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

Abstract

The invention relates to a building material preparation technology, and aims to provide a method for preparing modified regenerated magnesium oxide and magnesium phosphate cement from magnesium-containing waste. Comprising the following steps: screening, cleaning, crushing, grinding and screening the magnesium-containing waste to prepare waste powder; the preparation method comprises the following steps: mixing a silane coupling agent with an ethanol solvent, and hydrolyzing under heating and stirring conditions; adding the waste powder into the hydrolysis mixed solution, and continuously stirring to carry out modification reaction; and filtering the reacted suspension, washing with ethanol, and drying to obtain the modified regenerated magnesium oxide. By adding active excitation materials such as silica sol, the reaction activity of the regenerated magnesium oxide is improved, so that the final pouring structure is denser when the magnesium phosphate cement is further prepared, and the quality of the final product is improved; the silane coupling agent is used for performing surface modification on the regenerated magnesium oxide, so that the curing speed can be increased, and the early strength and physical properties of the product are improved; the product has the characteristics of low cost, fast strength development and excellent bonding performance.

Description

Technical Field

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

[0002] Phosphate cement, with its excellent rapid hardening and early strength development characteristics, is particularly suitable for emergency repairs of concrete structures in critical infrastructure such as highways, airport runways and bridges.

[0003] Magnesium phosphate cement is usually composed of dead-burned magnesium oxide, phosphate and retarder, of which dead-burned magnesium oxide accounts for more than 60% by weight and is the key component that determines the performance of magnesium phosphate cement. However, since dead-burned magnesium oxide is mainly obtained by high-temperature calcination of magnesite, the production cost of magnesium phosphate cement has increased significantly in recent years due to the limited mining of magnesite resources and the continuous rise in its price, which has largely hindered the large-scale application and promotion of this material.

[0004] Due to the need for industrial boiler operation, various industries will produce a large amount of waste magnesium refractory bricks during equipment maintenance every year. If the magnesium oxide in these waste materials can be properly treated and modified to meet the preparation standards of magnesium phosphate cement, it can not only significantly reduce the cost of magnesium phosphate cement, but also promote the recycling of waste magnesium resources, reduce dependence on native magnesite resources, and be beneficial to environmental protection. Therefore, researchers 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 publications CN202410898446.4, CN201811449709.4 and CN201711089392.3 respectively introduce methods of using boron mud to extract magnesium oxide or heavy magnesium oxide to replace traditional heavy-burned magnesium oxide, aiming to reduce production costs. However, the products prepared by these methods are relatively lacking in mechanical properties compared to ordinary phosphate cement. In addition, patent CN201810107470.6 proposes using dolomite instead of magnesite to generate dead-burned magnesium oxide, and reducing the adverse effects inside the dolomite by adding silicon-containing components, but this solution has not been widely used due to performance considerations.

[0005] Some other patent publications such as CN101891489A, CN102910924A, CN105908255A and CN102069036A respectively describe the recycling of waste magnesia bricks and the technology of preparing magnesium oxide whiskers. However, due to the long-term use of waste bricks in high temperature environments, the particle size and microscopic morphology of magnesium oxide crystals are significantly different from those of traditional dead-burned magnesium oxide, resulting in the recycled products directly affecting the hydration reaction and strength characteristics of magnesium phosphate cement, especially the early strength, when further applied.

[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: Provided is a method for preparing modified regenerated magnesium oxide using magnesium-containing waste, comprising: (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%; (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%; (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.

[0009] 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.

[0010] 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.

[0011] The present invention further provides a method for preparing magnesium phosphate cement using the modified regenerated magnesium oxide prepared by the aforementioned method, comprising: (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; (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.

[0012] 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 proportion of ammonium dihydrogen phosphate is 40% to 80%.

[0013] As a preferred embodiment of the present invention, the active stimulating material is at least one of silica sol, nano calcium carbonate or aluminum sol.

[0014] As a preferred embodiment of the present invention, the retarder is at least one of boric acid, triethanolamine, sodium acetate or sodium tripolyphosphate.

