Composite modification method for improving density of coal gangue ceramsite sand

Abstract

The invention relates to the technical field of ceramsite sand treatment, and discloses a composite modification method for improving the density of gangue ceramsite sand. The method comprises the following steps: crushing and grinding coal gangue, soaking and activating; preparing a composite modifier system; mixing the activated coal gangue and a modifier, and curing; preforming by using a granulator and spraying a binder; carrying out gradient calcination and surface modification; and carrying out gradient cooling strengthening and screening classification to obtain a high-density ceramsite sand finished product. The density of the coal gangue ceramsite sand is improved, the internal structure and surface characteristics of the coal gangue ceramsite sand are improved through a systematic composite modification method, the strength of the coal gangue ceramsite sand is remarkably improved while the light characteristic is kept, the water absorption rate is reduced, and the durability is enhanced.

Description

Technical Field

[0001] This application relates to the technical field of ceramsite sand treatment, and particularly to a composite modification method for improving the density of coal gangue ceramsite sand. Background Art

[0002] Coal gangue is a solid waste generated during coal mining and washing. Traditional treatment methods mostly involve stacking or landfilling, which not only occupy a large amount of land resources but also may cause environmental pollution problems, such as acidic leachate polluting groundwater and spontaneous combustion generating harmful gases. With the promotion of the concept of circular economy, the resource utilization of coal gangue has become an effective way to solve the problem. Among them, preparing coal gangue into ceramsite sand for the construction field is a relatively mature technical route. The traditional coal gangue ceramsite sand preparation process usually includes steps such as raw material crushing, mixing granulation, drying and calcination, and cooling and grading. Through high-temperature calcination, the minerals in coal gangue undergo phase transformation and sintering to form lightweight aggregates with certain strength and pore structure.

[0003] However, the coal gangue ceramsite sand prepared by the existing technology has obvious deficiencies. First, the density of traditional ceramsite sand is relatively low and the strength is insufficient. The single-grain compressive strength is generally lower than 5 MPa, which limits its application in high-strength concrete. Second, the water absorption rate of traditional ceramsite sand is high, generally between 10 - 15%, resulting in the need to increase additional water consumption during concrete mixing, which affects the performance of concrete. Third, the durability is poor, especially it is prone to cracking and damage in the freeze-thaw cycle and dry-wet alternation environment. In addition, the problems of high energy consumption and poor product quality stability in the traditional process also restrict the popularization and application of coal gangue ceramsite sand. The core of these problems lies in the insufficient density of ceramsite, which is manifested as unreasonable pore structure inside the particles, poor surface sealing, and low particle strength. Summary of the Invention

[0004] This application provides a composite modification method for improving the density of coal gangue ceramsite sand, which is used to improve the density of coal gangue ceramsite sand. Through a systematic composite modification method, its internal structure and surface characteristics are improved. While maintaining the lightweight characteristics, its strength is significantly increased, the water absorption rate is reduced, and the durability is enhanced to meet the application requirements of high-performance building materials, thereby realizing the high-value utilization of coal gangue resources.

[0005] In a first aspect, the present application provides a composite modification method for improving the density of coal gangue ceramsite sand. The composite modification method for improving the density of coal gangue ceramsite sand includes: crushing and grinding coal gangue by a jaw crusher and a ball mill, and then soaking and activating the obtained fine coal gangue powder with a hydrochloric acid solution under constant temperature conditions to obtain an activated coal gangue powder; mixing silica sol and water glass in a predetermined ratio, and successively adding a polyacrylamide solution, a cetyltrimethyl solution, and modified calcium lignosulfonate, and then adjusting the pH value to the neutral range with a phosphoric acid solution to obtain a composite modifier system; mixing the activated coal gangue powder and the composite modifier system in a solid-liquid ratio in a double-shaft forced mixer, and then curing under constant temperature and humidity conditions to obtain a modified coal gangue mixture; preforming the modified coal gangue mixture by a disk granulator, and simultaneously spraying a binder solution containing polyvinyl alcohol and sodium carboxymethylcellulose to obtain preformed ceramsite; performing multi-stage temperature gradient calcination treatment on the preformed ceramsite, then spraying a high-temperature stable composite modifier, and performing surface modification under an oxygen-controlled atmosphere to obtain dense ceramsite; performing cooling strengthening treatment on the dense ceramsite by a gradient cooling technique, and then performing particle size classification by a vibrating screening device to obtain a finished product of high-density coal gangue ceramsite sand.

[0006] In the technical solution provided by this application, a jaw crusher and a ball mill are used to precisely grind gangue, and combined with soaking and activating treatment with hydrochloric acid solution, which significantly improves the specific surface area and activity of gangue. Especially the porous structure formed during the hydrochloric acid soaking process enhances the penetration depth of the modifier and the reaction efficiency, and improves the physical properties of the final product from the source. Secondly, through the precise proportioning and mixing of silica sol and water glass, and successively adding functional components such as polyacrylamide solution, cetyltrimethyl solution, and modified calcium lignosulfonate, a multifunctional synergistic composite modifier system is constructed; this system simultaneously has functions such as bond enhancement, hydrophobic modification, and dispersion stability, and the precise regulation of the pH value ensures the balance of the system stability and reaction activity. Thirdly, the application of a double-shaft forced mixer realizes the full and uniform mixing of activated gangue powder and the composite modifier, and the constant temperature and humidity curing promotes the modifier to penetrate into the internal pores of gangue and react with it to form a networked silicon-aluminum-oxygen composite structure, significantly improving the integrity and density of the material. Fourthly, the pre-forming treatment by a disk granulator combined with the spraying of a specific binder solution realizes the efficient production and particle size control of pre-formed ceramsite. The obtained ceramsite has regular shape and smooth surface, providing a semi-finished product with uniform quality for subsequent heat treatment. Fifthly, the combination of multi-stage temperature gradient calcination and surface treatment with a high-temperature stable composite modifier realizes the high densification of ceramsite in an oxygen-controlled atmosphere. The surface modification layer is firmly combined with the matrix to form a protective layer with excellent sealing performance, effectively blocking the intrusion of external moisture. Finally, the gradient cooling technology creatively forms a residual compressive stress field inside the ceramsite, significantly improving the compressive strength and impact resistance of the ceramsite, and the vibration screening device ensures the precise control of the particle size distribution of the product. Brief Description of the Drawings

[0007] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0008] Figure 1 It is a schematic diagram of an embodiment of the composite modification method for improving the density of gangue ceramsite sand in the embodiment of this application; Detailed Embodiments

[0009] The embodiment of the present application provides a composite modification method for improving the density of coal gangue ceramsite sand. Terms such as "first", "second", "third", "fourth", etc. (if any) in the specification, claims and above-mentioned drawings of the present application are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances, so that the embodiments described here can be implemented in an order other than that illustrated or described here. In addition, the term "comprising" or "having" and any variation thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0010] For ease of understanding, the specific process of the embodiment of the present application will be described below. Please refer to Figure 1 , an embodiment of the composite modification method for improving the density of coal gangue ceramsite sand in the embodiment of the present application includes:

[0011] Step S101: Crush and grind coal gangue through a jaw crusher and a ball mill, and then soak and activate the obtained fine coal gangue powder with hydrochloric acid solution under constant temperature conditions to obtain activated coal gangue powder;

[0012] Step S102: Mix silica sol and water glass in a predetermined ratio, and sequentially add polyacrylamide solution, cetyltrimethyl solution and modified calcium lignosulfonate, and then adjust the pH value to the neutral range with phosphoric acid solution to obtain a composite modifier system;

[0013] Step S103: Mix the activated coal gangue powder and the composite modifier system in a solid-liquid ratio in a double-shaft forced mixer, and then cure under constant temperature and humidity conditions to obtain a modified coal gangue mixture;

[0014] Step S104: Preform the modified coal gangue mixture through a disk granulator, and at the same time spray a binder solution containing polyvinyl alcohol and sodium carboxymethylcellulose to obtain preformed ceramsite;

[0015] Step S105: Perform multi-stage temperature gradient calcination treatment on the preformed ceramsite, then spray a high-temperature stable composite modifier, and perform surface modification under an oxygen-controlled atmosphere to obtain dense ceramsite;

[0016] Step S106: Cool and strengthen the dense ceramsite through gradient cooling technology, and then perform particle size grading using a vibrating screening device to obtain the finished product of high-density coal gangue ceramsite sand.

