Mg-sulfate-oxygen gel material, its preparation method and application

Abstract

The application discloses a magnesium oxysulfate cementing material and a preparation method and application thereof. The preparation method comprises the following steps: calcining nesquehonite and bischofite at 600-850 DEG C for 0.5-3 h by one step to prepare magnesium oxide; and uniformly mixing the magnesium oxide with magnesium sulfate, and then performing mold curing at room temperature to prepare the magnesium oxysulfate cementing material. Through the synergistic effect of the bischofite and the nesquehonite, the magnesium oxide can be obtained by low-temperature calcining the nesquehonite, the magnesium oxysulfate cementing material prepared from the magnesium oxide has high strength and high water resistance, and the magnesium oxysulfate cementing material does not contain chloride ions, is not corrosive to metals, and can be used in an environment in contact with metals, and has a long service life.

Description

Technical Field

[0001] This invention belongs to the field of mineral resource processing technology, specifically relating to a magnesium oxysulfate cementitious material, its preparation method, and its application. Background Technology

[0002] The reactivity of magnesium oxide (MgO) largely depends on the calcination conditions. In most production processes, the preparation temperature of magnesium oxide is no lower than 800°C, and the processing time exceeds 2 hours to ensure complete decomposition of magnesite, resulting in low reactivity of magnesium oxide. If the decomposition is incomplete, the amorphous magnesium carbonate in it will cause the prepared magnesium oxysulfate cementitious material to react too quickly, resulting in poor mechanical properties.

[0003] Existing research on technologies to promote the calcination of magnesite mainly focuses on the structural optimization of the calcination process and scheme, such as improving the furnace body, improving heating methods, and adding mechanical processing procedures. However, the above methods have limited effect on promoting the decomposition of magnesite and cannot significantly reduce its decomposition temperature. There is also very little research on the co-calcination of minerals.

[0004] Current research reports the preparation of high-purity magnesium oxide using magnesite mixed with magnesium chloride through roasting. The magnesium chloride permeates into the magnesite, acting as a barrier, effectively increasing the specific surface area of ​​the magnesite and lowering the roasting temperature, thus achieving energy conservation and emission reduction. However, this theory is not yet complete. Hydromagnesite has an even lower calcination temperature than magnesite, but research on it is currently scarce.

[0005] Moreover, the overall production cost of existing magnesium oxide cementitious materials has increased due to the rising price of raw material magnesium oxide, so a method to reduce production costs is needed. Summary of the Invention

[0006] The main objective of this invention is to provide a magnesium oxysulfate cementitious material, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0008] The first aspect of the present invention provides a method for preparing a magnesium oxysulfate cementitious material, comprising:

[0009] Magnesium oxide is obtained by calcining magnesite and magnesium chloride at 600-850 °C for 0.5-3 h in one step.

[0010] The magnesium oxide and magnesium sulfate are mixed evenly, and then cured in a mold at room temperature to obtain a magnesium sulfate-magnesium oxide cementitious material.

[0011] A second aspect of the present invention provides a magnesium oxysulfate cementitious material prepared by the above-described preparation method.

[0012] A third aspect of the present invention provides the application of the above method in the field of preparing magnesium oxysulfate cement.

[0013] A fourth aspect of the present invention provides a magnesium oxysulfate cement comprising the aforementioned magnesium oxysulfate cementitious material.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects:

[0015] (1) In the preparation method provided by the present invention, by changing the decomposition process, under the synergistic effect of magnesia hydrate and magnesite, the existing decomposition temperature is reduced by about 100 °C while ensuring the complete decomposition of magnesite, which can produce more active MgO and effectively reduce energy consumption and CO2 generated during the production process; and the hydrogen chloride produced by the decomposition of magnesium chloride provides an acidic atmosphere, which accelerates the decomposition rate of carbonates in magnesite; in addition, the solid decomposition products of magnesium chloride are magnesium oxide, which will not introduce new impurities.

[0016] (2) The magnesium oxysulfate cementitious material provided by the present invention has high strength and strong water resistance. Moreover, since it does not contain chloride ions, it does not corrode metals and can be used in environments where there is contact with metals. Its service life can reach 20 years.

[0017] (3) The magnesium oxide cementitious material prepared by magnesium oxide obtained by the present invention at a lower calcination temperature also has good mechanical properties, and its compressive strength is above 70 MPa after 27 days of continuous curing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the preparation process of magnesium oxide and magnesium oxysulfate cementitious materials in a typical embodiment of the present invention. Detailed Implementation

[0020] In view of the problems existing in the prior art, the inventors of this invention, through extensive and in-depth research, provide a magnesium oxysulfate cementitious material, its preparation method, and its application. Magnesium oxide is mainly prepared through the synergistic effect of magnesia-hydrate and magnesite, and then the magnesium oxide is mixed with magnesium sulfate to obtain the magnesium oxysulfate cementitious material.

