Method for producing inorganic binder using reduced slag and solidified product formed therefrom

Abstract

A method for producing an inorganic binder using reducing slag comprises a raw material preparation step, a mixing step, a curing step, and a drying step. The raw material preparation step is to provide a powder mixture. In the powder mixture, reducing slag powder accounts for 30wt% to 55wt%, glass powder accounts for 45wt% to 70wt%, the glass powder contains more than 85wt% of SiO2, and the reducing slag powder contains 26wt% to 62wt% of CaO, 20wt% to 32wt% of SiO2, and 1.8wt% to 12.5wt% of Al2O3. The mixing step is to place the powder mixture in a mixing tank, add an alkali activator for mixing and reaction, and form a mixed slurry. The alkali equivalent of the mixed slurry is 2% to 7%, and the water-binder ratio is 0.25 to 0.4. The curing step is to place the mixed slurry in a high-temperature and high-pressure curing environment to obtain a binder. The drying step is to dry the binder.

Description

Technical Field

[0001] The present invention relates to the field of waste recycling, and in particular to a method for producing an inorganic binder by using reduced slag and a solidified product formed thereby. Background Art

[0002] The electric arc furnace steelmaking process can be divided into three phases: melting, oxidation, and reduction. The melting phase involves melting scrap steel in a high-temperature arc to form molten steel. During the oxidation phase, high-pressure oxygen is introduced to accelerate oxidation, generating a large amount of impurities, including gaseous oxide slag and solid oxides. At this point, the oxygen content in the molten steel is too high and must be reduced.

[0003] Finally, the process enters the reduction phase, where large amounts of secondary raw materials such as limestone and coke are added. The reduction reaction removes oxygen from the molten steel, forming slag. This also removes impurities such as sulfur, thus cleaning the molten steel. The slag is separated from the molten steel by its different specific gravity. The discharged slag, after cooling, becomes the electric arc furnace reduction slag.

[0004] Electric arc furnace (EAF) reducing slag is a major waste product of the steelmaking industry. Recent reports on industrial waste declarations indicate that approximately 260,000 metric tons of EAF reducing slag is generated, making it an urgent waste resource in need of disposal. Since reducing slag primarily originates from steel mills, it contains a high proportion of heavy metals. Direct landfilling poses concerns about heavy metal leaching.

[0005] Therefore, industrial nations around the world are focusing on technologies to recycle electric arc furnace (EAF) reduction slag. Currently, due to its fine, pulverized particles and chemical composition intermediate between cement and water-quenched blast furnace slag, it is primarily being used as a cement material. The chemical composition of reduction slag, primarily composed of compounds such as calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, sulfides, and manganese oxide, expands upon hydration, causing cracking and even damage to concrete, limiting its application in concrete engineering. Furthermore, its overall strength is insufficient, generally below 12 MPa, well below the minimum standard of 15 MPa for structural applications, limiting its use as a premixed concrete and cement material for non-structural applications. Furthermore, if concrete cracks, exposing the slag, poses the risk of strong alkaline contamination from heavy metals. Summary of the Invention

[0006] In order to solve the problems faced by the prior art, a method for making an inorganic binder using reducing slag is provided herein. The method for making an inorganic binder using reducing slag comprises a raw material preparation step, a mixing step, a curing step and a drying step. The raw material preparation step is to provide a powder mixture comprising reducing slag powder and glass powder. In the powder mixture, reducing slag powder accounts for 30wt% to 55wt%, glass powder accounts for 45wt% to 70wt%, the glass powder contains more than 85wt% of SiO2, and the reducing slag powder contains 26wt% to 62wt% of CaO, 20wt% to 32wt% of SiO2 and 1.8wt% to 12.5wt% of Al2O3.

[0007] The mixing step involves placing the powder mixture in a mixing tank and adding an alkali activator to the mixing tank for mixing and reacting to form a mixed slurry. The mixed slurry has an alkali equivalent of 2% to 7% and a water-binder ratio of 0.25 to 0.4. Here, the alkali equivalent is defined as in equation (1), and the water-binder ratio is defined as in equation (2).

[0008]

[0009] Equation (2):

[0010]

[0011] The curing step is to place the mixed slurry in a high temperature and high pressure curing environment for a curing time to obtain a cemented body, wherein the high temperature and high pressure curing environment has a temperature of 80 to 250 degrees Celsius, a pressure of 0.3 to 2.5 MPa, and a curing time of 0.5 to 24 hours. The drying step is to dry the cemented body.

