Composite chromium removal grinding aid and preparation method thereof

Abstract

The invention discloses a composite chromium removal grinding aid and a preparation method thereof, belongs to the technical field of cement grinding aids, and particularly relates to a composite grinding aid for improving the cement grinding efficiency and reducing the content of hexavalent chromium in cement. The grinding aid comprises the following raw materials: 40-70% of modified lignosulfonate, 4-15% of a synergistic antioxidant component, 15-35% of a chromium removal component, 3-10% of an organic acid regulator and 1-5% of an auxiliary agent, wherein the total amount is 100%. The modified lignosulfonate is introduced, and the antioxidant component and the chromium removal component are combined, so that the grinding aid performance is effectively improved, meanwhile, the content of hexavalent chromium in cement is remarkably reduced, and potential hazards caused by a traditional grinding aid to the environment and human health are avoided. The grinding aid not only improves the cement grinding efficiency, but also enhances the early strength and the later strength of cement, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of cement admixture technology, specifically relating to a composite chromium removal grinding aid and its preparation method. Background Technology

[0002] The cement industry is a major energy consumer, with its main production process involving "one firing and two grinding": grinding raw materials, grinding clinker, and firing the clinker. The rapid increase in cement production demand has led companies to focus on the application of cement grinding aids, aiming to increase output by adding appropriate amounts of these aids. Cement grinding aids are a general term for chemical agents added to the system during the grinding of solid materials. They mainly consist of surfactants, other modifying agents (dispersants, corrosion inhibitors, etc.), and inert carriers or solvents.

[0003] Currently, alkanolamine grinding aids are widely used. Triethanolamine (TEA) and triisopropanolamine (TIPA) are highly efficient grinding aids widely used in the cement industry, significantly improving grinding efficiency, increasing cement specific surface area, and improving particle distribution. However, their main drawbacks are: high cost and potential environmental impact during use. Furthermore, these grinding aids may not fully meet the needs of cement production under certain conditions; for example, their effectiveness is limited when processing raw materials with high chromium content.

[0004] Currently, chromium removal in cement mainly relies on adding ferrous sulfate (FeSO4) or its modified forms, and organic reducing agents (such as ascorbic acid and gluconate) during grinding. However, this method also presents the following problems: Compatibility with grinding aids: Adding it alone may affect the grinding effect or cement performance (e.g., FeSO4 may increase setting time). Stability issues: Fe... 2+ It is prone to oxidation and failure in the alkaline environment of cement, and its long-term storage performance is poor.

[0005] Non-alkanolamine grinding aids such as molasses, polyols, and inorganic salts (e.g., sodium thiosulfate and aluminates) have been studied as grinding aids, but they generally suffer from problems such as inferior grinding aid effects compared to alkanolamines, high dosage requirements, or negative impacts on cement performance. There is a lack of a solution that can simultaneously provide efficient grinding aids, low dosage requirements, stable chromium removal, and low cost.

[0006] Therefore, developing a composite grinding aid that can effectively remove chromium and also has good grinding performance has become an urgent problem to be solved in the industry. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by providing a composite chromium removal grinding aid and its preparation method, aiming to solve the issues of poor compatibility, insufficient stability, and high cost of existing grinding aids and chromium removal agents. By optimizing the raw material ratio and preparation process, this invention ensures that the product can stably remove chromium from cement while providing efficient grinding assistance, with low dosage and controllable cost. Specifically, this grinding aid uses modified lignin sulfonate as the main component, combined with synergistic antioxidant components, chromium removal components, organic acid regulators, and additives, thereby improving grinding performance and achieving effective reduction and fixation of chromium. Furthermore, the preparation method of this invention is simple to operate, suitable for large-scale industrial production, and has significant economic and social benefits.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A composite chromium removal grinding aid comprises, by weight percentage, the following raw materials: 40-70% modified lignin sulfonate, 4-15% synergistic antioxidant component, 15-35% chromium removal component, 3-10% organic acid regulator, and 1-5% additives, totaling 100%.

[0009] Furthermore, the chromium removal component is selected from at least one of stannous sulfide and stannous sulfate.

[0010] Furthermore, the synergistic antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0011] Furthermore, the preparation method of the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 8-10g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) dropwise, and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.2-1.4 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1.0-1.2:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours; c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

[0012] Furthermore, the organic acid regulator is tartaric acid or malic acid.

