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 dolomite milk by calcining and digesting dolomite; step S2: obtaining carbonization liquid by carbonizing the dolomite milk, wherein the carbonization liquid comprises magnesium bicarbonate; step S3: adding alkali to the carbonization liquid to carry out magnesium precipitation reaction, and obtaining magnesium carbonate precipitate; the amount of the alkali in the reaction system of the magnesium precipitation reaction is 1-1.2 times of the theoretical amount; the theoretical amount of the alkali is the theoretical amount of the alkali participating in the magnesium precipitation reaction; and step S4: calcining the magnesium carbonate precipitate to generate magnesium oxide. Compared with the prior art, the present application realizes low-temperature magnesium precipitation. By adding alkali to realize magnesium precipitation, magnesium precipitation can be realized at low temperature, and high-temperature pyrolysis is not needed for magnesium carbonate precipitation, so that the production energy consumption is greatly reduced, and the production cost is reduced.

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 (MgO) is an important chemical product, typically produced from dolomite. my country has abundant, widely distributed, and high-quality dolomite reserves. Dolomite's main components are calcium carbonate and magnesium carbonate, making it one of the primary raw materials for producing active MgO in my country. Current technology typically uses a carbonation method to process dolomite into MgO—the dolomite is calcined, crushed, and slaked to produce dolomite lime slurry. This lime slurry is then diluted and carbon dioxide is introduced to initiate the carbonation reaction. Magnesium, after carbonation, enters the carbonation solution as magnesium bicarbonate. The magnesium bicarbonate in the carbonation solution undergoes high-temperature pyrolysis to precipitate basic magnesium carbonate, which is then calcined to finally obtain MgO. However, this process suffers from high energy consumption and high production costs. Summary of the Invention

[0003] Based on this, the purpose of this invention is to overcome the defects and shortcomings of high energy consumption and high production cost in the prior art, and to provide a method for preparing magnesium oxide, comprising the following steps:

[0004] Step S1: Calcining and digesting dolomite to obtain dolomite lime milk; Step S2: Carbonize the dolomite lime slurry to obtain a carbonization solution, wherein the carbonization solution includes magnesium bicarbonate; Step S3: Add alkali to the carbonization liquid to carry out a magnesium precipitation reaction to obtain magnesium carbonate precipitate; the amount of alkali used in the magnesium precipitation reaction system is 1 to 1.2 times the theoretical amount; the theoretical amount of alkali is the theoretical amount of alkali to participate in the magnesium precipitation reaction; Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0005] Compared to existing technologies, this invention achieves magnesium precipitation by adding alkali, which can precipitate magnesium at low temperatures without the need for high-temperature pyrolysis to precipitate magnesium carbonate, greatly reducing production energy consumption and production costs.

[0006] In one embodiment, in step S3, the alkali is one or more of sodium hydroxide, sodium carbonate, ammonia, and ammonium carbonate.

[0007] In one embodiment, in step S3, the reaction time of the magnesium precipitation reaction is 0.5 to 2 hours. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate, and the filtrate is magnesium precipitation solution.

[0008] In one embodiment, in step S1, the calcination temperature is 800~1000℃, the calcination time is 1~3 h, and coarse particles are obtained after calcination; the coarse particles obtained by calcination are ground to a particle size of less than 100 mesh to obtain dolomite calcined powder, which is used for subsequent digestion steps. The digestion process specifically involves mixing calcined dolomite powder with water at a weight ratio of 1:(2~6) and stirring to carry out a digestion reaction. The digestion temperature is 80~95℃, the time is 1~3 h, and the stirring rate is 100~300 r / min to obtain dolomite lime milk.

[0009] In one embodiment, in step S2, the dolomite lime slurry is first diluted, and then carbon dioxide is introduced into the diluted dolomite lime slurry for carbonization.