[0021] The first aspect of the present invention provides a method for preparing a magnesium oxysulfate cementitious material, comprising:

[0022] Magnesium oxide is obtained by calcining magnesite and magnesium chloride at 600-850 °C for 0.5-3 h in one step.

[0023] The magnesium oxide and magnesium sulfate are mixed evenly, and then cured in a mold at room temperature to obtain a magnesium sulfate-magnesium oxide cementitious material.

[0024] In some embodiments, the method for preparing the magnesium oxide specifically includes: mixing a solution containing magnesia hydrate with magnesite, drying and crushing the mixture, and then calcining it in the aforementioned step to obtain the magnesium oxide.

[0025] Magnesium chloride hexahydrate, also known as magnesium chloride hexahydrate (MgCl2·6H2O), contains magnesium chloride in magnesium chloride hexahydrate, which accounts for 1 to 5 wt% of the mass of magnesite in this invention.

[0026] In some embodiments, the hydromagnesite is in powder form.

[0027] In some embodiments, the particle diameter of the hydromagnesite is 2 to 10 mm.

[0028] In some implementations, the particle diameter of the crushed mixture of magnesia-hydrate and magnesite is 2-5 mm.

[0029] Specifically, the reaction mechanism of low-temperature roasting of magnesium oxide from magnesite is as follows: During the initial decomposition of magnesite and magnesium chloride, a large amount of water vapor is generated, filling the furnace. Subsequently, MgCl2 and its hydrates decompose to produce HCl gas, which mixes with the water vapor. In a humid environment, HCl reacts with the water vapor to form an acidic atmosphere. HCl reacts with MgCO3, promoting the decomposition of MgCO3 to generate CO2 and MgCl2. MgCl2 then undergoes pyrolysis to generate MgO and HCl. This completes the reaction cycle until the MgCO3 in the calcining furnace is completely reacted. In this reaction process, MgCl2 acts as a catalyst.

[0030] In some embodiments, the magnesium oxide is in powder form, and the particle diameter includes: D 10 The diameter is 0.7~0.9 μm, D 50 The thickness is 2.9~3.3 μm and D 90 The thickness ranges from 9.4 to 10.8 μm.

[0031] In some embodiments, the magnesium oxide has a purity of 90% or higher.

[0032] In some embodiments, the activity of the magnesium oxide is greater than 78%.

[0033] The activity of magnesium oxide refers to the proportion of magnesium oxide that can participate in the hydration reaction. In this invention, the activity of magnesium oxide powder is tested by hydration. The specific test method is as follows: Weigh 2 g (accurate to 0.0001 g) of sample (W1), place it in a weighing bottle (40 mm × 25 mm) with known mass and constant weight, add 10 mL of distilled water, cover with a small gap (about 2 mm), and place it on a tray. Hydrate in an oven at 105 ℃ for 3 h, adjust the oven temperature to 150 ℃, dry for 3 h, remove and place in a desiccator to cool to room temperature. The weight is recorded as W2. Calculate the content of active MgO according to formula (1):

[0034]

[0035] In equation (1): W (MgO) W1 represents the content (%) of active MgO in the lightly calcined MgO powder; W2 represents the mass (g) of the lightly calcined MgO powder sample after hydration and drying.

[0036] In some embodiments, the molar ratio of magnesium oxide to magnesium sulfate is 6 to 8:1.

[0037] In some implementations, the maintenance period is 20-24 hours.

[0038] In some more specific embodiments, the preparation method of the magnesium oxysulfate cementitious material specifically includes the following steps:

[0039] (1) Dissolve magnesium chloride (magnesium chloride is about 1 to 5 wt% of the mass of magnesite) in water and mix it with magnesite powder;

[0040] (2) After mixing evenly, allow it to dry naturally or place it in an oven to accelerate drying. After drying, crush it.

[0041] (3) Place the magnesite in a crucible and then place it in a muffle furnace. Control the temperature of the muffle furnace at 600-850 degrees Celsius and calcine for 0.5-3 hours to obtain mineral powder.

[0042] (4) The above mineral powder is ground and sieved to become magnesium oxide powder;

[0043] (5) According to the molar ratio of magnesium oxide to magnesium sulfate of 6~8:1, stir the magnesium oxide powder and magnesium sulfate solution for 3~5 minutes, mix them evenly, and pour them into the mold;

[0044] (6) After curing at room temperature (25 ℃±2 ℃) for 20~24 h, the material is demolded to obtain the magnesium oxysulfate cementitious material.