[0017] Specifically, the gangue generated in coal mining is initially crushed by a jaw crusher into particles with a particle size less than 10 mm, and then further finely ground by a ball mill into fine gangue powder with an average particle size of 0.074 mm. This particle size control ensures the uniformity and efficiency of the chemical activation process. Then, the fine gangue powder is mixed with a hydrochloric acid solution with a concentration of 3% to 5% at a solid-liquid ratio of 1:2.5 and soaked at a constant temperature of 60 °C for 4 hours to promote the decomposition of carbonate minerals in the gangue and dissolve some alkaline metal ions such as calcium and magnesium at the same time, increasing the specific surface area. For example, a batch of gangue raw materials with an initial specific surface area of 2.5 m 2 / g after this activation treatment, the specific surface area increases to 3.8 m 2 / g, and the porosity increases from 15% to 27%. This change in the microstructure provides a basic condition for the subsequent penetration of the modifier.

[0018] The preparation of the composite modifier system involves precise proportioning of multiple components. First, silica sol with a mass fraction of 30% and water glass with a modulus of 2.5 are mixed at a volume ratio of 3:1 at 50 °C to form a silicon-based mixed solution. The nano-silica particles in this mixed solution are evenly dispersed, with an average particle size of about 20 nm. Subsequently, a polyacrylamide solution with a mass fraction of 0.5% (accounting for 5% of the total volume) is added. Through stirring, the macromolecular chains of polyacrylamide form hydrogen bond networks with the silicon-oxygen groups in the silicon-based mixed solution, endowing the system with enhanced adhesiveness. Then, the cetyltrimethyl solution added later (with a mass fraction of 2.0% and accounting for 4% of the total volume) forms a micelle structure in the mixture, with its hydrophobic alkyl chains pointing inward and the hydrophilic head groups facing outward. This structure provides good hydrophobicity for the modified gangue. Modified calcium lignosulfonate (with a mass fraction of 2.5% and accounting for 3% of the total volume) is added as a dispersant, and the sulfonic acid groups in its molecular structure significantly improve the stability of the system. The pH value is adjusted to 7.0 - 7.5 by titrating with a 10% phosphoric acid solution to form a composite modifier system with stable physical and chemical properties.

[0019] The activated coal gangue powder and the composite modifier system are mixed in a double-shaft forced mixer at a solid-liquid ratio of 1:0.8. In the mixing process, first mix at a low speed of 60 r / min for 10 minutes to ensure that the modifier evenly covers the surface of the coal gangue. At this time, monitor that the temperature of the mixture is maintained below 35°C to avoid premature curing of the modifier. Subsequently, increase the rotation speed to 120 r / min and continue mixing for 20 minutes to enhance the shear force and promote the penetration of the modifier into the internal pores of the coal gangue. Transfer the mixture to a constant temperature and humidity curing box and cure it for 36 hours at a temperature of 35°C and a relative humidity of 85%. At this time, the active silica in the modifier undergoes a topological chemical reaction with the aluminosilicate in the coal gangue to form a three-dimensional network silicon-aluminum-oxygen composite structure, and at the same time, the polymer component forms a protective film on the surface of the coal gangue. Use a disk granulator to preform the modified coal gangue mixture. The disk inclination angle of the disk granulator is set at 45°, and the rotation speed is 25 r / min. Under these parameters, the material forms a spiral upward trajectory in the disk and realizes uniform rolling into balls. At the same time, spray a binder solution containing 3% mass fraction of polyvinyl alcohol and sodium carboxymethylcellulose (mass ratio 1:1), and its moisture content is controlled at 5% to ensure that the surface of the ceramsite is wet but not sticky. When the diameter of the ceramsite reaches 4-8 mm, adjust the disk inclination angle to 50° to promote the qualified ceramsite to overflow from the disk edge. Subsequently, remove the particles with unqualified diameter through a rotary sieve to obtain the preformed ceramsite.

[0020] The preformed ceramsite is first in a tunnel drying kiln, heated from room temperature to 150°C and kept at a constant temperature for 2 hours to complete dehydration, and then heated to 350°C and kept for 30 minutes to achieve carbonization of organic matter. Subsequently, in a rotary kiln, it is heated to 750°C at a rate of 5°C / min and kept for 1 hour, heated to 950°C at a rate of 3°C / min and kept for 40 minutes, and finally heated to 1150°C at a rate of 2°C / min and kept for 30 minutes to achieve full sintering inside the ceramsite. When the temperature of the ceramsite leaving the kiln is about 800°C, spray a high-temperature stable composite modifier added with 20% kaolin and 5% zirconia nanopowder to form a protective layer. The ceramsite enters the oxidation-reduction atmosphere control device, and a gas with an oxygen content of 5% is introduced at 425°C and kept for 30 minutes to promote the chemical combination of the modifier and the ceramsite matrix. The ceramsite is first cooled to 550°C at a rate of 15°C / min, then quickly cooled to 120°C through fine water mist with an average droplet diameter of 20 μm, and finally air-cooled to room temperature at room temperature. This gradient cooling method forms a residual compressive stress field inside the ceramsite, significantly enhancing the overall strength. The cooled ceramsite is classified into three particle size grades of 3-5 mm, 5-8 mm, and 8-10 mm through a vibrating sieve device and subjected to quality evaluation. The bulk density of qualified products should reach 900-1100 kg / m 3, the average value of the single - grain compressive strength is greater than 7.5 MPa, the water absorption rate in 24 hours is less than 6%, and the mass loss rate after 25 freeze - thaw cycles is less than 2%. The coal gangue ceramsite sand prepared by this composite modification method has a bulk density increased by about 15% and a closed porosity increased by more than 40% compared with traditional coal gangue ceramsite, solving the technical problems of low density and insufficient strength of traditional coal gangue ceramsite, and can be widely applied in fields such as building lightweight aggregate concrete, landscaping substrate, and water treatment filter media.

