A cement grinding aid with a molecular weight gradient distribution, its preparation method and application

Abstract

The present invention discloses a cement grinding aid with a molecular weight gradient distribution. The components are as follows in parts by mass: 16 to 24 parts of the first-gradient molecular weight cement grinding aid, 12 to 20 parts of the second-gradient molecular weight cement grinding aid, 10 to 18 parts of the third-gradient molecular weight cement grinding aid, 8 to 15 parts of the fourth-gradient molecular weight cement grinding aid, 6 to 12 parts of the fifth-gradient molecular weight cement grinding aid, 4 to 10 parts of the sixth-gradient molecular weight cement grinding aid, and 50 to 60 parts of polyol-modified lithium slag. The present invention effectively matches substances with different molecular conformations and molecular weight gradient distributions and having a grinding aid effect to the changes in the particle size of the material during the grinding process and the crack characteristics generated during the grinding process. In the later stage of grinding, the grinding aid substances are released and adsorbed on the surface of ultrafine particles with a large specific surface area to shield the charges, weaken the strength of the material particles and disperse the particles at each stage of the cement grinding, effectively improving the grinding efficiency, improving the cement particle size distribution, and at the same time increasing the cement strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a cement grinding aid and its preparation method and application. Background Art

[0002] Cement concrete is the most widely used building material in modern times and is also the largest volume of artificial material at present. The cement industry is a high-energy-consuming industry. The power consumption in the grinding process accounts for 60%-70% of the total power consumption in cement production, and the grinding of cement finished products accounts for 30%-40% of the total power consumption. The cement grinding process is a process in which electrical energy is converted into mechanical energy and then into the surface energy of cement powder. It is completed by the mutual collision, extrusion, and friction of the grinding media in the mill. Most of the granular materials with a particle size of several centimeters in the mill are continuously ground and gradually become powders with a particle size of several micrometers to dozens of micrometers. Therefore, increasing the energy utilization rate of the mill can effectively achieve energy conservation and emission reduction in cement production.

[0003] During the cement grinding process, adding a small amount of cement grinding aid can effectively improve the grinding efficiency of the ball mill. The cement grinding aid mainly achieves physical and chemical modification of the particle surface through its surface activity and charge dispersion effects, and exerts the interface effect and mechanical efficiency. It can increase the output under the condition of the same fineness of cement and the power consumption of the mill; or it can increase the specific surface area of cement under the condition of the same cement output and the power consumption of the mill, optimize the cement particle gradation, and thus improve the strength and quality of cement.

[0004] Domestic and foreign scholars have conducted in-depth research on the action mechanism of cement grinding aids, and its action mechanism has been widely recognized. The "strength weakening theory" holds that the grinding aid molecules are adsorbed on the inner wall of the crack of the solid material and further enter the depth of the crack. With the formation and continuous expansion of the crack, it plays a "wedge" role, not only preventing the crack from closing, but also promoting the crack to expand and accelerating the crack width. The "particle dispersion theory" holds that the purpose of adding a grinding aid during the grinding process is to provide foreign ions or molecules to neutralize the unsaturated ionic bonds or covalent bonds on the cross-section and eliminate or weaken the attraction between the cross-sections. These theories well explain the action effect of the grinding aid and provide good guidance for the research and application of the grinding aid.

[0005] The commonly used grinding aids for cement mainly include polyols or polyol amines, such as ethylene glycol, triethanolamine, etc., all of which are small molecule organic compounds. In the existing publicly available technologies, there are also synthetic macromolecular polymer grinding aids for cement, generally with a molecular weight in the range of 10,000 - 100,000 g / mol, and mostly linear polymers. Since the cement particle size decreases during the grinding process, the crack widths and depths generated by particles at different grinding stages are different. The effect of a single molecular weight and single molecular conformation substance on promoting crack propagation and accelerating crack width is limited, and it cannot effectively match the change in the particle size of the material during the grinding process. In addition, in the later stage of grinding, the phenomenon of cement fine particles agglomerating under the action of electrostatic attraction becomes more and more obvious. Since fine powder has a large specific surface area and adsorbs more grinding aids, when a new surface is generated, it is difficult for the grinding aids that have already produced a stable adsorption and dispersion effect to be adsorbed onto the surface of the cement particles with the new surface, thereby eliminating or weakening the attraction between the fracture surfaces. Therefore, the existing technology has limited effect on grinding cement.

[0006] CN107098609 discloses a grinding aid for slag and its preparation method by compounding a polymer / small molecule surfactant. The polymer surfactant and the small molecule surfactant are used in combination. The unique molecular structure of the polymer surfactant is used to achieve the dispersion, surface coverage, and encapsulation effects on fine powder, while the small molecule surfactant has excellent permeability and the ability to reduce surface tension. The combined use of the two has better penetration, lubrication, and grinding aid effects than traditional polyol amine compounds such as triethanolamine. Further, with the cooperation of raw materials such as chelating agents and carbonaceous mesophase microspheres, it can further promote the activation and refinement of slag activity, and has a good improvement effect on the morphology of fine powder, and the morphology of the prepared slag fine powder is better. Although this invention uses polymer / small molecule surfactants with different molecular weights, it does not form a molecular weight gradient and cannot effectively match the change in the particle size of the material during the grinding process.

[0007] CN117623665 provides a composite grinding aid for cement. The formula of the composite grinding aid for cement includes, by mass percentage: 5 - 10% of alcohol amine grinding aid, 1 - 3% of polyol grinding aid, 20 - 50% of macromolecular grinding aid synergist, 5 - 10% of molasses, 1 - 2% of wetting agent, 10 - 20% of sodium chloride, and the balance is water. The molecular weight Mw of the macromolecular grinding aid synergist is 30,000 - 50,000, and it is a linear polymer. The wetting agent is selected from one or more of the complex products of triethylene glycol, tetraethylene glycol, PEG200, PEG300, and PEG400. Although this invention uses the combination of organic compounds with different molecular weights, it does not form a molecular weight gradient and cannot effectively match the change in the particle size of the material during the grinding process.