[0010] In one embodiment, in step S2, the kiln gas containing carbon dioxide generated from the calcination in step S1 is passed into diluted dolomite lime slurry for carbonization reaction; water or the magnesium precipitate is used to dilute the dolomite lime slurry; the liquid-to-solid volume-to-mass ratio of the diluted dolomite lime slurry is 100:(5~15); the temperature is controlled at 30~50℃ during the carbonization reaction, the final pH is 7~8, and the stirring rate is 200~400 r / min.

[0011] In one embodiment, in step S4, the magnesium carbonate precipitate is first dried at 100~120℃ for 2~4 h, and then calcined at 600~800℃ for 2~3 h to obtain magnesium oxide product.

[0012] In one embodiment, the method further includes step S5, alkali regeneration: when the concentration of sodium bicarbonate or ammonium bicarbonate, or the total concentration of sodium bicarbonate and ammonium bicarbonate in the magnesium precipitation solution of step S3 is greater than or equal to 0.5 mol / L, at least a portion of the magnesium precipitation solution is taken out, the dolomite lime slurry is added to it, and the reaction is carried out by stirring for 0.5 to 3 h. After the reaction is completed, the solution is filtered, the filtrate is the regenerated alkali solution, and the filter residue is a mixed residue of calcium carbonate and magnesium hydroxide.

[0013] In one embodiment, the regenerated alkali is used for the magnesium precipitation reaction in step S3.

[0014] In one embodiment, the filter residue generated from the alkali regeneration in step S5 is used in step S2 as a supplement to the dolomite lime slurry in the carbonization reaction.

[0015] The alkali is renewable and recyclable, resulting in low reagent consumption and low production costs; no wastewater is generated, leading to good environmental benefits. 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 present invention will now be described in detail.

[0019] A method for low-cost production of magnesium oxide from dolomite includes the following steps: Step S1: Calcining and digesting dolomite to obtain dolomite lime milk.

[0020] The calcination process specifically involves: crushing dolomite and calcining it in a muffle furnace at a controlled temperature of 800-1000℃ for 1-3 hours, resulting in coarse particles. These coarse particles are then ground into powder using a grinding mill to a particle size less than 100 mesh, yielding calcined dolomite powder for subsequent digestion steps. Additionally, the kiln gas generated during dolomite calcination is collected for subsequent carbonization steps; this kiln gas contains 25-40% carbon dioxide by volume.

[0021] The digestion process specifically involves mixing calcined dolomite powder with water at a weight ratio of 1:(2~6) and stirring to carry out the digestion reaction. The digestion temperature is controlled at 80~95℃, the time is 1~3 h, and the stirring rate is 100~300 r / min to obtain a suspension slurry containing magnesium hydroxide and calcium hydroxide, which is referred to in this invention as dolomite lime milk.

[0022] Step S2: Carbonize the dolomite lime slurry to obtain carbonized liquid.

[0023] Specifically, the dolomite lime slurry is diluted to a liquid-to-solid volume-to-mass ratio of 100:(5~15), and then fed into a carbonization reactor. The kiln gas is introduced into the diluted dolomite lime slurry in the carbonization reactor to react with it to form a carbonization liquid. The temperature is controlled at 30~50℃, the final pH is 7~8, and the stirring rate is 200~400 r / min.

[0024] The liquid-to-solid volume-to-mass ratio is the ratio of the liquid volume to the solid mass, expressed in mL / g. When diluting the dolomite lime slurry, water, magnesium precipitate, or a mixture of water and magnesium precipitate are used. The magnesium precipitate is the filtrate recovered in step S3.

[0025] In the carbonization reaction, diluted dolomite lime slurry reacts with carbon dioxide in the kiln gas to form a carbonization liquid. This carbonization liquid introduces bicarbonate ions, converting sparingly soluble magnesium hydroxide into relatively soluble magnesium bicarbonate, thereby achieving the effect of leaching magnesium and releasing it as ions in the solution. Therefore, the carbonization liquid contains magnesium bicarbonate. The reaction equation for the carbonization reaction is as follows: Mg(OH)₂ + 2CO₂ = Mg(HCO₃)₂ (1); Ca(OH)2+CO2= CaCO3+H2O(2).