[0045] For example, a flowchart of the preparation process of magnesium oxide and magnesium oxysulfate cementitious materials in a typical embodiment of the present invention is shown below. Figure 1 As shown, a solution containing hydrated magnesium chloride is mixed with hydrated magnesia, dried and crushed, and then calcined in one step to obtain magnesium oxide; magnesium oxide powder is mixed with magnesium sulfate solution, molded, and cured to obtain magnesium sulfate cementitious material.

[0046] A second aspect of the present invention provides a magnesium oxysulfate cementitious material prepared by the above method.

[0047] The compressive strength of the obtained magnesium oxysulfate cementitious material is 50~80 MPa. Compared with existing magnesium oxysulfate cementitious materials, the obtained magnesium oxysulfate cementitious material has better mechanical properties.

[0048] In some embodiments, the magnesium oxysulfate gelling material further includes a modifier, which includes citric acid.

[0049] Furthermore, the magnesium oxysulfate cementitious material may also include 0.5~2 wt% citric acid. By adding modifiers such as citric acid, its strength can be enhanced and cracking of the magnesium oxysulfate cementitious material can be prevented.

[0050] A third aspect of the present invention provides the application of the above method in the field of preparing magnesium oxysulfate cement.

[0051] A fourth aspect of the present invention provides a magnesium oxysulfate cement comprising the aforementioned magnesium oxysulfate cementitious material.

[0052] Furthermore, the magnesium oxysulfate cement provided by this invention can reduce the corrosion of internal metal components.

[0053] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0054] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0055] Example 1

[0056] Magnesia chloride (magnesium chloride accounting for 1 wt% of the mass of magnesite) was dissolved in water and mixed with magnesite powder. After thorough mixing, the mixture was allowed to dry naturally, then crushed and placed in a crucible. The crucible containing the mineral was placed in a muffle furnace and calcined to obtain lightly calcined powder. The temperature was set at 700 °C and the holding time was 2 h. After grinding and sieving, magnesium oxide powder was obtained. The activity of the magnesium oxide powder was tested using the water method. In this example, the activity of the magnesium oxide powder was 84.6%. The purity of the magnesium oxide powder was 92.8%.

[0057] Magnesium oxide powder and magnesium sulfate solution were mixed evenly at a molar ratio of 7:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxysulfate cementitious material. After demolding, it was cured indoors for another 27 days, and the compressive strength of the magnesium oxysulfate cementitious material was 70.57 MPa.

[0058] Example 2

[0059] Magnesia chloride (2 wt% of magnesium chloride by mass of magnesite) was dissolved in water and mixed with magnesite powder. After thorough mixing, the mixture was placed in an oven for accelerated drying. After drying, the powder was crushed and placed in a crucible. The crucible containing the mineral was placed in a muffle furnace and calcined to obtain lightly calcined powder. The temperature was set at 700 °C and the holding time was 2 h. After grinding and sieving, magnesium oxide powder was obtained. The activity of the magnesium oxide powder was tested using the water method. In this example, the activity of the magnesium oxide powder was 82.4%. The purity of the magnesium oxide powder was 93.4%.

[0060] Magnesium oxide powder and magnesium sulfate solution were mixed evenly at a molar ratio of 7:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxysulfate cementitious material. After demolding, it was further cured indoors for 27 days, and the compressive strength of the magnesium oxysulfate cementitious material was 78.57 MPa.

[0061] Example 3

[0062] Magnesia chloride (magnesium chloride comprising 5 wt% of the mass of magnesite) was dissolved in water and mixed with magnesite powder. After thorough mixing, the mixture was allowed to dry naturally or in an oven to accelerate drying. After drying, the powder was crushed and placed in a crucible. The crucible containing the mineral was placed in a muffle furnace and calcined to obtain lightly calcined powder at 700 °C for 2 hours. The powder was then ground and sieved to obtain magnesium oxide. The activity of the magnesium oxide powder was tested using a water-based method; in this example, the activity was 81.7%. The purity of the magnesium oxide powder was 94.5%.

[0063] Magnesium oxide powder and magnesium sulfate solution were mixed evenly at a molar ratio of 7:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxysulfate cementitious material. After demolding, it was cured indoors for another 27 days, and the compressive strength of the magnesium oxysulfate cementitious material was 74.59 MPa.

[0064] Example 4

[0065] The difference between this embodiment and Example 1 is that the molar ratio of active magnesium oxide to magnesium sulfate solution is 6:1, while the rest is the same as in Example 1.

[0066] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 70.24 MPa.

[0067] Example 5

[0068] The difference between this embodiment and Example 1 is that the molar ratio of active magnesium oxide to magnesium sulfate solution is 8:1, while the rest is the same as in Example 1.