[0008] CN110282901 discloses a cement grinding aid and its preparation method, belonging to the technical field of cement admixtures. The grinding aid of this invention is prepared from the following raw materials in parts by weight: 3 - 6 parts of alkanolamine substances, 10 - 20 parts of amino glycerol, 10 - 20 parts of polymeric glycerol, 0.1 - 0.5 parts of defoamer, and 40 - 65 parts of water. The raw materials used in this invention are all small - molecule organic compounds.

[0009] CN115417616 discloses a grinding aid for vertical - mill cement and its preparation method, belonging to the technical field of cement admixtures. The grinding aid of this invention is prepared from alkanolamine substances, copolymer, polyglycerol, triethylene glycol, and water as raw materials. The copolymer of this invention is synthesized from methallyl alcohol, acrylamide, and low - molecular - weight unsaturated polyether. The molecular structure of the copolymer is still a linear structure, and the molecular weight distributions of the raw materials of the grinding aid for vertical - mill cement are relatively narrow. Summary of the Invention

[0010] Aiming at two major problems existing in the prior art: First, the grinding aid cannot effectively match the changes in the particle size of the material during the grinding process and the crack characteristics generated during the grinding process; Second, in the later stage of grinding, the phenomenon of cement fine particles agglomerating under the action of electrostatic attraction becomes more and more obvious. Since fine powder has a huge specific surface area and adsorbs more grinding substances, when new surfaces are generated, it is difficult for the grinding substances that have already produced a stable adsorption and dispersion effect to be adsorbed onto the surface of cement particles with new surfaces, eliminating or weakening the attraction between cross - sections. The present invention provides a cement grinding aid with a molecular weight gradient distribution, its preparation method and application. Substances with different molecular conformations and molecular weight gradient distributions and having a grinding effect are effectively matched with the changes in the particle size of the material during the grinding process and the crack characteristics generated during the grinding process. In the later stage of grinding, the grinding substances are released and adsorbed onto the surface of ultrafine particles with a large specific surface area to shield charges, weakening the strength of material particles and dispersing particles at all stages of cement grinding, effectively improving the grinding efficiency, improving the particle size distribution of cement, playing a significant grinding role, and at the same time improving the strength of cement.

[0011] To achieve the above - mentioned purpose, the following technical solutions are adopted:

[0012] A cement grinding aid with a molecular weight gradient distribution, the composition of which is as follows by mass fraction:

[0013]

[0014] The first - gradient - molecular - weight cement grinding aid is a multi - arm polymer with a weight - average molecular weight of 293000 - 742000 g / mol. The multi - arm polymer is prepared by free - radical polymerization from amino polyethylene glycol methyl ether, binary unsaturated carboxylic acid or acid anhydride, and unsaturated polyol ether under the action of a primary - amine chain - transfer agent, initiator, and reducing agent;

[0015] The second gradient molecular weight cement grinding aid is a star-shaped alcohol amine ester polycarboxylic acid polymer with a weight average molecular weight of 60,000 to 180,000 g / mol. The star-shaped alcohol amine ester polycarboxylic acid polymer is prepared by free radical polymerization of an unsaturated alcohol amine esterification product, an unsaturated acid monomer, and an unsaturated polyether monomer under the action of a chain transfer agent, an initiator, and a reducing agent;

[0016] The third gradient molecular weight cement grinding aid is a polycarboxylic acid water reducing agent with a weight average molecular weight of 20,000 to 60,000 g / mol;

[0017] The fourth gradient molecular weight cement grinding aid is one or any combination of polyacrylic acid and polyethylene glycol with a molecular weight of 2,000 to 8,000 g / mol;

[0018] The fifth gradient molecular weight cement grinding aid is polyglycerol with a molecular weight range of 240 to 800 g / mol;

[0019] The sixth gradient molecular weight cement grinding aid is polyol A with a molecular weight range of 60 to 240 g / mol;

[0020] The polyol-modified lithium slag is lithium slag saturated with polyol B. The lithium slag is waste residue generated during the lithium extraction process from lithium ore.

[0021] According to the above scheme, the polyglycerol is one or any combination of diglycerol, triglycerol, tetraglycerol, pentaglycerol, hexaglycerol, heptaglycerol, octaglycerol, nonaglycerol, and decaglycerol.

[0022] According to the above scheme, the polyol A is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, glycerol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol.

[0023] According to the above scheme, the polyol B is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, glycerol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol.

[0024] According to the above scheme, the particle size range of the polyol-modified lithium slag is 10 to 200 μm.

[0025] According to the above scheme, the preparation method of the polyol-modified lithium slag includes the following steps:

[0026] The lithium slag is dried at 100 to 110 °C, and the dried lithium slag is fully mixed and aged with an aqueous solution of polyol B with a concentration of 20 to 30 wt% for 4 to 8 h. The mass ratio of the lithium slag to polyol B is (30 to 40):1.

[0027] The preparation method of the cement grinding aid with the above molecular weight gradient distribution includes the following steps:

[0028] Add the sixth-gradient molecular weight cement grinding aid, the fifth-gradient molecular weight cement grinding aid, the fourth-gradient molecular weight cement grinding aid, the third-gradient molecular weight cement grinding aid, the second-gradient molecular weight cement grinding aid, and the first-gradient molecular weight cement grinding aid to the polyol-modified lithium slag in sequence, and stir and mix evenly.

[0029] The application of the cement grinding aid with the above molecular weight gradient distribution in the cement grinding process.

[0030] According to the above scheme, the dosage of the cement grinding aid with the above molecular weight gradient distribution is 0.1-0.3 wt% of the total mass of each raw material in the cement grinding process.

[0031] According to the above scheme, the addition method of the cement grinding aid with the above molecular weight gradient distribution is to be ground together with each raw material of the cement.

