RU2847032C1 - Method of producing high-strength carbonised construction articles - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to production of high-strength construction articles and can be used in construction industry to produce various construction articles. In particular, the invention relates to production of carbonate hardened articles from industrial wastes of metallurgy and carbon dioxide. Invention provides a method of producing high-strength carbonised articles. Method involves preparation and mixing of raw material, addition of water, moulding, forced carbonisation with subsequent complete immersion of the obtained articles into a container with water and holding in an aqueous medium. Mineral raw materials and residual products of metallurgy – slags and sludges – are used as raw materials.

EFFECT: improved strength characteristics of construction articles.

8 cl, 4 dwg, 6 tbl, 3 ex

Description

A method for producing high-strength carbonized building products is claimed.

PURPOSE AND SCOPE OF APPLICATION

The invention relates to the production of high-strength building products and can be used in the construction industry for the production of various building components. Specifically, the invention relates to the production of carbonate-hardened products from metallurgical residual products, particularly metallurgical slags and sludges, and carbon dioxide. It is aimed at solving the fundamental problem of reducing the carbon footprint of the economy, particularly in the oil and gas refining, metallurgical, and construction industries. It is based on the development of scientific and technological foundations for the absorption and binding of anthropogenic CO2 by various metallurgical slags and sludges as a result of their processing into raw materials for building materials and products. In addition to solving the problem of CO2 utilization, the invention can be used in the production of concrete products, bricks, paving slabs, as well as in the construction of buildings and structures requiring materials with increased strength and durability.

LEVEL OF TECHNOLOGY

Solutions for the production of carbonized building materials are known from the prior art.

In particular, prior art discloses solutions that utilize by-products or secondary products of metallurgical production (in particular slags and sludges) as raw materials. In the Arcelormittal solution according to the invention [WO 2019064052, published 04.04.2019], molten steelmaking slag containing at least 2% by weight of free lime is solidified to produce solidified slag particles having a diameter of less than 1 mm. During solidification, the molten steelmaking slag is brought into contact with at least one first carbonization gas. The solidified slag particles are cooled to a temperature of 300°C or lower at a rate of 1 to 100°C/min, wherein during cooling, the solidified slag particles are brought into contact with at least one second carbonization gas. A device for continuously producing solidified steelmaking slag comprises a closed chamber containing a solidification device, a device for injecting a first carbonization gas, a device for injecting a second carbonization gas, a lower porous wall, and a device for injecting a third carbonization gas through the lower porous wall. This ensures the production of solidified slag with a low free lime content while maintaining a short processing time.

A device for producing bricks is known [CN 112318681, published 05.02.2021]. The invention discloses a method of operating a device for producing a brick body carbonized with carbon dioxide, and relates to the field of producing bricks for construction. The invention specially develops two processes of pre-carbonization and secondary carbonization, so that demolding and rapid strengthening are smoothly completed after the temporary stabilization of the shape and strength of the brick body. All systems in the device operate in accordance with a sequence of process operations, so that loading, molding, compaction and transportation of the brick mold are carried out simultaneously, the addition of brick material and uniform mixing are performed during the pre-carbonization process, productivity is increased due to the two-stage process and the transportation system; The upper conveyor belt and the lower conveyor belt rotate by means of a rotating shaft, the brick bodies are removed from the molds through spring stoppers in the brick molds, and the demoulding of the brick bodies and the effective cyclic use of empty brick molds are achieved through electromagnetic adsorption, release and transportation of the conveyor belts.

Also known from the prior art are solutions in which by-products or secondary products of metallurgical production or screenings from stone mining and stone crushing are used as raw materials. The paper “Method for producing composite carbonized products” [RU 2642573, published 18.08.2017] describes a method for producing composite carbonized products, which includes mixing slaked calcium or dolomite lime and a carbonate filler in the form of waste from the extraction and processing of limestones with a fraction of up to 5 mm to obtain a molding mass, carbonizing the products with carbon dioxide, characterized in that the products are additionally cut, the molding mass is prepared by extrusion, extrusion molding of products from the molding mass is carried out under a pressure of 55-75 kg-s/cm2, and waste from the sawing of shell limestones or nummulitic limestones, or waste from the crushing and processing of limestone rocks into crushed stone, or waste from the crushing and processing of igneous rocks into crushed stone are used as carbonate filler.

The author's certificate "Method for manufacturing lime-sand products" [Author's certificate 330128, published 24.11.1972] describes a method for manufacturing lime-sand products by preparing a raw mix based on quicklime dolomite, molding products from the mix, followed by their heat treatment, characterized in that, in order to eliminate deformations during heat and moisture treatment, increase the mechanical strength and service life of the products, the raw mix is kept for 15-20 minutes before molding, and freshly molded products are carbonized with carbon dioxide at a flow rate of 0.15-0.2 l/cm2 min, followed by heat and moisture treatment for 5-6 hours.