[0012] In some embodiments, the alkali activator is NaOH, and the alkali equivalent of the mixed slurry is 4% to 6%.

[0013] In some embodiments, the curing step further includes a slurry shaping step, in which the mixed slurry is placed in a shaping mold and maintained at an environment of 60 to 100 degrees Celsius for 40 to 180 minutes.

[0014] In some embodiments, the reduced slag powder further comprises less than 20 wt % MgO, less than 5 wt % MnO, and less than 18 wt % Fe 2 O 3 .

[0015] In some embodiments, the glass powder is selected from the group consisting of general glass, electronic grade glass fiber, and glass substrate.

[0016] In some embodiments, the glass powder further comprises 9 wt % to 15 wt % of CaO.

[0017] In some embodiments, the specific surface area of the reduced slag powder ranges from 1900 to 2600 cm 2 / g, the specific surface area of the glass powder ranges from 3500 to 5000 cm 2 / g.

[0018] In some embodiments, the temperature of the high temperature and high pressure curing environment is 150 to 230 degrees Celsius, the pressure is 0.5 to 2 MPa, and the curing time is 2 to 4 hours.

[0019] In some embodiments, the base activator is mixed with the powder mixture for a period of 10 to 30 minutes.

[0020] Here, a solidified inorganic binder is also provided, which is formed by the method of making an inorganic binder by reducing slag according to the above embodiment.

[0021] As shown in the aforementioned embodiments, the addition of waste glass powder to the reduced slag powder increases the overall silicon content. Consequently, subsequent alkali activation with an alkali activator dehydrates the silicon and aluminum ions in the slurry, leading to a polycondensation reaction and forming a predominantly silicon-aluminum network. After curing and drying, the resulting product becomes a hard, solidified product with sufficient strength for structural use. Furthermore, the heavy metal components of the reduced slag are encapsulated within the network, with the leaching rate far below the standard. This allows for the effective reuse of the reduced slag, achieving low-cost, high-volume recycling, helping to reduce landfill issues and enabling recycling, effectively minimizing environmental impact.

[0022] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this does not limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flow chart of a method for producing an inorganic binder using reduced slag.

[0024] Figure 2 The compressive strength curve of inorganic binder with a pressure of 0.5Mpa and curing time of 2 hours from 0 to 28 days.

[0025] Figure 3 The compressive strength curve of inorganic binder with a pressure of 0.5Mpa and curing time of 4 hours from 0 to 28 days.

[0026] Figure 4 The compressive strength curve of inorganic binder from 0 to 28 days with a pressure of 1Mpa and curing time of 2 hours.

[0027] Figure 5 The compressive strength curve of inorganic binder with a pressure of 1Mpa and curing time of 4 hours from 0 to 28 days.

[0028] Figure 6 The compressive strength curve of inorganic binder with a pressure of 2 MPa and curing time of 2 hours from 0 to 28 days.

[0029] Figure 7 The compressive strength curve of inorganic binder with a pressure of 2Mpa and curing time of 4 hours from 0 to 28 days.

[0030] Wherein, reference numeral S1: Method for producing inorganic binder using reduced slag

[0031] S10: Raw material preparation step

[0032] S20: Mixing step

[0033] S25: Shaping step

[0034] S30: Maintenance steps

[0035] S40: Drying step DETAILED DESCRIPTION

[0036] The structural principle and working principle of the present invention are described in detail below with reference to the accompanying drawings:

[0037] Figure 1 This is a flow chart of a method for producing inorganic binder using reduced slag. Figure 1 As shown, the method S1 for producing an inorganic binder using reduced slag includes a raw material preparation step S10, a mixing step S20, a curing step S30 and a drying step S40.

[0038] The raw material preparation step S10 provides a powder mixture of reducing slag powder and glass powder. The reducing slag powder accounts for 30 to 55 weight percent, and the glass powder accounts for 45 to 70 weight percent. The ratio of the reducing slag powder to the glass powder is adjusted to maximize slag consumption while providing a higher SiO2 content. Generally, the reducing slag powder preferably accounts for 45 to 55 weight percent, and the glass powder preferably accounts for 45 to 55 weight percent. The glass powder contains over 85 weight percent SiO2, while the reducing slag powder contains 26 to 62 weight percent CaO, 20 to 32 weight percent SiO2, and 1.8 to 12.5 weight percent Al2O3.

