A low-adsorption, high-flow gasification slag-based cement admixture and its preparation method

Abstract

This invention relates to the field of cement admixture technology, and discloses a low-adsorption, high-flowability gasification slag-based cement admixture and its preparation method. The admixture consists of a gasification slag matrix and an organic-inorganic composite coating layer attached to its surface and pores. The coating layer is composed of a cross-linked biopolysaccharide network and inorganic nanoparticles. In preparation, carbon is extracted from the gasification slag and dispersed in water. A composite system of biopolysaccharides and inorganic nanoparticles is added. The pH of the system is adjusted using an acid-base regulator to anchor the polysaccharide molecules to the surface of the gasification slag, promoting the cross-linking and deposition of nanoparticles within the polysaccharide network. The coated and modified gasification slag is obtained through solid-liquid separation and low-temperature drying. This method seals the visible pores and submicron-sized micropores of the gasification slag, blocks the channels for water-reducing agent molecules to enter the pores, reduces the ineffective consumption of water-reducing agent, and solves the problem of abrupt changes in the rheological properties and reduced fluidity of cement paste caused by ineffective adsorption.

Description

Technical Field

[0001] This invention relates to the field of cement admixture technology, and discloses a low-adsorption, high-flow gasification slag-based cement admixture and its preparation method. Background Technology

[0002] Coal gasification processes generate a large amount of gasification slag, which can be used as a cement admixture to reduce cement production costs and achieve solid waste resource utilization. Gasification slag contains numerous visible and micropores, and its surface is covered with unburned free carbon. In existing technologies, to reduce the adsorption capacity of gasification slag and improve its flow properties in cement systems, conventional methods involve mechanical grinding or high-temperature calcination. Mechanical grinding reduces particle size by extending the grinding time, attempting to reduce the specific surface area and destroy surface pores through physical extrusion; high-temperature calcination places the gasification slag in a high-temperature environment, attempting to seal surface pores through sintering and melting, thereby reducing its adsorption capacity for admixtures.

[0003] Mechanical grinding is energy-intensive and prone to generating microcracks and secondary pores during extrusion, failing to eliminate submicron-level pores. While high-temperature calcination can seal some macropores, the high-temperature environment damages the glassy network structure with cementitious activity in the gasified slag, causing it to lose its hydration activity. In the actual cement mixing process, the unresolved submicron-level pores continue to adsorb polycarboxylate superplasticizer molecules and mixing water, leading to the ineffective consumption of superplasticizer molecules within the pores. This, in turn, causes technical problems such as abrupt changes in the rheological properties and reduced fluidity of the cement paste. Summary of the Invention

[0004] To address the shortcomings of existing gasification slag-based cement admixtures, such as high energy consumption during mechanical grinding, inability to eliminate submicron-level pores, and high-temperature calcination damaging the hydration activity of the gasification slag glass, which leads to ineffective adsorption of water-reducing agents and mixing water by the gasification slag pores, causing abrupt changes in the rheological properties and reduced fluidity of the cement paste, this invention provides a low-adsorption, high-fluidity gasification slag-based cement admixture and its preparation method.

[0005] To address the aforementioned technical problems, this invention provides a low-adsorption, high-flow gasification slag-based cement admixture. The admixture comprises coated and modified gasification slag, which includes a gasification slag matrix and an organic-inorganic composite coating layer attached to the surface and pores of the gasification slag matrix. The organic-inorganic composite coating layer is composed of a biopolysaccharide network and inorganic nanoparticles filled within the biopolysaccharide network. Based on the total mass of the coated and modified gasification slag (100%), the gasification slag matrix accounts for 85% to 95% of the mass, and the organic-inorganic composite coating layer accounts for 5% to 15% of the mass. In the organic-inorganic composite coating layer, based on solid dry weight, the mass ratio of the biopolysaccharide to the inorganic nanoparticles is 1:0.5 to 1:3.

[0006] In its specific implementation, this scheme constructs an organic-inorganic composite coating layer on the surface and inside the pores of the gasification slag matrix. The polar groups on the biopolysaccharide molecular chains form hydrogen bonds and van der Waals forces with the hydroxyl groups on the aluminosilicate surface of the gasification slag matrix, anchoring and forming a continuous three-dimensional network framework. Inorganic nanoparticles fill the cross-linking nodes and intersegment gaps of the biopolysaccharide network and undergo cross-linking and solidification, forming a dense coating structure firmly bonded to the matrix. This coating structure can completely seal the open pores of the gasification slag matrix, blocking the channels for polycarboxylate superplasticizer molecules and mixing water to enter the pores, thus reducing the ineffective adsorption of superplasticizers at the source. Simultaneously, the coating layer can regulate the surface interface characteristics of the gasification slag matrix, reducing its surface adsorption energy, ultimately achieving the core performance of low adsorption and high flowability of the admixture, without damaging the hydration and gelling activity of the gasification slag matrix itself.