[0032] In the early stage of cement grinding, as the grinding time continues, the cement raw materials change from large particles to small particles, and the number of particles increases, gradually possessing powder properties. In this stage, it is necessary to overcome the cohesive force within the crystal structure and reduce the particle hardness. The first-gradient molecular weight cement grinding aid is a multi-arm polymer with a weight-average molecular weight of 293,000-742,000 g / mol, the second-gradient molecular weight cement grinding aid is a star-shaped alcohol amine ester polycarboxylic acid polymer with a weight-average molecular weight of 60,000-180,000 g / mol, and the third-gradient molecular weight cement grinding aid is a polycarboxylic acid water reducer with a weight-average molecular weight of 20,000-60,000 g / mol. On the one hand, it itself has an adsorption group that can adsorb at the crack of the particle cross-section, and the "volume effect" provided by the larger molecular weight has a greater "splitting" ability; on the other hand, the molecular conformations of the multi-arm polymer, the star-shaped alcohol amine ester polycarboxylic acid polymer, and the polycarboxylic acid water reducer are in a multi-branched structure, and the larger three-dimensional "steric hindrance" effect further improves its "wedge" effect, which can well promote the crack expansion and accelerate the crack width.

[0033] In the middle stage of cement grinding, as the grinding progresses, the rate of refinement of clinker particles and increase in specific surface area becomes slower and slower. Moreover, a large number of charges with opposite electricities generated during crystal fracture exist on the surface of ultra-fine cement particles. At this time, the particles will aggregate and agglomerate due to electrostatic attraction. The cement grinding aid with the fourth gradient molecular weight is polyacrylic acid and polyethylene glycol with a molecular weight of 2000 - 8000 g / mol, and the cement grinding aid with the fifth gradient molecular weight is polyglycerol with a molecular weight range of 240 - 800 g / mol. Its long-chain structure is more conducive to adsorbing on the surface of cement particles to form an adsorption film, thereby shielding a large number of charges with opposite electricities generated during crystal fracture and preventing the aggregation and agglomeration of cement particles.

[0034] In the later stage of cement grinding, the phenomenon of agglomeration of fine cement particles due to the action of electrostatic attraction becomes more and more obvious at this stage. Recrystallization of crystals may occur in ultra-fine particles, and the ultra-fine particles are re-aggregated under the action of electrostatic attraction and external force. The cement grinding aid with the sixth gradient molecular weight is polyol with a molecular weight range of 60 - 240 g / mol. Its own molecular weight is small and the molecular freedom is high, which can better adsorb on the surface of ultra-fine particles with a large specific surface area to shield charges and prevent the re-aggregation of particles. Using polyol-modified lithium slag, during the modification stage, polyol can easily adsorb into the pores of porous lithium slag due to the "cavity effect". In the later stage of cement grinding, as the lithium slag is ground finer, the polyol wrapped in it is released, making up for the vacancy of adsorbed small-molecule polyol in the later stage of grinding, better shielding charges, and strengthening the ability to prevent the re-aggregation of particles; at the same time, small-molecule polyol adsorbs on the surface of powder particles in the later stage of grinding, making them more "smooth", reducing the surface friction of the particles, making it difficult to be further ground finer, and can effectively reduce the content of ultra-fine particles with a size of 0 - 3 μm that contribute little to the cement strength, and optimize the particle size distribution of cement powder.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1. The cement grinding aid with a molecular weight gradient distribution provided by the present invention utilizes the molecular weight and molecular conformation characteristics of macromolecular organic substances, and can play a good "wedge" role in the early stage of cement grinding, can well promote crack propagation, and accelerate the crack width.

[0037] 2. The cement grinding aid with a molecular weight gradient distribution provided by the present invention utilizes medium-molecular-weight linear organic substances to adsorb on the surface of cement particles to form an adsorption film, thereby shielding a large number of charges with opposite electricities generated during crystal fracture and preventing the aggregation and agglomeration of cement particles.

[0038] 3. The cement grinding aid with a molecular weight gradient distribution provided by the present invention utilizes small-molecule organic substances with higher degrees of freedom to better adsorb on the surface of ultra-fine particles with a large specific surface area to shield charges and prevent the re-aggregation of particles.

[0039] 4. The grinding aid for cement with a molecular weight gradient distribution provided by the present invention releases polyols in the later stage of grinding by using polyol-modified lithium slag, compensates for the vacancy of adsorbed small-molecule polyols in the later stage of grinding, better shields charges, and enhances the ability to prevent particles from re-aggregating.

[0040] 5. The grinding aid for cement with a molecular weight gradient distribution provided by the present invention uses organic substances with different gradient molecular weights and different conformations in combination with polyol-modified lithium slag, and matches their dosages according to the change of the surface area of the material. On the one hand, it matches the particle size change in the cement particle grinding process, and on the other hand, they complement and promote each other, and the synergistic effect between different components can have a significant grinding aid effect on cement grinding, optimize the cement particle gradation, and improve the cement strength.

[0041] 6. The preparation method of the grinding aid for cement with a molecular weight gradient distribution provided by the present invention is simple, makes full use of the characteristics of industrial solid waste, can realize industrialization, and conforms to the concept of green development of composite building materials. Specific Embodiments

[0042] The following embodiments further illustrate the technical solutions of the present invention, but do not limit the protection scope of the present invention. The following specific embodiments are only some preferred embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, the modifications, substitutions and improvements made by those skilled in the art without creative efforts all fall within the protection scope of the present invention.

[0043] The specific embodiments provide a grinding aid for cement with a molecular weight gradient distribution, and its components are as follows by mass fraction: 16 parts to 24 parts of the grinding aid for cement with the first gradient molecular weight, 12 parts to 20 parts of the grinding aid for cement with the second gradient molecular weight, 10 parts to 18 parts of the grinding aid for cement with the third gradient molecular weight, 8 parts to 15 parts of the grinding aid for cement with the fourth gradient molecular weight, 6 parts to 12 parts of the grinding aid for cement with the fifth gradient molecular weight, 4 parts to 10 parts of the grinding aid for cement with the sixth gradient molecular weight, and 50 parts to 60 parts of polyol-modified lithium slag.

[0044] Specifically, the grinding aid for cement with the first gradient molecular weight is a multi-arm polymer with a weight-average molecular weight of 293,000 to 742,000 g / mol, and the multi-arm polymer is prepared by free radical polymerization of amino polyethylene glycol methyl ether, binary unsaturated carboxylic acid or anhydride, and unsaturated polyol ether under the action of a primary amine chain transfer agent, an initiator, and a reducing agent.

