Method for low-temperature calcination of hydromagnesite to produce magnesium oxide, magnesium oxide and applications

Abstract

This invention discloses a method for low-temperature roasting of magnesia from hydromagnesia, the resulting magnesium oxide, and its applications. The method includes: mixing a solution containing magnesia-chlorite with magnesia, drying and crushing the magnesia, followed by a one-step calcination to obtain magnesium oxide. The method provided by this invention ensures complete decomposition of magnesia while lowering the decomposition temperature, resulting in the production of magnesium oxide with higher activity and purity. It also effectively reduces energy consumption and CO2 emissions during the production process. Furthermore, the magnesium oxychloride cementitious material prepared using the aforementioned magnesium oxide exhibits superior mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of mineral resource processing technology, specifically relating to a method for low-temperature roasting of magnesium oxide from hydromagnesia, magnesium oxide, and its applications. 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 oxychloride 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 penetrates 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, compared to magnesite, has an even lower calcination temperature, but research on it is scarce. Summary of the Invention

[0005] The main objective of this invention is to provide a method for low-temperature roasting of magnesium oxide from hydromagnesite, magnesium oxide, and its applications, in order to overcome the deficiencies of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] The first aspect of the present invention provides a method for low-temperature roasting of magnesium oxide from magnesite, comprising:

[0008] Magnesium oxide is obtained by mixing a solution containing hydrated magnesium chloride with hydrated magnesite, drying and crushing the mixture, and then calcining it in one step.

[0009] A second aspect of the invention provides magnesium oxide prepared by the above method.

[0010] A third aspect of the invention provides the application of the above method in the field of calcining carbonate minerals.

[0011] A fourth aspect of the present invention provides the application of the above-mentioned magnesium oxide in the field of preparing magnesium phosphate cement or magnesium oxychloride cementitious materials.

[0012] The fifth aspect of the present invention provides a method for preparing a magnesium oxychloride gelling material, comprising: mixing magnesium oxide and magnesium chloride evenly, curing in a mold at room temperature, and obtaining the magnesium oxychloride gelling material.

[0013] A sixth aspect of the present invention provides a magnesium oxychloride cementitious material prepared by the above preparation method, wherein the magnesium oxychloride cementitious material has a compressive strength of 86 MPa or higher.

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

[0015] (1) The method provided by the present invention changes its decomposition process. There is a synergistic effect between magnesia hydrate and magnesite. The acidic substances produced by the thermal decomposition of magnesia hydrate can promote the decomposition of carbonate in magnesite, while magnesite reduces the acidic substances to MgCl2, forming a reaction cycle. While ensuring the complete decomposition of magnesite, the decomposition temperature is reduced by about 100 °C, which can produce MgO with higher activity and higher purity, and effectively reduce energy consumption and CO2 generated during the production process. Compared with the preparation of magnesium oxide by roasting magnesite mixed with magnesium chloride, the energy consumption is less. Moreover, the mechanical properties of magnesium oxychloride cementitious materials prepared by the above-mentioned magnesium oxide powder are better.

[0016] (2) In the method provided by the present invention, the hydrogen chloride produced by the decomposition of magnesium chloride provides an acidic atmosphere, which accelerates the decomposition rate of carbonates in magnesite.

[0017] (3) In the method provided by the present invention, the solid decomposition products of magnesium chloride are magnesium oxide, which will not introduce new impurities. 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 oxychloride 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 method for low-temperature roasting of magnesia from hydromagnesia, the resulting magnesium oxide, and its applications. Magnesia is mainly obtained through the synergistic effect of hydromagnesia and hydromagnesia.

[0021] The first aspect of the present invention provides a method for low-temperature roasting of magnesium oxide from magnesite, comprising: mixing a solution containing magnesia hydrate with magnesite, drying and crushing the magnesite, and then calcining it in one step to obtain magnesium oxide.

[0022] Magnesium chloride hexahydrate, also known as magnesium chloride hexahydrate (MgCl2·6H2O), contains magnesium chloride in a mass of 1-5 wt% of magnesite in this invention.

[0023] In some embodiments, the hydromagnesite is in powder form.

[0024] In some embodiments, the calcination temperature is 650~800 °C and the time is 1~4 h.

[0025] In some embodiments, the particle diameter of the hydromagnesite is 2 to 10 mm.

[0026] In some implementations, the particle diameter of the crushed mixture of magnesia-hydrate and magnesite is 2-5 mm.

[0027] In some more specific implementations, the method specifically includes the following steps:

[0028] (1) Dissolve magnesia in water and mix it with magnesite powder. The magnesium chloride in the magnesia is 1-5 wt% of the magnesite.