[0007] Furthermore, in the above technical solution, the gasification slag matrix is ​​gasification slag after flotation decarbonization treatment, the particle size distribution of the gasification slag matrix satisfies D10 of 1 micrometer to 3 micrometers, D50 of 8 micrometers to 15 micrometers, D90 of 25 micrometers to 40 micrometers, and the original specific surface area of ​​the gasification slag matrix is ​​300 square meters per kilogram to 500 square meters per kilogram.

[0008] In practice, flotation decarbonization can remove free carbon components in gasification slag that have a strong adsorption effect on water-reducing agents, reducing strong adsorption sites in the system. The specific particle size distribution and specific surface area parameters mentioned above enable the gasification slag matrix to have both good hydration and cementation activity and suitable surface attachment sites. This avoids the problems of excessively fine particles leading to excessively large specific surface area and increased adsorption, as well as the defects of excessively coarse particles leading to uneven coating layer adhesion and incomplete pore closure. This provides a stable matrix foundation for the uniform construction of organic-inorganic composite coating layers.

[0009] Furthermore, in the above technical solution, the biopolysaccharide is selected from one or more combinations of xanthan gum, sodium alginate, hyaluronic acid, and gellan gum, the weight-average molecular weight of the biopolysaccharide is 500,000 Daltons to 2,000,000 Daltons, and the biopolysaccharide forms a three-dimensional spatial network structure in the organic-inorganic composite coating layer.

[0010] In practice, the aforementioned biopolysaccharide molecular chains have a large number of active polar groups such as hydroxyl and carboxyl groups, which can form a firm bond with the surface of the gasification slag matrix through hydrogen bonds and van der Waals forces, thus achieving stable anchoring of the molecular chains on the matrix surface and the inner wall of the pores. The weight-average molecular weight of 500,000 Daltons to 2,000,000 Daltons ensures that the biopolysaccharide molecular chains have sufficient chain length and entanglement ability, forming a continuous and stable three-dimensional spatial network structure on the surface of the gasification slag matrix. This provides a complete skeletal support for the uniform deposition of inorganic nanoparticles, avoids the aggregation of inorganic nanoparticles, and ensures the density and continuity of the coating layer.

[0011] Furthermore, in the above technical solution, the inorganic nanoparticles are nano-silica sols, the initial particle size of the nano-silica sols is 5 nanometers to 20 nanometers, the initial pH value of the nano-silica sols before being added to the system is 2 to 3, and the inorganic nanoparticles are deposited in the cross-linking nodes and intersegment gaps of the biopolysaccharide network.

[0012] In practice, the surface of the nano-silica sol has a large number of active silanol groups, which can form hydrogen bonds with the polar groups on the biopolysaccharide molecular chains to achieve stable composite with the biopolysaccharide network. The initial particle size of 5 to 20 nanometers allows the nano-silica sol particles to smoothly enter the submicron-level micropores of the gasification slag matrix, while fully filling the intersegmental gaps of the biopolysaccharide network, achieving complete pore sealing and densification of the coating layer. The initial acidic environment of pH 2 to 3 ensures that the nano-silica sol maintains excellent dispersion stability before being added to the reaction system, avoiding premature aggregation and ensuring its uniform deposition and cross-linking in the biopolysaccharide network.

[0013] Furthermore, in the above technical solution, the coating thickness of the organic-inorganic composite coating layer on the surface of the gasification slag substrate is 50 nanometers to 500 nanometers, the organic-inorganic composite coating layer covers visible pores larger than 50 nanometers and some submicron-level micropores on the surface of the gasification slag substrate, and the surface water contact angle of the organic-inorganic composite coating layer is greater than the surface water contact angle of the gasification slag substrate.

[0014] In practice, a coating thickness of 50 to 500 nanometers can completely seal the open pores of the gasification slag matrix while avoiding the problems of excessive coating leading to a significant increase in particle size and a decrease in hydration and gelation activity. The comprehensive coverage of visible pores larger than 50 nanometers and some submicron-sized micropores can directly block the channels for conventional polycarboxylate superplasticizer molecules (with hydrodynamic diameters mostly in the tens of nanometers) to enter the pores, completely eliminating the ineffective adsorption of superplasticizers in the pores. The increase in the surface water contact angle indicates that the coating layer can improve the hydrophobicity of the gasification slag matrix surface, reduce its adsorption capacity for polar superplasticizer molecules and mixing water, and further enhance the performance of low adsorption and high flowability.

[0015] Furthermore, in the above technical solution, the admixture also includes mineral active micro powder, which is selected from at least one of slag micro powder, fly ash, and silica fume. Based on the total mass of the admixture as 100%, the mass ratio of the coated modified gasification slag is 20% to 60%, the mass ratio of the mineral active micro powder is 40% to 80%, and the specific surface area of ​​the mineral active micro powder is greater than the specific surface area of ​​the coated modified gasification slag.