[0045] The specific embodiments provide the preparation method of the multi-arm polymer as follows:

[0046] (1) Preparation of the primary amine chain transfer agent:

[0047] Mix tetra-hydroxyethyl ethylene diamine, amino mercapto acid compound, and inhibitor, stir and heat up to 100 - 120 °C, add catalyst and water-carrying agent, and carry out esterification reaction for 3 - 8 h; during the reaction, separate the water generated by the reaction by vacuum pumping, and obtain the primary amine chain transfer agent through purification treatment after completion.

[0048] (2) Preparation of multi-arm polymer cement grinding aid:

[0049] Mix amino poly(ethylene glycol) methyl ether, binary unsaturated carboxylic acid or anhydride, primary amine chain transfer agent, and water, stir and heat up to 30 - 50 °C, and add initiator; maintain the reaction temperature at 30 - 60 °C, and simultaneously dropwise add the aqueous solution of unsaturated polyol ether and the aqueous solution of reducing agent, with the dropping time being 4 - 6 h; keep warm at 50 - 60 °C for 1 - 2 h, and add water to obtain a multi-arm polymer cement grinding aid with a concentration of 40 - 70 wt%.

[0050] Specifically, the molar ratio of tetra-hydroxyethyl ethylene diamine to amino mercapto acid compound is 1:(4 - 6); the dosage of inhibitor is 0.2 - 1% of the total mass of tetra-hydroxyethyl ethylene diamine and amino mercapto acid compound; the dosage of catalyst is 3 - 6% of the total mass of tetra-hydroxyethyl ethylene diamine and amino mercapto acid compound; the dosage of water-carrying agent is 15 - 25% of the total mass of tetra-hydroxyethyl ethylene diamine and amino mercapto acid compound.

[0051] Specifically, in step (1), the amino mercapto acid compound is one of 2-amino-3-mercaptopropionic acid and 2-amino-4-mercaptobutyric acid; the inhibitor is one or any mixture of hydroquinone, p-methoxyphenol, 2-tert-butylhydroquinone, and 2,6-dinitrotoluene; the catalyst is one or any mixture of concentrated sulfuric acid, p-toluenesulfonic acid, and concentrated phosphoric acid; the water-carrying agent is one or any mixture of benzene and toluene.

[0052] Specifically, in step (2), the molar ratio of the primary amine chain transfer agent, amino poly(ethylene glycol) methyl ether, binary unsaturated carboxylic acid or anhydride, unsaturated polyol ether, initiator, and reducing agent is 1:(84 - 108):(84 - 108):(240 - 624):(47 - 140):(3 - 10), and the molar ratio of amino poly(ethylene glycol) methyl ether to binary unsaturated carboxylic acid or anhydride is 1:1.

[0053] Specifically, the structural formula of the amino poly(ethylene glycol) methyl ether is: The degree of polymerization p is an integer from 67 to 135; the binary unsaturated carboxylic acid or anhydride is one or any mixture of maleic acid, fumaric acid, and maleic anhydride; the unsaturated polyol ether is one of allyl glycerol ether, (allyloxy) propylene glycol, and allyl pentaerythritol ether; the initiator is one or any mixture of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is one or any mixture of sodium bisulfite, sodium formaldehyde sulfoxylate, sodium ascorbate, and isoascorbic acid.

[0054] In the following examples, the multi-arm polymers used were prepared by the following preferred scheme:

[0055] (1) Preparation of the primary amine-containing chain transfer agent: 1.0 mol of tetra-hydroxyethyl ethylenediamine, 5.1 mol of 2-amino-3-mercaptopropionic acid, and 5.97 g of hydroquinone were successively added to the reaction kettle. Under nitrogen protection, the temperature was raised to 65 °C and stirred for 28 minutes. Then the temperature was further raised to 100 °C, and 40.96 g of concentrated phosphoric acid and 196.28 g of benzene were added, and the reaction was carried out for 6.3 h. During the reaction, the water generated by the reaction was separated by means of vacuum pumping. After all the hydroxyl groups in tetra-hydroxyethyl ethylenediamine were completely esterified, the water-carrying agent was removed by vacuum pumping, and the temperature was lowered to room temperature to obtain the primary amine-containing chain transfer agent.

[0056] (2) Preparation of the multi-arm polymer cement grinding aid: 0.084 mol of amino polyethylene glycol methyl ether with a degree of polymerization of 116, 0.084 mol of maleic acid, 0.001 mol of the primary amine-containing chain transfer agent, and water were added to the reaction kettle. While stirring, the temperature was raised to 36 °C. After 23 minutes, 0.068 mol of ammonium persulfate was added to the reaction kettle, and water was added to adjust the system concentration to 79%. The reaction temperature was maintained at 42 °C. At the same time, the dropping material A composed of 0.576 mol of (allyloxy) propylene glycol aqueous solution and the dropping material B composed of 0.008 mol of sodium formaldehyde sulfoxylate aqueous solution were started to be dropped. The dropping time was 5.6 h. Then it was kept warm at 57 °C for 1.8 h, and water was added to obtain a multi-arm polymer cement grinding aid with a concentration of 68 wt%, and its weight-average molecular weight was 518790 g / mol.

[0057] Specifically, the second-gradient molecular weight cement grinding aid is a star-shaped alcohol amine ester polycarboxylic acid polymer with a weight-average molecular weight of 60,000 to 180,000 g / mol. The star-shaped alcohol amine ester polycarboxylic acid polymer is prepared by free radical polymerization of an unsaturated alcohol amine esterification product, an unsaturated acid monomer, and an unsaturated polyether monomer under the action of a chain transfer agent, an initiator, and a reducing agent.