[0029] (2) After mixing evenly, let it dry naturally or place it in an oven to accelerate drying. After drying, crush it and pass it through an 80-mesh sieve.

[0030] (3) Place the hydromagnesite in a crucible and then place it in a muffle furnace. Control the temperature of the muffle furnace at 650~800 ℃ and calcine for 1~4 h to obtain mineral powder.

[0031] (4) The above mineral powder is ground and sieved to become magnesium oxide powder.

[0032] 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.

[0033] A second aspect of the invention provides magnesium oxide prepared by the above method.

[0034] In some embodiments, the magnesium oxide is in powder form, and the particle diameter includes: D 10 0.6~0.8 μm, D 50 2.8~3.0 μm and D 90 8.2~10.1 μm.

[0035] In some embodiments, the magnesium oxide has a purity of 90% or higher.

[0036] In some embodiments, the activity of the magnesium oxide is 80% to 85%.

[0037] 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 using a hydration method, the specific test method of which is as follows:

[0038] Weigh 2 g (accurate to 0.0001 g) of sample (W1), place it in a weighing bottle (40 mm × 25 mm) of known mass and constant weight, add 10 mL of distilled water, cover with a small gap (about 2 mm), and place on a tray. Hydrate in an oven at 105 ℃ for 3 h, adjust the oven temperature to 150 ℃, dry for 3 h, remove and cool to room temperature in a desiccator. Weigh and record the weight as W2. Calculate the content of active MgO according to formula (1):

[0039] (1)

[0040] 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.

[0041] A third aspect of the invention provides the application of the above-described method in the field of calcining carbonate minerals. For example, the method of the present invention can be applied to the calcination of calcite minerals.

[0042] A fourth aspect of the present invention provides the application of the above-mentioned magnesium oxide in the field of preparing magnesium phosphate cement or magnesium oxychloride cementitious materials.

[0043] For example, the present invention can utilize the magnesium oxide powder to prepare magnesium phosphate cement, and the resulting magnesium phosphate cement can be used as a quick-setting repair material.

[0044] The fifth aspect of the present invention provides a method for preparing a magnesium oxychloride gelling material, comprising: mixing the magnesium oxide and magnesium chloride evenly, curing in a mold at room temperature, and obtaining the magnesium oxychloride gelling material.

[0045] In some embodiments, the molar ratio of magnesium oxide to magnesium chloride is 5 to 7:1.

[0046] In some implementations, the maintenance period is 20-24 hours.

[0047] In some more specific embodiments, the preparation method of the magnesium oxychloride cementitious material specifically includes the following steps:

[0048] (1) According to the molar ratio of magnesium oxide to magnesium chloride of 5~7:1, stir magnesium oxide powder and magnesium chloride solution for 3~5 minutes, mix evenly, and pour into mold;

[0049] (2) After curing at room temperature (25 ℃±2 ℃) for 24 h, the material was demolded to obtain the magnesium oxychloride cementitious material.

[0050] For example, a flowchart of the preparation process of magnesium oxide and magnesium oxychloride 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 and magnesium chloride solution are mixed, molded, and cured to obtain magnesium oxychloride cementitious material.

[0051] A sixth aspect of the present invention provides a magnesium oxychloride cementitious material prepared by the above-described preparation method, wherein the compressive strength of the magnesium oxychloride cementitious material is above 80 MPa. The obtained magnesium oxychloride cementitious material exhibits superior mechanical properties compared to existing magnesium oxychloride cementitious materials.

[0052] In some embodiments, the magnesium oxychloride gelling material further includes a modifier or admixture.

[0053] Furthermore, the modifiers include, but are not limited to, phosphoric acid. The water resistance can be enhanced by adding modifiers such as phosphoric acid.

[0054] Furthermore, the admixtures include, but are not limited to, sawdust or steel slag. Adding admixtures such as sawdust or steel slag can enhance its flexural strength.

[0055] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0056] 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.

[0057] Example 1

[0058] 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 84.2%. The purity of the magnesium oxide powder was 91.6%.

[0059] Magnesium oxide powder and magnesium chloride solution were mixed evenly at a molar ratio of 6:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxychloride cementitious material. After demolding, it was further cured indoors for 27 days, and the compressive strength of the magnesium oxychloride cementitious material was 86.33 MPa.

[0060] Example 2

[0061] 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 82.7%. The purity of the magnesium oxide powder was 92.9%.

[0062] Magnesium oxide powder and magnesium chloride solution were mixed evenly at a molar ratio of 6:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxychloride cementitious material. After demolding, it was cured indoors for another 27 days, and the compressive strength of the magnesium oxychloride cementitious material was 93.38 MPa.

[0063] Example 3

[0064] 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 81.6%. The purity of the magnesium oxide powder was 94.7%.

