Liquid grinding aid type cement hexavalent chromium reducing agent and its synthesis and application

Abstract

The application discloses a liquid grinding aid type cement hexavalent chromium reducing agent and synthesis and application thereof, and is characterized in that organic low-valence metal salt is generated by organic acid and metal oxide, alcohol amine ester complexation is formed by esterification of alcohol amine and organic acid, and high coordination activity is continuously generated under the reaction of uncompletely esterified organic acid, metal oxide continuously forms low-valence metal ions, the content of low-valence metal ions in solution is increased, direct solid-solid oxidation-reduction reaction of low-valence metal oxide with hexavalent chromium in cement is avoided, and problems such as insufficient reduction performance caused by difficulty in forming high-concentration low-valence metal salt are avoided; in addition, the thermal stability and long-term stability of the liquid grinding aid type cement hexavalent chromium reducing agent are improved due to a large number of coordination, and the efficiency of reduction of hexavalent chromium is greatly increased due to the existence of a large number of low-valence metal ions, that is, the existence of effective reducing components.

Description

Technical Field

[0001] This invention belongs to the field of building material additives technology, specifically relating to a liquid grinding aid type cement hexavalent chromium reducing agent and its synthesis and application. Background Technology

[0002] To reduce environmental impact and improve resource utilization, a large amount of low-grade raw materials (such as low-grade limestone, industrial solid waste, and certain minerals) are used in cement production. However, low-grade raw materials in some regions have significant drawbacks, severely impacting cement production. For example, in the high-temperature clinker production process using low-grade raw materials such as chromium-containing limestone, chromium-containing sludge, and steel slag, chromium easily dissolves in the clinker minerals and leaches out as ions during hydration, resulting in excessive levels of water-soluble hexavalent chromium in the cement, posing serious threats to human health and the ecological environment. Therefore, addressing the hexavalent chromium problem is an essential aspect of cement production.

[0003] Furthermore, in the production of silicate cement, the grinding process accounts for 60% to 70% of the total energy consumption. Some low-grade raw materials, such as steel slag and ferrochrome slag, are easily ground, leading to poor cement grinding efficiency, significantly increasing equipment wear and energy waste, and increasing greenhouse gas emissions. Therefore, the cement industry urgently needs to develop new cement admixtures that simultaneously possess both chromium reduction and grinding aid functions to address the issues of hexavalent chromium and easy grinding in the application of low-grade raw materials, thereby contributing to energy conservation, emission reduction, and green production.

[0004] The performance of liquid grinding aid cement hexavalent chromium reducing agent is mainly reflected in its excellent grinding aid function for cement clinker and its admixtures, as well as its ability to completely convert leached hexavalent chromium into insoluble trivalent chromium during cement use. The effective content of the reducing component and the grinding aid component are key factors affecting the reducing and grinding performance of the agent.

[0005] At present, the research and preparation of liquid grinding aid cement hexavalent chromium reducing agent at home and abroad is often achieved by simply compounding grinding aid components and reducing components. However, there are no in-depth research results on the optimal mixing ratio and stability of the grinding aid components and reducing components. In the cement grinding process, the temperature inside the mill can often reach 100-160℃. Under such high temperature environment, the compounded grinding aid reducing agent is very likely to fail. Summary of the Invention

[0006] The purpose of this invention is to provide a liquid grinding aid cement hexavalent chromium reducing agent, its synthesis and application, which can improve the stability of the liquid grinding aid cement hexavalent chromium reducing agent and ensure that it will not lose its reducing properties in high-temperature use environment and long-term storage.

[0007] To achieve the above objectives, the present invention provides a method for synthesizing a liquid grinding aid type cement hexavalent chromium reducing agent, comprising:

[0008] A suspension is formed by heating an aqueous solution containing organic acids and reduced metal oxides.

[0009] Alkylamine is added to the suspension under continuous heating conditions, causing the suspension to react and form a gel-like liquid;

[0010] The liquid grinding aid cement hexavalent chromium reducing agent is obtained by removing insoluble substances from the colloidal liquid.

[0011] Furthermore, the reduced metal oxide is at least one selected from stannous oxide, cuprous oxide, ferrous oxide, manganese oxide, and antimony oxide.