[0058] The preparation method of the star-shaped alcohol amine ester polycarboxylic acid polymer is provided in the specific implementation manner as follows:

[0059] 1) Add polyolamine, dibasic unsaturated acid or anhydride, and inhibitor into the reaction kettle in sequence. Under nitrogen protection, heat up to 50 - 70 °C, stir for 15 - 30 minutes, then continue to heat up to 100 - 130 °C, add catalyst and water-carrying agent, and react for 3 - 12 h. During the reaction, separate the water generated by the reaction by means of vacuum pumping. After all the hydroxyl groups in the polyolamine are completely esterified, remove the water-carrying agent by vacuum pumping, and cool down to room temperature to obtain the unsaturated alcohol amine esterification product;

[0060] 2) Add the unsaturated alcohol amine esterification product, 15 - 30% unsaturated acid monomer, and water into the reaction kettle, heat up to 60 - 80 °C, stir for 15 - 30 minutes, then cool down to room temperature. Then add unsaturated polyether monomer and initiator into the reaction kettle, add water to adjust the system concentration to 50 - 70%, keep the reaction temperature at 20 - 60 °C, and at the same time start to drip feed A composed of the remaining unsaturated acid monomer aqueous solution and drip feed B composed of chain transfer agent and reducing agent aqueous solution. The dripping time is 2 - 4 h, then keep warm at 50 - 60 °C for 1 - 2 h, add polyolamine to adjust the pH value to 6 - 7, and add water to obtain a star-shaped alcohol amine ester polycarboxylate cement grinding aid with a concentration of 30 - 60 wt%; the unsaturated polyether monomer is one or any combination of amino-terminated methallyl alcohol polyoxyethylene polyoxypropylene ether, amino-terminated isopentenol polyoxyethylene polyoxypropylene ether, and amino-terminated 4-hydroxybutyl vinyl polyoxyethylene polyoxypropylene ether, and its weight average molecular weight is 3000 - 6000 g / mol.

[0061] Specifically, the molar ratio of the polyolamine to the dibasic unsaturated acid or anhydride is 1:(3 - 4); the dosage of the inhibitor is 0.4 - 4% of the total mass of the polyolamine and the dibasic unsaturated acid or anhydride; the dosage of the catalyst is 1 - 5% of the total mass of the polyolamine and the dibasic unsaturated acid or anhydride; the dosage of the water-carrying agent is 10 - 20% of the total mass of the polyolamine and the dibasic unsaturated acid or anhydride.

[0062] Specifically, the polyolamine is one or any mixture of triethanolamine, diethanol monoisopropanolamine, hydroxyethyl diisopropanolamine, and triisopropanolamine; the dibasic unsaturated acid or anhydride is one or any mixture of maleic acid, fumaric acid, and maleic anhydride.

[0063] Specifically, the molar ratio of the unsaturated polyether monomer, the unsaturated alcohol amine esterification product, the unsaturated acid monomer, the initiator, the reducing agent, and the chain transfer agent is 1:(0.02 - 0.12):(3 - 8):(0.05 - 0.23):(0.015 - 0.038):(0.06 - 0.23);

[0064] Specifically, the unsaturated acid monomer is one or any combination of acrylic acid, methacrylic acid, maleic acid, fumaric acid, and aconitic acid. The polyol amine is one or any combination of triethanolamine, diethanol monoisopropanolamine, hydroxyethyl diisopropanolamine, and triisopropanolamine. The inhibitor is a combination of two or more of hydroquinone, p-methoxyphenol, 2-tert-butylhydroquinone, and 2,6-dinitrop-cresol. The catalyst is one of concentrated sulfuric acid, p-toluenesulfonic acid, and concentrated phosphoric acid. The water-carrying agent is one of benzene and toluene. The initiator is a persulfate or a peroxide, specifically one or any combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate. The chain transfer agent is one or any combination of mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, and sodium methallylsulfonate. The reducing agent is one or any combination of sodium bisulfite, sodium formaldehyde sulfoxylate, sodium ascorbate, and isoascorbic acid.

[0065] The star-shaped alcohol amine ester polycarboxylic acid polymer used in the following examples was prepared by the following preferred scheme:

[0066] 1) Add 0.25 mol of triethanolamine, 0.25 mol of diethanol monoisopropanolamine, 0.25 mol of hydroxyethyl diisopropanolamine, 0.25 mol of triisopropanolamine, 1.2 mol of maleic acid, 1.2 mol of fumaric acid, 1.2 mol of maleic anhydride, 14.5 g of hydroquinone, and 3.6 g of 2,6-dinitrop-cresol into the reaction kettle in sequence. Under the protection of nitrogen, heat up to 65 °C, stir for 27 minutes, then heat up to 118 °C, add 10.2 g of p-toluenesulfonic acid and 107.5 g of toluene, and react for 9.5 h. During the reaction, separate the water generated by the reaction by means of vacuum pumping. After all the hydroxyl groups in the polyol amine are completely esterified, remove the water-carrying agent by vacuum pumping, and cool down to room temperature to obtain the unsaturated alcohol amine esterification product;

[0067] 2) 0.005 mol of the unsaturated alcohol amine esterification product and 0.08 mol of the first part of aconitic acid water were added to the reactor, the temperature was raised to 72° C., stirred for 29 minutes and then cooled to room temperature, and then 0.02 mol of amino-terminated isopentanol polyoxyethylene polyoxypropylene ether with a weight average molecular weight of 4000 g / mol, 0.03 mol of amino-terminated 4-hydroxybutyl vinyl polyoxyethylene polyoxypropylene ether with a weight average molecular weight of 6000 g / mol, 0.00065 mol of ammonium persulfate, 0.0013 mol of sodium persulfate, 0.00455 mol of l potassium persulfate, add water to adjust the system concentration to 58%, maintain the reaction temperature at 46°C, and simultaneously start to drop a drop material A consisting of 0.205 mol of aconitic acid aqueous solution and a drop material B consisting of 0.0032 mol of sodium methyl allyl sulfonate, 0.0033 mol of thioglycolic acid, and 0.0009 mol of sodium bisulfite aqueous solution. The dropping time is 4 hours, and the mixture is kept warm at 51°C for 1.5 hours. Add triisopropanolamine to adjust the pH value to 6, and add water to obtain a 38% concentration of a star-shaped alcohol amine ester polycarboxylic acid cement grinding aid with a weight average molecular weight of 127920 g / mol.