[0015] As a preferred embodiment of the present invention, the mineral admixture is at least one of fly ash, silica fume or silica powder.

[0016] The present invention also provides a method for using the magnesium phosphate cement prepared by the above method, comprising: (1) Take out the finished powder from the package, or weigh the raw materials and mix them at the construction site to obtain a uniform powder; (2) Gradually add water to the uniformly mixed powder, with the mass ratio of water to powder being 0.12 to 0.18:1; after mixing to form a uniform slurry, use it for on-site pouring, vibrate it to make it dense, and then cover it and maintain moisture retention.

[0017] As a preferred embodiment of the present invention, a low-speed mixer is used for mixing, and the rotation speed is controlled at 30 to 60 r / min.

[0018] When mixing the slurry on site, the regenerated magnesium oxide reacts with the phosphate hydrolysis products to quickly form struvite, which is the main source of early strength of magnesium phosphate cement. Active stimulating materials are used to provide reaction sites to increase the early strength of magnesium phosphate cement. Retarder is used to control the setting time of each material; mineral admixture is used as a filler to improve the workability (such as fluidity) and volume stability of magnesium phosphate cement. Covering and moisturizing curing can accelerate the development of early strength.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention improves the reactivity of regenerated magnesium oxide by adding active stimulating materials such as silica sol, so that the final casting structure is more compact when magnesium phosphate cement is further prepared, thereby improving the quality of the final product.

[0020] 2. The present invention uses a silane coupling agent to modify the surface of the 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 the magnesium oxide, introducing a large number of new reaction sites. This increases the reaction opportunities between the regenerated magnesium oxide and the phosphate hydrolysis products, and promotes the rapid formation of struvite (the main source of early strength of magnesium phosphate cement). Not only does it speed up the curing speed, but it also greatly improves the early strength and physical properties of the product.

[0021] 3. The present invention uses waste magnesium bricks to extract magnesium oxide, realizes the recycling of resources, and meets environmental protection requirements. The performance of the prepared magnesium phosphate cement product is close to that of the traditional magnesium phosphate cement material of heavy-burned magnesium oxide, but the cost is reduced by 10-40%, and the application prospect in rapid repair engineering is promising.

[0022] 4. The magnesium phosphate cement product of the present invention has the characteristics of low cost, rapid strength development, excellent bonding performance, etc. It can significantly shorten the construction period and reduce maintenance costs, and is suitable for the rapid repair of infrastructure such as roads and bridges. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with specific implementation modes to facilitate a clearer understanding of the present invention, but it does not constitute a limitation of the present invention.

[0024] 1. The method for preparing modified regenerated magnesium oxide using magnesium-containing waste provided by the present invention comprises: (1) The magnesium-containing waste is screened, cleaned, crushed, ground and sieved to prepare waste powder with a specific surface area of ​​200 to 300 m2 / kg and a 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 slag; (2) mixing a silane coupling agent with an appropriate amount of ethanol solvent and hydrolyzing the mixture 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 the MgO in the waste powder is 3%; the heating condition is a 60° C. water bath environment; the stirring speed is 200 to 350 r / min, and the stirring time is 12 h; (3) Add the waste powder to the mixed solution obtained by hydrolysis and continue stirring to carry out the modification reaction; the modification reaction time is 30 minutes. The suspension after the reaction is filtered, washed with ethanol and dried to obtain modified regenerated magnesium oxide.

[0025] The prepared modified regenerated magnesium oxide can be used to further prepare magnesium phosphate cement at low cost. The preparation method includes: (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; 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 proportion of ammonium dihydrogen phosphate is 40% to 80%. The active excitation material is at least one of silica sol, nano calcium carbonate or aluminum sol, and the aluminum sol and silica sol can be selected from commercially available reagents with a solid content between 20% and 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 ash or silicon micropowder.

[0026] (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.

