Method for preparing magnesium oxysulfate cement from high-activity magnesium oxide

Abstract

The invention discloses a method for preparing magnesium oxysulfate cement by using high-activity magnesium oxide, and relates to a method for preparing the magnesium oxysulfate cement, which is characterized in that the hydration process of the high-activity magnesium oxide is regulated and controlled by adding a modifier, and the magnesium oxysulfate cement with good performance is prepared by controlling the feeding proportion of raw materials and process conditions. The invention aims to research and develop a preparation process of a green building material, and mainly aims to solve the problems of too short setting time, low mechanical strength, poorer water resistance and the like of magnesium oxysulfate cement prepared from high-activity magnesium oxide produced by new technologies such as flash light burning and the like due to too high content of the active magnesium oxide. The development of the high-activity magnesium oxide for preparing the environment-friendly magnesium oxysulfate cement is beneficial to expanding the wide application of the high-activity magnesium oxide, further promotes the popularization of a new technology for obtaining magnesium oxide such as flash light burning and the like, and provides a necessary technical support for energy conservation and carbon reduction of an industrial chain.

Description

Technical Field

[0001] This invention relates to a method for preparing magnesium oxysulfate cement, specifically a method for preparing magnesium oxysulfate cement using highly active magnesium oxide. Background Technology

[0002] Magnesium cement, also known as magnesium cement, is a type of air-hardening cementitious material produced by reacting active magnesium materials (such as active magnesium oxide) with various magnesium salt solutions. Compared to traditional silicate cement, magnesium cement has several unique advantages, such as rapid hardening and early strength development, short setting time, and rapid strength growth. Some magnesium cement products can even achieve a higher final strength than ordinary cement. Magnesium cement also possesses excellent impermeability, wear resistance, and resistance to brine corrosion, making it suitable for coastal and underground saline-alkali environments. Magnesium cement has good affinity with plant fibers and does not cause fiber degradation, making it an ideal matrix for manufacturing composite materials such as magnesium oxide boards and fireproof boards. The cured magnesium cement is weakly alkaline, exhibiting low corrosiveness to organic fillers. Its low-energy consumption and low-temperature curing characteristics during production further enhance its environmental potential. Notably, magnesium cement also possesses unique carbonization and curing capabilities, making it a highly promising new material for achieving carbon neutrality from a life-cycle perspective. Thanks to these properties, magnesium cement has been widely used in the production of building products such as fireproof boards and partition boards, as well as manhole covers and ventilation ducts for municipal engineering projects, and even in the carving and production of handicrafts.

[0003] Magnesium cement mainly includes three types: magnesium oxychloride cement, magnesium oxysulfide cement, and magnesium phosphate cement. Magnesium oxychloride cement was developed earlier, but long-term research and application have revealed its drawbacks, including efflorescence and corrosion of reinforcing steel. Magnesium oxysulfide cement exhibits virtually no efflorescence or efflorescence, and due to the absence of halogens, it overcomes the corrosion problem of reinforcing steel. Furthermore, its water resistance is superior to magnesium oxychloride cement, and it is often considered an "improved" version of magnesium oxychloride cement. Magnesium phosphate cement, due to its rapid setting time, is suitable for some quick repair projects, but its production process faces disadvantages such as high phosphate costs and high energy consumption from the re-firing of magnesium oxide raw materials. Therefore, magnesium oxysulfide cement has received more attention in current research and application fields.

[0004] Magnesium oxysulfate cement is mainly produced through the reaction of active magnesium oxide, magnesium sulfate heptahydrate, and water. According to research reports, the strength of magnesium oxysulfate cement primarily depends on the density of its crystal structure. The strength phase that plays a major role in the mechanical strength of magnesium oxysulfate cement is the 5·1·7 phase, with the chemical composition 5Mg(OH)₂·MgSO₄·7H₂O. It is mainly formed through the hydration reaction of raw materials and possesses high strength and stability. The 5·1·7 phase consists of needle-like, rod-shaped crystals that are tightly packed, effectively filling the magnesium oxysulfate cement matrix, reducing its porosity, and effectively preventing water penetration. This gives it excellent mechanical strength, water resistance, and durability. Therefore, the key to improving the performance of magnesium oxysulfate cement is to promote the formation of the 5·1·7 phase by regulating the hydration reaction of raw materials and increasing its content in the cement.