[0013] Furthermore, the additive is obtained by mixing triethanolamine and sodium polycarboxylate in a mass ratio of 1:(0.5-1).

[0014] A method for preparing a composite chromium removal grinding aid includes the following preparation steps: (1) Preparation of modified lignin sulfonate; (2) Weigh the modified lignin sulfonate, the enhanced antioxidant component, the chromium removal component, the organic acid regulator and the additives according to the formula ratio, mix them thoroughly and then add water to dilute them. Continue stirring until they are completely dissolved to form a homogeneous solution. Transfer the solution to the reaction vessel and stir it at a constant temperature of 60±5℃ for 60 minutes. Then filter to remove trace amounts of insoluble impurities to obtain a transparent liquid product. Finally, adjust the solid content to 50% according to the application requirements, and complete the packaging and storage for later use.

[0015] The grinding aid of this invention is added at a dosage of 0.03%-0.05% of the cement mass.

[0016] Beneficial effects (1) This invention uses modified lignin sulfonate as the main grinding aid component. First, the lignin sulfonate is oxidized and activated to improve the activity of lignin molecules, increase the number of active sites in the molecules, and make it easier to react with other substances. At the same time, the polar groups (such as carboxyl groups) generated after oxidation enhance the hydrophilicity of lignin sulfonate, making it easier to disperse in the cement system. Subsequently, quaternization introduces cationic groups. The cationic groups can be adsorbed on the surface of negatively charged cement particles through electrostatic attraction, reducing the electrostatic repulsion between particles, reducing agglomeration, and enhancing the dispersibility and adsorption capacity of lignin in the cement system, thereby significantly improving the grinding aid effect. At the same time, the polarity of the quaternized lignin sulfonate is enhanced, which can better react with Ca in the cement. 2+ Al 3+Plasma action promotes the dispersion and hydration of cement particles. The thiolization reaction further endows the modified lignin sulfonate with the ability to reduce chromium ions, enabling it to effectively reduce hexavalent chromium to trivalent chromium and fix it through complexation, preventing secondary oxidation. Simultaneously, the thiol groups react with metal ions in the cement (such as Ca2+). 2+ Fe 3+ This process forms a complex, further reducing interparticle adhesion and enhancing grinding efficiency. This multi-modification process not only optimizes the chemical structure of lignin but also fully utilizes its dual functions as a grinding aid and chromium remover, achieving a comprehensive performance improvement. Using it as the main grinding aid component, it effectively adsorbs onto the surface of cement particles, reducing interparticle friction and cohesion, improving grinding efficiency, and simultaneously removing chromium efficiently. Additionally, the addition of stannous chloride and stannous sulfate provides stannous ions, reducing hexavalent chromium in cement to trivalent chromium. Trivalent chromium has high stability and is far less toxic than hexavalent chromium, thus reducing the harmful effects of chromium in cement. This dual chromium removal effect effectively reduces the chromium content.

[0017] (2) Secondly, the addition of an antioxidant synergist composed of tannic acid and 2,6-di-tert-butyl-p-cresol in a 1:1 ratio inhibits the oxidation of the chromium removal components, especially in the alkaline environment of cement, protecting the reducing properties of the chromium removal components and ensuring their long-term effective chromium removal function. On the other hand, it can also delay the oxidation and decomposition of the grinding aid itself, enhancing the storage stability of the product. In addition, organic acids can also undergo esterification or complexation reactions with the hydroxyl and carboxyl groups in lignin molecules, further improving their dispersibility and adsorption capacity in cement, thereby improving the grinding aid effect. Furthermore, the introduction of organic acid regulators can further enhance the reducing capacity of the system. When mixed in equal proportions, they can form a synergistic effect with modified lignin sulfonate, improving the grinding aid effect and the reduction efficiency of hexavalent chromium.

[0018] (3) The triethanolamine and sodium polycarboxylate additives used together can enhance the stability and solubility of the system, prevent performance fluctuations caused by changes in water quality or environment, and ultimately achieve the synergistic effect of grinding aid and efficient chromium removal, thereby improving the quality and safety of cement products.