[0021] In the embodiment of the present application, a jaw crusher and a ball mill are used to precisely pulverize coal gangue and combined with hydrochloric acid solution soaking activation treatment, significantly improving the specific surface area and activity of coal gangue. Especially the porous structure formed during the hydrochloric acid soaking process enhances the penetration depth and reaction efficiency of the modifier, improving the physical properties of the final product from the source. Secondly, through the precise proportioning and mixing of silica sol and water glass, and successively adding functional components such as polyacrylamide solution, cetyltrimethyl solution, and modified lignosulfonate calcium, a multi - functional synergistic composite modifier system is constructed; this system simultaneously has functions such as bond enhancement, hydrophobic modification, and dispersion stability, and the precise regulation of the pH value ensures the balance of system stability and reaction activity. Thirdly, the application of a double - shaft forced mixer realizes the full and uniform mixing of activated coal gangue powder and the composite modifier, and the constant - temperature and constant - humidity curing promotes the modifier to penetrate into the internal pores of coal gangue and react with it to form a network - like silicon - aluminum - oxygen composite structure, significantly improving the integrity and density of the material. Fourthly, the pre - forming treatment by a disk granulator combined with the spraying of a specific binder solution realizes the efficient production and particle size control of pre - formed ceramsite. The obtained ceramsite has regular shape and smooth surface, providing a semi - finished product with uniform quality for subsequent heat treatment. Fifthly, the combination of multi - stage temperature - gradient calcination and surface treatment with a high - temperature stable composite modifier realizes the high densification of ceramsite in an oxygen - controlled atmosphere. The surface modification layer is firmly bonded to the matrix to form a protective layer with excellent sealing performance, effectively blocking the intrusion of external moisture. Finally, the gradient cooling technology creatively forms a residual compressive stress field inside the ceramsite, significantly improving the compressive strength and impact resistance of the ceramsite, and the vibration screening device ensures the precise control of the particle size distribution of the product.

[0022] In a specific embodiment, the process of executing step S101 may specifically include the following steps:

[0023] (1) The raw coal gangue block is crushed into particles with a preset particle size by a jaw crusher, and then the particles are transported to a ball mill for fine grinding to obtain coal gangue fine powder;

[0024] (2) The coal gangue fine powder is mixed with hydrochloric acid solution with a target concentration according to a preset solid - liquid ratio to form a slurry, and is soaked and treated for a predetermined time under constant - temperature conditions in a stirring device to promote the decomposition of carbonate minerals in coal gangue;

[0025] (3) Solid-liquid separation of the soaked slurry is carried out through a vacuum filtration device to obtain a filter cake, and the filter cake is rinsed with deionized water until neutral.

[0026] (4) The filter cake is dried in a constant-temperature drying oven to prepare activated coal gangue powder.

[0027] Specifically, a jaw crusher is used to crush the coal gangue raw material blocks into particles with a particle size less than 10 mm. The jaw crusher applies a huge pressure to the coal gangue through the periodic extrusion movement between the moving jaw and the fixed jaw, causing it to crack along natural fissures. The gap adjustment mechanism of the jaw crusher precisely controls the discharge particle size to ensure that the crushed product meets the requirements of subsequent ball milling. The initially crushed particles are transported to a ball mill through a belt conveyor. The ball mill is equipped with steel balls of different diameters. When the cylinder rotates, the steel balls present a throwing motion under the action of centrifugal force and gravity, generating impact, grinding, and shearing effects on the coal gangue particles, and grinding the particles into a fine powder state with an average particle size of 0.074 mm. The ball milling time and rotational speed are related parameters. Usually, the rotational speed of the ball mill is set at 75% of the critical speed to ensure the balance between grinding efficiency and energy consumption.

[0028] The coal gangue fine powder is mixed with a hydrochloric acid solution with a concentration of 3% to 5% at a solid-liquid ratio of 1:2.5 to form a uniform slurry. The solid-liquid ratio directly affects the activation efficiency and economy. If the ratio is too large, the viscosity of the slurry will be too high and the reaction will be incomplete; if the ratio is too small, reagent waste will occur. The mixed slurry is fed into a reactor equipped with a temperature control system and a stirring device. The temperature is set at 60 °C, the stirring rate is 100 r / min, and the soaking treatment is carried out for 4 hours. The constant-temperature condition ensures a stable reaction rate. The hydrochloric acid solution reacts with carbonate minerals (such as calcite, dolomite, etc.) in the coal gangue through an acid-base neutralization reaction, and at the same time dissolves some interfering elements such as calcium and magnesium. The carbon dioxide released during the reaction forms microbubbles, which helps to form a porous structure, increase the specific surface area, and improve the subsequent modification effect.

[0029] Use a vacuum filtration device to separate the solid and liquid of the soaked slurry. The vacuum filtration device consists of a Buchner funnel, filter paper, a suction flask, and a vacuum pump. During the suction filtration process, control the vacuum degree at 0.05 - 0.08 MPa to ensure rapid separation of the filtrate without damaging the filter cake structure. The acidic substances remaining in the filter cake will affect the subsequent modification effect, so the filter cake needs to be repeatedly rinsed with deionized water until it is neutral (pH = 6.5 - 7.5). The rinsing is carried out by the step-by-step rinsing method. Each time, add deionized water equal to the volume of the filter cake, gently stir and then perform suction filtration again. Repeat the operation 4 - 6 times. Measure the pH value of the filtrate after each suction filtration until it reaches neutral. The use of deionized water avoids the interference of calcium and magnesium ions in tap water on the surface properties of activated coal gangue. Transfer the neutral filter cake to an electrothermal constant temperature drying oven with a temperature control accuracy of ±1°C, set the temperature at 105°C, and the drying time at 24 hours. This temperature setting can efficiently remove physically adsorbed water without causing significant changes in the material structure. The drying process follows two stages: constant rate drying and falling rate drying. In the first 8 hours, the water evaporation rate is relatively fast, belonging to the constant rate drying stage; in the next 16 hours, it enters the falling rate drying stage, and the water evaporation gradually slows down. The specific surface area of the activated coal gangue powder after drying is significantly increased compared with the original coal gangue, the porous structure is increased, and more surface active sites are exposed.

[0030] In a specific embodiment, the process of performing step S102 may specifically include the following steps:

[0031] (1) Mix colloidal silica with a mass fraction of 30% and water glass with a modulus of 2.5 at a volume ratio of 3:1, and stir in a constant temperature stirrer at 50°C to form a silicon-based mixed liquid;

[0032] (2) Add a polyacrylamide solution accounting for 5% of the total volume to the silicon-based mixed liquid, and perform medium-speed stirring treatment with a paddle stirrer to obtain a reinforced bonding intermediate;

[0033] (3) Add a cetyltrimethyl solution accounting for 4% of the total volume to the reinforced bonding intermediate, and perform stirring and mixing treatment to obtain a hydrophobic modified intermediate;

[0034] (4) Add modified calcium lignosulfonate to the hydrophobic modified intermediate, and make it evenly distributed by stirring and dispersing to form a multifunctional complex;

[0035] (5) Add aluminum hydroxide nanopowder to the multifunctional complex to provide crystal nucleus induction points to obtain a structure-strengthened premix;

[0036] (6) Regulate the pH value of the structure-strengthened premix by the phosphoric acid solution titration method, and perform shear dispersion under a high-speed disperser to obtain a composite modifier system.

