Method for producing magnesium oxide

Abstract

The present application relates to the technical field of chemical production, and particularly relates to a magnesium oxide preparation method, comprising the following steps: step S1: obtaining a suspension slurry by calcining and digesting magnesite; step S2: obtaining a carbonized liquid by carbonizing the suspension slurry; step S3: mixing the carbonized liquid with alkali to perform a magnesium precipitation reaction, and obtaining magnesium carbonate precipitation and a magnesium precipitation liquid; and step S4: obtaining a magnesium oxide product by drying and calcining the magnesium carbonate precipitation. Compared with the prior art, the present application does not need high-temperature pyrolysis when precipitating magnesium, and can effectively reduce energy consumption and production cost.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, and in particular to a method for preparing magnesium oxide. Background Technology

[0002] Magnesium oxide is an important chemical product, which can be prepared by calcining magnesite. my country has abundant magnesite reserves, amounting to approximately 3.1 billion tons, accounting for 25% of the world's reserves and ranking first in the world. The characteristics of my country's magnesite resources are large-scale deposits, shallow burial, and high quality, giving it a significant resource advantage.

[0003] Magnesite contains impurities such as silicon, iron, aluminum, and calcium. To remove these impurities and prepare high-purity magnesium oxide, existing techniques involve calcining and grinding the raw material into powder, hydrating it to form a slurry primarily containing magnesium hydroxide, and then reacting it at a relatively high temperature (100-120°C) with an acidic ammonium salt (ammonium chloride or ammonium sulfate) to obtain a solution of magnesium chloride and calcium chloride or magnesium sulfate and calcium sulfate, along with ammonia gas (above 100°C, the ammonia evaporates). At this point, iron oxide is separated due to its insolubility. Carbon dioxide is then introduced into the magnesium chloride and calcium chloride or magnesium sulfate and calcium sulfate solution to obtain a carbide solution containing magnesium bicarbonate and a calcium carbonate precipitate. The calcium carbonate precipitate is removed, and ammonia gas is introduced into the carbide solution to obtain a magnesium hydroxide precipitate. Finally, the magnesium hydroxide is dried and calcined to produce magnesium oxide. However, existing magnesium oxide preparation methods are energy-intensive and have high production costs. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the defects or deficiencies of the prior art and provide a method for preparing magnesium oxide, comprising the following steps:

[0005] Step S1: Calcination and digestion of magnesite to obtain a suspension slurry; Step S2: Carbonize the suspension slurry to obtain a carbonized liquid; Step S3: Mix the carbonation solution with alkali to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation solution; Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0006] Compared with existing technologies, this invention eliminates the need for high-temperature pyrolysis during magnesium deposition, effectively reducing energy consumption and production costs.

[0007] In one embodiment, the alkali in step S3 is ammonia and / or ammonium carbonate.

[0008] In one embodiment, the magnesium precipitation reaction time in step S3 is 0.5 to 2 hours, and the amount of ammonia and / or ammonium carbonate used is 1 to 1.5 times the theoretical amount.

[0009] In one embodiment, in step S3, when the concentration of ammonium bicarbonate in the obtained magnesium precipitation solution is <3.5 mol / L, the magnesium precipitation solution is returned to step S2 for diluting the suspension slurry before carbonization.

[0010] In one embodiment, in step S2, the suspension slurry is first diluted to a liquid-to-solid volume-to-mass ratio of 100:1~3, and then carbon dioxide is introduced to carry out a carbonization reaction.

[0011] In one embodiment, in step S2, the kiln gas containing carbon dioxide generated from the calcination in step S1 is passed into the diluted suspension slurry to carry out the carbonization reaction.

[0012] In one embodiment, in step S2, the carbonization reaction takes 1 to 3 hours and the temperature is 20 to 40°C.

[0013] In one embodiment, in step S4, the magnesium carbonate precipitate from step S3 is dried at 100~120°C for 2~4 h, and then calcined at 600~800°C for 2~3 h to obtain magnesium oxide product.

