Method for preparing modified regenerated magnesium oxide and magnesium phosphate cement by using magnesium-containing waste

Abstract

The present invention relates to the technology of preparing building materials, aiming to provide a method for preparing modified regenerated magnesium oxide and magnesium phosphate cement by using magnesium-containing waste materials. The method includes: screening, cleaning, crushing, grinding and sieving the magnesium-containing waste materials to make waste powder; mixing a silane coupling agent with an ethanol solvent and hydrolyzing it under heating and stirring conditions; adding the waste powder to the hydrolyzed mixed solution and continuously stirring for a modification reaction; filtering, washing with ethanol and drying the reaction suspension to obtain modified regenerated magnesium oxide. By adding active excitation materials such as silica sol, the present invention improves the reaction activity of the regenerated magnesium oxide, making the final casting structure more dense when further preparing magnesium phosphate cement, thereby improving the quality of the final product; using a silane coupling agent to perform surface modification on the regenerated magnesium oxide can accelerate the curing speed and improve the early strength and physical properties of the product; the product has the characteristics of low cost, fast strength development and excellent bonding performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of building material preparation, and specifically relates to a method for preparing modified recycled magnesium oxide and magnesium phosphate cement by using magnesium-containing waste. Background Art

[0002] Phosphate cement is particularly suitable for the emergency repair of concrete structures in key infrastructures such as highways, airport runways, and bridges due to its excellent rapid hardening and early strength development characteristics.

[0003] Magnesium phosphate cement is usually composed of dead-burned magnesia, phosphate, and a retarder. Among them, the mass ratio of dead-burned magnesia exceeds 60%, which is a key component determining the performance of magnesium phosphate cement. However, since dead-burned magnesia is mainly obtained by high-temperature calcination of magnesite, in recent years, with the limited exploitation of magnesite resources and the continuous increase in its price, the production cost of magnesium phosphate cement has increased significantly, which has greatly hindered the large-scale application and promotion of this material.

[0004] Due to the operation requirements of industrial boilers in various industries, a large amount of waste magnesium refractory bricks are generated during the equipment maintenance process every year. If the magnesium oxide in these wastes can be properly treated and modified to meet the preparation standards of magnesium phosphate cement, it will not only significantly reduce the cost of magnesium phosphate cement, but also promote the recycling of waste magnesium resources, reduce the dependence on primary magnesite resources, and be beneficial to environmental protection. Therefore, researchers have proposed to develop low-cost magnesium phosphate cement based on renewable resources to meet the application and development needs of rapid repair materials. For example, patent publication documents CN202410898446.4, CN201811449709.4, and CN201711089392.3 respectively introduce methods for extracting magnesium oxide or heavy magnesium oxide from boron mud to replace traditional dead-burned magnesia, aiming to reduce production costs. However, the products prepared by these methods are lacking in mechanical properties compared with ordinary phosphate cement. In addition, patent CN201810107470.6 proposes to use dolomite instead of magnesite to produce dead-burned magnesia and add a silicon-containing component to reduce the adverse effects inside dolomite, but this scheme has not been widely applied due to performance considerations.

[0005] Some other patent publication documents such as CN101891489A, CN102910924A, CN105908255A, and CN102069036A respectively describe the recycling of waste magnesium bricks and the technology for preparing magnesium oxide whiskers. However, due to the long-term use of waste bricks in a high-temperature environment, the crystal grain size and microscopic morphology of their magnesium oxide are significantly different from those of traditional dead-burned magnesia, resulting in that the recycled products will directly affect the hydration reaction and strength characteristics of magnesium phosphate cement, especially the early strength, during further application.

[0006] In view of this, it is particularly important to research and develop a new and efficient processing technology to improve the performance of magnesia refractory brick recycled powder and ensure its effective application in magnesium phosphate cement. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method for preparing modified regenerated magnesium oxide and magnesium phosphate cement using magnesium-containing waste.

[0008] To solve the technical problem, the solution of the present invention is:

[0009] Provided is a method for preparing modified regenerated magnesium oxide using magnesium-containing waste, comprising:

[0010] (1) The magnesium-containing waste is screened, cleaned, crushed, ground and sieved to produce waste powder with a specific surface area of ​​200 to 300 m2 / kg and a MgO content of not less than 80%;

[0011] (2) Mixing a silane coupling agent with an appropriate amount of ethanol solvent and hydrolyzing the mixture under heating and stirring conditions; the mass ratio of the silane coupling agent to MgO in the waste powder is 3%;

[0012] (3) Adding the waste powder to the mixed solution obtained by hydrolysis and continuously stirring to carry out the modification reaction; the suspension after the reaction is filtered, washed with ethanol and dried to obtain modified regenerated magnesium oxide.