[0005] The development focus of various industries in my country is concentrated on energy conservation, environmental protection, and green low-carbon development. In the construction sector, magnesium cement is considered an excellent alternative building material, which can reduce the carbon emissions associated with the use of traditional silicate cement to a certain extent. Furthermore, my country is rich in magnesium resources, with total reserves accounting for about one-third of the world's total, and the mineral products are of excellent quality, laying a solid foundation for the development and widespread application of magnesium cement in my country. Calcining magnesium ore in kilns is currently the main process for obtaining active magnesium oxide, but traditional processes such as reverberatory kilns and rotary kilns have drawbacks such as high energy consumption and heavy pollution. With increasing environmental pressure, traditional calcination equipment faces obsolescence, making transformation and upgrading inevitable. In recent years, new technologies, such as flash calcination, have become a research hotspot for the preparation of active magnesium oxide from calcined magnesium ore. This type of technology has higher thermal utilization and shorter operating time, thus significantly reducing overall energy consumption compared to traditional processes. However, the magnesium oxide products obtained through these new technologies have a very high activity content, which is highly unfavorable for the production of high-performance magnesium building materials.

[0006] Therefore, developing and utilizing this type of highly active magnesium oxide to prepare high-performance magnesium cement will effectively promote the widespread adoption of new magnesium ore calcination technologies. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing magnesium oxysulfate cement using highly reactive magnesium oxide. This method converts highly reactive magnesium oxide raw materials with magnesium sulfate heptahydrate into a high-value-added green magnesium building material product. A modifier is added to regulate the hydration process of the highly reactive magnesium oxide, inhibiting the formation of magnesium hydroxide. The mixture is then further mixed and reacted with a magnesium sulfate heptahydrate solution to form mortar. The mortar is poured into a mold, allowed to harden, demolded, and then cured to obtain the magnesium oxysulfate cement product. This method makes highly reactive magnesium oxide an excellent raw material for producing high-value-added chemical products, providing a superior method for the comprehensive utilization of highly reactive magnesium oxide.

[0008] The technical solution adopted in this invention is: A method for preparing magnesium oxysulfate cement using highly active magnesium oxide, the method comprising the following steps: First, weigh out the highly active magnesium oxide, magnesium sulfate heptahydrate, deionized water, and modifier according to the set molar ratio. Second, add the deionized water, modifier, and magnesium sulfate heptahydrate to the cement paste mixer in sequence and stir at room temperature until fully dissolved. Then add the highly active magnesium oxide. After the cement mortar is evenly mixed, pour it into a mold. Finally, shake to remove the gas from the cement mortar and let it stand to solidify. Demold the solidified cement and place it in a specific cultivation environment for 7-28 days to obtain magnesium oxysulfate cement.

[0009] The method for preparing magnesium oxysulfate cement using highly active magnesium oxide, wherein the content of active magnesium oxide in the highly active magnesium oxide is 78-92%; The method for preparing magnesium sulfate cement using highly active magnesium oxide is described above, wherein the molar ratio of active magnesium oxide to magnesium sulfate heptahydrate in the highly active magnesium oxide ranges from 6:1 to 9:1. The method for preparing magnesium sulfate-oxygenated cement using highly active magnesium oxide is described above, wherein the molar ratio of magnesium sulfate heptahydrate to deionized water is in the range of 1:7 to 1:10. The method for preparing magnesium oxysulfate cement using highly active magnesium oxide, wherein the modifier is ascorbic acid, sodium ascorbate, or a mixture of the two in any proportion; The method for preparing magnesium oxysulfate cement using highly active magnesium oxide, wherein the amount of modifier added is 1-5.5% of the mass of highly active magnesium oxide; The method for preparing magnesium oxysulfate cement using highly active magnesium oxide, wherein the specific cultivation environment refers to a curing temperature of 15-25℃ and a curing humidity of 45-65%.