[0012] Furthermore, the organic acid includes one or a mixture of two or more of acetic acid, oleic acid, and lauric acid.

[0013] Furthermore, the molar ratio of alkanolamine to organic acid is 1:(0.6 to 1.2).

[0014] Furthermore, the heating temperature range during the synthesis process is 80–120°C, and the holding time after adding the alcohol amine to the suspension is 30–240 min.

[0015] To achieve the above-mentioned technical effects, the present invention also provides a liquid grinding aid type cement hexavalent chromium reducing agent, characterized in that the liquid grinding aid type cement hexavalent chromium reducing agent is prepared by the synthesis method of the liquid grinding aid type cement hexavalent chromium reducing agent.

[0016] Furthermore, the percentage content of reduced metal oxides in the liquid grinding aid cement hexavalent chromium reducing agent is 9-20%.

[0017] To achieve the above-mentioned technical effects, the present invention also provides an application of liquid grinding aid type cement hexavalent chromium reducing agent in cement grinding, characterized in that, before or during cement grinding, the liquid grinding aid type cement hexavalent chromium reducing agent is added to a mixture containing cement clinker, gypsum and cement admixtures, and then ground together to prepare cement.

[0018] Furthermore, the amount of the liquid grinding aid cement hexavalent chromium reducing agent added is 0.1‰ to 0.6‰ of the cement clinker dosage.

[0019] In summary, the present invention has the following advantages:

[0020] The hexavalent chromium reducing agent synthesized in this invention is obtained by reacting organic acids, alkanolamines, and reduced metal oxides. However, due to its low solubility, its concentration is difficult to increase. In this invention, organic acids react with metal oxides to form organic low-valent metal salts. Under the complexation of alkanolamines formed by the esterification of alkanolamines with organic acids and the reaction of incompletely esterified organic acids, high coordination activity is continuously generated. Low-valent metal oxides continuously form low-valent metal ions, increasing their content in the solution and avoiding the problem that the solid phase of low-valent metal oxides cannot directly undergo solid-solid redox reactions with hexavalent chromium in cement. At the same time, due to the presence of a large number of residual hydroxyl groups, the additive also has a grinding aid function. In addition, due to the large amount of coordination generated, the thermal stability and long-term stability of the liquid grinding aid cement hexavalent chromium reducing agent can be increased. Furthermore, due to the presence of a large number of low-valent metal ions, that is, the presence of effective reducing components, the efficiency of hexavalent chromium reduction is greatly increased, and the reduction effect is improved. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0022] Example 1

[0023] A method for synthesizing a liquid grinding aid type cement hexavalent chromium reducing agent includes:

[0024] A suspension is formed by heating an aqueous solution containing organic acids and reduced metal oxides.

[0025] Alkylamine is added to the suspension under continuous heating conditions, causing the suspension to react and form a gel-like liquid;

[0026] The liquid grinding aid cement hexavalent chromium reducing agent is obtained by removing insoluble substances from the colloidal liquid.

[0027] In this embodiment, organic acids and alkanolamines react with metal oxides to generate high-concentration low-valence metal salts through esterification complexation. On the one hand, organic acids react with metal oxides to generate organic low-valence metal salts, but due to their low solubility, the concentration is difficult to increase. Therefore, in this invention, under the esterification complexation of alkanolamines with organic acids and the reaction of incompletely esterified organic acids, high coordination activity is continuously generated, causing low-valence metal oxides to continuously form low-valence metal ions, increasing their content in the solution. This avoids the difficulty of the solid phase of low-valence metal oxides directly reacting with hexavalent chromium in cement to undergo solid-solid redox reactions, which would affect the reduction efficiency of hexavalent chromium. In addition, due to the large amount of coordination generated, the spontaneous reaction of low-valence metal ions to higher valence states is severely restricted, increasing the thermal stability and long-term stability of this type of reagent. Furthermore, due to the presence of a large number of low-valence metal ions, that is, the presence of effective reducing components, the reduction efficiency of hexavalent chromium is greatly increased, and the reduction effect is improved. Meanwhile, the residual hydroxyl groups in alkanolamines and organic acids have a certain grinding-aiding effect; in addition, the reaction between organic acids and alkanolamines will bring ester groups, alkyl chains and more hydroxyl groups. These multiple effects increase the adsorption of the compound molecules on cement particles, making it easier for them to be adsorbed into the cracks of cement particles. The adsorbed compound molecules neutralize the unsaturated charge on the fracture surface to prevent crack recovery, and reduce the surface energy of cement particles, which can greatly improve the grindability of the material.