In another similar work by Roland BAYER and Wolfgang BURCHER, “Method for producing mineral molded articles” [RU2248952C2], a method for producing molded articles with bound phases of calcium silicate hydrate (CSH) is described, in which a mixture of raw materials from mineral components and at least one substance containing calcium that can interact with the phases of calcium silicate hydrate, at least one plasticizer and water are mixed until plasticization, condensed in a screw extruder, pressed through a die and the resulting blanks are cured by means of a hydrothermal reaction at a pressure of 8 to 25 bar and a high temperature of 180 to 240°C in a water vapor atmosphere to produce molded articles with CSH-bound phases, wherein polyethylene oxide or a cellulose ether is used as a plasticizer, which preferably has one or more substituents from the methyl, ethyl, hydroxyethyl, hydroxypropyl and sulfoethyl.

Also known from the prior art are a number of solutions related to equipment for carbonate hardening and forced carbonization of building materials.

A technical solution is known in the field of carbonization and graphitization equipment [CN219433778 (U), published 07/28/2023]. The integrated carbonization and graphitization furnace comprises a furnace body and an internal container chamber, which is located in the center of the furnace body interior. The furnace body and the outer door are connected so as to rotate relative to the inner part. A cylindrical exhaust opening is formed in the upper part of the furnace body; inlet and outlet openings for cooling water are located on the outer side door of the furnace; an air inlet opening and an air outlet opening are formed on the left and right sides of the furnace body, respectively.

The closest analogue chosen was "Method for manufacturing lime-sand products" [Author's Certificate 630236, published 10/30/1978]. The method for manufacturing lime-sand products based on quicklime or dolomite lime includes molding the products, their carbonization and subsequent hardening, characterized in that, in order to increase strength, reduce heat consumption and simplify the technology by eliminating heat and moisture treatment, subsequent hardening is carried out in an alkaline medium under normal conditions, and then the products are dried. Hardening is carried out in a recirculated sodium hydroxide solution of 0.3-0.5 normal concentration.

PROBLEMS AND TECHNICAL RESULTS

The disadvantages of the solutions discussed include the insufficient strength of the resulting carbonate-cured products compared to the present invention. Other common drawbacks of the prior art include the use of energy-intensive curing methods (autoclave curing at pressures up to 25 bar and temperatures up to 240°C or heat-moisture curing at temperatures up to 100°C and times up to 6 hours), as well as the low mechanical strength of the resulting building products obtained with these production methods. Consequently, low strength will result in a short service life for the products, high production costs, and significant metal consumption in the production line, especially when using autoclave equipment.

This entails high competition in the construction products market in a segment with similar strength characteristics and similar cost.

The disadvantages of the closest analogue include the low strength (15.7 MPa) of the resulting carbonate-cured products compared to the present invention. Furthermore, the additional curing of the products after carbonation in a recirculated sodium hydroxide solution of 0.3-0.5% of the normal concentration necessitates a significant fleet of expensive corrosion-resistant tanks and, consequently, significant production space. Furthermore, the need to dry the products at temperatures up to 100°C after removing them from the tanks containing the sodium hydroxide solution increases overall energy consumption for production and, consequently, the cost of the finished product.

The technical result of the invention is to increase the strength characteristics of building products. Moreover, this technical result can be achieved without increasing energy consumption or material intensity.

DISCLOSURE OF THE INVENTION

The technical result is achieved by solving the problem of improving the method for producing high-strength carbonized building products through final processing of carbonized products.

The method for producing high-strength carbonized products includes the preparation and mixing of raw materials, which are mineral raw materials and residual metallurgical products, the addition of water, molding, forced carbonization, and subsequent curing of the resulting products in an aqueous environment for a period of 12 to 28 days.

The invention is based on the technical task of improving the method for producing high-strength carbonized building products through final processing of carbonized products.

The technical problem is solved by a method for producing high-strength carbonized building products, which involves molding the products by pressing from a molding raw mix, carbonization with carbon dioxide, and subsequent curing of the products in an aqueous medium. According to the invention, the raw mix is prepared using residual metallurgical products: crushed metallurgical slag/sludge and fillers. Man-made metallurgical waste with a fraction of up to 5 mm is used as fillers. The products are molded at a specific pressing pressure of 10-30 MPa. After molding, the products are carbonized in a chamber at a CO2 concentration of up to 99% for 3-6 hours at atmospheric pressure and a temperature of 20-50°C. The products removed from the carbonization chamber are placed in containers with water for subsequent curing in an aqueous medium for a specified period of time (discussed in more detail in the implementation examples).