[0065] Magnesium oxide powder and magnesium chloride solution were mixed evenly at a molar ratio of 6:1, then molded and naturally cured indoors for 1 day before demolding to obtain magnesium oxychloride cementitious material. After demolding, it was cured indoors for another 27 days, and the compressive strength of the magnesium oxychloride cementitious material was 86.92 MPa.

[0066] Example 4

[0067] The difference between this embodiment and Example 1 is that the molar ratio of active magnesium oxide to magnesium chloride solution is 5:1, while the rest is the same as in Example 1.

[0068] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 84.49 MPa.

[0069] Example 5

[0070] The difference between this embodiment and Example 1 is that the molar ratio of active magnesium oxide to magnesium chloride solution is 7:1, while the rest is the same as in Example 1.

[0071] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 80.68 MPa.

[0072] Example 6

[0073] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 650 ℃ and the time is 2 h, while the rest is the same as Embodiment 1.

[0074] The activity of the magnesium oxide powder in this embodiment is 80.4%. The purity of the magnesium oxide powder is 90.5%.

[0075] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 81.57 MPa.

[0076] Example 7

[0077] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 800 ℃ and the time is 4 h, while the rest is the same as Embodiment 1.

[0078] The activity of the magnesium oxide powder in this embodiment is 81.7%. The purity of the magnesium oxide powder is 97.6%.

[0079] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 88.59 MPa.

[0080] Comparative Example 1

[0081] The difference between this embodiment and Embodiment 1 is that the aqueous solution without magnesia hydrate is mixed with magnesite powder, while the rest is the same as in Embodiment 1.

[0082] The activity of the magnesium oxide powder in this embodiment is 80.3%. The purity of the magnesium oxide powder is 86.5%.

[0083] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 26.47 MPa.

[0084] Comparative Example 2

[0085] 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.

[0086] The activity of the magnesium oxide powder in this embodiment is 81.4%. The purity of the magnesium oxide powder is 95.6%.

[0087] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 89.64 MPa.

[0088] 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.

[0089] Comparative Example 3

[0090] The difference between this embodiment and Embodiment 1 is that the calcination temperature is 900 ℃ and the time is 6 h, while the rest is the same as Embodiment 1.

[0091] The activity of the magnesium oxide powder in this embodiment is 56.8%. The purity of the magnesium oxide powder is 98.4%.

[0092] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 80.61 MPa.

[0093] Comparative Example 4

[0094] 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.

[0095] The activity of the magnesium oxide powder in this embodiment is 86.45%. The purity of the magnesium oxide powder is 70.5%.

[0096] The compressive strength of the magnesium oxychloride cementitious material after demolding and indoor curing for 27 days was 23.95 MPa.

[0097] 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.

[0098] 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 low-temperature roasting of magnesium oxide from hydromagnesite, characterized in that, include: Magnesium oxide is obtained by mixing a solution containing hydrated magnesium chloride with hydrated magnesite, drying and crushing the mixture, and then calcining it.

2. The method according to claim 1, characterized in that: The magnesium chloride in the hydrated magnesia stone is 1-5 wt% of the mass of magnesite. And / or, the hydromagnesite is in powder form; And / or, the calcination temperature is 650~800 ℃, and the time is 1~4 h.

3. The method according to claim 2, 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.

4. Magnesium oxide prepared by any one of claims 1-3.

5. The magnesium oxide according to claim 4, characterized in that, The magnesium oxide is in powder form, and the particle diameter includes: D 10 0.6~0.8 μm, D 50 2.8~3.0 μm and D 90 8.2~10.1 μm; And / or, the purity of the magnesium oxide is above 90%; And / or, the activity of the magnesium oxide is 80-85%.

6. The application of the method according to any one of claims 1 to 3 in the field of calcining carbonate minerals.

7. The application of the magnesium oxide as described in claim 4 or 5 in the preparation of magnesium phosphate cement or magnesium oxychloride cementitious materials.

8. A method for preparing a magnesium oxychloride cementitious material, characterized in that, include: The magnesium oxide and magnesium chloride described in claim 4 or 5 are mixed evenly, and then cured in a mold at room temperature to obtain magnesium oxychloride cementitious material. Preferably, the molar ratio of magnesium oxide to magnesium chloride is 5~7:1; Preferably, the maintenance time is 20-24 hours.

9. The magnesium oxychloride cementitious material prepared by the preparation method according to claim 8, characterized in that, The compressive strength of the magnesium oxychloride cementitious material is above 80 MPa.

10. The magnesium oxychloride cementitious material according to claim 9, characterized in that: The magnesium oxychloride cementitious material also includes modifiers or admixtures; Preferably, the modifier includes phosphoric acid; Preferably, the admixture includes sawdust or steel slag.

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