[0028] In summary, this embodiment, through the combined action of organic acid and alkanolamine, can increase the solubility of reduced metal oxides in the alkanolamine-organic acid mixture, thereby enhancing the reducing power of the unit mass of liquid grinding aid cement hexavalent chromium reducing agent. This allows for a reduction in the dosage of the liquid grinding aid cement hexavalent chromium reducing agent to achieve the target of reducing hexavalent Cr. Furthermore, in the synthesized liquid grinding aid cement hexavalent chromium reducing agent, the alkanolamine and organic acid undergo a chemical reaction, and the metal ions in the reduced metal oxide are integrated into the molecules after the reaction of the alkanolamine and organic acid. This further enhances the thermal stability of the liquid grinding aid cement hexavalent chromium reducing agent, ensuring that it will not lose its reducing properties at high temperatures.

[0029] The reduced metal oxide used in this embodiment is at least one of stannous oxide, cuprous oxide, ferrous oxide, manganese oxide, and antimony oxide. Other low-valence metal oxides that have both low and high valence can also be used in this invention.

[0030] The organic acid in this embodiment includes one or more of acetic acid, oleic acid, and lauric acid. The molar ratio of alkanolamine to organic acid is 1:(0.6-1.2), the heating temperature range during synthesis is 80-120°C, and the holding time after adding alkanolamine to the suspension is 30-240 min.

[0031] Based on the same inventive concept, this embodiment also provides a liquid grinding aid cement hexavalent chromium reducing agent, which is prepared by a synthesis method of liquid grinding aid cement hexavalent chromium reducing agent.

[0032] In this embodiment, the percentage content of reduced metal oxides in the liquid grinding aid cement hexavalent chromium reducing agent is 9-20%.

[0033] Based on the same inventive concept, this embodiment also provides a method for applying liquid grinding aid cement hexavalent chromium reducing agent in cement grinding. Before or during cement grinding, the liquid grinding aid cement hexavalent chromium reducing agent is added to a mixture containing cement clinker, gypsum and cement admixtures, and then ground together to prepare cement.

[0034] In this embodiment, the amount of liquid grinding aid cement hexavalent chromium reducing agent added is 0.1‰ to 0.6‰ of the cement clinker dosage.

[0035] Example 2

[0036] In this embodiment, stannous oxide was selected as the reduced metal oxide, and the molar ratio of alkanolamine to organic acid was 1:1. The heating temperature range during the synthesis process was 100±5℃. After adding alkanolamine to the suspension, the temperature was kept for 120 min to synthesize a liquid grinding aid cement hexavalent chromium reducing agent, which is a light yellow colloidal liquid.

[0037] Figure 1 This is the infrared spectrum of the synthesized grinding aid reducing agent; the horizontal axis represents wavenumber, and the vertical axis represents absorbance. Figure 1 It can be seen that the characteristic peaks of the hydroxyl and carboxyl groups of organic acids and the characteristic peaks of alcoholamines appear simultaneously in the infrared spectrum. (3382 cm⁻¹) -1 The characteristic absorption peak is broad, resembling a "bun" shape. This is due to the stretching vibration of the -OH group in the alcohol amine, and the 3411 cm⁻¹ peak in the organic acid spectrum. -1 and 3361cm -1 Both involve the stretching vibration of -OH. Comparing the spectra of organic acids and alcoholic amines, the synthesized compound exhibits a stretching vibration at 1734 cm⁻¹. -1 The newly formed absorption peak is due to the esterification reaction between the alcohol amine and the organic acid. The characteristic peaks of ester compounds are generally C=O and CO. (1635 cm⁻¹) -1 The characteristic absorption peak at [value] is due to the carbonyl group's symmetric stretching vibration. The 1100–1300 cm⁻¹ peak was also observed in the spectrum of the synthesized compound. -1 The presence of multiple absorption peaks within the range is likely due to the absorption vibrations of carbon-carbon single bonds and CO in alkanes. At 812 cm⁻¹... -1 734cm -1 623cm -1 551cm -1The four characteristic peaks at the α-axis are absorption peaks generated by the stretching or anti-stretching vibrations of the RO bond. Therefore, it can be seen from the infrared spectrum of the synthesized compound that the alkanolamine reacted chemically with the organic acid and the metal ions in the reduced metal oxide were successfully integrated into the molecule.