DESCRIPTION OF DRAWINGS AND DRAWINGS

The general flow chart of the process is shown in Figure 1, where:

1 - raw material preparation unit;

2 - molding block;

3 - carbonation block;

4 - water holding unit;

5 - finished goods warehouse.

Figures 2-4 show images of products obtained according to the invention, namely bricks and paving slabs according to embodiment examples.

DETAILED DESCRIPTION OF THE INVENTION

The following cause-and-effect relationship exists between the essential features of the invention and the technical result. The claimed method utilizes ground metallurgical slag/sludge as a binder. These slags contain significant amounts of calcium and magnesium oxides, which actively react with carbon dioxide to form nanoscale calcium carbonate crystals. As a result of this reaction, after 3-6 hours of exposure to carbonation in the chamber, the strength of the products reaches 50-60 MPa, while the structure of the products retains some ground metallurgical slag/sludge that has not undergone the carbonation reaction but possesses latent hydraulic properties. The resulting products are then placed in water-filled containers for subsequent aging in an aqueous medium for 12 to 28 days, which activates the hydration process of the ground metallurgical slag/sludge particles that have not undergone the carbonation reaction. Carbonized products are maintained in an aqueous environment under normal conditions. Due to the hydration of these particles, additional crystalline formations form in the product's structure, increasing the product's strength to 90-95 MPa and reducing water absorption by 3-7%. Taken together, this interaction increases the service life of the resulting products by increasing frost resistance cycles, a property that primarily determines the durability of construction products. In the claimed method, carbonization of products in a carbonation chamber is carried out without excess pressure for 3-6 hours at a temperature of 20-50°C. The temperature in the carbonation chamber rises to 50°C due to the exothermic chemical reaction of carbonation. In the claimed method, the products are maintained after carbonization in containers with ordinary tap water for 28 days. According to the prototype, the products are aged in a sodium hydroxide solution, an aggressive alkaline compound that requires corrosion-resistant containers, which increases capital investment in the equipment. The proposed method, using water as the aging medium, significantly reduces the corrosion resistance requirements for the container material and, consequently, the investment costs.

The manufacturing process consists of the operations of preparing binders and fillers, mixing these components to obtain a molding raw mix, pressing products from the raw mix, carbonization of the products with carbon dioxide in a carbonization chamber, followed by aging the resulting products in an aqueous environment to impart high strength characteristics to the products.

The preparation of binders and fillers for use in raw material compositions should include drying to a moisture content of 0-1% by weight and subsequent grinding (for binders) to obtain a powder with a specific particle surface area of 250 to 450 ^m2 /kg. Filler sizes up to 5 mm are used and are obtained by screening out large fractions of metallurgical slags and sludge or, if necessary, by grinding, followed by classification and selection of the required fractions.

To prepare raw mixes, crushed binder and aggregate up to 5 mm in size are loaded into a high-speed mixer (homogenizer) in the required proportions and mixed. After homogenization, the required amount of water is added to the mixer, and the mixing process is repeated to evenly distribute the water throughout the mixture. Additional components, such as pigments, are added to the mixer if necessary. The prepared mixture is then fed to a press, where the products are formed. The pressed products are loaded into a carbonation chamber, where they are artificially carbonized. Forced carbonation of the products obtained after pressing is carried out in the carbonation chamber for 3 to 6 hours in an artificially created environment with a CO2 concentration ranging from 30 to 99 vol%. After carbonization, the products are removed from the chamber and placed in an aqueous medium for subsequent aging for 12 to 28 days.

Specifically, finished products are placed in an aqueous environment by completely immersing them in an open container. The container size depends on the number of products. After this time, the products reach the required characteristics and can be shipped to the customer or warehouse.

In a particular case of the invention implementation, after keeping the products in an aqueous environment for a specified time, steaming was carried out to conduct further studies of the strength of the products.

The raw material preparation unit is a platform where the following equipment, which is part of the installation, is located:

- drum dryer for drying sludge/slag and mineral raw materials;

- crushing, grinding and sorting complex for processing sludge/slag and mineral raw materials;

- belt and screw conveyors for feeding prepared raw materials for processing and storage;

- pneumatic transport for transporting ground raw materials to the silo;

- silo for storing ground raw materials;

- consumption bins for storing mineral filler.

The molding unit includes:

- high-speed mixer-activator with a dosing complex;

- hydraulic presses for semi-dry pressing;

- robots for stacking molded products on pallets;

- water container;

- belt and screw conveyors for transporting raw materials and molding sand.