[0019] (4) This invention achieves synergistic effects of grinding aid and chromium removal through the scientific formulation of its components, significantly improving cement grinding efficiency and effectively reducing the harmful effects of chromium. Tests have shown that using the product of this invention can reduce the hexavalent chromium content in cement by more than 90%, resulting in stable cement performance and strong adaptability, especially suitable for cement raw material systems with high chromium content. This process is simple to operate, cost-controllable, and has good prospects for industrial application. Attached Figure Description

[0020] Figure 1 Electron micrographs of cement samples using the grinding aid of Example 1 of the present invention and electron micrographs of blank cement; Figure 2Electron micrographs of cement samples using grinding aids from Example 1 and Comparative Examples 1-6, and electron micrograph of blank cement. Figure 3 The particle size distribution diagrams are for cement samples using grinding aids from Example 1 and Comparative Examples 1-6. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0022] Example 1 A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% modified lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0023] The chromium removal component is stannous sulfide.

[0024] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0025] The preparation method of the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 8g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.2 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours. c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

[0026] The organic acid regulator is tartaric acid.

[0027] The additive is obtained by mixing triethanolamine and sodium polycarboxylate in a mass ratio of 1:0.5.

[0028] A method for preparing a composite chromium removal grinding aid includes the following preparation steps: (1) Preparation of modified lignin sulfonate; (2) Weigh the modified lignin sulfonate, the enhanced antioxidant component, the chromium removal component, the organic acid regulator and the additives according to the formula ratio, mix them thoroughly and then add water to dilute them. Continue stirring until they are completely dissolved to form a homogeneous solution. Transfer the solution to the reaction vessel and stir it at a constant temperature of 60±5℃ for 60 minutes. Then filter to remove trace amounts of insoluble impurities to obtain a transparent liquid product. Finally, adjust the solid content to 50% according to the application requirements, and complete the packaging and storage for later use.

[0029] Example 2 A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 55% modified lignin sulfonate, 15% synergistic antioxidant component, 15% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0030] The chromium removal component is stannous sulfate.

[0031] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0032] The preparation method of the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 10g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) dropwise, and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.4 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours. c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

[0033] Example 3 A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 60% modified lignin sulfonate, 11% synergistic antioxidant component, 20% chromium removal component, 6% organic acid regulator, and 3% additives, for a total of 100%.

[0034] The chromium removal component is stannous sulfide.

[0035] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0036] The preparation method of the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 10g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) dropwise, and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.4 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1.2:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours. c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

[0037] Example 4 A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 70% modified lignin sulfonate, 4% synergistic antioxidant component, 22% chromium removal component, 3% organic acid regulator, and 1% additives, for a total of 100%.

[0038] The chromium removal component is stannous sulfate.

[0039] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0040] The preparation method of the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 10g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) dropwise, and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.4 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1.2:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours. c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

[0041] Comparative Example 1 In this comparative example, except that unmodified sodium lignin sulfonate was used instead of the modified lignin sulfonate in Example 1, all other steps and conditions were the same as in Example 1. That is: A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0042] The chromium removal component is stannous sulfide.

[0043] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1.

[0044] The lignin sulfonate is sodium lignin sulfonate.

[0045] The organic acid regulator is tartaric acid.

[0046] The additive is obtained by mixing triethanolamine and sodium polycarboxylate in a mass ratio of 1:0.5.

[0047] A method for preparing a composite chromium removal grinding aid includes the following preparation steps: (1) Weigh out lignin sulfonate, synergistic antioxidant, chromium removal component, organic acid regulator and additives according to the formula ratio, mix thoroughly and add water to dilute, and continue stirring until completely dissolved to form a homogeneous solution; transfer the solution to the reaction vessel and stir at a constant temperature of 60±5℃ for 60 minutes; then filter to remove trace insoluble impurities to obtain a transparent liquid product; finally adjust the solid content to 50% according to the application requirements, and complete the packaging and storage for later use.

[0048] Comparative Example 2 In this comparative example, except that only tannic acid was used in the synergistic antioxidant component, all other steps and conditions were the same as in Example 1. That is: A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% modified lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0049] The synergistic antioxidant component is tannic acid.

[0050] Comparative Example 3 In this comparative example, except that only 2,6-di-tert-butyl-p-cresol was used in the synergistic antioxidant component, all other steps and conditions were the same as in Example 1. That is: A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% modified lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0051] The synergistic antioxidant component is 2,6-di-tert-butyl-p-cresol.

[0052] Comparative Example 4 In this comparative example, except for changing the mass ratio of tannic acid and 2,6-di-tert-butyl-p-cresol in the synergistic antioxidant component, the raw materials and preparation steps are the same as in Example 1. That is: A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% modified lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0053] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 2:1.