[0027] Furthermore, the magnesium phosphate cement prepared by the above method is used by on-site pouring, and the specific method includes: (1) Take out the finished powder from the package, or weigh the raw materials and mix them at the construction site to obtain a uniform powder; (2) Gradually add water to the uniformly mixed powder, with the mass ratio of water to powder being 0.12-0.18:1; use a low-speed mixer for mixing, with the speed controlled at 30-60 r / min; after forming a uniform slurry, use it for on-site pouring, vibrate it to make it dense, and then cover it and maintain moisture retention.

[0028] 2. According to the above description, the present invention provides 5 specific embodiments; the operating steps of each embodiment are consistent, and the raw material ratios, preparation processes, optional items, and specific parameters of the methods of use in each embodiment are shown in Tables 1 and 2.

[0029] Table 1

[0030] ;

[0031] Table 2

[0032] .

[0033] 3. Comparative Example 1 The waste powder that has been screened, cleaned, crushed, ground, and sieved but not modified in Example 1 of the present invention is directly used to replace the modified regenerated magnesium oxide; the specific selection of options and parameters in other preparation and use processes remains consistent with Example 5.

[0034] 4. Product performance testing and comparison The dry powders prepared in Examples 1, 5 and Comparative Example 1 were respectively subjected to the following operations: the dry powders were added to a low-speed mixer and mixed evenly, water accounting for 0.15 of the dry powder mass ratio was gradually added, and a uniform slurry was formed at a speed of 50 r / min. The slurry was poured into a test mold with a size of 40×40×160 mm, placed on a cement mortar vibration table and vibrated for 1 min, then smoothed, covered with polypropylene plastic wrap, and cured to the test age.

[0035] The samples after curing were tested to evaluate their impact on the performance of the repair materials. The compressive strength test was conducted in accordance with the standard GB-T17671-1999 "Test Method for Cement Mortar Strength", and the bonding strength test was conducted in accordance with the standard JGJ70-2009 "Test Method Standard for Basic Performance of Building Mortar".

[0036] The test results show that: The compressive strength of the sample of Example 1 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 bonding strength reached 9.8 MPa.

[0037] The compressive strength of the sample of Example 5 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 bonding strength reached 8.2 MPa.

[0038] The compressive strength of the sample of Comparative Example 1 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 bonding strength reached 4.9 MPa.

[0039] It can be seen from this that compared with magnesium phosphate cement prepared directly using unmodified magnesium oxide-containing waste powder, the modification treatment of the present invention has a significant effect on improving both early strength and long-term strength.

[0040] The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims

1. A method for preparing modified regenerated magnesium oxide using magnesium-containing waste, characterized in that: include: (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%; (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%; (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.

2. The method according to claim 1, characterized in that: 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.

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

4. A method for preparing magnesium phosphate cement using modified regenerated magnesium oxide prepared by the method described in any one of claims 1 to 3, characterized in that: include: (1) Weigh the powdered raw materials by mass: 40-60 parts of modified regenerated magnesium oxide; 23-30 parts of composite phosphate; 1 to 5 parts of active stimulating material; 3 to 5 parts of retarder; 10 to 20 parts of mineral admixture; (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.

5. The method according to claim 4, characterized in that 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 proportion of ammonium dihydrogen phosphate is 40% to 80%.

6. The method according to claim 4, characterized in that The active stimulating material is at least one of silica sol, nano calcium carbonate or aluminum sol.

7. The method according to claim 4, characterized in that The retarder is at least one of boric acid, triethanolamine, sodium acetate or sodium tripolyphosphate.

8. The method according to claim 4, characterized in that The mineral admixture is at least one of fly ash, silica fume or silica powder.

9. A method for using the magnesium phosphate cement prepared by the method of claim 4, characterized in that: include: (1) Take out the finished powder from the package, or weigh the raw materials and mix them at the construction site to obtain a uniform powder; (2) Gradually add water to the uniformly mixed powder, with the mass ratio of water to powder being 0.12 to 0.18:1; after mixing to form a uniform slurry, use it for on-site pouring, vibrate it to make it dense, and then cover it and maintain moisture retention.

10. The method according to claim 9, characterized in that Use a low-speed mixer for mixing operations, and control the speed at 30-60r / min.