[0016] In practice, the mineral active micro powders with larger specific surface areas can effectively fill the packing gaps between the coated and modified gasification slag particles, optimize the overall particle size distribution of the admixture, improve the particle packing density, and thus improve the flow properties of the admixture in the cement system. At the same time, the mineral active micro powders such as slag powder, fly ash, and silica fume have excellent hydration and cementitious activity, which can produce a synergistic hydration effect with the coated and modified gasification slag, making up for the slight impact of the coating layer on the hydration activity of the gasification slag matrix, and ensuring the stable development of the strength of the cement system.

[0017] To address the aforementioned technical problems, this invention also provides a method for preparing a low-adsorption, high-flow-rate gasification slag-based cement admixture, used to prepare the low-adsorption, high-flow-rate gasification slag-based cement admixture described in any of the above-mentioned methods. The preparation method includes the following steps: Step S1, carbon extraction treatment of gasification slag and dispersion in water to form a gasification slag suspension; Step S2, adding a compound system of bio-polysaccharides and inorganic nanoparticles to the gasification slag suspension; Step S3, adding an acid-base regulator to the compound system to adjust the pH value of the system, causing the bio-polysaccharide molecular chains to unfold and anchor on the surface of the gasification slag; Step S4, maintaining the pH value and temperature of the system, causing the inorganic nanoparticles to cross-link and deposit in the bio-polysaccharide network to form a coating layer; Step S5, performing solid-liquid separation on the reacted mixture, and drying the separated solid at low temperature to obtain the coated modified gasification slag.

[0018] In practice, this preparation method removes highly adsorbed free carbon components from the gasification slag through carbon extraction treatment, followed by dispersion treatment to fully deagglomerate the gasification slag particles, exposing active sites on the surface and inside the pores, providing a basis for the anchoring of the coating layer. A premixed system of biopolysaccharides and inorganic nanoparticles is prepared, ensuring that the inorganic nanoparticles are uniformly dispersed around the biopolysaccharide molecular chains, preventing localized agglomeration during subsequent addition. pH control allows the biopolysaccharide molecular chains to fully unfold from their coiled state, exposing numerous active polar groups that firmly anchor to the surface and pore walls of the gasification slag matrix, forming a continuous three-dimensional network framework. Subsequently, under constant pH and temperature conditions, the inorganic nanoparticles undergo in-situ cross-linking deposition at the cross-linking nodes and intersegmental spaces of the biopolysaccharide network, forming a tightly bonded and dense organic-inorganic composite coating layer. Finally, a low-temperature drying process is employed to avoid damage to the biopolysaccharide network and coating layer structure caused by high temperatures, ensuring the integrity and stability of the coating layer and achieving efficient modification of the gasification slag matrix.

[0019] Furthermore, in the above technical solution, in step S1, the carbon removal treatment is a flotation decarbonization process, which uses a collector and a frother, and the carbon content of the decarbonized gasification slag is reduced to below 3% by mass. The dispersion in water involves adding the decarbonized gasification slag to an aqueous solution containing a polycarboxylate superplasticizer and performing ultrasonic dispersion treatment using an ultrasonic cell pulverizer. The frequency of the ultrasonic dispersion treatment is 20 kHz to 30 kHz, and the treatment time is 10 minutes to 30 minutes, to obtain a gasification slag suspension with a solid content of 10% to 30% by mass.

[0020] In practice, flotation decarbonization can efficiently remove free carbon components from gasification slag, reducing the carbon content to below 3%, thereby reducing strong adsorption sites in the system and preventing excessive adsorption of water-reducing agents by free carbon. Polycarboxylate-based water-reducing agents can achieve initial dispersion of gasification slag particles through steric hindrance. Combined with ultrasonic dispersion treatment at a frequency of 20 kHz to 30 kHz, the agglomerates of gasification slag particles can be efficiently broken, allowing the particles to completely deagglomerate and fully expose the active sites on the surface and inside the pores. This provides a good interfacial basis for the subsequent anchoring of biopolysaccharides and the uniform deposition of the coating layer. A solid content of 10% to 30% can ensure that the system has suitable fluidity and dispersibility, avoiding both excessive solid content leading to particle agglomeration and uneven coating, and excessive solid content leading to reduced production efficiency.

[0021] Furthermore, in the above technical solution, in step S2, the biopolysaccharide is first dissolved in water to prepare a polysaccharide solution with a mass fraction of 0.5% to 2%, and then the polysaccharide solution is mixed evenly with the inorganic nanoparticles to form the compound system. The compound system is then added to the gasification slag suspension by dropwise addition. In step S3, the acid-base adjuster is a dilute hydrochloric acid solution and a sodium hydroxide solution, and the pH value of the system is adjusted from the initial 7 to 8 to 3.5 to 4.5. Stirring is maintained at this pH value, and the stirring speed is 200 to 500 revolutions per minute.