[0026] Step S3: Add alkali to the carbonized liquid to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0027] Specifically, the carbonized liquid obtained in step S2 is added to a reaction tank, alkali is added and stirred to carry out a magnesium precipitation reaction. The amount of alkali in the reaction system for the magnesium precipitation reaction is 1 to 1.2 times its theoretical amount, and the reaction time is 0.5 to 2 hours. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate, while the filtrate is magnesium precipitation liquid. The magnesium precipitation liquid can be returned to step S2 to dilute dolomite lime milk and participate in the carbonation leaching of magnesium bicarbonate.

[0028] The alkali is one or more of sodium hydroxide, sodium carbonate, ammonia, and ammonium carbonate.

[0029] The theoretical amount of alkali used in this step, i.e., the theoretical amount of alkali required for the magnesium precipitation reaction, is calculated based on the reaction equation below, after detecting and calculating the total amount of magnesium bicarbonate in the carbonization solution, according to the specific type of alkali used. The method for detecting the magnesium bicarbonate content in the carbonization solution is a conventional technique and will not be elaborated upon here.

[0030] The reaction equations for the precipitation of magnesium carbonate in various alkali solutions to form magnesium carbonate precipitate and magnesium precipitation solution are as follows: Mg(HCO3)2+ NaOH = MgCO3+ NaHCO3+ H2O(3); Mg(HCO3)2+ Na2CO3= MgCO3+ 2NaHCO3(4); Mg(HCO3)2+ NH3 H2O = MgCO3+ NH4HCO3+ H2O(5); Mg(HCO3)2+(NH4)2CO3= MgCO3+ 2NH4HCO3(6).

[0031] Magnesium carbonate precipitate solution containing bicarbonate ions introduces more bicarbonate ions into diluted dolomite lime slurry, which can improve the formation efficiency of magnesium carbonate.

[0032] Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0033] Specifically, the magnesium carbonate precipitate 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 the target magnesium oxide product.

[0034] In this way, compared with the prior art, the magnesium oxide preparation method provided by the present invention uses a chemical magnesium precipitation method that does not require heating. Compared with the high-temperature pyrolysis magnesium precipitation method that requires long-term heating in the prior art, it can effectively reduce energy consumption and reduce production costs.

[0035] Furthermore, this invention has found that as the magnesium precipitation solution is continuously recycled, the concentration of sodium bicarbonate or ammonium bicarbonate gradually increases. If the concentration of sodium bicarbonate or ammonium bicarbonate in the solution is too high, when the solution is recycled back to the carbonation reaction in step S2, the presence of sodium bicarbonate or ammonium bicarbonate in the solution will significantly reduce the solubility of magnesium bicarbonate, and the concentration of magnesium bicarbonate in the carbonation solution will decrease significantly. Tests have shown that when the concentration of sodium bicarbonate or ammonium bicarbonate in the solution, or the total concentration of sodium bicarbonate and ammonium bicarbonate, is less than 0.5 mol / L, the concentration of magnesium bicarbonate in the carbonation solution remains essentially unchanged or decreases only slightly, without affecting the formation of magnesium bicarbonate from magnesium in the solution; however, concentrations greater than 0.5 mol / L will begin to negatively affect the solubility of magnesium bicarbonate in magnesium carbonate.

[0036] Therefore, in a preferred embodiment, the present invention further includes step S5: alkali regeneration. This involves reacting calcium hydroxide in the dolomite slurry with sodium bicarbonate or ammonium bicarbonate in the magnesium precipitation solution, causing the sodium bicarbonate or ammonium bicarbonate in the magnesium precipitation solution to revert to an alkali of ammonium carbonate, sodium carbonate, sodium hydroxide, and ammonia. The regenerated alkali can then be returned to step S3 to react with the carbonation solution for magnesium precipitation. This alkali regeneration step allows for the continuous cyclical transformation of bicarbonate and carbonate ions, eliminating the need for continuous alkali addition during the magnesium precipitation reaction and reducing the discharge of wastewater containing bicarbonate ions. The reaction equation for alkali regeneration is as follows: 2NaHCO3+Ca(OH)2= Na2CO3+CaCO3+2H2O(7); NaHCO3+Ca(OH)2= NaOH+CaCO3+H2O(8); 2NH4HCO3+Ca(OH)2= (NH4)2CO3+CaCO3+2H2O(9); NH4HCO3 + Ca(OH)2 = NH3 H2O + CaCO3 + H2O (10).

