to about 4 kg / t steel, or about 2 kg / t steel to about 3 kg / t steel.

[0098] Oxygen is consumed in first furnace 110 at a rate of about 10 kg / t steel to about 60 kg / t steel, about 25 kg / t steel to about 40 kg / t steel, or about 30 kg / t steel to about 40 kg / t steel.

[0099] First furnace 110 can comprise magnesia-based refractories, magnesia-carbon bricks, silica, or high-alumina refractories. Refractories are consumed in first furnace 110 at a rate of about 0.5 kg / t steel to about 10 kg / t steel, about 1 kg / t steel to about 4 kg / t steel, or about 2 kg / t steel to about 3 kg / t steel.

[0100] Electrodes are consumed in second furnace 125 at a rate of about 0.5 kg / t steel to about 5 kg / t steel, about 1 kg / t steel to about 4 kg / t steel, or about 2 kg / t steel to about 3 kg / t steel.

[0101] Second furnace 125 can include magnesia-based refractories, magnesia-carbon bricks, silica, or high-alumina refractories. Refractories are consumed in second furnace 125 at a rate of about 0.5 kg / t steel to about 10 kg / t steel, about 1 kg / t steel to about 4 kg / t steel, or about 2 kg / t steel to about 3 kg / t steel.

[0102] The present invention can also provide a system for treating iron comprising materials. From a source of DRI, for example, a shaft furnace, DRI can be fed to a first heating furnace. Additionally, scrap can be added. Slag can be pulled from the first heating furnace and fed into a second heating furnace in which the post treatment is performed. The metal phase material tapped from the second heating furnace can be fed to the first heating furnace. Typically, this step occurs in the production cycle—for example, after the metal phase material of the first heating furnace is tapped, which is crude steel, and the final product of the system of the invention. The final slag which is pulled off the second heating furnace can be used e.g., in the cement industry or as a fertilizer after granulation and grinding.INDUSTRIAL APPLICABILITY

[0103] The invention is further illustrated by the following non-limiting examples.Example 1

[0104] The DRI of the composition exposed in Table 1 was used to test the phosphorous distribution during the main melting operation.TABLE 1Initial DRI compositionComponent% wt.Fe2O30.00FeO8.03Fe82.95SiO26.43Al2O32.31CaO0.05MgO0.09P0.14C0.00

[0105] The melting temperature in all experiments was 1600° C. To preserve the desired values of basicity and FeO content in the final slag, CaO, MgO, and Fe3O4 were added before the start of the melting operation. To prevent uncontrollable oxidation of the material during melting, the furnace with a non-oxidized atmosphere was used.

[0106] Several levels of FeO concentration in the final slag were tested during the experiments. FeO concentration varied from 22% to 68%, and the basicity (B2) of the slag phase ranged from 0.6 to 2.2. The final phosphorous concentration in the steel phase in all tests was below 300 ppm and in 7 tests below 200 ppm.Input Materials for Mass Balance CalculationsDRI (%)Fe2O30.00FeO7.47Fe77.16SiO28.36Al2O32.09CaO2.35MgO1.05MnO0.68P2O50.52

[0107] For slag treatment process testing several slags were used, one chemical composition exposed in Table 2.TABLE 2Initial slag compositionComponent% wt.FeO33.0SiO215.5Al2O39.9CaO26.1MgO2.8P2O50.4

[0108] Final concentration of FeO after reduction process was obtained below 1.0%.

[0109] All concentrations described herein are weight concentrations.

[0110] The preceding examples can be repeated with similar success by substituting the generically or specifically described components, reactants, and / or operating conditions of embodiments of the present invention for those used in the preceding examples.

[0111] The terms, “a”, “an”, “the”, and “said” mean “one or more” unless context explicitly dictates otherwise.

[0112] Note that in the specification and claims, “about”, “approximately”, and / or “substantially” means within twenty percent (20%) of the amount, value, or condition given. All computer software disclosed herein can be embodied on any non-transitory computer-readable medium (including combinations of mediums).

[0113] Embodiments of the present invention can include every combination of features that are disclosed herein independently from each other. Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and this application is intended to cover, in the appended claims, all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. Unless specifically stated as being “essential” above, none of the various components or the interrelationship thereof are essential to the operation of the invention. Rather, desirable results can be achieved by substituting various components and / or reconfiguring their relationships with one another.

Claims

1. A method for refining metal and processing slag, the method comprising:processing a feed material with a melting process, wherein the melting process comprises:conveying the feed material into a first furnace;heating the feed material inside the first furnace to a first temperature to produce a crude steel and an initial slag;introducing one or more oxidizing agents into the first furnace;introducing a slag forming agent into the first furnace; andallowing the one or more oxidizing agents and the slag forming agent to react with the feed material within the first furnace at least until the initial slag comprises a basicity of below 1.5 and an iron oxide (“FeO”) content of at least 35%, wherein the basicity comprises a binary basicity of the ratio of calcium oxide to silicon dioxide; andprocessing the initial slag with a slag post-treatment process, wherein the slag post treatment process comprises:providing one or more post-treatment reducing agents; andproducing a slag treatment metal and a slag product by allowing the one or more post-treatment reducing agents to react with the initial slag.