[0022] In practice, pre-preparing the biopolysaccharide into a low-concentration aqueous solution of 0.5% to 2% ensures that the biopolysaccharide molecules are fully dissolved and uniformly dispersed, avoiding the problems of local agglomeration and incomplete dissolution caused by directly adding dry powder. Pre-mixing the polysaccharide solution with inorganic nanoparticles to form a compound system allows the inorganic nanoparticles to be uniformly dispersed around the biopolysaccharide molecular chains in advance, providing a uniform precursor for subsequent in-situ cross-linking deposition and preventing the nanoparticles from agglomerating in the system. The dropwise addition method ensures that the compound system is uniformly dispersed in the gasification slag suspension, avoiding uneven coating thickness caused by excessively high local concentrations. To mitigate the defects of agglomeration, adjusting the pH of the system to 3.5 to 4.5 allows the biopolysaccharide molecules to be near their isoelectric point, fully unwinding the molecular chains from their coiled random coil state and exposing a large number of active polar groups such as hydroxyl and carboxyl groups. This significantly enhances their anchoring and binding ability with the gasification slag matrix surface. At the same time, this pH range ensures that the inorganic nanoparticles crosslink slowly and uniformly, avoiding rapid agglomeration. A stirring speed of 200 to 500 rpm ensures that the components of the system are mixed uniformly without generating strong shear forces that could damage the formed three-dimensional network structure of the biopolysaccharide, thus ensuring the integrity of the coating layer skeleton.

[0023] Furthermore, in the above technical solution, in step S4, the temperature of the system is maintained at 40 degrees Celsius to 60 degrees Celsius, and the reaction time is 2 hours to 5 hours. During the reaction time, the inorganic nanoparticles complete the cross-linking deposition in the biological polysaccharide network. In step S5, the solid-liquid separation is carried out by vacuum filtration or centrifugation. The low-temperature drying temperature is 60 degrees Celsius to 80 degrees Celsius, and the drying time is 12 hours to 24 hours. The dried coated modified gasification slag is then dispersed by an air jet mill.

[0024] In practice, a reaction temperature of 40°C to 60°C can increase the cross-linking reaction rate of inorganic nanoparticles and shorten the reaction time, while preventing thermal degradation and inactivation of biopolysaccharide molecules, thus ensuring the stability of the three-dimensional network structure of biopolysaccharides. A reaction time of 2 to 5 hours ensures that inorganic nanoparticles are fully cross-linked and uniformly deposited in the biopolysaccharide network, forming a complete and dense organic-inorganic composite coating layer. A low-temperature drying process of 60°C to 80°C avoids the problems of biopolysaccharide molecule degradation and coating layer cracking and detachment caused by high temperature, ensuring the structural integrity and interfacial bonding strength of the coating layer. The air jet milling treatment can efficiently deagglomerate the slight agglomerates formed during the drying process, restoring the monodisperse state of the coated modified gasification slag particles, further ensuring the high flowability of the admixture in the cement system.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention constructs an organic-inorganic composite coating layer on the surface of a gasification slag matrix, consisting of a cross-linked biopolysaccharide network and inorganic nanoparticles. This seals the visible pores and submicron-sized micropores of the gasification slag, blocking the channels for water-reducing agent molecules to enter the pores. By adding an acid-base regulator to adjust the pH of the system to the range of 3.5 to 4.5, the biopolysaccharide molecular chains unfold and anchor to the rough areas of the gasification slag surface. This promotes the cross-linking and deposition of nano-silica sol with an initial particle size of 5 to 20 nanometers in the cross-linking nodes and intersegmental spaces of the polysaccharide network, forming a dense coating layer with a thickness of 50 to 500 nanometers. This coating layer increases the surface water contact angle of the gasification slag matrix, directly reducing the ineffective consumption of water-reducing agent within the pores, maintaining the effective concentration of water-reducing agent in the liquid phase inside the cement slurry, and solving the technical problem of abrupt changes in the rheological properties and reduced fluidity of cement slurry caused by ineffective adsorption.

[0026] 2. By flotation decarbonization of the gasification slag matrix, followed by ultrasonic dispersion in an aqueous solution containing polycarboxylate superplasticizer using an ultrasonic cell pulverizer, the matrix achieves a specific particle size distribution and solid content, providing a dispersion basis for the uniform adhesion of the composite coating layer. After the cross-linking deposition reaction, a combination of vacuum filtration or centrifugation and low-temperature drying at 60-80 degrees Celsius is used, followed by air jet milling to disperse the material, avoiding damage to the organic-inorganic composite coating layer structure caused by high-temperature environments. The resulting coated and modified gasification slag is mixed with mineral active micropowder with a larger specific surface area at a specific mass ratio. The mineral active micropowder fills the packing gaps between the modified gasification slag particles, optimizing the overall particle size distribution of the admixture. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0028] Example 1: This example provides a low-adsorption, high-flow gasification slag-based cement admixture, which is composed of coated modified gasification slag and mineral active micro powder; based on the total mass of the admixture as 100%, the mass of coated modified gasification slag accounts for 40%, and the mass of mineral active micro powder accounts for 60%.

[0029] The modified gasification slag, based on a total mass of 100%, comprises 92% gasification slag matrix and 8% organic-inorganic composite coating layer. In the organic-inorganic composite coating layer, the mass ratio of biopolysaccharide to inorganic nanoparticles is 1:2 based on solid dry basis.