[0014] In one embodiment, the method further includes step S5: freezing and crystallizing the magnesium precipitate solution to recover ammonium bicarbonate. Timely freezing and recovery of ammonium bicarbonate ensures production efficiency while preventing ammonia gas spillage and environmental pollution. The recovered ammonium bicarbonate can also be sold as a fertilizer product.

[0015] In one embodiment, in step S5, when the concentration of ammonium bicarbonate in the magnesium precipitation solution of step S3 is ≥ 3.5 mol / L, it is taken out and added to a freeze crystallizer. The final temperature of the freeze crystallization is controlled at 0~10 ℃. After freeze crystallization, it is filtered. The ammonium bicarbonate recovered from the filter residue and the filtrate are returned to step S2 to dilute the suspension slurry.

[0016] To better understand and implement this invention, the invention will be described in detail below. Detailed Implementation

[0017] Based on analysis, this invention recognizes that existing technologies for converting magnesium bicarbonate in carbonation solutions into basic magnesium carbonate precipitate rely on high-temperature pyrolysis. This requires heating a large volume of solution to near boiling to maximize magnesium conversion into magnesium carbonate precipitate. This process demands prolonged, high-power heating, making it a major energy-consuming step. Therefore, this invention proposes a novel magnesium oxide preparation method that utilizes chemical precipitation to avoid high-temperature pyrolysis, addressing the issues of high energy consumption and high production costs in existing technologies.

[0018] The following is a detailed explanation.

[0019] A method for producing high-purity magnesium oxide from magnesite includes the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry.

[0020] Specifically, magnesite is crushed and calcined in a muffle furnace at a controlled temperature of 650–900°C for 0.5–6 h. The coarse particles obtained from calcination are then ground into calcined magnesite powder (preferably around 200 mesh) using a grinding mill. The calcined magnesite powder is then mixed with water at a weight ratio of 1:(2–8) for a digestion reaction at a controlled temperature of 50–90°C for 1–5 h and a stirring rate of 100–300 r / min, resulting in a suspension slurry primarily containing magnesium hydroxide. Additionally, the kiln gas generated during calcination is collected for subsequent carbonization steps; this kiln gas contains 25–40% carbon dioxide by volume.

[0021] Step S2: Carbonize the suspension slurry to obtain carbonized liquid.

[0022] Specifically, the magnesium hydroxide suspension slurry from step S1 is diluted to maintain a liquid-to-solid volume-to-mass ratio of 100:(1~3), and then fed into a carbonization reactor. Kiln gas containing 25~40% carbon dioxide (by volume) generated in step S1 is introduced to initiate the carbonization reaction. The temperature is controlled at 20~40℃ for 1~3 hours. After the reaction, the mixture is filtered; the filtrate is the carbonized liquid, mainly containing magnesium bicarbonate; the filter residue mainly consists of precipitated impurities. In this carbonization reaction, since the iron, silicon, and aluminum impurities in magnesite mainly exist in the form of oxides, when the magnesite is calcined, digested, and then carbon dioxide is introduced for the carbonization reaction, the magnesium hydroxide in the original suspension slurry is converted into magnesium bicarbonate and enters the solution. The iron, silicon, and aluminum oxides do not react and remain in the residue. Simultaneously, the calcium impurities, after calcination into oxides and digestion, form calcium hydroxide, which also reacts with carbon dioxide to form calcium carbonate, precipitating in the residue. The liquid-to-solid volume-to-mass ratio is the ratio of the liquid volume to the solid mass, expressed in mL / g. The carbonization reaction equation for magnesium is as follows: Mg(OH)2+2CO2= Mg(HCO3)2(1).

[0023] Step S3: Mix the carbonized liquid with ammonia and / or ammonium carbonate to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0024] Specifically, the carbonized liquid from step S2 is added to a reaction tank, and ammonia or ammonium carbonate is added to react. The reaction time is controlled at 0.5~2 h, and the amount of ammonia and / or ammonium carbonate added is 1~1.5 times the theoretical amount. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate. The filtrate becomes magnesium precipitation solution, which mainly contains ammonium bicarbonate. When the concentration of ammonium bicarbonate in the magnesium precipitation solution is <3.5 mol / L, the magnesium precipitation solution is returned to step S2 to dilute the suspension slurry. The reaction equation is as follows.