[0068] Specifically, the third gradient molecular weight cement grinding aid is a polycarboxylate water reducer with a weight average molecular weight of 20,000 to 60,000 g / mol.

[0069] The specific embodiment provides the source of the polycarboxylate water-reducing agent, which is obtained from the market. The manufacturer is Jiangsu Aolaite New Materials Co., Ltd., the product model is M13 high water-reducing polycarboxylate water-reducing agent, the solid content is 45.13%, and the weight average molecular weight is 35713 g / mol.

[0070] Specifically, the fourth gradient molecular weight cement grinding aid is one or any combination of polyacrylic acid and polyethylene glycol with a molecular weight of 2000 to 8000 g / mol;

[0071] Specifically, the fifth gradient molecular weight cement grinding aid is a polyglycerol with a molecular weight range of 240 to 800 g / mol, and the polyglycerol is one or any combination of diglycerol, triglycerol, tetraglycerol, pentaglycerol, hexaglycerol, heptaglycerol, octaglycerol, nonaglycerol, and decaglycerol;

[0072] Specifically, the sixth gradient molecular weight cement grinding aid is a polyol A with a molecular weight range of 60 to 240 g / mol, and the polyol is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol;

[0073] Specifically, the polyol-modified lithium slag is lithium slag saturated with polyol B, and the lithium slag is waste residue generated during the lithium extraction process in the processing of lithium ore. The polyol B is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, glycerol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol.

[0074] Specifically, if there is no special instruction, the raw materials can be obtained through commercial channels.

[0075] The following is the preparation method of the cement grinding aid with the molecular weight gradient distribution provided by the specific embodiment:

[0076] (1) Preparation of polyol-modified lithium slag: The lithium slag is dried at 100-110°C, and the dried lithium slag is fully mixed and aged for 4-8 h with an aqueous solution of polyol B with a concentration of 20-30 wt% to obtain polyol-modified lithium slag; the mass ratio of the lithium slag to polyol B is (30-40):1;

[0077] (2) Preparation method of the cement grinding aid with molecular weight gradient distribution: The sixth-gradient molecular weight cement grinding aid, the fifth-gradient molecular weight cement grinding aid, the fourth-gradient molecular weight cement grinding aid, the third-gradient molecular weight cement grinding aid, the second-gradient molecular weight cement grinding aid, and the first-gradient molecular weight cement grinding aid are successively added to the obtained polyol-modified lithium slag, and stirred and mixed evenly to obtain the cement grinding aid with molecular weight gradient distribution.

[0078] The specific embodiment also provides the application of the cement grinding aid with molecular weight gradient distribution in the cement grinding process; the dosage of the cement grinding aid with molecular weight gradient distribution is 0.1-0.3 wt% of the total mass of each raw material of the cement. The addition method is to be ground together with each raw material of the cement.

[0079] Example 1

[0080] (1) Preparation of polyol-modified lithium slag: The lithium slag is dried at 110°C, and 900 g of the dried lithium slag is fully mixed and aged for 4 h with 100 g of an aqueous solution of ethylene glycol with a concentration of 30 wt% to obtain polyol-modified lithium slag;

[0081] (2) Preparation method of the cement grinding aid with molecular weight gradient distribution: 10 parts of threitol, 6 parts of decaglycerol, 8 parts of polyacrylic acid with a molecular weight of 2000 g / mol, 10 parts of polycarboxylate superplasticizer, 20 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 16 parts of multi-arm polymer cement grinding aid are successively added to 50 parts of the polyol-modified lithium slag prepared in step (1), and stirred and mixed evenly to obtain the cement grinding aid with molecular weight gradient distribution.

[0082] Example 2

[0083] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 100 °C. 800 g of the dried lithium slag was fully mixed with 100 g of a 20 wt% diethylene glycol aqueous solution and aged for 8 h to obtain polyol-modified lithium slag;

[0084] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 60 parts of the polyol-modified lithium slag prepared in step (1), 4 parts of 1,2,3-butanetriol, 12 parts of pentaglycerol, 15 parts of polyethylene glycol with a molecular weight of 8000 g / mol, 18 parts of polycarboxylate superplasticizer, 12 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 24 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0085] Example 3

[0086] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 102 °C. 735 g of the dried lithium slag was fully mixed with 100 g of a 21 wt% triethylene glycol aqueous solution and aged for 5 h to obtain polyol-modified lithium slag;

[0087] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 51 parts of the polyol-modified lithium slag prepared in step (1), 5 parts of glycerol, 8 parts of triglycerol, 12 parts of polyethylene glycol with a molecular weight of 6000 g / mol, 12 parts of polycarboxylate superplasticizer, 13 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 23 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0088] Example 4

[0089] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 105 °C. 800 g of the dried lithium slag was fully mixed with 100 g of a 25 wt% tetraethylene glycol aqueous solution and aged for 6 h to obtain polyol-modified lithium slag;

[0090] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 53 parts of the polyol-modified lithium slag prepared in step (1), 8 parts of tetraethylene glycol, 11 parts of heptaglycerol, 10 parts of polyacrylic acid with a molecular weight of 5000 g / mol, 14 parts of polycarboxylate superplasticizer, 19 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 20 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0091] Example 5

[0092] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 104 °C. After drying, 1092 g of the lithium slag was thoroughly mixed with 100 g of a 28 wt% pentaerythritol aqueous solution and aged for 7 h to obtain polyol-modified lithium slag;

[0093] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 59 parts of the polyol-modified lithium slag prepared in step (1), 9 parts of diethylene glycol, 12 parts of diglycerol, 11 parts of polyethylene glycol with a molecular weight of 3000 g / mol, 15 parts of polycarboxylate superplasticizer, 15 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 21 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0094] Example 6

[0095] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 105 °C. After drying, 999 g of the lithium slag was thoroughly mixed with 100 g of a 27 wt% glycerol aqueous solution and aged for 4 h to obtain polyol-modified lithium slag;

[0096] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 55 parts of the polyol-modified lithium slag prepared in step (1), 6 parts of ethylene glycol, 6 parts of tetraerythritol, 9 parts of polyacrylic acid with a molecular weight of 7000 g / mol, 16 parts of polycarboxylate superplasticizer, 17 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 19 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0097] Example 7

[0098] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 109 °C. After drying, 950 g of the lithium slag was thoroughly mixed with 100 g of a 25 wt% 1,2,4-butanetriol aqueous solution and aged for 8 h to obtain polyol-modified lithium slag;

[0099] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 54 parts of the polyol-modified lithium slag prepared in step (1), 7 parts of triethylene glycol, 9 parts of hexaglycerol, 13 parts of polyacrylic acid with a molecular weight of 4000 g / mol, 11 parts of polycarboxylate superplasticizer, 16 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 17 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed evenly to obtain a cement grinding aid with molecular weight gradient distribution.