[0037] Specifically, a silicon-based mixture is prepared by mixing silica sol with a mass fraction of 30% and water glass with a modulus of 2.5 in a volume ratio of 3:1. Silica sol is a colloidal dispersion system containing nano-scale silica particles, where the diameter of the silica particles is usually 10-20 nm, forming a stable system when dispersed in water. Water glass is an aqueous solution of sodium silicate, and the modulus refers to the molar ratio of Na 2 O to SiO 2 . A modulus of 2.5 means that the SiO 2 content is moderate, having both good activity and certain stability. The two are added to a constant-temperature stirrer in a volume ratio of 3:1, and the temperature is set at 50 °C. This temperature point can promote the molecular movement of the two components without causing excessive evaporation of water. The stirring process lasts for 30 minutes, and the rotation speed is controlled at 200 rpm to ensure that the nano-silica particles in the silica sol are fully mixed with the silicate ions in the water glass, forming a uniform silicon-based mixture.

[0038] Precisely add a polyacrylamide solution accounting for 5% of the total volume to the silicon-based mixture. Polyacrylamide is a linear polymer with a large number of amide groups on its molecular chain, having excellent bonding properties and flocculation effects. The solution mass fraction is controlled at 0.5%. Excessive amount will cause the system viscosity to be too high and affect uniform dispersion. The addition process uses a slow dropping method, and at the same time, medium-speed stirring treatment (150 rpm) is carried out by a paddle stirrer for 15 minutes to ensure that the polyacrylamide macromolecules are fully extended and evenly distributed in the silicon-based mixture. Medium-speed stirring avoids the problems of polymer molecular chain breakage caused by high-speed stirring and unevenness caused by low-speed stirring, forming a reinforced bonding intermediate with ideal bonding properties. Add a cetyltrimethyl solution accounting for 4% of the total volume to the reinforced bonding intermediate, and the mass fraction of this solution is 2.0%. Cetyltrimethyl is a cationic surfactant with a hydrophilic head group and a hydrophobic long chain. Its molecular structure contains an alkyl chain with 16 carbon atoms and a nitrogen atom head group connected by three methyl groups. During the addition process, the stirring rate is maintained at 120 rpm for 20 minutes, and the temperature is maintained at 45 °C. Under these conditions, the surfactant molecules form a special micelle structure in the aqueous solution, with the hydrophobic alkyl chains facing inwards and the hydrophilic head groups facing outwards. This structure can impart significant hydrophobicity to the surface and internal pores of the coal gangue particles in subsequent treatments, reducing the water absorption rate of the ceramsite during use and obtaining a hydrophobic modified intermediate.

[0039] Add calcium lignosulfonate modified into the hydrophobic modified intermediate. Calcium lignosulfonate modified is an efficient dispersant obtained by sulfonation and calcium salification modification of lignin, a by-product of the papermaking industry. Its molecular structure contains a large number of sulfonic acid groups and hydroxyl groups, which can prevent particle aggregation through the dual mechanisms of electrostatic repulsion and steric hindrance. The addition amount accounts for 3% of the total volume and the mass fraction is 2.5%. The addition process adopts a strategy of adding in batches, adding 1 / 3 of the total amount each time, and stirring for 5 minutes, for a total of three times, with a total stirring time of 15 minutes and a stirring rate of 180 rpm. This method ensures that calcium lignosulfonate modified is evenly distributed throughout the system, forming a multifunctional complex with functions including bonding, hydrophobicity, and dispersion.

[0040] Add aluminum hydroxide nanometer powder into the multifunctional complex, and the addition amount accounts for 1.5% of the total solid mass. The average particle size of the aluminum hydroxide nanometer powder is 50 nm, and the specific surface area exceeds 200 m 2 / g, with a large number of surface hydroxyl groups, which can act as crystal nucleus induction points to promote the formation of crystalline phases during the subsequent ceramsite sintering process and improve the density of the ceramsite. The addition process adopts spray drying pretreatment technology. First, disperse the aluminum hydroxide nanometer powder in a small amount of ethanol to form a suspension, and then atomize and add it to the multifunctional complex through a pneumatic spray device to avoid agglomeration of the nanometer powder. Subsequently, carry out medium and high-speed stirring (250 rpm) for 10 minutes to ensure uniform dispersion of the nanoparticles and obtain a structure-strengthened premix. The pH value of the structure-strengthened premix is regulated by the phosphoric acid solution titration method. Use a 10% mass fraction phosphoric acid solution, control the dropping rate at 2 mL / min through a precision titration device, and continuously monitor the change of the pH value at the same time. The initial pH value is usually around 9.5 and gradually decreases with the dropping of the phosphoric acid solution. Stop dropping when the pH value drops to the range of 7.0 - 7.5. Subsequently, transfer the mixture with the adjusted pH value to a high-speed disperser, set the rotation speed at 8000 r / min, and the shear dispersion time at 30 minutes. The high-speed shear process generates a strong shear force, enabling full mixing of each component at the nanoscale and simultaneously breaking possible micro-agglomerates to obtain a stable and uniform composite modifier system.

[0041] In a specific embodiment, the process of executing step S103 may specifically include the following steps:

[0042] (1) Conduct preheating treatment on the double-shaft forced mixer, adjust the inner cavity temperature to the appropriate reaction temperature, and set the rotation speed parameter at the same time to construct an ideal mixing environment;

[0043] (2) Through the pneumatic conveying device, introduce the activated coal gangue powder into the feed port of the double-shaft forced mixer at a constant rate to establish the basis for material transmission;

[0044] (3) Use a precision metering pump to spray the composite modifier system into the twin-shaft forced mixer in an atomized state according to the preset solid-liquid ratio of 1:0.8 for preliminary physical mixing;

[0045] (4) Adjust the mixer speed to the low-speed gear, maintain a uniform stirring state, and promote the formation of a coating film on the surface of the activated gangue powder by the composite modifier system to generate primary mixed materials;

[0046] (5) Use a temperature sensor to monitor the thermodynamic changes during the mixing process in real time, control the reaction temperature not to exceed the stability threshold of the mixed materials, and prevent the modifier from curing prematurely;

[0047] (6) Transfer the primary mixed materials to a constant temperature and humidity curing box, and continuously cure them under the preset temperature and humidity conditions to form a network-like silicon-aluminum-oxygen composite structure, obtaining modified gangue mixtures.

[0048] Specifically, perform a preheating treatment on the twin-shaft forced mixer, accurately adjust the inner cavity temperature of the mixer to 35 °C. This temperature can not only promote the reaction but also prevent the modifier from curing prematurely. At the same time, set the initial speed of the mixer to 60 r / min. This low speed can ensure the preliminary uniform mixing of the materials and prevent the destruction of the modifier structure due to excessive shear force. The twin-shaft forced mixer is an efficient mixing device with two parallel stirring shafts. Its spiral stirring blades are arranged in a staggered manner to form a three-dimensional mixed flow field, which can achieve the forced mixing of materials without dead corners. After preheating, introduce the activated gangue powder into the mixer feed port through a pneumatic conveying device. The pneumatic conveying device consists of a silo, a rotary star feeder valve, a pneumatic conveying pipeline, and a pulse dust removal system. Driven by compressed air, it transports the powdery materials in a suspended flow manner. Control the conveying rate at 120 kg / h in this link, keep it stable and uniform, and avoid insufficient mixing caused by uneven feeding. The average particle size of the activated gangue powder is 0.074 mm, and its specific surface area is relatively large, making it extremely easy to generate flying dust. Therefore, a special dust-proof device is installed at the end of the conveying pipeline to ensure that all the powder accurately enters the mixer without material loss.