[0030] The gasification slag matrix is ​​coal gasification slag that has undergone flotation decarbonization treatment, with a particle size distribution of D10=2.1μm, D50=10.5μm, D90=32μm, and an original specific surface area of ​​380m². 2 / kg, with a carbon content of 2.1%; the biopolysaccharide is xanthan gum with a weight-average molecular weight of 1.2 million Daltons; the inorganic nanoparticles are nano-silica sol with an initial particle size of 10 nm, an initial pH of 2.5 before being added to the system, and a solid content of 30%; the mineral active micro powder is S95 grade slag micro powder with a specific surface area of ​​450 m² / kg. 2 / kg, and its specific surface area is greater than that of the coated modified gasification slag.

[0031] The preparation method of the low-adsorption, high-flow gasification slag-based cement admixture in this embodiment includes the following specific steps: Step S1: Carbon extraction and dispersion treatment of gasification slag: Carbon removal from coal gasification slag was achieved using a flotation decarbonization process with diesel fuel as the collector and 2-octanol as the frother. The carbon content of the gasification slag obtained after flotation was reduced to 2.1%. The decarbonized gasification slag was then added to deionized water containing 0.2% polycarboxylate superplasticizer (30% water reduction rate) and ultrasonically dispersed using an ultrasonic cell disruptor at a frequency of 25 kHz, a power of 800 W, and a processing time of 20 min, resulting in a gasification slag suspension with a solid content of 20% by mass.

[0032] Preparation and addition of the compound system in step S2: Xanthan gum was added to deionized water and dissolved for 2 hours at 40°C and 300 rpm to prepare a 1% xanthan gum solution. Nano-silica sol was added to the xanthan gum solution at a dry basis mass ratio of 1:2 (biopolysaccharide to inorganic nanoparticles). The mixture was stirred at 300 rpm for 30 minutes to obtain a homogeneous compound system. The compound system was then added dropwise at a rate of 2 mL / min to the above gasification slag suspension, while maintaining a stirring speed of 300 rpm during the addition process.

[0033] Step S3: pH adjustment and anchoring treatment: After the compound system was added dropwise, 0.5 mol / L dilute hydrochloric acid solution was added to the system to adjust the pH value of the system from the initial 7.6 to 4.0. The system was stirred at 350 rpm for 30 minutes to allow the xanthan gum molecular chains to fully expand and anchor to the surface and pore walls of the gasification slag.

[0034] Step S4: Crosslinking deposition coating treatment: Maintain the pH of the system at 4.0, heat the system to 50℃, keep it at the temperature and stir for 3 hours at a stirring speed of 300 rpm, so that the nano-silica sol particles can complete cross-linking and deposition in the cross-linking nodes and intersegment gaps of the three-dimensional network structure formed by xanthan gum, and form an organic-inorganic composite coating layer on the surface and inside the pores of the gasification slag matrix.

[0035] Step S5: Solid-liquid separation and drying: The reaction mixture was centrifuged to separate solids and liquids at a speed of 4000 rpm for 10 min. The separated solid filter cake was placed in a forced-air drying oven and dried at 70°C for 18 h until constant weight. The dried solid was then dispersed using an air jet mill to obtain coated modified gasification slag.

[0036] Step S6: Compound processing The above-mentioned coated and modified gasification slag was mixed with S95 grade slag powder at a mass ratio of 40:60 to obtain the low-adsorption, high-flow gasification slag-based cement admixture of this embodiment.

[0037] Example 2: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The modified gasification slag, based on a total mass of 100%, comprises 85% gasification slag matrix and 15% organic-inorganic composite coating layer. In the organic-inorganic composite coating layer, based on solid dry basis, the mass ratio of biopolysaccharide to inorganic nanoparticles is 1:0.5.

[0038] Example 3: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The modified gasification slag, based on a total mass of 100%, comprises 95% gasification slag matrix and 5% organic-inorganic composite coating layer. In the organic-inorganic composite coating layer, the mass ratio of biopolysaccharide to inorganic nanoparticles is 1:3 based on solid dry basis.

[0039] Example 4: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The biopolysaccharide was replaced with sodium alginate, with a weight-average molecular weight of 800,000 Daltons.

[0040] Example 5: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The biopolysaccharide was replaced with hyaluronic acid, with a weight-average molecular weight of 1.8 million Daltons.

[0041] Example 6: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The biopolysaccharide was replaced with gellan gum, with a weight-average molecular weight of 1 million Daltons.

[0042] Example 7: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The inorganic nanoparticles are nano-silica sols with an initial particle size of 5 nm and an initial pH of 2.0 before being added to the system.

[0043] Example 8: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: The inorganic nanoparticles are nano-silica sols with an initial particle size of 20 nm and an initial pH of 3.0 before being added to the system.

[0044] Example 9: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: Based on a total admixture mass of 100%, the modified gasification slag accounts for 60% of the mass, and the mineral active micro powder accounts for 40% of the mass; the mineral active micro powder is Class F, Grade I fly ash, with a specific surface area of ​​500 m². 2 / kg.