[0037] The specific steps of step S5 are as follows.

[0038] Specifically, when the concentration of sodium bicarbonate or ammonium bicarbonate, or the total concentration of sodium bicarbonate and ammonium bicarbonate in the magnesium precipitation solution of step S3 is greater than or equal to 0.5 mol / L, at least a portion of the magnesium precipitation solution is taken out, and dolomite lime slurry obtained in step S1 (used in step S2) is added to it for reaction. The amount of dolomite lime slurry added is controlled to be 1 to 1.5 times its theoretical amount. The reaction is stirred for 0.5 to 3 hours. After the reaction is completed, the solution is filtered. The filtrate is a regenerated alkali solution, and the filter residue is a mixed residue of calcium carbonate and magnesium hydroxide. The filter residue, as a supplement to the raw material dolomite lime slurry, is returned to step S2 to participate in the carbonation reaction to leach out the magnesium hydroxide in the filter residue to form magnesium bicarbonate, playing the same role as the dolomite lime slurry. The filtrate is the regenerated alkali solution, which can be used for the magnesium precipitation reaction in step S3.

[0039] The theoretical amount of dolomite lime slurry in this step is the theoretical amount of dolomite lime slurry used in the alkali regeneration reaction: after detecting the calcium hydroxide content in the dolomite lime slurry and detecting and calculating the total amount of target sodium bicarbonate or ammonium bicarbonate or sodium bicarbonate and ammonium bicarbonate in the magnesium precipitation solution to be used for alkali regeneration, the theoretical amount of dolomite lime slurry required is calculated according to the above-mentioned alkali regeneration reaction equations (7) to (10). Among them, the detection methods for the calcium hydroxide in the dolomite lime slurry and the sodium bicarbonate or ammonium bicarbonate or sodium bicarbonate and ammonium bicarbonate in the magnesium precipitation solution are conventional techniques and will not be described in detail here.

[0040] In a preferred embodiment, the precipitate from the magnesium precipitate after alkali regeneration in step S5 using dolomite lime slurry can be returned to step S2 to participate in the carbonation reaction. Since calcium hydroxide is converted to calcium carbonate first during alkali regeneration of dolomite lime slurry, while magnesium hydroxide does not participate in the alkali regeneration reaction, during the carbonation reaction, carbon dioxide no longer reacts with calcium hydroxide to form calcium carbonate first and then with magnesium hydroxide to form magnesium bicarbonate; instead, it can react directly with magnesium hydroxide, significantly shortening the carbonation reaction time.

[0041] In summary, the present invention also has the following advantages: (1) Achieve low-temperature magnesium precipitation. By adding alkali to achieve magnesium precipitation, magnesium can be precipitated at low temperature without the need for high-temperature pyrolysis to precipitate magnesium carbonate, which greatly reduces production energy consumption and production costs.

[0042] (2) The alkali is regenerable, the reagent consumption is small, and the production cost is low. Dolomite lime milk can be used for alkali regeneration without the need to add calcium hydroxide. The calcium hydroxide in the filter residue has already reacted and been converted into calcium carbonate. During carbonation, the amount of carbon dioxide consumed can be reduced and the carbonation time can be shortened.

[0043] (3) No wastewater is generated, resulting in good environmental benefits. The solution in the entire process is recycled, and there is no wastewater discharge.

[0044] This invention effectively solves the problems of high energy consumption, high cost, and serious environmental pollution in the existing process of producing magnesium oxide from dolomite. This invention is applicable to the production of magnesium oxide from dolomite and realizes green, efficient, and low-cost production of magnesium oxide.

[0045] Based on the above method, the following describes specific embodiments using different specific parameters.