The carbonization curing unit is a complex of carbonization chambers and a manipulator complex for loading and unloading pallets with products and transporting products after carbonization to the packaging area.

A unit for curing carbonized products in an aqueous environment to increase their strength consists of open or closed containers in which carbonized products are placed for a specified period of time to enhance their strength. The container should be large enough to completely cover the products with water, plus an additional 10 cm of water above the top row of products.

The finished goods warehouse is a covered area. Forklifts are used for storing and loading finished goods.

EXAMPLES OF IMPLEMENTATION

The method for producing high-strength carbonized building products is illustrated by a number of examples implemented in pilot industrial operation of the invention.

EXAMPLE 1

Raw material base:

- prepared (crushed) nepheline sludge;

- waste nepheline sludge (without preliminary crushing);

- water;

- carbon dioxide captured from exhaust gas streams (concentration ≈80 vol.%).

The production cycle for Example 1 was launched using 1,000 carbonate-hardened bricks. A sketch and general view of the brick are shown in Figure 2.

Carbonate hardening mode of bricks

The forced carbonization mode of products in the chamber takes place in an artificially created environment with an increased concentration of CO2 in three stages:

1st stage - active carbonate hardening:

- duration - 30 min,

- the amount of CO2 that needs to be supplied to the chamber is 200 kg;

2nd stage - moderate carbonate hardening:

- duration - 90 min,

- the amount of CO2 that needs to be supplied to the chamber is 100 kg;

Stage 3 - exposure to carbon dioxide:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 100 kg.

Once the carbonization process is complete, the finished products are immersed in water to impart strength before storage. The curing period is 28 days. The time period depends on the type of product, its dimensions, and the required strength characteristics.

Results of testing samples after 28 days of exposure in a container with distilled water before steaming.

Table 1. Strength characteristics after exposure to water.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after exposure to water, MPa A b Samples of bricks based on nepheline mud 1 25 12 110500 10.1 36.8 45.6 2 25 12 109675 10.2 36.6 44.5 3 25 12 111250 9.9 37.1 46.1 Average 10.1 36.8 45.4

Results of testing samples after 28 days of exposure in a container with distilled water and subsequent three steaming cycles.

Table 2. Strength characteristics after exposure to water and steaming.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after the steaming cycle, MPa A b Samples of bricks based on nepheline mud 1 25 12 115750 9.6 - 48.1 2 25 12 117,000 9.9 - 49.5 3 25 12 116250 9.7 - 48.6 Average 9.7 - 48.7

During tests of brick samples for silicate decomposition, no processes indicating material degradation (such as cracks or surface peeling) were detected. As can be seen from Tables 1 and 2, water absorption by weight of the samples before and after steam curing remained virtually unchanged, and the variation in values was within the experimental error. If silicate decomposition occurs within the material (the polymorphic transformation of 2CaO∙ _SiO2 from one form to another), its water absorption should increase significantly. These tests demonstrated the resistance of the resulting carbonized brick material to silicate decomposition.

EXAMPLE 2

Similar to the first experiment, experiment 2 was conducted in which the time of exposure of carbonized products in an aqueous environment was reduced.

For this experiment, paving slabs based on steel slag were chosen as carbonized products.

Raw material base:

- steelmaking slag, prepared crushed (ground);

- waste steelmaking slag of fraction 0.63-5 mm (without preliminary crushing);

- water;

- carbon dioxide captured from exhaust gas streams (concentration ≈80 vol.%).

The launch of the technological cycle according to example 2 was carried out on 1000 pieces of carbonate-hardened paving slabs

The forced carbonization mode of products in the chamber takes place in an artificially created environment with an increased concentration of CO2 in three stages:

1st stage - active carbonate hardening:

- duration - 60 min,

- the amount of CO2 that needs to be supplied to the chamber is 130 kg;

2nd stage - moderate carbonate hardening:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 90 kg;

Stage 3 - exposure to carbon dioxide:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 40 kg.

Once the carbonization process is complete, the finished products are placed in an aqueous medium to impart strength before storage. The curing period lasts for 12 days. The timeframe depends on the type of product, its dimensions, and the required strength characteristics.

Results of testing samples after 12 days of exposure in a container with distilled water before steaming.

Table 3. Strength characteristics after exposure to water.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after exposure to water, MPa A b Samples of tiles based on steel slag 1 7 7 49500 6.7 75.2 99.0 2 7 7 53625 6.7 81.5 107.3 3 7 7 48000 6.6 73.0 96, 0 Average 6.7 76.6 100.8

Results of testing samples after 12 days of exposure in a container with distilled water and subsequent three steaming cycles.