[0025] Mg(HCO3)2+NH3·H2O = MgCO3+NH4HCO3+H2O(2); Mg(HCO3)2+(NH4)2CO3= MgCO3+2NH4HCO3(3).

[0026] The theoretical amount of ammonia and / or ammonium carbonate in magnesium precipitation is the theoretical amount required when the ammonia and / or ammonium carbonate participate in the magnesium precipitation reaction according to reaction equations (2) and (3). This is the theoretical amount required after detecting the amount of magnesium bicarbonate in the carbonization liquid using conventional methods, based on the type or ratio of ammonia and / or ammonium carbonate used and the corresponding reaction equation.

[0027] Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0028] Specifically, the magnesium carbonate precipitate from step S3 is added to an oven and dried at 100~120℃ for 2~4 h, and then calcined at 600~800℃ for 2~3 h to obtain a high-purity magnesium oxide product.

[0029] Step S5: Recover ammonium bicarbonate by freezing and crystallizing the magnesium precipitate solution.

[0030] As the number of magnesium precipitation cycles increases, the concentration of ammonium bicarbonate in the precipitation solution continuously increases. To prevent the precipitation of ammonium bicarbonate from the precipitation solution, the release of ammonia gas that pollutes the environment, and to avoid reducing the solubility of magnesium bicarbonate during the carbonation reaction due to excessively high ammonium bicarbonate concentration, it is necessary to remove ammonium bicarbonate from the precipitation solution in a timely manner. Since the solubility of ammonium bicarbonate increases with increasing temperature, it can be precipitated by freezing crystallization to achieve supersaturation. Simultaneously, freezing crystallization can lower the solution temperature, offsetting the temperature rise caused by the exothermic digestion and carbonation reactions, thus maintaining the solution at a lower temperature and facilitating an increase in the concentration of magnesium bicarbonate in the carbonation solution. The specific procedure for this step is as follows.

[0031] When the ammonium bicarbonate concentration in the filtrate from step S3 (i.e., the magnesium precipitation solution) is ≥ 3.5 mol / L, it is taken out and added to a cryo-crystallizer. The final temperature of the cryo-crystallization is controlled at 0~10 ℃ for cryo-crystallization. The freezing time is more than 4 hours, preferably overnight. After cryo-crystallization, it is filtered. The filter residue is the recovered ammonium bicarbonate, and the filtrate is returned to step S2 to dilute the suspension slurry. The ammonium bicarbonate precipitate obtained by crystallization can be sold or used as fertilizer, and the filtrate is recovered to step S2 to dilute the suspension slurry. The method for testing the ammonium bicarbonate concentration in this step is a conventional method and will not be described in detail here.

[0032] The present invention has the following advantages: (1) Achieve low-temperature magnesium precipitation. Adding ammonia or ammonium carbonate to the carbonization liquid can precipitate magnesium at low temperatures, eliminating the need for high-temperature pyrolysis to precipitate magnesium carbonate, which greatly reduces production energy consumption and production costs.

[0033] (2) No wastewater is generated, resulting in good environmental benefits. After the magnesium precipitation solution is frozen and crystallized to recover ammonium bicarbonate, it can be recycled and reused. The entire process generates no wastewater.

[0034] The following are specific examples.

[0035] Example 1 This embodiment describes the production of magnesium oxide from magnesite (whose main components, by weight percentage, are 47.23% MgO, 0.41% CaO, 0.24% SiO2, 0.12% Al2O3, and 0.28% Fe2O3) by the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry.

[0036] Magnesite was crushed and calcined in a muffle furnace at a controlled temperature of 800℃ for 3 hours. The coarse particles obtained from calcination were then ground to 200 mesh using a grinding mill. The powder was then mixed with water at a weight ratio of 1:5 for a digestion reaction at a controlled temperature of 60℃ for 3 hours to obtain a suspension slurry containing magnesium hydroxide.

[0037] Step S2: Carbonize the suspension slurry to obtain carbonized liquid.