[0046] Example 1 This embodiment prepares magnesium oxide from dolomite (whose main components, by weight percentage, are 21.18% MgO, 30.35% CaO, 0.87% SiO2, 0.31% Al2O3, and 0.76% Fe2O3) by the following steps: Step S1: Calcining and digesting dolomite to obtain dolomite lime milk.

[0047] Dolomite was crushed and calcined in a muffle furnace at 900℃ for 2 hours. The coarse particles obtained from calcination were ground into 200-mesh dolomite calcined powder using a grinding mill. The dolomite calcined powder was mixed with water at a weight ratio of 1:4 and stirred for digestion reaction at 80℃ for 2 hours with a stirring rate of 200 r / min to obtain a suspension slurry containing magnesium hydroxide and calcium hydroxide—dolomite lime milk.

[0048] Step S2: Carbonize the dolomite lime slurry to obtain carbonized liquid.

[0049] Dolomite lime slurry was diluted with water, and the liquid-to-solid volume-to-mass ratio was controlled at 100:8 (unit: mL / g). It was then fed into a carbonization reactor, and kiln gas containing 35% carbon dioxide by volume of dolomite was introduced to carry out the carbonization reaction. The temperature was controlled at 30℃, the final pH was 7.5, and the stirring rate was 300 r / min. After the reaction, the mixture was filtered, and the filtrate was the carbonized liquid.

[0050] Step S3: Add alkali to the carbonized liquid to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0051] Add the carbonized liquid from step S2 into the reaction tank, add sodium hydroxide to react, control the reaction time to 2 h, and add the theoretical amount of sodium hydroxide. After the reaction is completed, filter, and the filter residue is magnesium carbonate precipitate. The filtrate, i.e. magnesium precipitate, is returned to step S2 to dilute dolomite lime milk.

[0052] Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0053] The magnesium carbonate precipitate was dried in an oven at 100°C for 4 hours, and then calcined at 800°C for 2 hours to obtain the magnesium oxide product. The final product obtained in this embodiment has a magnesium oxide content of 99.62%.

[0054] In the above-mentioned production process, this embodiment also simultaneously performs alkali regeneration.

[0055] Step S5: Alkali regeneration.

[0056] When the concentration of sodium bicarbonate solution in step S3 reaches 0.5 mol / L, a portion of the sodium bicarbonate solution is added to dolomite lime slurry for reaction. The amount of dolomite lime slurry added is controlled to be 1.2 times the theoretical amount. The reaction is stirred for 2 hours. After the reaction is completed, the mixture is filtered, and the filter residue is returned to step S2 for carbonation reaction to leach magnesium bicarbonate. The filtrate is a regenerated sodium hydroxide solution.

[0057] The regenerated sodium hydroxide can be recycled to step S3 for magnesium precipitation: add the regenerated sodium hydroxide to the reactor, add the carbonized liquid from step S2 to react, control the sodium hydroxide to be 1.1 times the theoretical amount, stir the reaction for 1 h, filter after the reaction, the filter residue is magnesium carbonate precipitate, which can be used to continue calcination to generate magnesium oxide; the filtrate is divided into two parts, one part is returned to step S2 to dilute dolomite lime milk, and the remaining filtrate is returned to step S5 for alkali regeneration.

[0058] Example 2 This embodiment describes the production of magnesium oxide from dolomite (whose main components, by weight percentage, are 21.92% MgO, 29.78% CaO, 0.42% SiO2, 0.15% Al2O3, and 0.27% Fe2O3) by the following steps: Step S1: Calcining and digesting dolomite to obtain dolomite lime milk.

[0059] Dolomite was crushed and calcined in a muffle furnace at 800℃ for 3 hours. The coarse particles obtained from calcination were ground into 150-mesh dolomite calcined powder using a grinding mill. The dolomite calcined powder was then reacted with water at a weight ratio of 1:6, with the temperature controlled at 95℃ for 1 hour and the stirring rate at 100 r / min, to obtain a suspension slurry containing magnesium hydroxide and calcium hydroxide—dolomite lime milk.