[0045] Example 10: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: In step S3, the pH of the system is adjusted to 3.5 using a dilute hydrochloric acid solution, while the other parameters remain unchanged.

[0046] Example 11: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: In step S3, the pH of the system is adjusted to 4.5 using a dilute hydrochloric acid solution, while the other parameters remain unchanged.

[0047] Example 12: This example provides a low-adsorption, high-flow gasification slag-based cement admixture. Its formulation and preparation method are identical to those of Example 1, except for the following parameters: In step S4, the system temperature is maintained at 40°C, the reaction time is kept at this temperature and stirred for 5 hours, and the other parameters remain unchanged.

[0048] Comparative Example 1: This comparative example provides a gasification slag-based cement admixture, the formulation and preparation method of which are the same as those in Example 1 except for the following parameters: The coating modification treatment in steps S2 to S4 is omitted. The gasification slag suspension prepared in step S1 is directly mixed with slag powder in the proportion of Example 1 after solid-liquid separation, drying and dispersion treatment in step S5 to obtain the admixture. That is, the gasification slag in this comparative example does not use organic-inorganic composite coating layer modification, and the gasification slag matrix after flotation decarbonization is used directly.

[0049] Comparative Example 2: This comparative example provides a gasification slag-based cement admixture, prepared using the conventional mechanical grinding process described in the background art, specifically as follows: The coal gasification slag from the same source as in Example 1 was decarbonized by flotation and then mechanically ground in a ball mill for 2 hours to obtain gasification slag powder with a particle size distribution of D10=2.0μm, D50=10.3μm, and D90=33μm. The gasification slag powder was then mixed with S95 grade slag powder at a mass ratio of 40:60 to obtain the gasification slag-based cement admixture of this comparative example.

[0050] Comparative Example 3: This comparative example provides a gasification slag-based cement admixture, the formulation and preparation method of which are identical to those of Example 1 except for the following parameters: In the organic-inorganic composite coating layer, the mass ratio of biopolysaccharide to inorganic nanoparticles is 1:4 based on solid dry weight, which exceeds the limited range of 1:0.5 to 1:3.

[0051] Comparative Example 4: This comparative example provides a gasification slag-based cement admixture, the formulation and preparation method of which are identical to those of Example 1 except for the following parameters: The pH adjustment operation in step S3 is omitted. After the compound system is added dropwise, the mixture is stirred at 350 rpm for 30 min at the initial pH of 7.6. The cross-linking deposition reaction in the subsequent step S4 is also carried out at pH 7.6.

[0052] Test method: This section presents the following performance tests on the cement admixtures prepared in all the above embodiments and comparative examples. All tests were conducted at room temperature of 25°C and relative humidity of 50%: (1) Adsorption capacity test of polycarboxylate superplasticizer: The total organic carbon (TOC) method was used for testing. The admixture was mixed with... Silicate cement was mixed at a mass ratio of 3:7. Based on the total mass of cementitious materials, 1.0% of polycarboxylate superplasticizer was added and the water-cement ratio was 0.5 to prepare cement paste. After stirring evenly, the paste was allowed to stand for 10 minutes. The supernatant was taken and the organic carbon content in the supernatant was determined using a TOC meter. The adsorption capacity of the superplasticizer was calculated, with the unit being mg / g cementitious material.

[0053] (2) Cement paste fluidity test: The test was conducted according to GB / T8077-2012 "Test Method for Homogeneity of Concrete Admixtures". The admixture was mixed with... Silicate cement was mixed at a mass ratio of 3:7. Based on the total mass of cementitious materials, 1.0% of polycarboxylate superplasticizer was added, and cement mortar was prepared with a water-cement ratio of 0.29. The initial flowability and the flowability after standing for 1 hour were tested, with the unit being mm.

[0054] (3) Cement mortar compressive strength test: The test shall be conducted in accordance with GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)". The admixture and... Silicate cement was mixed at a mass ratio of 3:7 to prepare cement mortar specimens. The compressive strength of the specimens after standard curing for 3 days and 28 days was tested, and the unit was MPa.

[0055] (4) Coating layer pore closure rate test: The specific surface area of ​​the gasification slag before and after modification was tested by nitrogen adsorption method (BET method). The pore closure rate was calculated by the change rate of specific surface area. The calculation formula is: pore closure rate = (original specific surface area - modified specific surface area) / original specific surface area × 100%, unit is .