[0069] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 73.46 MPa.

[0070] Example 6

[0071] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 600 ℃ and the time is 2 h, while the rest is the same as Embodiment 1.

[0072] The activity of the magnesium oxide powder in this embodiment is 80.3%. The purity of the magnesium oxide powder is 90.4%.

[0073] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 71.54 MPa.

[0074] Example 7

[0075] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 850 ℃ and the time is 3 h, while the rest is the same as Embodiment 1.

[0076] The activity of the magnesium oxide powder in this embodiment is 82.7%. The purity of the magnesium oxide powder is 95.6%.

[0077] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 78.64 MPa.

[0078] Comparative Example 1

[0079] The difference between this embodiment and Embodiment 1 is that an aqueous solution without hydrated magnesium chloride is mixed with hydrated magnesite powder, while the rest is the same as in Embodiment 1.

[0080] The activity of the magnesium oxide powder in this embodiment is 79.5%. The purity of the magnesium oxide powder is 87.4%.

[0081] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 18.64 MPa.

[0082] Comparative Example 2

[0083] The difference between this embodiment and Embodiment 1 is that: an aqueous solution of magnesia hydrate (magnesia hydrate accounts for 10 wt% of the mass of magnesia hydrate) is mixed with magnesia hydrate powder, and the rest is the same as in Embodiment 1.

[0084] The activity of the magnesium oxide powder in this embodiment is 82.1%. The purity of the magnesium oxide powder is 95.8%.

[0085] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 79.63 MPa.

[0086] However, due to the large amount of magnesium chloride added, hydrogen chloride gas will be generated during the preparation process, posing a risk of equipment corrosion.

[0087] Comparative Example 3

[0088] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 950 ℃ and the time is 5 h, while the rest is the same as Embodiment 1.

[0089] The activity of the magnesium oxide powder in this embodiment is 50.2%. The purity of the magnesium oxide powder is 98.9%.

[0090] The compressive strength of the magnesium oxysulfate cementitious material after demolding and indoor curing for 27 days was 63.86 MPa.

[0091] Comparative Example 4

[0092] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 550 ℃ and the time is 0.5 h, while the rest is the same as Embodiment 1.

[0093] The activity of the magnesium oxide powder in this embodiment is 25.4%. The purity of the magnesium oxide powder is 13.5%.

[0094] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 2.41 MPa.

[0095] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0096] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing a magnesium oxysulfate cementitious material, characterized in that, include: Magnesium oxide is obtained by calcining magnesite and magnesium chloride at 600-850 °C for 0.5-3 h in one step. The magnesium oxide and magnesium sulfate are mixed evenly, and then cured in a mold at room temperature to obtain a magnesium sulfate-magnesium oxide cementitious material.

2. The preparation method according to claim 1, characterized in that, The method for preparing the magnesium oxide specifically includes: mixing a solution containing magnesia hydrate with magnesite, drying and crushing the mixture, and then calcining it in the aforementioned step to obtain the magnesium oxide.

3. The preparation method according to claim 2, characterized in that: The magnesium chloride in the hydromagnesia contains 1-5 wt% of the mass of hydromagnesite. And / or, the hydromagnesite is in powder form.

4. The preparation method according to claim 3, characterized in that: The particle diameter of the hydromagnesite is 2~10 mm; And / or, the particle diameter of the crushed mixture of hydromagnesia and hydromagnesite is 2-5 mm.

5. The preparation method according to any one of claims 1-4, characterized in that, The magnesium oxide is in powder form, and the particle diameter includes: D 10 The diameter is 0.7~0.9 μm, D 50 The thickness is 2.9~3.3 μm and D 90 The thickness is 9.4~10.8 μm; And / or, the purity of the magnesium oxide is above 90%; And / or, the activity of the magnesium oxide is greater than 78%.

6. The preparation method according to claim 1, characterized in that: The molar ratio of magnesium oxide to magnesium sulfate is 6~8:1; And / or, the maintenance time is 20~24 h.

7. The magnesium oxysulfate cementitious material prepared by any one of claims 1-6.

8. The magnesium oxysulfate cementitious material according to claim 7, characterized in that: The compressive strength of the magnesium oxysulfide cementitious material is above 70 MPa; And / or, the magnesium oxysulfate cementitious material further includes a modifier; Preferably, the modifier includes citric acid; Preferably, the magnesium oxysulfate cementitious material includes 0.5~2wt% modifier.

9. The application of the magnesium oxysulfate cementitious material according to claim 7 or 8 in the preparation of magnesium oxysulfate cement.

10. A magnesium oxysulfate cement, characterized in that, Includes the magnesium oxysulfate cementitious material as described in claim 7 or 8.

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