[0060] Step S2: Carbonize the dolomite lime slurry to obtain carbonized liquid.

[0061] Dolomite lime slurry was diluted with water, and the liquid-to-solid volume-to-mass ratio was controlled at 100:5 (unit: mL / g). It was then fed into a carbonization reactor, and kiln gas containing 40% carbon dioxide by volume of dolomite was introduced to carry out the carbonization reaction. The temperature was controlled at 40℃, the final pH was 7, and the stirring rate was 200 r / min. After the reaction, the mixture was filtered, and the filtrate was the carbonized liquid.

[0062] Step S3: Add alkali to the carbonized liquid to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0063] The carbonized liquid from step S2 was added to a reaction tank, and sodium carbonate was added to initiate the reaction. The reaction time was controlled at 0.5 h, and the amount of sodium carbonate added was 1.2 times the theoretical amount. After the reaction was completed, the mixture was filtered, and the filter residue was magnesium carbonate precipitate. The filtrate was returned to step S2 for diluting the dolomite lime slurry. The final product obtained in this embodiment had a magnesium oxide content of 99.47%.

[0064] Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0065] The magnesium carbonate precipitate was added to an oven and dried at 120°C for 2 hours, and then calcined at 600°C for 3 hours to obtain magnesium oxide product.

[0066] Step S5: Alkali regeneration.

[0067] When the sodium bicarbonate solution concentration in step S3 is 0.6 mol / L, a portion of the sodium bicarbonate solution is taken and added to dolomite lime slurry for reaction. The amount of dolomite lime slurry added is controlled to be 1.5 times the theoretical amount. The reaction is stirred for 0.5 h, and then filtered after the reaction is complete. The filtrate is a regenerated sodium carbonate solution, and the filter residue is returned to step S2 for carbonation reaction to leach magnesium bicarbonate.

[0068] The regenerated sodium carbonate solution can be recycled to step S3 for magnesium precipitation: the regenerated sodium carbonate solution is added to the reaction vessel, and the carbonation liquid from step S2 is added to react. The amount of sodium carbonate is controlled to be 1.2 times the theoretical amount. The reaction is stirred for 2 hours. After the reaction is completed, the mixture is filtered. The filter residue is magnesium carbonate precipitate. The filtrate is divided into two parts. One part is returned to step S2 to dilute the dolomite lime milk, and the remaining filtrate is returned to step S5 for alkali regeneration.

[0069] Example 3 This embodiment describes the production of magnesium oxide from dolomite (whose main components, by weight percentage, are 20.45% MgO, 31.29% CaO, 0.22% SiO2, 0.17% Al2O3, and 0.36% Fe2O3) by the following steps: Step S1: Calcining and digesting dolomite to obtain dolomite lime milk.

[0070] Dolomite was crushed and calcined in a muffle furnace at 1000℃ for 1 hour. The coarse particles obtained from calcination were ground to 200 mesh using a grinding mill to obtain calcined dolomite powder. The calcined dolomite powder was then mixed with water at a weight ratio of 1:3 for a digestion reaction at 90℃ for 1.5 hours with a stirring rate of 300 r / min, resulting in a suspension slurry containing magnesium hydroxide and calcium hydroxide—dolomite lime milk.

[0071] Step S2: Carbonize the dolomite lime slurry to obtain carbonized liquid.

[0072] Dolomite lime slurry was diluted with water, and the liquid-to-solid volume-to-mass ratio was controlled at 100:15 (unit: mL / g). It was then fed into a carbonization reactor, and kiln gas containing 40% carbon dioxide by volume of dolomite was introduced to carry out the carbonization reaction. The temperature was controlled at 40℃, the final pH was 7.5, and the stirring rate was 400 r / min. After the reaction, the mixture was filtered, and the filtrate was the carbonized liquid.

[0073] Step S3: Add alkali to the carbonized liquid to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0074] The carbonized liquid from step S2 is added to the reaction tank, and ammonia water is added to carry out the reaction. The reaction time is controlled at 1 hour, and the amount of ammonia water added is 1.1 times the theoretical amount. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate. The filtrate is returned to step S2 to dilute the dolomite lime milk.