Table 4. Strength characteristics after exposure to water and steaming.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after the steaming cycle, MPa A b Samples of tiles based on steel slag 1 7 7 45,000 6.8 - 96.0 2 7 7 54000 6.2 - 98.2 3 7 7 47125 6.9 - 94.3 Average 6.6 - 96.2

During silicate decomposition testing of paving slab samples, no processes (cracking or surface peeling) indicating material degradation were detected. As can be seen from Tables 3 and 4, water absorption by weight of the samples before and after steam curing remained virtually unchanged, and the variation in values was within the experimental error. If silicate decomposition occurs within the material (the polymorphic transformation of 2CaO∙ _SiO2 from one form to another), its water absorption should increase significantly. These tests demonstrated the resistance of the resulting carbonized slab material to silicate decomposition. The decrease in average product strength after three steam curing cycles was within the error limit and was not a consequence of a decrease in product strength.

EXAMPLE 3

To compare the results obtained after two experiments, an experiment was conducted with keeping paving slabs in an aqueous environment for 20 days.

Slag from an electrometallurgical plant was chosen as the raw material base for the production of paving slabs.

Raw material base:

- prepared crushed (ground) electric steelmaking slag;

- electric steelmaking waste slag of fraction 0.63-5 mm (without preliminary crushing);

- water;

- carbon dioxide captured from exhaust gas streams (concentration ≈80 vol.%).

The launch of the technological cycle according to example 2 was carried out on 1000 pieces of carbonate-hardened paving slabs.

The forced carbonization mode of products in the chamber takes place in an artificially created environment with an increased concentration of CO2 in three stages:

1st stage - active carbonate hardening:

- duration - 60 min,

- the amount of CO2 that needs to be supplied to the chamber is 130 kg;

2nd stage - moderate carbonate hardening:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 90 kg;

Stage 3 - exposure to carbon dioxide:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 40 kg.

Once the carbonization process is complete, the finished products are immersed in water to impart strength before storage. The curing period is 20 days. The time frame depends on the type of product, its dimensions, and the required strength characteristics.

Results of testing samples after 20 days of exposure in a container with distilled water before steaming.

Table 5. Strength characteristics after exposure to water.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after exposure to water, MPa A b Samples of tiles based on electrometallurgical slag 1 7 7 41125 8.3 59.4 80.5 2 7 7 40750 8.3 67.5 83.3 3 7 7 41250 9.3 69.3 85.5 Average 8.6 66.5 83.1

Results of testing samples after 20 days of exposure in a container with distilled water and subsequent three steaming cycles.

Table 6. Strength characteristics after exposure to water and steaming.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength of the sample after the steaming cycle, MPa A b samples of tiles based on electrometallurgical slag 1 7 7 36625 9.1 - 82.3 2 7 7 41625 8.9 - 81.5 3 7 7 42750 9.5 - 82.5 Average 9.2 - 82.1

During silicate decomposition testing of paving slab samples, no processes (cracking or surface peeling) indicating material degradation were detected. As can be seen from Tables 5 and 6, the water absorption by weight of the samples before and after steam curing remained virtually unchanged, and the variation in values was within the experimental error. If silicate decomposition occurs within the material (the polymorphic transformation of 2CaO∙ _SiO2 from one form to another), its water absorption should increase significantly. These tests demonstrated the resistance of the resulting carbonized slab material to silicate decomposition.

Claims (8)

1. A method for producing high-strength carbonized products, which includes the preparation and mixing of raw materials, which are mineral raw materials and residual products of metallurgy - slags and sludge, the addition of water, molding, forced carbonization, followed by complete immersion of the resulting products in a container with water and maintaining the resulting products in an aqueous environment for a period of time from 12 to 28 days. 2. The method according to paragraph 1, in which the molding of the products is carried out by pressing from the molding raw material mixture. 3. The method according to claim 1, wherein carbonization is carried out for 3 to 6 hours in artificially created environments with a CO2 concentration in the range of 30 to 99 vol.%. 4. The method according to claim 1, wherein the holding is carried out in distilled water. 5. The method according to claim 1, wherein the holding in an aqueous medium is carried out under normal conditions. 6. The method according to paragraph 1, in which the holding in an aqueous medium is carried out in open or closed containers. 7. The method according to paragraph 1, in which the holding in an aqueous environment is carried out with the products arranged in such a way as to ensure a water layer on top of the products or the top row of products of at least 0.1 m. 8. The method according to paragraph 1, wherein the manufactured products are paving slabs or bricks.