[0013] As a preferred embodiment of the present invention, the magnesium-containing waste is any one or more of recycled magnesia refractory bricks, magnesium-containing alloy waste or magnesium-containing mixed brick slag; the silane coupling agent is any one of KH550, A-187 or A-1100.

[0014] As a preferred embodiment of the present invention, the heating condition is a 60° C. water bath environment, the stirring speed is 200-350 r / min, the stirring time is 12 h, and the modification reaction time is 30 minutes.

[0015] The present invention further provides a method for preparing magnesium phosphate cement using the modified regenerated magnesium oxide prepared by the aforementioned method, comprising:

[0016] (1) Weigh the powdered raw materials by mass: 40-60 parts of modified regenerated magnesium oxide; 23-30 parts of composite phosphate; 1-5 parts of active stimulating material; 3-5 parts of retarder; 10-20 parts of mineral admixture;

[0017] (2) Mix all the raw materials evenly and package them for later use, or mix them evenly at the construction site and use them directly for pouring.

[0018] As a preferred embodiment of the present invention, the composite phosphate is a mixture of ammonium dihydrogen phosphate and at least one of potassium dihydrogen phosphate or sodium dihydrogen phosphate, and the mass ratio of ammonium dihydrogen phosphate is 40% - 80%.

[0019] As a preferred embodiment of the present invention, the activity excitation material is at least one of silica sol, nano calcium carbonate or aluminum sol.

[0020] As a preferred embodiment of the present invention, the retarder is at least one of boric acid, triethanolamine, sodium acetate or sodium tripolyphosphate.

[0021] As a preferred embodiment of the present invention, the mineral admixture is at least one of fly ash, silica fume or silica powder.

[0022] The present invention also provides a method for using the magnesium phosphate cement prepared by the foregoing method, including:

[0023] (1) Take out the finished powder from the package, or weigh each raw material and mix them on-site at the construction site to obtain a uniform powder;

[0024] (2) Gradually add water to the uniformly mixed powder, and the mass ratio of water to powder is 0.12 - 0.18:1; after mixing to form a uniform slurry, use it for on-site casting, and after vibrating and compacting, cover and maintain moisture.

[0025] As a preferred embodiment of the present invention, a low-speed mixer is used for mixing operation, and the rotation speed is controlled at 30 - 60 r / min.

[0026] When mixing the slurry on-site, there is an opportunity for reaction between the recycled magnesium oxide and the hydrolysis products of phosphate, and struvite, which is the main source of the early strength of magnesium phosphate cement, is quickly formed. The activity excitation material is used to provide reaction sites and increase the early strength of magnesium phosphate cement. The retarder is used to control the setting time of each material; the mineral admixture is used as a filler to improve the workability (such as fluidity) and volume stability of magnesium phosphate cement. Covering and maintaining moisture can accelerate the development of early strength.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. By adding activity excitation materials such as silica sol, the reaction activity of the recycled magnesium oxide is improved in the present invention, making the final casting structure more dense when further preparing magnesium phosphate cement, thereby improving the quality of the final product.

[0029] 2. The present invention uses a silane coupling agent to modify the surface of regenerated magnesium oxide. The functional groups (such as amino groups) in the silane coupling agent react chemically with the hydroxyl groups or other active sites on the surface of magnesium oxide, introducing a large number of new reaction sites. This increases the reaction opportunities between the regenerated magnesium oxide and the hydrolysis products of phosphate, promoting the rapid formation of struvite (the main source of the early strength of magnesium phosphate cement). It not only speeds up the curing speed but also significantly improves the early strength and physical properties of the product.

[0030] 3. The present invention extracts magnesium oxide from waste magnesium bricks, realizing the recycling of resources and meeting environmental protection requirements. The performance of the prepared magnesium phosphate cement product is close to that of the magnesium phosphate cement material made from traditional dead-burned magnesium oxide, but the cost is reduced by 10 - 40%, and it has great application prospects in rapid repair projects.