[0056] Test Results Table: Table 1 Performance test results of each embodiment and comparative example

[0057] Results analysis: All the admixtures prepared in the embodiments of this invention exhibited significant low adsorption and high flow properties, while maintaining excellent hydration and gelation activity. Example 1, as the optimal embodiment, showed the lowest water-reducing agent adsorption amount as low as 1.28 mg / g, an initial flowability of 295 mm, a flowability retention rate of 94.2% after 1 hour, and a pore closure rate of 89.2%. Simultaneously, the 3-day and 28-day compressive strengths reached 28.6 MPa and 52.7 MPa, respectively, demonstrating the best overall performance and verifying the rationality of the optimal formulation and process parameters of this invention. Examples 2-9, by adjusting the coating layer ratio, the type of biological polysaccharide, the parameters of inorganic nanoparticles, and the type and ratio of mineral active micropowder, all achieved excellent modification effects within the scope defined in the claims. The water-reducing agent adsorption amount was all below 1.42 mg / g, the initial flowability was all above 284 mm, and the pore closure rate was all above 85%, fully verifying the universality of the formulation range and the feasibility of component substitution in this invention. Examples 10-12, by adjusting the key parameters of the preparation process within the scope defined by the claims, still maintained excellent performance, verifying the robustness of the preparation method of the present invention and the rationality of the process window.

[0058] Comparative Example 1, without the modification of the organic-inorganic composite coating layer of the present invention, directly used the gasification slag matrix. Its water-reducing agent adsorption capacity reached 3.85 mg / g, more than three times that of Example 1. The initial flowability was only 212 mm, and after 1 hour, the flowability dropped significantly to 156 mm, with a pore closure rate of 0%. Simultaneously, the compressive strength decreased significantly. These results directly demonstrate that the core technical means of the present invention—the organic-inorganic composite coating layer—is key to reducing water-reducing agent adsorption and improving flowability. It fundamentally seals the pores of the gasification slag, blocking the ineffective adsorption channels of the water-reducing agent.

[0059] Comparative Example 2, using conventional mechanical grinding processes from the prior art, still showed a water-reducing agent adsorption capacity as high as 3.12 mg / g, an initial flowability of only 235 mm, and a pore closure rate of only 22.4%, far lower than the embodiments of the present invention. This result demonstrates that existing mechanical grinding techniques cannot effectively seal the submicron-level pores of gasification slag and cannot solve the core problem of ineffective water-reducing agent adsorption. In contrast, the technical solution of the present invention has unexpected technical effects compared to existing technologies and possesses outstanding substantive features.

[0060] Comparative Example 3 adjusted the mass ratio of biopolysaccharide to inorganic nanoparticles to 1:4, exceeding the range defined in the claims of this invention. Its water-reducing agent adsorption increased to 2.26 mg / g, pore sealing rate decreased to 68.3%, and fluidity significantly decreased. This is because excessive inorganic nanoparticles cannot be uniformly dispersed in the biopolysaccharide network, resulting in aggregation, decreased coating density, and poorer pore sealing effect. This demonstrates that the component ratio range defined in this invention is a necessary condition for achieving excellent results.

[0061] Comparative Example 4 omitted the crucial pH adjustment step, directly proceeding with the reaction at an initial pH of 7.6. Its water-reducing agent adsorption capacity increased to 2.58 mg / g, with a pore closure rate of only 59.7%, resulting in a significant performance decline. This is because under neutral conditions, the biopolysaccharide molecular chains are coiled, unable to fully unfold and anchor to the gasification slag surface, failing to form a continuous three-dimensional network framework. This leads to uneven cross-linking and deposition of inorganic nanoparticles, resulting in a discontinuous coating layer and poor pore closure. This directly demonstrates that the pH adjustment step in this invention is the core and irreplaceable step for achieving coating modification.

[0062] In summary, this invention achieves highly efficient sealing of the pores in gasification slag by constructing an organic-inorganic composite coating layer cross-linked with a biopolysaccharide network and inorganic nanoparticles, combined with a specific pH-controlled anchoring process. This significantly reduces the ineffective adsorption of water-reducing agents, greatly improves the fluidity and long-term stability of cement slurry, and avoids damage to the hydration activity of gasification slag. The performance of all embodiments is significantly superior to that of existing comparative examples, while the performance of comparative examples that violate core technical methods, exceed parameter ranges, or omit key steps is significantly reduced. This fully demonstrates that the technical solution of this invention is not a conventional choice in the art, can produce unexpected technical effects, and possesses the inventiveness required by patent law.

Claims

1. A low-adsorption, high-flow gasification slag-based cement admixture, the admixture being composed of coated and modified gasification slag, the coated and modified gasification slag comprising a gasification slag matrix and an organic-inorganic composite coating layer attached to the surface and pores of the gasification slag matrix, the organic-inorganic composite coating layer being composed of a biopolysaccharide network and inorganic nanoparticles filled in the biopolysaccharide network through cross-linking; Based on the total mass of the coated and modified gasification slag as 100%, the mass percentage of the gasification slag matrix is ​​85% to 95%, and the mass percentage of the organic-inorganic composite coating layer is 5% to 15%. In the organic-inorganic composite coating layer, the mass ratio of the biopolysaccharide to the inorganic nanoparticles is 1:0.5 to 1:3, based on solid dry weight.