[0100] Example 8

[0101] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 110 °C. 957 g of the dried lithium slag was thoroughly mixed with 100 g of a 29 wt% 1,2,3-butanetriol aqueous solution and then aged for 5 h to obtain the polyol-modified lithium slag;

[0102] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 53 parts of the polyol-modified lithium slag prepared in step (1), 9 parts of pentaethylene glycol, 7 parts of nonaethylene glycol, 11 parts of polyethylene glycol with a molecular weight of 2000 g / mol, 18 parts of polycarboxylate superplasticizer, 15 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 16 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed thoroughly to obtain the cement grinding aid with molecular weight gradient distribution.

[0103] Example 9

[0104] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 106 °C. 930 g of the dried lithium slag was thoroughly mixed with 100 g of a 30 wt% 1,1,4,4-butanetetraol aqueous solution and then aged for 5 h to obtain the polyol-modified lithium slag;

[0105] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 60 parts of the polyol-modified lithium slag prepared in step (1), 10 parts of 1,2,4-butanetriol, 9 parts of octaethylene glycol, 13 parts of polyacrylic acid with a molecular weight of 8000 g / mol, 17 parts of polycarboxylate superplasticizer, 18 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 24 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed thoroughly to obtain the cement grinding aid with molecular weight gradient distribution.

[0106] Example 10

[0107] (1) Preparation of polyol-modified lithium slag: The lithium slag was dried at 108 °C. 720 g of the dried lithium slag was thoroughly mixed with 100 g of a 20 wt% threitol aqueous solution and then aged for 6 h to obtain the polyol-modified lithium slag;

[0108] (2) Preparation method of cement grinding aid with molecular weight gradient distribution: To 50 parts of the polyol-modified lithium slag prepared in step (1), 5 parts of 1,1,4,4-butanetetraol, 10 parts of octaethylene glycol, 12 parts of polyethylene glycol with a molecular weight of 5000 g / mol, 13 parts of polycarboxylate superplasticizer, 17 parts of star-shaped alcohol amine ester polycarboxylate cement grinding aid, and 22 parts of multi-arm polymer cement grinding aid were successively added, and stirred and mixed thoroughly to obtain the cement grinding aid with molecular weight gradient distribution.

[0109] Comparative Example 1

[0110] Repeat Example 1, without adding multi-arm polymer cement grinding aid, with other conditions unchanged, to obtain Comparative Sample 1.

[0111] Comparative Example 2

[0112] Repeat Example 2, without adding the star-shaped alkanolamine ester polycarboxylate cement grinding aid, with other conditions remaining unchanged, to obtain Comparative Sample 2.

[0113] Comparative Example 3

[0114] Repeat Example 3, without adding the star polycarboxylate water reducer, with other conditions remaining unchanged, to obtain Comparative Sample 3.

[0115] Comparative Example 4

[0116] Repeat Example 4, without adding polyacrylic acid, with other conditions remaining unchanged, to obtain Comparative Sample 4.

[0117] Comparative Example 5

[0118] Repeat Example 5, without adding diglycerol, with other conditions remaining unchanged, to obtain Comparative Sample 5.

[0119] Comparative Example 6

[0120] Repeat Example 6, without adding ethylene glycol, with other conditions remaining unchanged, to obtain Comparative Sample 6.

[0121] Comparative Example 7

[0122] Repeat Example 6, without adding the polyol-modified lithium slag, with other conditions remaining unchanged, to obtain Comparative Sample 7.

[0123] Comparative Example 8

[0124] Purchase a commercially available cement grinding aid as Comparative Sample 8, which is a compound product of polyol and polyolamine.

[0125] Comparative Example 9

[0126] Repeat Example 6, remove step (1), and use lithium slag dried at 105°C to replace the polyol-modified lithium slag in step (2) in equal mass, with other conditions remaining unchanged, to obtain Comparative Sample 9.

[0127] Test and evaluate the samples of the above Examples 1 to 10 and Comparative Examples 1 to 9.

[0128] Referring to the test methods in GB / T 26748-2011 "Cement Grinding Aids", 5 kg of various cement raw materials were taken and added to the test small mill according to the proportion of P.O42.5 cement. The cement proportion was: 78% of clinker, 5% of slag, 8% of fly ash, 4% of limestone, 5% of desulfurized gypsum. Before grinding, the samples of Examples 1 to 10 and Comparative Examples 1 to 9 were added to the cement raw materials at an admixture amount of 0.2%. The grinding time was fixed at 23 minutes to obtain the P.O 42.5 cement samples leaving the mill. A cement particle size analyzer was used to analyze the cement particle size distribution. The cement fineness test referred to GB / T 1345-2005 "Test Method for Cement Fineness - Sieving Method". The cement specific surface area test referred to GB / T 8074-2008 "Determination Method for Cement Specific Surface Area - Blaine Method". The cement strength test referred to GB / T 17671-2021 "Test Method for Cement Mortar Strength (ISO Method)". The samples of Examples 1 to 10 and Comparative Examples 1 to 9 were tested and evaluated.