[0075] Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0076] The magnesium carbonate precipitate was added to an oven and dried at 110°C for 3 hours, then calcined at 700°C for 2.5 hours to obtain the magnesium oxide product. The final product obtained in this embodiment has a magnesium oxide content of 99.53%.

[0077] Step S5: Alkali regeneration.

[0078] When the concentration of sodium bicarbonate solution in step S3 reaches 0.7 mol / L, take a portion of the ammonium bicarbonate solution and add dolomite lime slurry to react. Control the amount of dolomite lime slurry added to be 1.1 times the theoretical amount. Stir the reaction for 3 hours. After the reaction is completed, filter the solution. The filter residue is returned to step S2 for carbonation reaction to leach magnesium bicarbonate. The filtrate is a regenerated ammonia solution.

[0079] The regenerated ammonia solution can be recycled to step S3 for magnesium precipitation: add the regenerated ammonia solution to the reactor, add the carbonized liquid from step S2 to react, control the ammonia solution to the theoretical amount, stir the reaction for 0.5 h, filter after the reaction, the filter residue is magnesium carbonate precipitate, the filtrate is divided into two parts, one part is returned to step S2 to dilute dolomite lime milk, and the remaining filtrate is returned to step S5 for alkali regeneration.

[0080] Example 4 This embodiment describes the production of magnesium oxide from dolomite (whose main components, by weight percentage, are 21.05% MgO, 30.28% CaO, 0.33% SiO2, 0.39% Al2O3, and 0.54% Fe2O3) by the following steps: Step S1: Calcining and digesting dolomite to obtain dolomite lime milk.

[0081] Dolomite was crushed and calcined in a muffle furnace at 850℃ for 3 hours. The coarse particles obtained from calcination were then ground into 300-mesh dolomite calcined powder using a grinding mill. The dolomite calcined powder was then reacted with water at a weight ratio of 1:5, with the temperature controlled at 90℃ for 1 hour and the stirring rate at 150 r / min, to obtain a suspension slurry containing magnesium hydroxide and calcium hydroxide.

[0082] Step S2: Carbonize the dolomite lime slurry to obtain carbonized liquid.

[0083] Dolomite lime slurry was diluted with water, and the liquid-to-solid volume-to-mass ratio was controlled at 100:10 (unit: mL / g). It was then fed into a carbonization reactor, and dolomite calcination kiln gas containing 25% carbon dioxide by volume was introduced to carry out the carbonization reaction. The temperature was controlled at 45℃, the final pH was 7.6, and the stirring rate was 250 r / min. After the reaction, the mixture was filtered, and the filtrate was the carbonized liquid.

[0084] Step S3: Add alkali to the carbonized liquid to carry out a magnesium precipitation reaction, and obtain magnesium carbonate precipitate and magnesium precipitation liquid.

[0085] The carbonized liquid from step S2 is added to the reaction tank, and ammonium carbonate is added to react. The reaction time is controlled at 1.5 h, and the amount of ammonium carbonate added is 1.05 times the theoretical amount. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate. The filtrate is returned to step S2 to dilute the dolomite lime milk.

[0086] Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

[0087] The magnesium carbonate precipitate was added to an oven and dried at 120°C for 3 hours, then calcined at 750°C for 3 hours to obtain the magnesium oxide product. The final product obtained in this embodiment has a magnesium oxide content of 99.38%.

[0088] Step S5: Alkali regeneration.

[0089] When the concentration of the ammonium bicarbonate solution in step S3 reaches 0.65 mol / L, take a portion of the ammonium bicarbonate solution and add dolomite lime slurry to react. Control the amount of dolomite lime slurry added to be 1.35 times the theoretical amount. Stir the reaction for 1 h. After the reaction is completed, filter the solution. The filtrate is the regenerated ammonium bicarbonate solution. The filter residue is returned to step S2 for carbonation reaction to leach magnesium bicarbonate.