[0039] The glass powder is derived from one or more of general glass, electronic-grade glass fiber, or glass substrate. General glass, electronic-grade glass fiber, or glass substrate are primarily sourced from recycled scrap glass products. The glass powder is obtained through a crushing process. The glass powder contains over 85% SiO2 by weight and may also contain 9% to 15% CaO, primarily providing the silicon component.

[0040] Reducing slag powder comes from the reducing slag left behind by electric arc furnaces or converters in steel mills. Because the raw steel used varies, even with the same raw materials, the resulting reducing slag composition varies. After pulverization, the reducing slag powder is obtained. Generally, reducing slag powder contains less than 20% by weight of MgO, less than 5% of MnO, and less than 18% of Fe₂O₃.

[0041] Compared to the significant variations in the composition of the reduced slag powder from one run to the next, the composition of the glass powder is relatively stable. In practice, the composition ratio of the reduced slag powder can be measured first, and the ratio of glass powder and the added alkali activator can be adjusted accordingly. Specifically, the specific surface area of the pulverized reduced slag powder ranges from 1900 to 2600 cm 2 / g, the specific surface area of the glass powder ranges from 3500 to 5000 cm 2 / g. In this way, the surface area of the powder mixture is increased to increase the reaction rate.

[0042] In the mixing step S20, the powder mixture is placed in a mixing tank and an alkali activator is added thereto for mixing and reaction to form a mixed slurry. Here, the alkali activator is NaOH for cost-effectiveness, but KOH or other alkaline solutions can be substituted. However, when KOH is used as the alkalizing agent, Na2O in equation (1) below is replaced with K2O.

[0043] In the mixed slurry, the alkali activator can be adjusted based on the composition of the reduced slag powder, the desired strength of the final product, and the desired alkali equivalent and water-binder ratio. Generally speaking, the reduced slag powder itself contains high levels of calcium oxide and magnesium oxide, so only a small amount of alkali activator is required as a trigger. In some embodiments, the alkali equivalent is 2% to 7%, preferably 4% to 6%. This corresponds to a water-binder ratio of 0.25 to 0.4, preferably 0.3 to 0.35.

[0044] Here, the alkali equivalent is defined as in equation (1), and the water-binder ratio is defined as in equation (2).

[0045]

[0046] Equation (2):

[0047]

[0048] The mixing step S20 mainly allows CaO, MgO, MnO, MnS and other substances in the reduced slag powder, which expand in volume when exposed to water, to react first, causing the volume of the cement to expand first in the state of the mixed slurry. Then, the silicon and aluminum ions in the mixed slurry are dehydrated and subjected to condensation reactions, solidifying into silicon and aluminum inorganic polymers, so that the volume of the cement can be stabilized.

[0049] In more detail, during the mixing stage, the base activator is mixed with the powder mixture for a period of 10 to 30 minutes.

[0050] Since the reducing slag powder contains high contents of CaO, MgO, and MnO, which may cause volume expansion, the curing step S30 is to place the mixed slurry in a high-temperature and high-pressure curing environment. The high temperature and high pressure increase the dehydration of silicon and aluminum ions, accelerate the polycondensation reaction, and at the same time, reduce the gas molecules and pores in the silicon and aluminum inorganic polymer, thereby making the silicon and aluminum inorganic polymer harder and improving the overall mechanical strength.

[0051] In the curing step S30, the high-temperature, high-pressure curing environment is maintained at a temperature of 80 to 250°C and a pressure of 0.3 to 2.5 MPa. Preferably, the temperature is 120 to 230°C and the pressure is 0.5 to 2 MPa. The curing time is 0.5 to 24 hours, preferably 1 to 6 hours, and more preferably less than 2 to 4 hours, to better meet industrial requirements.

[0052] The chemical reactions occurring during the mixing step S20 and the curing step S30 are described in detail below. Generally speaking, the SiO2 in the reduced slag powder and glass powder reacts with NaOH, breaking the original glassy O-Si-O bonds and producing a dissociation reaction known as alkali activation, the reaction equation of which is shown in Equation (1). In practice, since the reduced slag powder may vary from one run to another, the alkalinity of the reduced slag powder itself is considered to adjust the amount of alkali activator added and set the alkali equivalent required for the reaction.