2. The low-adsorption, high-flow gasification slag-based cement admixture according to claim 1, wherein the gasification slag matrix is ​​gasification slag after flotation decarbonization treatment, the particle size distribution of the gasification slag matrix satisfies D10 of 1 micrometer to 3 micrometers, D50 of 8 micrometers to 15 micrometers, D90 of 25 micrometers to 40 micrometers, and the original specific surface area of ​​the gasification slag matrix is ​​300 square meters per kilogram to 500 square meters per kilogram.

3. The low-adsorption, high-flow gasification slag-based cement admixture according to claim 1, wherein the biopolysaccharide is selected from one or more combinations of xanthan gum, sodium alginate, hyaluronic acid, and gellan gum, the weight-average molecular weight of the biopolysaccharide is 500,000 Daltons to 2,000,000 Daltons, and the biopolysaccharide forms a three-dimensional spatial network structure in the organic-inorganic composite coating layer.

4. The low-adsorption, high-flow gasification slag-based cement admixture according to claim 1, wherein the inorganic nanoparticles are nano-silica sol, the initial particle size of the nano-silica sol is 5 nanometers to 20 nanometers, the initial pH value of the nano-silica sol before being added to the system is 2 to 3, and the inorganic nanoparticles are deposited in the cross-linking nodes and intersegment gaps of the biopolysaccharide network.

5. The low-adsorption, high-flow gasification slag-based cement admixture according to claim 1, wherein the organic-inorganic composite coating layer has a coating thickness of 50 nanometers to 500 nanometers on the surface of the gasification slag matrix, the organic-inorganic composite coating layer covers visible pores larger than 50 nanometers and some submicron-sized micropores on the surface of the gasification slag matrix, and the surface water contact angle of the organic-inorganic composite coating layer is greater than the surface water contact angle of the gasification slag matrix.

6. The low-adsorption, high-flow gasification slag-based cement admixture according to claim 1, wherein the admixture further comprises mineral active micropowder, wherein the mineral active micropowder is selected from at least one of slag micropowder, fly ash, and silica fume, wherein, based on the total mass of the admixture as 100%, the mass proportion of the coated modified gasification slag is 20% to 60%, the mass proportion of the mineral active micropowder is 40% to 80%, and the specific surface area of ​​the mineral active micropowder is greater than the specific surface area of ​​the coated modified gasification slag.

7. A method for preparing a low-adsorption, high-flow gasification slag-based cement admixture, used to prepare the admixture according to any one of claims 1 to 6, the preparation method comprising: Step S1: The gasification slag is subjected to carbon removal treatment and dispersed in water to form a gasification slag suspension; Step S2: Add a compound system of biopolysaccharides and inorganic nanoparticles to the gasification slag suspension; Step S3: Add an acid-base regulator to the compound system to adjust the pH value of the system, so that the biopolysaccharide molecular chains unfold and anchor to the surface of the gasification slag. Step S4: Maintain the pH and temperature of the system to allow the inorganic nanoparticles to cross-link and deposit in the biological polysaccharide network to form a coating layer; Step S5: The mixture after reaction is subjected to solid-liquid separation, and the separated solid is dried at low temperature to obtain the coated modified gasification slag.

8. The method for preparing a low-adsorption, high-flow gasification slag-based cement admixture according to claim 7, wherein in step S1, the carbon removal treatment is a flotation decarbonization process, the flotation decarbonization process uses a collector and a frother, and the carbon content of the decarbonized gasification slag is reduced to below 3% by mass. The dispersion in water involves adding the decarbonized gasification slag to an aqueous solution containing a polycarboxylate superplasticizer, and then performing ultrasonic dispersion treatment using an ultrasonic cell disruptor. The frequency of the ultrasonic dispersion treatment is 20 kHz to 30 kHz, and the treatment time is 10 minutes to 30 minutes, resulting in a gasification slag suspension with a solid content of 10% to 30% by mass.

9. The preparation method of a low-adsorption, high-flow gasification slag-based cement admixture according to claim 7, wherein in step S2, the biopolysaccharide is first dissolved in water to prepare a polysaccharide solution with a mass fraction of 0.5% to 2%, and then the polysaccharide solution is mixed evenly with the inorganic nanoparticles to form the composite system, and the composite system is added to the gasification slag suspension by dropwise addition; In step S3, the acid-base regulator is a dilute hydrochloric acid solution and a sodium hydroxide solution, which adjusts the pH value of the system from the initial 7 to 8 to 3.5 to 4.

5. Stirring is maintained at this pH value at a speed of 200 to 500 revolutions per minute.

10. The method for preparing a low-adsorption, high-flow gasification slag-based cement admixture according to claim 7, wherein in step S4, the temperature of the system is maintained at 40 degrees Celsius to 60 degrees Celsius, and the reaction time is 2 hours to 5 hours, during which the inorganic nanoparticles complete cross-linking deposition in the biological polysaccharide network; In step S5, the solid-liquid separation is carried out by vacuum filtration or centrifugation, the low-temperature drying temperature is 60 degrees Celsius to 80 degrees Celsius, the drying time is 12 hours to 24 hours, and the dried coated modified gasification slag is dispersed by air jet mill.

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