[0038] Studies have shown that cement particles in the 3–30 μm range help improve the mechanical properties of cement-based materials. To further understand the effect of synthetic liquid grinding aid hexavalent chromium reducing agent on the particle size distribution of cement powder, a laser particle size analyzer was used to test the particle size distribution of cement powder with different dosages of the liquid grinding aid hexavalent chromium reducing agent. The test results are shown in Table 1.

[0039]

[0040] Analysis of the test results in Table 1 shows that the particle size distribution of cement powder changed significantly after using 0.3‰ and 0.5‰ synthetic liquid grinding aid hexavalent chromium reducing agent during the grinding process. The control group had more coarse particles, while the content of coarse particles decreased significantly after adding 0.3‰ synthetic liquid grinding aid hexavalent chromium reducing agent, while the content of fine particles in the 3–30 μm range increased significantly. This indicates that the liquid grinding aid hexavalent chromium reducing agent can significantly reduce the average particle size of cement powder and increase the content of fine particles in the 3–30 μm range. At a dosage of 0.3‰, compared to the control group with a dosage of 0%, the content of fine particles smaller than 3 μm and 3–30 μm increased from 16.43% and 55.10% to 18.90% and 63.62%, respectively, while coarse particles of 60–80 μm and larger than 80 μm were almost completely ground. When the dosage was increased to 0.5‰, the content of particles in the 3-30μm range decreased to 60.44%. This was because the dosage of liquid grinding aid cement hexavalent chromium reducing agent exceeded the limit value. The excessive content of liquid grinding aid cement hexavalent chromium reducing agent caused fine particles to agglomerate and reform into coarse particles.

[0041] The liquid grinding aid cement hexavalent chromium reducing agent synthesized in this embodiment was added to a mixture containing cement clinker, gypsum, and cement admixtures, and then ground together for 0.5 hours to prepare cement. A comparative sample was prepared by directly adding stannous oxide to a mixture of alkanolamine and organic acid at a molar ratio of 1:1 at room temperature (20±5℃) and stirring for 120 minutes to obtain a compounded liquid grinding aid cement hexavalent chromium reducing agent. This compounded liquid grinding aid cement hexavalent chromium reducing agent was then added to a mixture containing cement clinker, gypsum, and cement admixtures, and ground together for 0.5 hours to prepare cement. The specific surface area of ​​the cement and the residual hexavalent chromium content in the cement paste were then measured for different dosages of the two liquid grinding aid cement hexavalent chromium reducing agents. The relevant data are shown in Table 2 below.

[0042] Table 2. Cement specific surface area and residual hexavalent chromium content in cement paste for two types of liquid grinding aids at different dosages.

[0043]

[0044]

[0045] As shown in Table 2 above, within a certain dosage range, the cement 80μm particle size sieve residue and the residual hexavalent chromium content in cement decrease with the increase of the dosage of the two grinding aid reducing agents. The synthetic liquid grinding aid cement hexavalent chromium reducing agent dosage of 0.3‰ can reduce all hexavalent chromium in cement to trivalent chromium, while the compounded liquid grinding aid cement hexavalent chromium reducing agent needs to reach a dosage of 0.8‰ to achieve a similar effect.