[0010] Advantages and effects of the present invention: 1. This invention effectively utilizes highly active magnesium oxide to prepare magnesium oxysulfate cement, filling a gap in this field; 2. The magnesium oxysulfate cement product prepared by this invention has strong morphological plasticity, controllable setting time, and good mechanical strength. It has broad application prospects and has the potential to replace traditional magnesium oxychloride cement and magnesium oxysulfate cement. 3. The preparation process of this invention is simple, the preparation method is safe, energy consumption is low, and it is easy to achieve large-scale production; 4. This invention utilizes a method for preparing magnesium oxysulfate cement using highly active magnesium oxide, which expands the application scope of highly active magnesium oxide and brings new economic growth points. Attached Figure Description

[0011] Figure 1The image shows a SEM image of magnesium oxide cement prepared by magnesium oxide powder with an active content of 81% and the addition of 2 wt% ascorbic acid after 7 days of curing. Figure 2 The image shows a SEM image of magnesium oxide cement prepared by adding 2 wt% ascorbic acid to magnesium oxide powder with an active content of 81% after curing for 28 days. Figure 3 The image shows a SEM image of magnesium oxide cement prepared by adding 3 wt% sodium ascorbate to magnesium oxide powder with an active content of 81% after curing for 28 days. Figure 4 The image shows a SEM image of magnesium oxide cement prepared by adding 3 wt% sodium ascorbate to magnesium oxide powder with an active content of 85% after curing for 28 days. Figure 5 This invention compares the XRD test results of magnesium oxide cement prepared by adding 2 wt% ascorbic acid to magnesium oxide powder with an active content of 81% after curing for 7 days and 28 days. Figure 6 This invention compares the XRD test results of magnesium oxide cement prepared by adding 3 wt% sodium ascorbate to magnesium oxide powder with active contents of 81% and 85% after curing for 28 days. Figure 7 The following are diagrams showing the curing conditions of the prepared magnesium oxysulfate cement: (A) Magnesium oxysulfate cement cured for 7 days was prepared using magnesium oxide powder with an active content of 81% and 2 wt% ascorbic acid; (B) Magnesium oxysulfate cement cured for 28 days was prepared using magnesium oxide powder with an active content of 81% and 2 wt% ascorbic acid; (C) Magnesium oxysulfate cement cured for 28 days was prepared using magnesium oxide powder with an active content of 81% and 3 wt% sodium ascorbate; (D) Magnesium oxysulfate cement cured for 28 days was prepared using magnesium oxide powder with an active content of 85% and 3 wt% sodium ascorbate. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the embodiments. Example 1

[0013] This invention utilizes highly active magnesium oxide to prepare magnesium sulfate-magnesium cement. The method specifically includes the following steps: (1) Measure 162 mL of deionized water, the content of highly active magnesium oxide is tested to be 81%, weigh 400 g of highly active magnesium oxide powder, 246.4 g of magnesium sulfate heptahydrate, and 8 g of ascorbic acid; (2) Pour the deionized water into a clean cement mortar mixer, add the modifier and start stirring; (3) After the ascorbic acid is fully dissolved, add magnesium sulfate heptahydrate; (4) After the magnesium sulfate heptahydrate is completely dissolved and the temperature of the solution system is constant, add highly active magnesium oxide powder; (5) After stirring thoroughly for 4-5 min, pour the cement mortar into the mold and vibrate it; (6) After the gas in the mortar is fully vibrated out, scrape the surface of the cement mortar to be smooth, and then let it stand and wait for solidification; (7) Demold the solidified cement and place it in an environment with a curing temperature of 25 ℃ and a curing humidity of 50% for 7 days. The obtained magnesium oxysulfate cement has a 7-day compressive strength of 42.3 MPa and a flexural strength of 2.1 MPa. Example 2

[0014] This invention utilizes highly active magnesium oxide to prepare magnesium sulfate-oxygenated cement. The method specifically includes the following steps: (1) Measure 162 mL of deionized water, the content of highly active magnesium oxide is tested to be 81%, weigh 400 g of highly active magnesium oxide powder, 246.4 g of magnesium sulfate heptahydrate, and 8 g of ascorbic acid; (2) Pour the deionized water into a clean cement mortar mixer, add the modifier and start stirring; (3) After the ascorbic acid is fully dissolved, add magnesium sulfate heptahydrate; (4) After the magnesium sulfate heptahydrate is completely dissolved and the temperature of the solution system is constant, add highly active magnesium oxide powder; (5) After stirring thoroughly for 4-5 min, pour the cement mortar into the mold and vibrate it; (6) After the gas in the mortar is fully vibrated out, scrape the surface of the cement mortar to be smooth, and then let it stand and wait for solidification; (7) Demold the solidified cement and place it in an environment with a curing temperature of 25 ℃ and a curing humidity of 50% for 28 days. The obtained magnesium oxysulfate cement has a 28-day compressive strength of 53.9 MPa and a flexural strength of 3.2 MPa. Example 3