2. The method of claim 1 wherein providing one or more post-treatment reducing agents comprises providing at least one of hydrogen, carbon, hydrocarbon, silicon, aluminum, other metallothermic reduction agents, and electricity.

3. The method of claim 1 wherein introducing one or more oxidizing agents and the slag forming agent comprises introducing a metal oxide.

4. The method of claim 1 further comprising transferring the initial slag to a second furnace and performing the slag post treatment process therein.

5. The method of claim 4 further comprising applying the second furnace as a retrofit unit such that an existing production furnace is the first furnace.

6. The method of claim 1 wherein conveying the feed material into the first furnace comprises conveying hot briquetted iron into the first furnace.

7. The method of claim 1 wherein conveying the feed material into the first furnace comprises conveying direct reduced iron into the first furnace.

8. The method of claim 1 wherein conveying the feed material into the first furnace comprises conveying iron scrap into the first furnace.

9. The method of claim 1 wherein conveying the feed material into the first furnace comprises conveying the feed material into an electric furnace.

10. The method of claim 1 wherein conveying the feed material into the first furnace comprises conveying the feed material into a basic oxygen furnace.

11. The method of claim 1 wherein the method is performed in batches and not as a continuous flow.

12. The method of claim 1 wherein the method is performed as a continuous flow and not in batches.

13. The method of claim 1 further comprising heating the initial slag with an electric furnace and wherein producing a slag treatment metal and a slag product comprises producing a slag product comprising an FeO concentration of less than 5%.

14. The method of claim 13 wherein producing a slag treatment metal and a slag product comprises producing a slag product comprising an FeO concentration of less than 1%.

15. The method of claim 1 further comprising heating the initial slag with a blast furnace and wherein producing a slag treatment metal and a slag product comprises producing a slag product comprising an FeO concentration of less than 5%.

16. The method of claim 1 further comprisinq heating the initial slag with a top blown rotary converter and wherein producing a slag treatment metal and a slag product comprises producing a slag product comprising an FeO concentration of less than 5%.

17. The method of claim 1 further comprisinq heating the initial slag having an FeO concentration of at least 40%.

18. The method of claim 1 further comprising heating the feed material in a preheating chamber.

19. The method of claim 1 wherein processing the initial slag with a slag post-treatment process further comprises producing one or more grades of slag treatment metal using a step process with controllable reduction of the initial slag.

20. The method of claim 19 wherein producing one or more grades of slag treatment metal using a step process with controllable reduction of the initial slag comprises a full reduction of the initial slag and further metal treatment with an oxidizing agent.

21. The method of claim 1 further comprisinq heating the initial slag at a second temperature, wherein the second temperature is lower than the first temperature.

22. A method for processing metallurgical slag to recover differentiated metallic fractions, the method comprising:receiving a slag into a slag treatment reactor; andrefining the slag by introducing a reducing agent in at least one step comprising:reducing an iron oxide (“FeO”) content of the slag to a predetermined concentration lower than a previous concentration and separating at least one metallic fraction.

23. The method of claim 22 further comprising performing an impurity removal step on at least one of the separated at least one metallic fractions, the impurity removal step comprising introducing an oxidizing agent to the separated at least one metallic fraction to selectively oxidize trace impurities and transferring said oxidized impurities back into a slag phase.

24. The method of claim 23 wherein the oxidizing agent comprises at least one of mill scale, iron ore, and an iron oxide containing material.

25. The method of claim 22 wherein refining the slag by introducing a reducing agent in at least one step comprises refining the slag by introducing a reducing agent in a plurality of sequential reduction stages.

26. The method of claim 25 wherein introducing a reducing agent in a plurality of sequential reduction stages further comprises a final reduction stage that reduces the FeO content to a final concentration of less than 5% and produces a residual slag phase comprising a final binary basicity of calcium oxide to silicon dioxide of less than 1.5.

27. The method of claim 26 wherein the slag is mixed with a metallurgical byproduct, comprising an initial FeO content of at least 35% in an initial mix.

28. The method of claim 27 wherein the metallurgical byproduct comprises a mill scale.

29. The method of claim 26, wherein the plurality of sequential reduction stages comprises at least three stages comprising:a first stage of reducing the FeO content to a first concentration of below 25% and separating a first metallic fraction;a second stage of reducing the FeO content to a second concentration of below 15% and separating a second metallic fraction; anda third stage of reducing the FeO content such that the final concentration is achieved and separating a third metallic fraction.

30. The method of claim 26, wherein the plurality of sequential reduction stages comprises at least two stages comprising:a first stage of reducing the FeO content to a first concentration of between 15% and 25% and separating a first metallic fraction; anda second stage of reducing the FeO content such that the final concentration is achieved and separating a second metallic fraction.

31. The method of claim 26, wherein the residual slag phase produced after the final reduction stage is discharged and solidified to form a product comprising a binary basicity below 1.5 and a residual FeO content of less than 1%.

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