[0049] Subsequently, use a precision metering pump to spray the composite modifier system into the mixer in an atomized state. The flow control accuracy of the precision metering pump reaches ±0.5%. The set flow rate is automatically calculated according to the solid-liquid ratio of 1:0.8. When the powder conveying rate is 120 kg / h, the composite modifier conveying flow rate is 96 kg / h. The atomizing nozzle uses gas-liquid two-fluid atomization technology, and the atomizing pressure is controlled at 0.4 MPa to form a fine mist-like liquid with an average droplet diameter of about 50 μm. Spraying it into the mixer can quickly cover the surface of the gangue powder and avoid local over-wetting and agglomeration. The nozzles are arranged in a ring at the top of the mixer to ensure uniform distribution of the liquid throughout the material system.

[0050] After the composite modifier is sprayed in, adjust the rotational speed of the mixer to the low-speed gear of 60 r / min and maintain this speed for 10 minutes. During the low-speed mixing stage, it is allowed for the modifier to form a preliminary coating on the surface of coal gangue. At this time, the silica sol and sodium silicate components in the modifier start to undergo physical adsorption and ion exchange reactions with the surface of coal gangue, and the macromolecules of polyacrylamide form a network structure among the coal gangue particles, connecting the particles into clusters. After this stage ends, the surface of the mixture is wet but not sticky, and a preliminary structure has been formed among the particles. This low-shear mixing method avoids the breakage of polymer chains in the composite modifier and the excessive aggregation of nanoparticles. The change of the reaction temperature is monitored in real time through temperature sensors buried at different positions on the inner wall of the mixer. The sensor acquisition frequency is once per second, and the data is displayed and recorded in real time through the control system. When a rapid increase in the local temperature is detected, the cooling system is automatically started to cool down. The temperature during the mixing process is controlled within the range of 35 - 40 °C. If it exceeds 40 °C, it will cause the premature cross-linking and curing of the polymer components in the modifier, affecting the penetration depth and modification effect. Temperature monitoring ensures the stability and consistency of the mixture quality.

[0051] The primary mixed material after sufficient mixing is transferred to a constant temperature and humidity curing box, with the set temperature of 35 °C, relative humidity of 85%, and curing time of 36 hours. The internal air circulation system of the constant temperature and humidity curing box ensures that the temperature and humidity are uniform in all areas of the box, with the error controlled within ±0.5 °C and ±2% RH. During the curing process, the reactive silica in the composite modifier reacts chemically with the aluminosilicate in the coal gangue to form a three-dimensional network silicon-aluminum oxide composite structure. At the same time, the polymer components in the modifier cure on the surface and in the pores of the coal gangue to form a dense protective film. The modified coal gangue mixture obtained after curing has strong integrity, a dense and smooth surface, and a stable internal structure.

[0052] In a specific embodiment, the process of performing step S104 may specifically include the following steps:

[0053] (1) Adjust the disk inclination angle of the disk granulator through a frequency controller, set the disk inclination angle to 45°, and construct the material rolling trajectory;

[0054] (2) Use a rotational speed adjustment device to control the rotational speed parameter of the disk granulator at 25 r / min to form a uniform rotation platform;

[0055] (3) Quantitatively add the modified coal gangue mixture according to the material supply curve, and make it start to roll and nucleate under the combined action of gravity and centrifugal force of the disk granulator;

[0056] (4) Uniformly spray a polyvinyl alcohol and sodium carboxymethylcellulose binder solution with a water content of 5% on the surface of the rolling modified coal gangue mixture through an atomizing nozzle to promote surface adhesion;

[0057] (5) By means of the centrifugal force gradient principle, adjust the disk inclination angle of the disk granulator to 50°, so that the materials meeting the particle size requirements overflow from the disk edge to achieve automatic sorting;

[0058] (6) Use a rotary sieve to conduct preliminary screening on the overflowing materials, screen out particles with a diameter less than 3 mm and greater than 10 mm, and obtain preformed ceramsite with a wet surface and capable of withstanding extrusion.

[0059] Specifically, convert the modified coal gangue mixture into ceramsite with an ideal shape and strength through disk granulation technology. Precisely adjust the disk inclination angle of the disk granulator through a frequency controller and set it to 45°. The disk granulator is an inclined rotating disk device, usually with a working surface diameter of 1.5 - 2.5 m, and its inner surface is lined with wear-resistant plates. The disk inclination angle refers to the angle between the disk and the horizontal plane, and this angle directly affects the movement trajectory of the materials in the disk. A disk inclination angle of 45° can enable the materials to form a spiral upward rolling trajectory in the disk, neither causing the materials to stay at the bottom of the disk and unable to form balls due to too small an angle, nor causing the materials to quickly slide out of the granulation disk due to too large an angle. After adjusting the inclination angle, use a speed regulating device to set the rotation speed of the disk granulator at 25 r / min. The rotation speed parameter directly affects the magnitude of the centrifugal force received by the materials in the disk, and thus affects the ball forming effect. Too low a rotation speed will result in insufficient centrifugal force and the materials are difficult to roll into balls; too high a rotation speed will cause the materials to overflow prematurely and have insufficient residence time. A rotation speed of 25 r / min forms a uniform rotation platform, providing appropriate centrifugal force for the materials, ensuring there is sufficient energy to drive the materials to roll and gradually form into spheres, while also ensuring sufficient residence time for the spherical particles to grow to the ideal size.

[0060] Subsequently, the modified coal gangue mixture is quantitatively added according to the pre-set material supply curve. The material supply curve is a graph of the feed rate change formulated based on the processing capacity of the granulator and the ideal pelletization rate. Usually, the supply rate is relatively low in the initial stage and gradually increases after some materials in the pan have formed cores. The initial supply rate is controlled at 60 - 80 kg / h and increases to 120 - 150 kg / h after a stable material bed layer is formed in the pan. After the modified coal gangue mixture enters the rotating granulation pan, it starts to roll under the combined action of gravity and centrifugal force. Fine particles are initially aggregated through van der Waals force and weak liquid bridge force to form original cores with a diameter of 1 - 2 mm. These cores continue to roll with the rotation of the pan, continuously adsorbing fine particles around them and gradually growing into spherical bodies. During the rolling process of the materials, a binder solution is evenly sprayed onto the surface of the modified coal gangue mixture through an atomizing nozzle set above the granulation pan. This binder solution is prepared by mixing polyvinyl alcohol and sodium carboxymethylcellulose in a mass ratio of 1:1, with a total mass fraction of 3% and a moisture content controlled at 5%. Polyvinyl alcohol is a semi-crystalline water-soluble polymer with excellent binding and film-forming properties; sodium carboxymethylcellulose is a water-soluble cellulose ether that can increase the solution viscosity and provide good water retention. The two act synergistically to form a uniform binding layer on the surface of the ceramsite. The nozzle uses gas-liquid two-fluid atomization technology, with an atomization pressure of 0.3 MPa and 6 - 8 nozzles evenly distributed above the granulation pan to ensure that the binder droplets are small and uniform and have a comprehensive coverage range.