[0038] The magnesium hydroxide suspension slurry from step S1 is diluted, and the liquid-to-solid volume-to-mass ratio is controlled at 100:2. It is then fed into the carbonization reactor, and the kiln gas containing 30% carbon dioxide by volume generated in step S1 is introduced into it to carry out the carbonization reaction. The temperature is controlled at 30°C and the time is 2 hours. After the reaction, the mixture is filtered, and the filtrate is a carbonization liquid containing magnesium bicarbonate.

[0039] Step S3: Mix the carbonation solution with ammonia water and / or ammonium carbonate solution to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation solution.

[0040] Add the carbonized liquid from step S2 into the reaction tank, add ammonia water to react, control the reaction time to 1 h, and add ammonia water or ammonium carbonate at 1.2 times the theoretical amount. After the reaction is completed, filter. The filter residue is magnesium carbonate precipitate, and the filtrate is magnesium precipitation solution containing ammonium bicarbonate. When the concentration of ammonium bicarbonate in the magnesium precipitation solution is <3.5 mol / L, return it to step S2 to dilute the magnesium hydroxide slurry.

[0041] Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0042] The magnesium carbonate from step S3 was added to an oven and dried at 120°C for 2 hours, and then calcined at 800°C for 2 hours to obtain a high-purity magnesium oxide product with a magnesium oxide content of 99.58%.

[0043] Step S5: Recover ammonium bicarbonate by freezing and crystallizing the magnesium precipitate solution.

[0044] When the concentration of ammonium bicarbonate in the filtrate of step S3 is ≥ 3.5 mol / L, it is taken out and added to a freeze crystallizer. The final temperature of the freeze crystallization is controlled at 5 ℃. After freeze crystallization, it is filtered. The filter residue is ammonium bicarbonate precipitate. The filtrate is returned to step S2 to dilute the magnesium hydroxide suspension slurry.

[0045] Example 2 This embodiment describes the production of magnesium oxide from magnesite (whose main components, by weight percentage, are 46.37% MgO, 0.62% CaO, 0.28% SiO2, 0.29% Al2O3, and 0.44% Fe2O3) by the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry.

[0046] Magnesite was crushed and calcined in a muffle furnace at a controlled temperature of 900℃ for 0.5 h. The coarse particles obtained from calcination were then ground to 200 mesh using a grinding mill. The powder and water were then subjected to a digestion reaction at a weight ratio of 1:8, with the temperature controlled at 50℃ for 5 h, to obtain a suspension slurry containing magnesium hydroxide.

[0047] Step S2: Carbonize the suspension slurry to obtain carbonized liquid.

[0048] The magnesium hydroxide suspension slurry from step S1 is diluted, and the liquid-to-solid volume-to-mass ratio is controlled at 100:1. It is then fed into a carbonization reactor, and kiln gas containing 25% carbon dioxide by volume from step S1 is introduced into it to carry out the carbonization reaction. The temperature is controlled at 40°C and the time is 1 hour. After the reaction, the mixture is filtered, and the filtrate is a carbonization liquid containing magnesium bicarbonate solution.

[0049] Step S3: Mix the carbonized liquid with ammonia and / or ammonium carbonate to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0050] Add the carbonized liquid from step S2 into the reaction tank, add ammonium carbonate to react, control the reaction time to 1 h, and add ammonia or ammonium carbonate in the theoretical amount. After the reaction is completed, filter, the filter residue is magnesium carbonate precipitate, and the filtrate is magnesium precipitation solution. When the concentration of ammonium bicarbonate in the magnesium precipitation solution is <3.5 mol / L, return to step S2 to dilute the magnesium hydroxide suspension slurry.

[0051] Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0052] The magnesium carbonate from step S3 was added to an oven and dried at 100°C for 4 hours, and then calcined at 600°C for 3 hours to obtain a high-purity magnesium oxide product with a magnesium oxide content of 99.61%.

[0053] Step S5: Recover ammonium bicarbonate by freezing and crystallizing the magnesium precipitate solution.