[0054] Comparative Example 5 In this comparative example, except for changing the mass ratio of tannic acid and 2,6-di-tert-butyl-p-cresol in the synergistic antioxidant component, the raw materials and preparation steps are the same as in Example 1. That is: A composite chromium removal grinding aid comprises the following raw materials by mass percentage: 40% modified lignin sulfonate, 10% synergistic antioxidant component, 35% chromium removal component, 10% organic acid regulator, and 5% additives, for a total of 100%.

[0055] The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:2.

[0056] Comparative Example 6 The grinding aid is prepared according to the patent technology solution of the applicant's application number CN201811492520.3.

[0057] Performance testing The grinding aid was prepared according to the methods described in the examples and comparative examples. The cement raw material mix proportions were: clinker 80%, slag 5%, fly ash 5%, natural gypsum 5%, and limestone 5%.

[0058] Cement preparation: Before grinding, the clinker was crushed using a jaw crusher, and the crushed material was sieved to control the particle size at approximately 1-6 mm. 5 kg of test material was weighed, and grinding aid was added to each sample. For Examples 1-4 and Comparative Examples 1-5, the addition was 0.03% of the cement mass. For Comparative Example 6, the addition was 0.15% as stated therein. The mixture was ground in a SYMФ500 mm x 500 mm standard cement test chamber for 25 minutes, with a discharge time of 5 minutes. The discharged cement was sieved through a 0.6 mm standard sieve to remove large, unground particles, then sealed in bags and stored in a dry environment for cement performance testing. A blank control (without grinding aid) was also included. Five replicates were set up for each experimental group, and the results were averaged.

[0059] Test methods Specific surface area test: The specific surface area of ​​cement is tested using the Blaine method.

[0060] Fineness test: The negative pressure sieve residue test was conducted according to the GB / T 1345 method, using an FSY-150B cement fineness negative pressure sieve analyzer to determine the residue at 80 μm and 45 μm respectively.

[0061] Cement strength test: The flexural and compressive strength of cement are tested in accordance with the "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021).

[0062] Chromium content analysis: The content of water-soluble hexavalent chromium in cement under different conditions was tested according to the "Limits and Determination Methods for Water-soluble Chromium (VI) in Cement" (GB 31893-2015), and the chromium-reducing effect of grinding aid was analyzed.

[0063] Particle size distribution: LS-POP (VI) laser particle size analyzer, manufactured by Zhuhai Omec Instruments Co., Ltd., China. Test method: Weigh a certain mass of cement sample, control the solution's shading ratio between 10% and 20%, prepare a suspension with 100 mg / L sodium hexametaphosphate solution, ultrasonically vibrate for 5 min, remove the sample and immediately measure its particle size using the laser particle size analyzer, and automatically generate a particle size distribution map using software.

[0064] Cement morphology SEM determination: The surface morphology and microstructure of cement particles were observed using scanning electron microscopy (SEM). Specific test results are shown in Table 1. Table 1. Test results of grinding-aiding performance Table 2 Chromium Removal Performance Test Results As shown in Table 1, with the increase of grinding aid dosage, the specific surface area of ​​cement significantly increased, the particle size decreased, and the sieve residue value decreased, indicating that the grinding aid can effectively improve the fineness and dispersibility of cement. In Examples 1 to 4, the specific surface area increased from 475 m² / kg to 492 m² / kg, and the 45μm sieve residue decreased from 10.2% to 9.5%, indicating that the grinding aid at a dosage of 0.03% already has a good grinding aid effect. Meanwhile, the compressive strength data show that the 3-day and 28-day compressive strengths of the examples are higher than those of the comparative example and the control group, especially the 28-day compressive strength of Example 4, which reached 59.8 MPa, showing that the grinding aid not only improves the fineness of cement but also significantly enhances its mechanical properties. Comparing the performance data of the examples and the comparative example further reveals the crucial role of the ratio of modified lignin sulfonate and the synergistic antioxidant components in the overall performance of the grinding aid. In Comparative Example 1, unmodified sodium lignosulfonate was used instead of modified lignosulfonate, resulting in a specific surface area of ​​only 415 m² / kg, significantly lower than that of the Example group. This indicates that the modification process effectively improved the dispersibility and grinding aid ability of lignosulfonate. Furthermore, Comparative Examples 2 and 3, using tannic acid or 2,6-di-tert-butyl-p-cresol as synergistic antioxidant components alone, showed lower compressive strength and sieve residue values ​​compared to the Example group, indicating that a single component cannot fully exert its synergistic antioxidant effect. Comparative Examples 4 and 5 adjusted the mass ratio of tannic acid to 2,6-di-tert-butyl-p-cresol, and although the performance improved somewhat, it was still lower than the optimal ratio in Example 4, indicating that a mass ratio of 1:1 provides the best grinding aid and enhanced mechanical properties.