[0061] When the diameter of the ceramsite grows to a certain extent, based on the principle of centrifugal force gradient, the pan inclination angle is adjusted from 45° to 50° through the granulator control system. The principle of centrifugal force gradient means that as the radial position of the materials in the rotating pan is different, the centrifugal force they receive is different. The closer the position is to the edge of the pan, the greater the centrifugal force. After the pan inclination angle increases, the component of the gravity of the materials along the pan surface increases, and together with the centrifugal force, it enables the ceramsite with a certain particle size and mass to overcome the frictional force and overflow from the edge of the pan. Smaller ceramsite, due to its lighter mass, has insufficient centrifugal force to make it overflow and remains in the pan to continue growing. Through this automatic sorting mechanism, the preliminary classification of ceramsite by particle size is achieved. The overflowed ceramsite is collected by the collection device and immediately sent to a rotary sieve for precise screening. The rotary sieve consists of two layers of screens with different pore sizes. The pore size of the upper screen is 10 mm, the pore size of the lower screen is 3 mm, the screen inclination angle is 15°, and the rotation speed is 8 r / min. Through this structural design, the ceramsite can be divided into three grades: over-sized particles with a diameter greater than 10 mm, under-sized particles with a diameter less than 3 mm, and qualified particles with a diameter between 3 - 10 mm. The over-sized and under-sized particles are separately collected and returned to the granulation system for re-granulation, while the preformed ceramsite that meets the particle size requirements enters the next process. These preformed ceramsite have a round appearance, a moist but non-sticky surface, and will not break when squeezed into a fist by hand, and their physical properties have reached the ideal state before calcination.

[0062] In a specific embodiment, the process of performing step S105 may specifically include the following steps:

[0063] (1) Place the preformed ceramsite in a tunnel drying kiln for dehydration drying to form primary heat-treated ceramsite;

[0064] (2) Transport the primary heat-treated ceramsite to a rotary kiln and raise the temperature according to a preset temperature curve through a temperature control system to cause mineral phase transformation inside the ceramsite;

[0065] (3) Conduct high-temperature calcination on the ceramsite in the rotary kiln to promote the formation of a dense sintered structure inside the ceramsite;

[0066] (4) When the ceramsite exits the kiln, spray a high-temperature stable composite modifier containing kaolin and zirconia nanoparticles on the surface of the ceramsite through a high-temperature spraying device to form a surface modification layer;

[0067] (5) Introduce the ceramsite with the surface modification layer into a redox atmosphere control device and introduce a gas with an oxygen content of 5% to promote the combination of the modifier and the ceramsite matrix;

[0068] (6) Change the gas composition through an atmosphere switching device to perform a sealing treatment on the surface of the ceramsite to obtain dense ceramsite with an increased bulk density and an increased closed porosity.

[0069] Specifically, a qualitative leap in the properties of ceramsite is achieved through multi-stage heat treatment and surface modification. The preformed ceramsite is placed in a tunnel drying kiln for dehydration drying treatment. The tunnel drying kiln is a long strip-shaped channel-like heat treatment equipment with an internal temperature gradient control system. The preformed ceramsite moves along the tunnel on a conveyor belt and gradually experiences different temperature zones. The temperature in the inlet zone is set from room temperature to 100 °C, the temperature in the middle zone rises from 100 °C to 150 °C and remains constant for 2 hours, and the temperature in the outlet zone gradually rises to 350 °C and remains for 30 minutes. This gradient heating method ensures that the moisture inside the ceramsite evaporates slowly and evenly, avoiding the bursting phenomenon caused by rapid heating. At the same time, the temperature of 350 °C can preliminarily carbonize the organic matter in the ceramsite, laying the foundation for subsequent high-temperature calcination to form primary heat-treated ceramsite with a certain strength. The dried primary heat-treated ceramsite is transferred to a rotary kiln through a special high-temperature conveying device. The rotary kiln is a slightly inclined rotating cylinder with an inner diameter usually of 2 - 3 meters and a length of 30 - 40 meters, lined with refractory materials. The rotary kiln is equipped with a precise temperature control system, and a complex temperature curve is achieved through independent control of multiple sections. After the ceramsite enters the rotary kiln, it experiences a preheating zone where the temperature rises from 350 °C to 750 °C at a rate of 5 °C / min and remains for 1 hour. In this stage, the clay minerals in the ceramsite begin to dehydroxylate, the organic matter is completely carbonized, and the carbonate minerals in the coal gangue decompose. Subsequently, it enters the transformation zone where the temperature rises to 950 °C at a rate of 3 °C / min and remains for 40 minutes. In this stage, the aluminosilicate minerals begin to undergo a phase change to form mullite nuclei. Finally, it enters the sintering zone where the temperature rises to 1150 °C at a rate of 2 °C / min and remains for 30 minutes. At this time, the inside of the ceramsite is fully sintered, the silicate minerals form a liquid phase, filling the particle gaps, and a glass phase is formed after cooling, making the internal structure of the ceramsite densified.

[0070] The ceramsite in the rotary kiln undergoes sufficient calcination in a high-temperature environment. During the calcination process, the ceramsite will experience volume shrinkage, a dense sintered layer will form on the particle surface, and the internal pore structure will be optimized and reorganized. The ceramsite stays at a high temperature of 1150 °C for sufficient time to fully melt minerals such as quartz and feldspar in the coal gangue, forming a continuous liquid phase. These liquid phases transform into glass phases during the cooling process and fill between the crystal particles, forming a dense sintered structure. At the same time, a closed vitreous shell forms on the surface of the ceramsite at high temperature. This structure not only ensures that the ceramsite has sufficient strength but also ensures that the interior remains in a lightweight and porous state, achieving a balance between strength and lightness. When the temperature of the ceramsite leaving the kiln is about 800 °C, a special high-temperature stable composite modifier is sprayed onto the surface of the ceramsite through a high-temperature spraying device set at the kiln tail. This modifier is modified from a basic composite modifier by adding 20% kaolin and 5% zirconia nanopowder, and has good high-temperature stability and interfacial compatibility. Kaolin provides aluminosilicate components, which are similar to the matrix components of the ceramsite, ensuring good bonding strength; zirconia nanopowder provides excellent refractoriness and mechanical strength. The spraying device uses high-pressure gas-assisted atomization technology to evenly spray the modifier on the surface of the rotating ceramsite, forming a surface modification layer with a thickness of about 0.1 - 0.2 mm.

[0071] The ceramsite after spraying the modifier is immediately introduced into a redox atmosphere control device. This device is a closed furnace body that can precisely control the internal gas composition. The internal temperature is maintained at 425 °C, and a gas mixture with an oxygen content of 5% is introduced, and the gas flow rate is controlled at 1.5 m 3 / h. Under the condition of a mild oxidation atmosphere, the organic components in the modifier are moderately oxidized and crosslinked, and the inorganic components form chemical bonds with the surface of the ceramsite, achieving a firm bond between the modifier and the ceramsite matrix. This process lasts for 30 minutes to ensure that the surface modification layer is fully cured and firmly bonded to the matrix.

[0072] The gas composition is switched from a 5% oxygen-containing mixture to pure nitrogen or a 1% hydrogen-containing gas mixture through an atmosphere switching device. The gas temperature is maintained at 350 °C, the flow rate is 1.2 m 3 / h, and the treatment time is 15 minutes. Under the condition of a reducing atmosphere, the open pores on the surface of the ceramsite are further sealed, forming a dense shell structure. This treatment method significantly improves the closed pore rate of the ceramsite, reduces the connected pores, reduces the water absorption performance of the ceramsite, and at the same time increases the bulk density and improves the compressive strength. After this series of treatments, the obtained dense ceramsite has ideal physical and mechanical properties and durability, with a bulk density reaching 900 - 1100 kg / m 3 and the closed pore rate exceeding 80%.