[0129] Table 1 Grinding Aid Effect

[0130]

[0131]

[0132] As can be seen from Table 1, compared with the blank, after adding the cement grinding aids with molecular weight gradient distribution prepared in Examples 1 to 10, the cement specific surface area increased significantly, and the residues on the 80μm and 45μm sieves decreased significantly, indicating that the cement grinding aids with molecular weight gradient distribution had a significant grinding aid effect; at the same time, the volume contents of particles with sizes of 0 - 3μm and above 60μm decreased significantly, and the volume content of particles with sizes of 3 - 30μm, which mainly contributed to the cement strength, increased significantly, indicating that the cement grinding aids with molecular weight gradient distribution had a good optimization effect on the cement powder particle size distribution. Compared with Comparative Examples 1 to 9, the cement specific surface area was higher, and the residues on the 80μm and 45μm sieves were lower; the volume contents of particles with sizes of 0 - 3μm and above 60μm were less, and the volume content of particles with sizes of 3 - 30μm, which mainly contributed to the cement strength, was more, indicating that the molecular weight gradient distribution prepared in Examples 1 to 10 had a better effect on the cement grinding aid effect and improving the cement particle size distribution, and the same effect could not be achieved without any one of these materials.

[0133] Table 2 Cement Mortar Strength

[0134]

[0135]

[0136] As can be seen from Table 2, compared with the blank, after adding the cement grinding aids with molecular weight gradient distribution prepared in Examples 1 to 10, the strength of cement at each age is significantly improved, indicating that the cement grinding aids with molecular weight gradient distribution effectively improve the cement strength by improving the cement particle gradation. Compared with Comparative Examples 1 to 9, the strength of cement at each age is higher, indicating that the molecular weight gradient distribution prepared in Examples 1 to 10 has a better effect on improving the cement particle gradation, thus effectively improving the strength of cement at each age, and the same effect cannot be achieved without any one of these materials.

Claims

1. A cement grinding aid with a molecular weight gradient distribution, characterized in that The composition is as follows by mass fraction: The first gradient molecular weight cement grinding aid: 16 to 24 parts, The second gradient molecular weight cement grinding aid: 12 to 20 parts, The third gradient molecular weight cement grinding aid: 10 to 18 parts, The fourth gradient molecular weight cement grinding aid: 8 to 15 parts, The fifth gradient molecular weight cement grinding aid: 6 to 12 parts, The sixth gradient molecular weight cement grinding aid: 4 to 10 parts, Polyol-modified lithium slag: 50 to 60 parts; The first gradient molecular weight cement grinding aid is a multi-arm polymer with a weight average molecular weight of 293,000 to 742,000 g / mol. The multi-arm polymer is prepared by free radical polymerization of amino polyethylene glycol methyl ether, binary unsaturated carboxylic acid or anhydride, and unsaturated polyol ether under the action of a primary amine chain transfer agent, initiator, and reducing agent; The second gradient molecular weight cement grinding aid is a star-shaped alcohol amine ester polycarboxylic acid polymer with a weight average molecular weight of 60,000 to 180,000 g / mol. The star-shaped alcohol amine ester polycarboxylic acid polymer is prepared by free radical polymerization of unsaturated alcohol amine esterification product, unsaturated acid monomer, and unsaturated polyether monomer under the action of a chain transfer agent, initiator, and reducing agent; The third gradient molecular weight cement grinding aid is a polycarboxylate superplasticizer with a weight average molecular weight of 20,000 to 60,000 g / mol; The fourth gradient molecular weight cement grinding aid is one or any combination of polyacrylic acid and polyethylene glycol with a molecular weight of 2,000 to 8,000 g / mol; The fifth gradient molecular weight cement grinding aid is polyglycerol with a molecular weight range of 240 to 800 g / mol; The sixth gradient molecular weight cement grinding aid is polyol A with a molecular weight range of 60 to 240 g / mol; The polyol-modified lithium slag is lithium slag saturated with polyol B. The lithium slag is the waste residue generated during the lithium extraction process from lithium ore. The polyol B is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, glycerol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol; 2. The grinding aid for cement with a molecular weight gradient distribution according to claim 1, characterized in that The polyglycerol is one or any combination of triglycerol, tetraglycerol, pentaglycerol, hexaglycerol, heptaglycerol, octaglycerol, nonaglycerol, and decaglycerol; 3. The grinding aid for cement with a molecular weight gradient distribution according to claim 1, characterized in that The polyol A is one or any combination of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, glycerol, 1,2,4-butanetriol, 1,2,3-butanetriol, 1,1,4,4-butanetetraol, and threitol; 4. The grinding aid for cement with a molecular weight gradient distribution according to claim 1, characterized in that The particle size range of the lithium slag is 10 to 200 μm; 5. The grinding aid for cement with a molecular weight gradient distribution according to claim 1, characterized in that The preparation method of the polyol-modified lithium slag includes the following steps: Dry the lithium slag at 100 to 110 °C, and fully mix and age the dried lithium slag with an aqueous solution of polyol B with a concentration of 20 to 30 wt% for 4 to 8 h. The mass ratio of the lithium slag to polyol B is (30 to 40):1; 6. The preparation method of the grinding aid for cement with the molecular weight gradient distribution as described in claim 1, characterized in that It includes the following steps: Add the sixth-gradient molecular weight cement grinding aid, the fifth-gradient molecular weight cement grinding aid, the fourth-gradient molecular weight cement grinding aid, the third-gradient molecular weight cement grinding aid, the second-gradient molecular weight cement grinding aid, and the first-gradient molecular weight cement grinding aid to the polyol-modified lithium slag in sequence, and stir and mix evenly.

7. Application of the cement grinding aid with the molecular weight gradient distribution as described in Claim 1 in the cement grinding process.

8. Use of the grinding aid for cement with a molecular weight gradient distribution according to claim 7 in the process of cement grinding, characterized in that The dosage of the cement grinding aid with the molecular weight gradient distribution is 0.1~0.3 wt% of the total mass of each raw material in the cement grinding process.

9. Use of the grinding aid for cement with molecular weight gradient distribution according to claim 7 in the process of cement grinding, characterized in that The addition method of the cement grinding aid with the molecular weight gradient distribution is to be ground together with each raw material of the cement.

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