[0065] Further analysis of the chromium content test results showed that the water-soluble hexavalent chromium content in the cement of the example groups was significantly reduced, especially in Example 4, where the chromium reduction effect was most prominent. Combined with SEM measurements, the cement particles in Example 1 showed more uniform surface morphology, more concentrated particle distribution, and smaller particle size, which explains its high strength and low sieve residue. In conclusion, by combining modified lignin sulfonate with rationally designed synergistic antioxidant components, excellent grinding aid, strengthening, and chromium reduction effects can be achieved at relatively low dosages.

[0066] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A composite chromium removal grinding aid, characterized in that, The product comprises the following raw materials by weight percentage: 40-70% modified lignin sulfonate, 4-15% synergistic antioxidant components, 15-35% chromium removal components, 3-10% organic acid regulators, and 1-5% additives, for a total of 100%.

2. The composite chromium removal grinding aid according to claim 1, characterized in that, The chromium removal component is selected from at least one of stannous sulfide and stannous sulfate.

3. The composite chromium removal grinding aid according to claim 1, characterized in that, The enhanced antioxidant component is obtained by mixing tannic acid and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:

1.

4. The composite chromium removal grinding aid according to claim 1, characterized in that, The method for preparing the modified lignin sulfonate is as follows: (1) Dissolve 100 g of sodium lignin sulfonate in 600 mL of deionized water and stir until completely dissolved. Adjust the pH to 10.0±0.2 with 10% NaOH solution. Heat to 60±2℃ and slowly add 15 g of 30% H2O2 solution. React at a constant temperature for 2 hours while maintaining pH=10.

0. After the reaction is complete, cool to 40℃ to obtain a dark brown oxidized activated lignin sulfonate solution. (2) Quaternization reaction: Add 8-10g of formaldehyde solution with a mass concentration of 37% to the oxidized activated lignin sulfonate solution obtained in step (1), heat to 70±2℃, react for 40 minutes, slowly add 25g of dimethylethanolamine (DMEA) dropwise, and adjust the pH to 11.5±0.2; react at a constant temperature for 4 hours, maintaining pH=11.5; after the reaction is completed, cool to 50℃ to obtain a brownish-red quaternized solution QO-LS; (3) Thiolation reaction: a) Add epichlorohydrin (ECH) to QO-LS. The amount of ECH is 1.2-1.4 times the molar amount of phenolic hydroxyl groups in oxidized lignin. Control the pH to 11.0-11.5 and react at 70±2℃ for 2 hours to obtain the epoxy-modified intermediate EP-QO-LS. b) Add sodium hydrosulfide (NaSH) aqueous solution to EP-QO-LS, with a NaSH to ECH molar ratio of 1.0-1.2:1, adjust the pH to 9.0-10.0, and react at 60±2℃ for 4 hours; c) Adjust the pH of the reaction solution to pH=7.0, concentrate under reduced pressure, and then spray dry to obtain modified lignin sulfonate.

5. The composite chromium removal grinding aid according to claim 1, characterized in that, The organic acid regulator is tartaric acid or malic acid.

6. The composite chromium removal grinding aid according to claim 1, characterized in that, The additive is obtained by mixing triethanolamine and sodium polycarboxylate in a mass ratio of 1:(0.5-1).

7. A method for preparing the composite chromium removal grinding aid according to any one of claims 1-6, characterized in that, The preparation steps include the following: (1) Preparation of modified lignin sulfonate; (2) Weigh the modified lignin sulfonate, the enhanced antioxidant component, the chromium removal component, the organic acid regulator and the additives according to the formula ratio, mix them thoroughly and then add water to dilute them. Continue stirring until they are completely dissolved to form a homogeneous solution. Transfer the solution to the reaction vessel and stir it at a constant temperature of 60±5℃ for 60 minutes. Then filter to remove trace amounts of insoluble impurities to obtain a transparent liquid product. Finally, adjust the solid content to 50% according to the application requirements, and complete the packaging and storage for later use.

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