[0073] In a specific embodiment, the process of executing step S106 may specifically include the following steps:

[0074] (1) The dense ceramsite is introduced into the gradient cooling zone through a constant-speed conveyor belt, and a slow cooling process is adopted in the front cooling zone to form temperature-controlled ceramsite;

[0075] (2) The temperature-controlled ceramsite is conveyed to the fine water mist area, and rapid cooling is carried out with the help of uniformly sprayed fine water mist to produce surface stress-strengthened ceramsite;

[0076] (3) The surface stress-strengthened ceramsite is cooled by a normal-temperature air-cooling system to form internally residually stressed ceramsite;

[0077] (4) The internally residually stressed ceramsite is screened by a vibrating screening device into three particle size groups: small particle size group, medium particle size group and large particle size group;

[0078] (5) The bulk density, compressive strength, water absorption and freeze-thaw cycle tests are carried out on the ceramsite in the three particle size groups respectively. The ceramsite in the three particle size groups that meet the quality standards are mixed according to a preset ratio and then packaged to obtain the finished product of high-density coal gangue ceramsite sand.

[0079] Specifically, the dense ceramsite coming out of the kiln at high temperature is introduced into the gradient cooling zone through a constant-speed conveyor belt for preliminary cooling. The constant-speed conveyor belt adopts a high-temperature-resistant metal mesh belt structure, and the drive system is equipped with a variable-frequency speed regulation device, and the running speed is stable at 0.5 m / min to ensure that the residence time of the ceramsite in the cooling zone is precisely controllable. The front section of the gradient cooling zone is designed as a slow cooling area, and a combination of natural cooling and controlled air volume is adopted to make the temperature of the ceramsite slowly drop from the kiln outlet temperature to 550 °C at a rate of 15 °C / min. This slow cooling process avoids the cracking of the ceramsite caused by sudden temperature drop, and at the same time forms a preliminary temperature gradient inside the ceramsite, laying a foundation for subsequent strengthening treatment to obtain temperature-controlled ceramsite. Subsequently, the temperature-controlled ceramsite is conveyed to the fine water mist cooling area. This area is equipped with an array of high-pressure micro-mist nozzles with a nozzle spacing of 10 cm, which are evenly arranged 20 - 30 cm above the conveyor belt. The water mist system adopts a high-pressure pump plus atomizing nozzle design, and the working pressure is controlled at 2.5 - 3.0 MPa to produce fine water mist with an average diameter of only 20 μm. When water mist particles of this size come into contact with the high-temperature ceramsite, they instantly vaporize, absorbing a large amount of heat energy to achieve rapid and efficient cooling. The temperature of the ceramsite in this area drops rapidly from 550 °C to 120 °C, and the temperature drop rate is about 40 °C / min. This sharp temperature drop causes the surface of the ceramsite to cool and shrink rapidly, while the inside still remains at a relatively high temperature, forming a compressive stress layer on the surface of the ceramsite, producing a surface stress strengthening effect, and significantly improving the flexural strength and impact resistance of the ceramsite.

[0080] The ceramsite after being cooled by fine water mist enters the normal-temperature air-cooling system for temperature reduction treatment. The air-cooling system consists of a high-efficiency centrifugal fan, a wind guide pipe, and multiple layers of wind grids. The wind speed is controlled at 8 - 10 m / s, and the wind temperature is the ambient temperature. The normal-temperature air-cooling system adopts a countercurrent design, with the cold air direction opposite to the moving direction of the ceramsite, maximizing the cooling efficiency. The temperature of the ceramsite in the air-cooling system drops from 120 °C to below 40 °C. During the cooling process, the internal temperature gradient of the ceramsite further develops, forming a stable residual compressive stress field. This internal residual compressive stress field is similar to the stress distribution of tempered glass, greatly enhancing the overall strength of the ceramsite, especially the compressive strength and crack resistance. The compressive strength of the ceramsite after three-stage cooling treatment is increased by more than 30% compared with the conventional cooling process.

[0081] The internally residual compressive stress ceramsite after being completely cooled is accurately classified through a vibrating screening device. The vibrating screening device consists of three layers of screens with different pore sizes. The pore size of the upper-layer screen is 8 mm, the middle-layer screen is 5 mm, and the lower-layer screen is 3 mm. The vibrating screen adopts a double-eccentric block drive mode, with the vibration frequency controlled at 960 - 1200 times per minute and the amplitude at 3 - 5 mm. After screening, the ceramsite is divided into three particle size groups: the large particle size group (8 - 10 mm), the medium particle size group (5 - 8 mm), and the small particle size group (3 - 5 mm). This accurate classification ensures a uniform particle size distribution of the product, meeting the requirements of different application scenarios. The three groups of classified ceramsite are respectively subjected to comprehensive quality assessment tests. The bulk density is measured. Using the standard container method, the ceramsite is freely poured into a standard container with a known volume, its mass is measured, and the bulk density is calculated. The bulk density of qualified products should be within the range of 900 - 1100 kg / m 3 range. Secondly, the single-grain compressive strength test is carried out. Randomly select 30 samples, conduct a compressive test on a material testing machine, record the destructive force, calculate the average compressive strength, and the average value of qualified products should be greater than 7.5 MPa. Thirdly, the 24-hour water absorption rate is detected. The dried ceramsite is immersed in water for 24 hours and then weighed, and the water absorption rate is calculated. The water absorption rate of qualified products should be less than 6%. Finally, the freeze-thaw cycle test is carried out. The ceramsite sample is immersed in water for 4 hours and then placed in an environment of -20 °C for 4 hours to freeze, and then placed in 20 °C water for 4 hours, which is one cycle. Repeat 25 times, measure the mass loss rate, and the loss rate of qualified products should be less than 2%.

[0082] The three particle size groups of ceramsite qualified through quality assessment are mixed according to a preset ratio: the large particle size group accounts for 30%, the medium particle size group accounts for 50%, and the small particle size group accounts for 20%. This ratio can obtain the best bulk density and the smallest void ratio. The mixed finished product is packaged into bags through an automatic packaging line, with each bag having a net weight of 50 kg or stored in bulk in a silo, forming a finished product of high-density coal gangue ceramsite sand.

[0083] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present application.

Claims

1. A composite modification method for improving the density of coal gangue ceramsite sand, characterized in that: The composite modification method for improving the density of coal gangue ceramsite sand comprises: The gangue is crushed and ground by a jaw crusher and a ball mill, and then the obtained gangue fine powder is immersed in a hydrochloric acid solution under a constant temperature condition for activation to obtain activated gangue powder; The silica sol and water glass are mixed in a predetermined ratio, and polyacrylamide solution, hexadecyl trimethylol solution and modified calcium lignin sulfonate are added in sequence, and the pH value is adjusted to a neutral range by a phosphoric acid solution to obtain a composite modifier system; The activated gangue powder and the composite modifier system are mixed in a double-shaft forced mixer according to a solid-liquid ratio, and then cured under constant temperature and humidity conditions to obtain a modified gangue mixture; The modified coal gangue mixture is preformed by a disc granulator, and a binder solution containing polyvinyl alcohol and sodium carboxymethyl cellulose is sprayed on the preformed ceramsite; The preformed ceramsite is subjected to a multi-stage temperature gradient calcination treatment, and then a high-temperature stable composite modifier is sprayed on the preformed ceramsite, and surface modification is performed under an oxygen-controlled atmosphere to obtain dense ceramsite; The dense expanded clay is subjected to cooling and strengthening treatment by using a gradient cooling technology, and then subjected to particle size classification by using a vibration screening device to obtain a high-density coal gangue expanded clay sand product.

2. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The method comprises crushing and grinding the coal gangue by a jaw crusher and a ball mill, and then immersing the obtained coal gangue fine powder in a hydrochloric acid solution under a constant temperature condition for activation to obtain an activated coal gangue powder, comprising: The raw gangue blocks are crushed into particles of a preset particle size by a jaw crusher, and then the particles are transported to a ball mill for fine grinding to obtain fine gangue powder; The fine powder of coal gangue is mixed with a hydrochloric acid solution of a target concentration according to a preset solid-liquid ratio to form a slurry, and the slurry is soaked in a stirring device under a constant temperature condition for a predetermined time to promote the decomposition of carbonate minerals in the coal gangue; The slurry after the soaking treatment is subjected to solid-liquid separation by a vacuum filtration device to obtain a filter cake, and the filter cake is washed with deionized water until it becomes neutral; The filter cake is dried in a constant temperature drying oven to obtain activated coal gangue powder.

3. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The silica sol and water glass are mixed in a predetermined ratio, and polyacrylamide solution, hexadecyl trimethylol solution and modified calcium lignin sulfonate are added in sequence, and then the pH value is adjusted to a neutral range by a phosphoric acid solution to obtain a composite modifier system, including: Silica sol with a mass fraction of 30% and water glass with a modulus of 2.5 were mixed in a volume ratio of 3:1, and stirred in a constant temperature stirrer at 50° C. to form a silica-based mixed liquid; Adding 5% of the total volume of polyacrylamide solution to the silicon-based mixed liquid, stirring at a medium speed with a paddle stirrer to obtain an enhanced bonding intermediate; Adding 4% of the total volume of hexadecyltrimethylol solution to the enhanced bonding intermediate, stirring and mixing, to obtain a hydrophobically modified intermediate; Adding modified calcium lignin sulfonate to the hydrophobically modified intermediate and distributing it evenly by stirring and dispersing to form a multifunctional complex; Adding aluminum hydroxide nanopowder to the multifunctional complex to provide crystal nucleus induction points to obtain a structure-reinforced premix; The structure strengthening premix is ​​subjected to pH value control treatment by phosphoric acid solution titration method, and sheared and dispersed in a high-speed disperser to obtain a composite modifier system.

4. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The activated gangue powder and the composite modifier system are mixed in a double-shaft forced mixer according to a solid-liquid ratio, and then cured under constant temperature and humidity conditions to obtain a modified gangue mixture, comprising: Preheating the double-shaft forced mixer, adjusting the inner cavity temperature to a suitable reaction temperature, and setting the speed parameter to create an ideal mixing environment; The activated coal gangue powder is introduced into the feed port of the double-shaft forced mixer at a constant rate by a pneumatic conveying device to establish a material transmission basis; The composite modifier system is sprayed into the double-shaft forced mixer in an atomized state according to a preset solid-liquid ratio of 1:0.8 using a precision metering pump for preliminary physical mixing; The mixer speed is adjusted to a low speed gear to maintain a uniform stirring state, so as to enable the composite modifier system to form a coating film on the surface of the activated coal gangue powder to generate a primary mixed material; Use temperature sensors to monitor the thermodynamic changes of the mixing process in real time, control the reaction temperature not to exceed the stability threshold of the mixed material, and prevent the modifier from solidifying prematurely; The primary mixed material is transferred to a constant temperature and humidity curing box, and continuously cured under preset temperature and humidity conditions to form a network silicon-aluminum-oxygen composite structure to obtain a modified coal gangue mixture.

5. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The modified coal gangue mixture is preformed by a disc granulator, and a binder solution containing polyvinyl alcohol and sodium carboxymethyl cellulose is sprayed to obtain preformed ceramsite, comprising: The disc inclination angle of the disc granulator is adjusted by a frequency controller, and the disc inclination angle is set to 45° to construct a material rolling track; The speed parameter of the disc granulator is controlled at 25r / min by a speed regulating device to form a uniform rotating platform; The modified coal gangue mixture is quantitatively added according to the material supply curve, so that it starts to roll and form nuclei under the combined action of gravity and centrifugal force of the disc granulator; Evenly spraying a polyvinyl alcohol and sodium carboxymethyl cellulose binder solution with a water content of 5% on the surface of the modified coal gangue mixture in a rolling state through an atomizing nozzle to promote surface bonding; By using the centrifugal force gradient principle, the disc inclination angle of the disc granulator is adjusted to 50°, so that the materials meeting the particle size requirements overflow from the disc edge, thus achieving automatic sorting; The overflowed material is preliminarily screened by a rotary screener to remove particles with diameters less than 3 mm and greater than 10 mm, thereby obtaining preformed ceramsite with a moist surface that can withstand extrusion.

6. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The preformed ceramsite is subjected to a multi-stage temperature gradient calcination treatment, and then a high-temperature stable composite modifier is sprayed on the preformed ceramsite, and surface modification is performed under an oxygen-controlled atmosphere to obtain dense ceramsite, comprising: The preformed ceramsite is placed in a tunnel drying kiln for dehydration and drying to form primary heat-treated ceramsite; The primary heat-treated ceramsite is transported to a rotary kiln and heated according to a preset temperature curve by a temperature control system to cause a mineral phase transformation inside the ceramsite; The ceramsite is calcined at high temperature in the rotary kiln to form a dense sintered structure inside the ceramsite; When the ceramsite is discharged from the kiln, a high-temperature stable composite modifier containing kaolin and zirconium oxide nanopowder is sprayed on the surface of the ceramsite through a high-temperature spraying device to form a surface modification layer; The ceramsite with the surface modified layer is introduced into a redox atmosphere control device, and a gas with an oxygen content of 5% is introduced to promote the combination of the modifier and the ceramsite matrix; The gas composition is changed by an atmosphere switching device, and the surface of the ceramsite is sealed to obtain dense ceramsite with increased volume density and closed porosity.

7. The composite modification method for improving the density of coal gangue ceramsite sand according to claim 1, characterized in that: The dense ceramsite is subjected to cooling and strengthening treatment by gradient cooling technology, and then subjected to particle size classification by a vibration screening device to obtain a high-density coal gangue ceramsite sand product, including: The dense ceramsite is introduced into a gradient cooling zone through a constant speed conveyor belt, and a slow cooling process is adopted in the front cooling zone to form temperature-controlled ceramsite; The temperature-controlled ceramsite is transported to a fine water mist area, and the temperature is rapidly reduced by means of the uniformly sprayed fine water mist, thereby generating surface stress-strengthened ceramsite; Using a normal temperature air cooling system to cool the surface stress-strengthening ceramsite to form internal residual compressive stress ceramsite; The internal residual compressive stress ceramsite is subjected to three-level particle size screening by a vibrating screening device to divide the ceramsite into a small particle size group, a medium particle size group and a large particle size group; The three particle size groups of expanded clay were subjected to bulk density measurement, compressive strength test, water absorption test and freeze-thaw cycle test respectively. The three particle size groups of expanded clay that met the quality standards were mixed in a preset proportion and packaged to obtain high-density coal gangue expanded clay sand finished products.

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