[0090] The regenerated ammonium carbonate solution can be recycled to step S3 for magnesium precipitation: the regenerated ammonium carbonate solution is added to the reactor, and the carbonation liquid from step S2 is added to react. The amount of ammonium carbonate is controlled to be 1.15 times the theoretical amount. The reaction is stirred for 1.5 h. After the reaction is completed, the mixture is filtered. The filter residue is magnesium carbonate precipitate. The filtrate is divided into two parts. One part is returned to step S2 to dilute the dolomite lime milk, and the remaining filtrate is returned to step S5 for alkali regeneration.

[0091] 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 terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. 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.

[0092] 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: Calcining and digesting dolomite to obtain dolomite lime milk; Step S2: Carbonize the dolomite lime slurry to obtain a carbonization solution, wherein the carbonization solution includes magnesium bicarbonate; Step S3: Add alkali to the carbonization liquid to carry out a magnesium precipitation reaction to obtain magnesium carbonate precipitate; the amount of alkali used in the magnesium precipitation reaction system is 1 to 1.2 times the theoretical amount; the theoretical amount of alkali is the theoretical amount of alkali to participate in the magnesium precipitation reaction; Step S4: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.

2. The method according to claim 1, characterized in that, In step S3, the alkali is one or more of sodium hydroxide, sodium carbonate, ammonia, and ammonium carbonate.

3. The method according to claim 2, characterized in that, In step S3, the reaction time for the magnesium precipitation reaction is 0.5 to 2 hours. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium carbonate precipitate, while the filtrate is magnesium precipitation solution.

4. The method according to claim 3, characterized in that, In step S1, the calcination temperature is 800~1000℃ and the calcination time is 1~3 h. After calcination, coarse particles are obtained. The coarse particles obtained by calcination are ground to a particle size of less than 100 mesh to obtain dolomite calcined powder, which is used for subsequent digestion steps. The digestion process specifically involves mixing calcined dolomite powder with water at a weight ratio of 1:(2~6) and stirring to carry out a digestion reaction. The digestion temperature is 80~95℃, the time is 1~3 h, and the stirring rate is 100~300 r / min to obtain dolomite lime milk.

5. The method according to claim 4, characterized in that, In step S2, the dolomite lime slurry is first diluted, and then carbon dioxide is introduced into the diluted dolomite lime slurry for carbonization.

6. The method according to claim 5, characterized in that, In step S2, the kiln gas containing carbon dioxide generated from the calcination in step S1 is passed into diluted dolomite lime slurry to carry out a carbonization reaction. The dolomite lime slurry is diluted with water or the magnesium precipitation solution; the liquid-to-solid volume ratio of the diluted dolomite lime slurry is 100:(5~15). During the carbonization reaction, the temperature is controlled at 30~50℃, the final pH is 7~8, and the stirring rate is 200~400 r / min.

7. The method according to claim 6, characterized in that, In step S4, the magnesium carbonate precipitate is first dried at 100-120°C for 2-4 hours, and then calcined at 600-800°C for 2-3 hours to obtain magnesium oxide product.

8. The method according to claim 3, characterized in that, The process also includes step S5, alkali regeneration: when the concentration of sodium bicarbonate or ammonium bicarbonate or the total concentration of sodium bicarbonate and ammonium bicarbonate in the magnesium precipitation solution of step S3 is greater than or equal to 0.5 mol / L, at least a portion of the magnesium precipitation solution is taken out, the dolomite lime slurry is added to it, and the reaction is carried out by stirring for 0.5 to 3 hours. After the reaction is completed, the solution is filtered, the filtrate is the regenerated alkali solution, and the filter residue is a mixed residue of calcium carbonate and magnesium hydroxide.

9. The method according to claim 8, characterized in that, The regenerated alkali is used in the magnesium precipitation reaction of step S3.

10. The method according to claim 8, characterized in that, The filter residue generated from the alkali regeneration in step S5 is used in step S2 as a supplement to the dolomite lime slurry in the carbonization reaction.