[0053] Reaction formula (1): ≡Si-O-Si≡+OH - →≡Si-OH+≡Si-O - .

[0054] Then, the dissociated silicon-oxygen monomer anions, such as ≡Si-O - And ≡Si-OH continues to react with water to generate Si(OH)4, as shown in reaction formula (2) and reaction formula (3).

[0055] Reaction formula (2): ≡Si-O - +H2O→≡Si-OH+OH - .

[0056] Reaction formula (3): ≡Si-OH≡+H2O→Si(OH)4.

[0057] Then, Si(OH)4 and NaOH continue to react to form silicate monomers, as shown in reaction formula (4).

[0058] Reaction (4): Si(OH)4+NaOH→[Si(OH)3O] - Na + +H2O.

[0059] When the reaction continues, causing the concentration of silicate monomers in the mixed slurry to continue to increase, a condensation reaction may occur to form silicate dimers, as shown in reaction formula (5), and continue to undergo polymerization reactions with other silicate monomers to further form a silicate framework structure.

[0060] Reaction formula (5):

[0061] OSi(OH)3+Na + O - Si(OH)3+Na + →Na +- OSi(OH)3-O-Si(OH)3+NaOH.

[0062] Furthermore, in the reaction formula, part of the silicon will be replaced by aluminum, forming a silicon-aluminum-oxygen framework structure. Since the reducing slag powder also contains less than 20wt% MgO, less than 5% MnO, and less than 18% Fe2O3. After the reaction forms the silicon-aluminum-oxygen framework structure, ions such as calcium, magnesium, manganese, and sulfur will be fixed on the framework structure to form stable oxides. After sufficient curing time, a cemented body with a stable volume is obtained. Since the heavy metal ions can be stabilized in the framework structure, no free ions will be formed, and the dissolution of heavy metals can be avoided to cause environmental pollution.

[0063] The drying step S40 involves drying the binder. Excess moisture can be removed by standing, drying, or air-drying, resulting in a solidified inorganic binder. When needed, water can be added to replace cement and form mortar with sand.

[0064] Furthermore, the curing step S30 further includes a shaping step S25, in which the mixed slurry is placed in a shaping mold and maintained in an environment of 60 to 100 degrees Celsius for 40 to 180 minutes, preferably in an environment of 80 to 90 degrees Celsius for 60 to 150 minutes, so that the slurry can be initially shaped for subsequent applications.

[0065] The following will illustrate the method S1 of making an inorganic binder using reduced slag with a practical example.

[0066] First, in step S10, raw materials are prepared to prepare reducing slag powder and glass powder. After receiving the reducing slag, it is powdered and analyzed by XRF. The reducing slag powder contains 44.92wt% CaO, 24.84wt% SiO2, 11.02wt% Al2O3, 15.83wt% MgO, 0.25wt% MnO, 0.81wt% Fe2O3, and 0.80wt% TiO2.

[0067] The glass from the waste glass plant was powdered and analyzed by XRF. The glass powder contained 87.36 wt% SiO2, 11.15 wt% CaO, 0.25 wt% Al2O3, 0.27 wt% Fe2O3, and 0.63 wt% K2O.

[0068] The reducing slag powder and the glass powder were mixed in a weight ratio of 1:1, and flake caustic soda (98.31% NaOH) was added to prepare experimental groups with alkali equivalents of 4%, 6%, and 8%. The mixing step S20 was performed for 15 minutes.

[0069] Next, the mixed slurry is placed in a 3cm*3cm*3cm silica gel membrane and subjected to a shaping step S25 in which the slurry is initially shaped in an oven at 80 degrees Celsius for 120 minutes.

[0070] After the slurry was set, a curing step ( S30 ) was performed. Different experimental groups were cured at pressures of 0.5 MPa, 1 MPa, and 2 MPa for 2 and 4 hours, respectively. The curing environment used a steam chamber pressure boiler, with temperatures corresponding to 0.5 MPa at 155°C, 1 MPa at 184°C, and 2 MPa at 215°C. After drying, the slurry was placed in a curing environment at room temperature and pressure, and its compressive strength was measured daily.