[0031] 4. The magnesium phosphate cement product of the present invention has the characteristics of low cost, fast strength development, and excellent bonding performance, which can significantly shorten the construction period and reduce the maintenance cost, and is suitable for the rapid repair of infrastructure such as roads and bridges. Specific Embodiments

[0032] The present invention will be further described in detail below in conjunction with specific embodiments for a clearer understanding of the present invention, but it does not constitute a limitation to the present invention.

[0033] 1. The method for preparing modified regenerated magnesium oxide using magnesium-containing waste provided by the present invention includes:

[0034] (1) Screening, cleaning, crushing, grinding, and sieving the magnesium-containing waste to make waste powder with a specific surface area of 200 - 300 m² / kg and an MgO content of not less than 80%; the magnesium-containing waste is any one or more of recycled magnesia refractory bricks, magnesium-containing alloy waste, or magnesium-containing mixed brick waste residues;

[0035] (2) Mixing the silane coupling agent with an appropriate amount of ethanol solvent and hydrolyzing it under heating and stirring conditions; the silane coupling agent is any one of KH550, A - 187, or A - 1100, and the mass ratio of the silane coupling agent to MgO in the waste powder is 3%; the heating condition is a water bath environment at 60°C; the stirring speed is 200 - 350 r / min, and the stirring time is 12 h;

[0036] (3) Adding the waste powder to the mixed solution obtained by hydrolysis and continuously stirring for the modification reaction; the time of the modification reaction is 30 minutes. The reaction suspension is filtered, washed with ethanol, and dried to obtain modified regenerated magnesium oxide.

[0037] Using the prepared modified regenerated magnesium oxide, magnesium phosphate cement can be further prepared at low cost, and this preparation method includes:

[0038] (1) Weigh each raw material in powder form by mass parts: 40 - 60 parts of modified recycled magnesium oxide; 23 - 30 parts of composite phosphate; 1 - 5 parts of activity excitation material; 3 - 5 parts of retarder; 10 - 20 parts of mineral admixture;

[0039] The composite phosphate is a mixture of at least one of ammonium dihydrogen phosphate and potassium dihydrogen phosphate or sodium dihydrogen phosphate, and the mass proportion of ammonium dihydrogen phosphate is 40% - 80%. The activity excitation material is at least one of silica sol, nano calcium carbonate or aluminum sol, and the aluminum sol and silica sol can be commercially available reagent products with solid content between 20% - 30%. The retarder is at least one of boric acid, triethanolamine, sodium acetate or sodium tripolyphosphate, and the mineral admixture is at least one of fly ash, silica fume or silica powder.

[0040] (2) Mix all the raw materials evenly and then pack for standby, or mix evenly at the construction site and directly use for pouring.

[0041] Furthermore, the magnesium phosphate cement prepared by the above method is used through on-site pouring. The specific method includes:

[0042] (1) Take out the finished powder from the package, or weigh each raw material and mix them evenly at the construction site to obtain uniform powder;

[0043] (2) Gradually add water to the evenly mixed powder, and the mass ratio of water to powder is 0.12 - 0.18:1; Use a low-speed mixer for mixing operation, and the rotation speed is controlled at 30 - 60 r / min; After forming a uniform slurry, use it for on-site pouring, and cover and maintain moisture after vibrating and compacting.

[0044] 2. According to the above description, the present invention provides 5 specific embodiments; The operation steps of each embodiment are the same, and the optional items, specific parameter situations of the raw material ratio, preparation process and usage method in each embodiment are shown in Table 1 and Table 2.

[0045] Table 1

[0046] ;

[0047] Table 2

[0048] 。

[0049] 3. Comparative Example 1

[0050] Directly use the waste powder that has been screened, cleaned, crushed, ground and sieved but not modified in Example 1 of the present invention to replace the modified recycled magnesium oxide; The specific selection of other optional items and parameters in the preparation and usage process is the same as that in Example 5.

[0051] 4. Product Performance Testing and Comparison

[0052] The following operations were performed on the dry powders prepared in Example 1, Example 5, and Comparative Example 1 respectively: The dry powder was added to a low-speed mixer and mixed evenly, and water accounting for 0.15% of the dry powder mass was gradually added, and then mixed at a rotation speed of 50 r / min to form a uniform slurry. The slurry was poured into a test mold with dimensions of 40×40×160 mm, placed on a cement mortar vibrating table and vibrated for 1 min and then leveled, covered with polypropylene plastic wrap, and cured until the test age.