[0015] This invention utilizes highly active magnesium oxide to prepare magnesium sulfate-oxygenated cement. The method specifically includes the following steps: (1) Measure 162 mL of deionized water, the content of highly active magnesium oxide is tested to be 81%, weigh 400 g of highly active magnesium oxide powder, 246.4 g of magnesium sulfate heptahydrate, and 12 g of sodium ascorbate; (2) Pour the deionized water into a clean cement mortar mixer, add the modifier and start stirring; (3) After the sodium ascorbate is fully dissolved, add magnesium sulfate heptahydrate; (4) After the magnesium sulfate heptahydrate is completely dissolved and the temperature of the solution system is constant, add highly active magnesium oxide powder; (5) After stirring thoroughly for 4-5 min, pour the cement mortar into the mold and vibrate it; (6) After the gas in the mortar is fully vibrated out, scrape the surface of the cement mortar to be smooth, and then let it stand and wait for solidification; (7) Demold the cement after it has solidified and returned to room temperature, mark it and place it in an environment with a curing temperature of 25 ℃ and a curing humidity of 50% for 28 days. The obtained magnesium oxysulfate cement has a 28-day compressive strength of 57.1 MPa and a flexural strength of 2.0 MPa. Example 4

[0016] This invention utilizes highly active magnesium oxide to prepare magnesium sulfate-oxygenated cement. The method specifically includes the following steps: (1) Measure 162 mL of deionized water, the highly active magnesium oxide is tested to have an active magnesium oxide content of 85%, weigh 400 g of highly active magnesium oxide powder, 246.4 g of magnesium sulfate heptahydrate, and 12 g of sodium ascorbate; (2) Pour the deionized water into a clean cement mortar mixer, add the modifier and start stirring; (3) After the sodium ascorbate is fully dissolved, add magnesium sulfate heptahydrate; (4) After the magnesium sulfate heptahydrate is completely dissolved and the solution system temperature is constant, add the highly active magnesium oxide powder; (5) After stirring thoroughly for 4-5 min, pour the cement mortar into a mold and vibrate it; (6) After the gas in the mortar is fully vibrated out, scrape the surface of the cement mortar until smooth, and then let it stand and wait for solidification; (7) Demold the cement after it has solidified and returned to room temperature, mark it, and place it in an environment with a curing temperature of 25 ℃ and a curing humidity of 50% for 28 days. The obtained magnesium oxysulfate cement has a 28-day compressive strength of 49.3 MPa and a flexural strength of 1.4 MPa.

Claims

1. A method for preparing magnesium oxysulfate cement using highly active magnesium oxide, characterized by, The method comprises the following steps: First, the high-activity magnesium oxide, magnesium sulfate heptahydrate, deionized water and modifier are weighed according to the set molar ratio; second, the deionized water, the modifier, the magnesium sulfate heptahydrate are sequentially added into a cement paste stirrer and stirred at normal temperature, and then the high-activity magnesium oxide is added after being fully dissolved; after the cement mortar is uniformly mixed, it is poured into a mold; finally, the cement mortar is shaken to remove the gas, and then is left to solidify; after the solidification, the cement is demolded and placed in a specific culture environment for curing for 7-28 days to obtain the magnesium oxysulfate cement.

2. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The content of the active magnesium oxide in the high-activity magnesium oxide is 78-92%.

3. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The molar ratio of the active magnesium oxide to the magnesium sulfate heptahydrate in the high-activity magnesium oxide ranges from 6:1 to 9:

1.

4. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The mass ratio of the magnesium sulfate heptahydrate to the deionized water ranges from 1:7 to 1:

10.

5. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The modifier is ascorbic acid, sodium ascorbate or a mixture of the two in a certain proportion.

6. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The amount of the modifier added is 1-5.5% of the mass of the high-activity magnesium oxide.

7. The method for preparing magnesium oxysulfate cement using high-activity magnesium oxide according to claim 1, characterized in that, The specific culture environment refers to a culture environment with a curing temperature of 15-25 DEG C and a curing humidity of 45-65%.

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