[0054] When the concentration of ammonium bicarbonate in the magnesium precipitation solution in step S3 is ≥ 3.5 mol / L, it is taken out and added to a freeze crystallizer. The final temperature of the freeze crystallization is controlled at 0℃. After freeze crystallization, it is filtered. The filter residue is ammonium bicarbonate precipitate. The filtrate is returned to step S2 to dilute the magnesium hydroxide slurry.

[0055] Example 3 This embodiment describes the production of magnesium oxide from magnesite (whose main components, by weight percentage, are 45.11% MgO, 1.17% CaO, 0.81% SiO2, 0.48% Al2O3, and 0.45% Fe2O3) by the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry.

[0056] Magnesite was crushed and calcined in a muffle furnace at a controlled temperature of 700℃ for 5 hours. The coarse particles obtained from calcination were then ground to 200 mesh using a grinding mill. The powder was then mixed with water at a weight ratio of 1:3 for a digestion reaction at a controlled temperature of 90℃ for 1 hour to obtain a suspension slurry containing magnesium hydroxide.

[0057] Step S2: Carbonize the suspension slurry to obtain carbonized liquid.

[0058] The magnesium hydroxide suspension slurry from step S1 is diluted, and the liquid-to-solid volume-to-mass ratio is controlled at 100:3. It is then fed into the carbonization reactor, and the kiln gas containing 40% carbon dioxide by volume generated in step S1 is introduced into it to carry out the carbonization reaction. The temperature is controlled at 20°C and the time is 3 hours. After the reaction, the mixture is filtered, and the filtrate is a carbonization liquid containing magnesium bicarbonate.

[0059] Step S3: Mix the carbonized liquid with ammonia and / or ammonium carbonate to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0060] Add the carbonized liquid from step S2 into the reaction tank, add ammonia water to react, control the reaction time to 0.5 h, and add ammonia water or ammonium carbonate at 1.1 times the theoretical amount. After the reaction is completed, filter. The filter residue is magnesium carbonate precipitate, and the filtrate is magnesium precipitation solution mainly containing ammonium bicarbonate. When the concentration of ammonium bicarbonate in the magnesium precipitation solution is <3.5 mol / L, return it to step S2 to dilute the magnesium hydroxide slurry.

[0061] Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0062] The magnesium carbonate from step S3 was added to an oven and dried at 110°C for 3 hours, and then calcined at 700°C for 3 hours to obtain a high-purity magnesium oxide product with a magnesium oxide content of 99.65%.

[0063] Step S5: Recover ammonium bicarbonate by freezing and crystallizing the magnesium precipitate solution.

[0064] When the concentration of ammonium bicarbonate in the filtrate of step S3 is ≥ 3.5 mol / L, it is taken out and added to a freeze crystallizer. The final temperature of the freeze crystallization is controlled at 10 ℃. After freeze crystallization, it is filtered. The filter residue is ammonium bicarbonate precipitate. The filtrate is returned to step S2 to dilute the magnesium hydroxide slurry.

[0065] Example 4 This embodiment describes the production of magnesium oxide from magnesite (whose main components, by weight percentage, are 47.42% MgO, 0.26% CaO, 0.20% SiO2, 0.07% Al2O3, and 0.31% Fe2O3) by the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry.

[0066] Magnesite was crushed and calcined in a muffle furnace at a controlled temperature of 650℃ for 6 hours. The coarse particles obtained from calcination were then ground to 200 mesh using a grinding mill. The powder was then mixed with water at a weight ratio of 1:8 for a digestion reaction at a controlled temperature of 80℃ for 2 hours to obtain a suspension slurry containing magnesium hydroxide.

[0067] Step S2: Carbonize the suspension slurry to obtain carbonized liquid.

[0068] The magnesium hydroxide suspension slurry from step S1 is diluted, and the liquid-to-solid volume-to-mass ratio is controlled at 100:1.5. It is then fed into the carbonization reactor, and kiln gas containing 35% carbon dioxide by volume from step S1 is introduced into it to carry out the carbonization reaction. The temperature is controlled at 25°C and the time is 3 hours. After the reaction, the mixture is filtered, and the filtrate is the carbonized liquid.