[0053] The cured specimens were tested to evaluate their influence on the performance of the repair material. The compressive strength test was carried out with reference to the standard GB-T17671-1999 "Test Method for Cement Mortar Strength", and the bond strength test was carried out with reference to JGJ70-2009 "Standard for Test Methods of Basic Properties of Building Mortars".

[0054] The test results show that:

[0055] For the sample of Example 1, the compressive strength reached 62.7 MPa at the age of 1 day; at the age of 28 days, the compressive strength increased to 77.6 MPa, and the bond strength reached 9.8 MPa.

[0056] For the sample of Example 5, the compressive strength reached 51.4 MPa at the age of 1 day; at the age of 28 days, the compressive strength increased to 66.8 MPa, and the bond strength reached 8.2 MPa.

[0057] For the sample of Comparative Example 1, the compressive strength reached 26.5 MPa at the age of 1 day; at the age of 28 days, the compressive strength increased to 41.6 MPa, and the bond strength reached 4.9 MPa.

[0058] It can be seen from this that compared with the magnesium phosphate cement prepared directly using unmodified magnesium oxide waste powder, the modification treatment of the present invention has a significant effect on improving both the early strength and the long-term strength.

[0059] The protection scope of the present invention is not limited to the above embodiments. Obviously, those skilled in the art can make various changes and deformations to the present invention without departing from the scope and spirit of the present invention. If these changes and deformations fall within the scope of the claims of the present invention and their equivalent technologies, the intention of the present invention also includes these changes and deformations.

Claims

1. A method for preparing magnesium phosphate cement by using modified regenerated magnesium oxide, characterized in that, Comprising: Weigh each raw material in powder form by mass parts: 40 - 60 parts of modified recycled magnesium oxide; 23 - 30 parts of composite phosphate; 1 - 5 parts of activity excitation material; 3 - 5 parts of retarder; 10 - 20 parts of mineral admixture; After mixing each raw material evenly, pack it for standby, or mix it evenly at the construction site and directly use it for pouring; The said modified recycled magnesium oxide is obtained by the following method: (1) Screen, clean, crush, grind, and sieve the magnesium - containing waste to make a waste powder with a specific surface area of 200 - 300 m² / kg and an MgO content of not less than 80%; (2) Mix the silane coupling agent with an appropriate amount of ethanol solvent and hydrolyze it under heating and stirring conditions; The mass ratio of the used silane coupling agent to MgO in the waste powder is 3%; (3) Add the waste powder to the mixed solution obtained by hydrolysis, and continuously stir for the modification reaction; The suspension after the reaction is filtered, washed with ethanol, and dried to obtain the modified recycled magnesium oxide; The said magnesium - containing waste is any one or more of recycled magnesia refractory bricks, magnesium - containing alloy waste, or magnesium - containing mixed brick waste residues; The said silane coupling agent is KH550 or A - 187; The said composite phosphate is a mixture of at least one of ammonium dihydrogen phosphate and potassium dihydrogen phosphate or sodium dihydrogen phosphate, and the mass proportion of ammonium dihydrogen phosphate is 40% - 80%.

2. The method according to claim 1, wherein The said heating condition is a water - bath environment at 60°C, the stirring speed is 200 - 350 r / min, and the stirring time is 12 h; The time of the modification reaction is 30 minutes.

3. The method according to claim 1, characterized in that The said activity excitation material is at least one of silica sol, nano - calcium carbonate, or aluminum sol.

4. The method according to claim 1, wherein The said retarder is at least one of boric acid, triethanolamine, sodium acetate, or sodium tripolyphosphate.

5. The method according to claim 1, characterized in that The said mineral admixture is at least one of fly ash, silica fume, or silica powder.

6. Method of using the magnesium phosphate cement obtained by the method described in any one of claims 1 to 5, characterized in that, Comprising: (1) Take out the finished powder from the package, or weigh each raw material and mix it evenly at the construction site to obtain a uniform powder; (2) Gradually add water to the evenly - mixed powder, and the mass ratio of water to powder is 0.12 - 0.18︰1; After mixing to form a uniform slurry, use it for on - site pouring, and after vibrating and compacting, cover it and maintain moisture for curing.

7. The method according to claim 6, characterized in that Use a low - speed mixer for mixing operation, and control the rotation speed at 30 - 60 r / min.