[0071] Figures 2 to 7 The compressive strength curves are at different curing pressures and curing times from 0 to 28 days. Figures 2 to 7 The curing pressure and curing time are 0.5Mpa, curing for 2 hours; 0.5Mpa, curing for 4 hours; 1Mpa, curing for 2 hours; 1Mpa, curing for 4 hours; 2Mpa, curing for 2 hours; and 2Mpa, curing for 4 hours.

[0072] like Figures 2 to 7As shown, under the same composition ratio, the 4% alkali equivalent group achieved the highest compressive strength of 21.4 MPa after 28 days at a curing pressure of 2 MPa. The 4% and 6% alkali equivalent groups both achieved strengths exceeding 15 MPa under curing pressures of 1 MPa and 2 MPa, respectively. However, in the 0.5 MPa curing group, only the 4% and some 6% groups reached 15 MPa.

[0073] In addition, the inorganic binder was analyzed for toxic dissolution, and the measured dissolution concentrations were compared with regional and international standards as shown in Table 1 below. It can be understood that the silicon-aluminum-oxygen framework structure captures heavy metal ions for coordination, and the dissolution concentrations are lower than international standards. Therefore, in terms of application, it can reduce the impact on the environment more than directly burying the reduced slag.

[0074] Table 1

[0075]

[0076] In summary, by adding waste glass powder to the mixture with reducing slag powder, the overall silicon content can be increased. Consequently, subsequent alkali activation with an alkali activator dehydrates the silicon and aluminum ions in the slurry, causing a polycondensation reaction and forming a predominantly silicon-aluminum network. After curing and drying, the resulting product becomes a hard, solidified product with sufficient strength to serve as a structural object. Furthermore, the heavy metal components of the reducing slag are encapsulated within the network, with the dissolution rate far below the standard. This allows for the effective reuse of the reducing slag, achieving low-cost, high-volume recycling, helping to reduce landfill issues and enabling recycling, effectively minimizing environmental impact.

[0077] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for producing an inorganic binder using reduced slag, characterized in that: Include: a raw material preparation step, providing a powder mixture comprising reducing slag powder and glass powder, wherein the reducing slag powder accounts for 30 wt% to 55 wt% of the powder mixture, and the glass powder accounts for 45 wt% to 70 wt% of the glass powder, wherein the glass powder contains more than 85 wt% of SiO2 and 9 wt% to 15 wt% of CaO, and the reducing slag powder contains 26 wt% to 62 wt% of CaO, 20 wt% to 32 wt% of SiO2, and 1.8 wt% to 12.5 wt% of Al2O3; a mixing step of placing the powder mixture in a mixing tank and adding an alkali activator in the mixing tank for mixing and reacting to form a mixing slurry, wherein the alkali equivalent of the mixing slurry is 2% to 7% and the water-binder ratio is 0.25 to 0.4; a curing step, placing the mixed slurry in a high-temperature and high-pressure curing environment for a curing time to obtain a cementitious body, wherein the high-temperature and high-pressure curing environment has a temperature of 150 to 230 degrees Celsius, a pressure of 0.5 to 2 MPa, and a curing time of 2 to 4 hours; and a drying step of drying the colloid; The base equivalent is defined as in equation (1), and the water-binder ratio is defined as in equation (2). Equation (1): Equation (2): The specific surface area of the reduced slag powder ranges from 1900 to 2600 cm 2 / g, the specific surface area of the glass powder ranges from 3500 to 5000 cm 2 / g.

2. The method for producing an inorganic binder using reduced slag according to claim 1, wherein: The alkali activator is NaOH, and the alkali equivalent of the mixed slurry is 4% to 6%.

3. The method for producing an inorganic binder using reduced slag according to claim 1, wherein: Before the curing step, a slurry shaping step is also included, in which the mixed slurry is placed in a shaped mold and maintained in an environment of 60 to 100 degrees Celsius for 40 to 180 minutes.

4. The method for producing an inorganic binder using reduced slag according to claim 1, wherein: The reduced slag powder further contains less than 20 wt% of MgO, less than 5% of MnO and less than 18% of Fe2O3.

5. The method for producing an inorganic binder using reduced slag according to claim 1, wherein: The glass powder is selected from the group consisting of general glass and electronic grade glass fiber.

6. The method for producing an inorganic binder using reduced slag according to claim 1, wherein: The base activator is mixed with the powder mixture for a period of 10 to 30 minutes.

7. An inorganic binder solidified product, formed by the method for producing an inorganic binder by using reduced slag as claimed in any one of claims 1 to 6.

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