[0069] Step S3: Mix the carbonized liquid with ammonia and / or ammonium carbonate to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0070] Add the carbonized liquid from step S2 into the reaction tank, add ammonium carbonate to react, control the reaction time to 2 h, and add ammonia or ammonium carbonate at 1.05 times the theoretical amount. After the reaction is completed, filter. The filter residue is magnesium carbonate precipitate, and the filtrate is ammonium bicarbonate. When the concentration of ammonium bicarbonate in the solution is <3.5 mol / L, return it to step S2 to dilute the magnesium hydroxide slurry.

[0071] Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

[0072] The magnesium carbonate from step S3 was added to an oven and dried at 120°C for 3 hours, and then calcined at 650°C for 3 hours to obtain a high-purity magnesium oxide product with a magnesium oxide content of 99.72%.

[0073] Step S5: Recover ammonium bicarbonate by freezing and crystallizing the magnesium precipitate solution.

[0074] When the concentration of ammonium bicarbonate in the filtrate of step S3 is ≥ 3.5 mol / L, it is taken out and added to a freeze crystallizer. The final temperature of the freeze crystallization is controlled at 5 ℃. After freeze crystallization, it is filtered. The filter residue is ammonium bicarbonate precipitate. The filtrate is returned to step S2 to dilute the magnesium hydroxide suspension slurry.

[0075] This invention effectively solves the problems of high energy consumption, high cost, and serious environmental pollution in existing magnesium oxide production processes. This invention is applicable to the production of magnesium oxide from magnesite. The total magnesium recovery rate of this invention is greater than 95%, achieving green, pollution-free, and low-cost purification of magnesium oxide.

[0076] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. In the description of this application, those skilled in the art will understand the specific meaning of the above terms in this application according to the specific circumstances.

[0077] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing magnesium oxide, characterized in that, Includes the following steps: Step S1: Calcination and digestion of magnesite to obtain a suspension slurry; Step S2: Carbonize the suspension slurry to obtain a carbonized liquid; Step S3: Mix the carbonation solution with alkali to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation solution; Step S4: Magnesium carbonate precipitate is dried and calcined to obtain magnesium oxide product.

2. The method according to claim 1, characterized in that, The alkali mentioned in step S3 is ammonia and / or ammonium carbonate.

3. The method according to claim 2, characterized in that, The magnesium precipitation reaction time in step S3 is 0.5 to 2 hours, and the amount of ammonia and / or ammonium carbonate used is 1 to 1.5 times the theoretical amount.

4. The method according to claim 3, characterized in that, In step S3, when the concentration of ammonium bicarbonate in the obtained magnesium precipitation solution is <3.5 mol / L, the magnesium precipitation solution is returned to step S2 for diluting the suspension slurry before carbonization.

5. The method according to claim 4, characterized in that, In step S2, the suspension slurry is first diluted to a liquid-to-solid volume-to-mass ratio of 100:1~3, and then carbon dioxide is introduced to carry out a carbonization reaction.

6. The method according to claim 5, characterized in that, In step S2, the kiln gas containing carbon dioxide generated during calcination in step S1 is passed into the diluted suspension slurry to carry out the carbonization reaction.

7. The method according to claim 6, characterized in that, In step S2, the carbonization reaction takes 1 to 3 hours and the temperature is 20 to 40°C.

8. The method according to claim 7, characterized in that, In step S4, the magnesium carbonate precipitate from step S3 is dried at 100~120℃ for 2~4 h, and then calcined at 600~800℃ for 2~3 h to obtain magnesium oxide product.

9. The method according to any one of claims 1-8, characterized in that, It also includes step S5: freezing and crystallizing the magnesium solution to recover ammonium bicarbonate.

10. The method according to claim 9, characterized in that, In step S5, when the concentration of ammonium bicarbonate in the magnesium precipitation solution of step S3 is ≥ 3.5 mol / L, it is taken out for freeze crystallization. The final temperature of freeze crystallization is controlled at 0~10 ℃. After freeze crystallization, it is filtered. The ammonium bicarbonate recovered from the filter residue and the filtrate are returned to step S2 to dilute the suspension slurry.