[0046] In this embodiment, the synthesized liquid grinding aid for cement hexavalent chromium reducing agent and the compounded liquid grinding aid for cement hexavalent chromium reducing agent were stored under the same storage conditions in the air without being protected from light for 1 day, 30 days, and 90 days, respectively. Cement was then ground using the synthesized liquid grinding aid for cement hexavalent chromium reducing agent at a dosage of 0.3‰ and the compounded liquid grinding aid for cement hexavalent chromium reducing agent at a dosage of 0.8‰, and the residual hexavalent chromium content in the cement paste of the obtained cement was compared. The relevant data are shown in Table 3 below:

[0047] Table 3. Cement specific surface area and residual hexavalent chromium content in cement paste for two types of liquid grinding aids at different dosages.

[0048]

[0049]

[0050] As shown in Table 2, with prolonged storage time, the hexavalent chromium content in cement gradually increases due to the failure of the reducing components caused by long-term exposure to air. With a liquid grinding aid containing 0.8‰ hexavalent chromium reducing agent, the residual hexavalent chromium content in the cement increased from 0.1 mg / kg after 1 day to 0.9 mg / kg after 30 days, reaching 3.1 mg / kg after 90 days. In cement with a 0.3‰ synthetic liquid grinding aid hexavalent chromium reducing agent dosage, the residual hexavalent chromium content increased from 0 mg / kg after 1 day to 0.5 mg / kg after 30 days, reaching 1.9 mg / kg after 90 days. Within 90 days, the residual hexavalent chromium was controlled within the harmless standard (2 mg / kg). Regarding the grinding aid effect, in cement with a 0.3‰ synthetic liquid grinding aid hexavalent chromium reducing agent dosage, the 80μm particle size sieve residue increased from 1.4% after 1 day to 2.6% after 30 days, reaching 4.7% after 90 days. In cement with a 0.8‰ compounded liquid grinding aid hexavalent chromium reducing agent dosage, the 80μm particle size sieve residue increased from 4.4% after 1 day to 5.9% after 30 days, reaching 8.2% after 90 days. This indicates that the liquid grinding aid hexavalent chromium reducing agent synthesized in this invention has good high-temperature resistance and long-term stability.

[0051] While specific embodiments of the present invention have been described in detail, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this patent.

Claims

1. A method for synthesizing a liquid grinding aid type cement hexavalent chromium reducing agent, characterized in that, include: A suspension is formed by heating an aqueous solution containing an organic acid and a reduced metal oxide; the organic acid includes one or a mixture of two or more of acetic acid, oleic acid, and lauric acid. Alkylamine was added to the suspension under continuous heating to react and form a gel-like liquid. The heating temperature range during the synthesis was 80–120 °C, and the holding time after adding the amine to the suspension was 30–240 min. The liquid grinding aid cement hexavalent chromium reducing agent is obtained by removing insoluble substances from the colloidal liquid.

2. The method for synthesizing the liquid grinding aid type cement hexavalent chromium reducing agent according to claim 1, characterized in that, The reduced metal oxide is at least one of stannous oxide, cuprous oxide, ferrous oxide, manganese oxide, and antimony oxide.

3. The method for synthesizing the liquid grinding aid cement hexavalent chromium reducing agent according to claim 1, characterized in that, The molar ratio of alcohol amines to organic acids is 1:(0.6 to 1.2).

4. A liquid grinding aid type cement hexavalent chromium reducing agent, characterized in that, The liquid grinding aid cement hexavalent chromium reducing agent is prepared by the synthesis method of the liquid grinding aid cement hexavalent chromium reducing agent according to any one of claims 1-3.

5. The liquid grinding aid cement hexavalent chromium reducing agent according to claim 4, characterized in that, The percentage content of reduced metal oxides in liquid grinding aid cement hexavalent chromium reducing agent is 9-20%.

6. The application of a liquid grinding aid type hexavalent chromium reducing agent in cement grinding, characterized in that, Before or during cement grinding, the liquid grinding aid type hexavalent chromium reducing agent of claim 4 is added to a mixture containing cement clinker, gypsum and cement admixtures, and then ground together to prepare cement.

7. The application of the liquid grinding aid type hexavalent chromium reducing agent for cement according to claim 6 in cement grinding, characterized in that, The amount of the liquid grinding aid cement hexavalent chromium reducing agent added is 0.1‰ to 0.6‰ of the cement clinker dosage.

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