Method for producing magnesium oxide
By using magnesium hydroxide instead of commonly used alkalis for low-temperature precipitation reactions and recycling regenerated magnesium hydroxide and strong alkalis, the problems of high energy consumption and high cost in magnesium oxide preparation have been solved, achieving the preparation of high-purity, low-cost magnesium oxide.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUIZHOU INST OF TECH
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-05
AI Technical Summary
Existing magnesium oxide preparation processes are energy-intensive, have high production costs, and suffer from impurity ions that contaminate product purity.
Magnesium hydroxide is used instead of common alkali for precipitation reaction. Combined with the recycling of regenerated magnesium hydroxide and regenerated strong alkali, the high-temperature pyrolysis step is avoided, and magnesium oxide is prepared through low-temperature magnesium precipitation reaction.
This reduces production energy consumption, lowers production costs, and improves the purity of magnesium oxide, achieving green and pollution-free magnesium oxide preparation.
Abstract
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, mainly obtained from dolomite lime slurry. The main components of dolomite lime slurry are calcium hydroxide and magnesium hydroxide, and it is primarily produced by the calcination and digestion of dolomite. In existing technologies, magnesium oxide is typically prepared by carbonation of dolomite lime slurry—the lime slurry is diluted and then carbon dioxide is introduced to initiate a carbonation reaction. Magnesium, after carbonation, enters the solution as magnesium bicarbonate, forming a carbonation liquid. The magnesium bicarbonate in the carbonation liquid undergoes high-temperature pyrolysis to precipitate basic magnesium carbonate, which is then calcined to finally yield magnesium oxide. 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 or shortcomings of existing technologies, such as high energy consumption and high production costs, and to provide a method for preparing magnesium oxide, comprising the following steps:
[0004] Step S1: Carbonize dolomite lime slurry to obtain carbonized liquid, wherein the carbonized liquid includes magnesium bicarbonate; Step S2: Magnesium hydroxide is mixed with the carbonation solution to carry out a magnesium precipitation reaction to obtain magnesium carbonate precipitate; Step S3: Calcining at least a portion of the magnesium carbonate precipitate to produce magnesium oxide product.
[0005] Compared to existing technologies, this invention uses magnesium hydroxide to precipitate magnesium, avoiding the high-temperature pyrolysis carbonization step in existing technologies, thus reducing energy consumption and production costs.
[0006] In one embodiment, in the magnesium precipitation reaction of step S2, the amount of magnesium hydroxide used is 1 to 1.2 times the theoretical amount; the theoretical amount of magnesium hydroxide is the theoretical amount of magnesium hydroxide used in the magnesium precipitation reaction.
[0007] In one embodiment, the reaction time for the magnesium precipitation reaction in step S2 is 0.5 to 2 hours, and the mixture is stirred during the reaction at a rate of 200 to 400 r / min.
[0008] In one embodiment, the process further includes step S4, regenerating magnesium hydroxide: at least a portion of the magnesium carbonate precipitate from step S2 is mixed and reacted with a strong alkaline solution, filtered, and the filter residue is regenerated magnesium hydroxide. By recycling the regenerated magnesium hydroxide, production costs can be further reduced.
[0009] In one embodiment, the strong alkaline solution in step S4 is a sodium hydroxide and / or potassium hydroxide solution.
[0010] In one embodiment, in step S4, the reaction temperature for regenerating magnesium hydroxide is 25~95°C, the reaction time is 0.5~3 hours, and the stirring rate is 300~500 r / min.
[0011] In one embodiment, the process further includes step S5, regenerating the strong alkali: the filtrate obtained from the filtration in step S4 is mixed with dolomite slurry and reacted, then filtered. The filtrate is a regenerated strong alkali solution, which is returned to step S4 for regenerating magnesium hydroxide. By regenerating the strong alkali used in the magnesium hydroxide regeneration step, production costs are further reduced.
[0012] In one embodiment, the filter residue obtained in step S5 is returned to step S1 as a supplement to the dolomite lime slurry and participates in the carbonization reaction.
[0013] In one embodiment, in step S5, the amount of dolomite lime slurry used is 1 to 1.5 times the theoretical amount, the reaction temperature is 50 to 95°C, and the reaction is stirred for 0.5 to 3 hours; the theoretical amount of dolomite lime slurry in step S5 is the theoretical amount of dolomite lime slurry used in the reaction of regenerating strong alkali.
[0014] In one embodiment, step S3 specifically involves taking 40-60% of the magnesium carbonate precipitate obtained from filtration in step S2, drying it in an oven at 100-120°C for 2-4 hours, and then calcining it at 600-800°C for 2-3 hours to obtain magnesium oxide product.
[0015] To better understand and implement this invention, the invention will be described in detail below. Detailed Implementation
[0016] Analysis of this invention reveals that after calcination, digestion, and carbonization of dolomite, the resulting product is a carbonized liquid primarily containing magnesium bicarbonate. However, existing technologies use high-temperature pyrolysis to convert the magnesium bicarbonate in the obtained solution into basic magnesium carbonate precipitate. This requires heating a large volume of solution to near boiling to maximize the conversion of magnesium into magnesium carbonate precipitate, a process that demands prolonged, high-power heating and is a major energy-consuming step. Therefore, this invention proposes a novel method for preparing magnesium oxide by employing chemical precipitation to avoid high-temperature pyrolysis of the solution, thereby addressing the problems of high energy consumption and high production costs in existing technologies.
[0017] To precipitate magnesium using chemical methods, this invention initially considered adding an alkali to the carbonized liquid after calcining and digesting dolomite. Commonly used alkalis for chemical precipitation include sodium hydroxide, ammonia, or ammonium carbonate. However, this invention found that the purity of the magnesium oxide product produced using these types of alkalis was unsatisfactory. Analysis revealed that these commonly used alkalis continuously introduce other impurity ions (such as sodium and ammonium ions) into the reaction system during the precipitation process. These impurity ions remain in the magnesium carbonate precipitation and calcination processes, resulting in low product purity (i.e., the magnesium oxide content in the product). Therefore, this invention chose magnesium hydroxide, a weak alkali not typically used for precipitation, for the magnesium precipitation reaction. Although it is a weak alkali and not a commonly used alkali for precipitation, the magnesium oxide product produced by calcining magnesium carbonate precipitated with magnesium hydroxide has higher magnesium oxide purity. Furthermore, this invention also includes steps for preparing / regenerating magnesium hydroxide using intermediate products from the magnesium oxide preparation process, as well as regenerating some intermediate reactants, for recycling, thereby reducing the purchase of magnesium hydroxide and some materials, and the amount of wastewater discharged.
[0018] The method for preparing magnesium oxide provided by the present invention will be described in detail below.
[0019] Step S1: Dilute the dolomite lime slurry and then carbonize it to obtain carbonized liquid.
[0020] Preparation of dolomite lime slurry: The dolomite lime slurry is a suspension slurry containing magnesium hydroxide and calcium hydroxide, produced by calcining and digesting dolomite. The specific preparation method is as follows: Dolomite is crushed and calcined at 800-1000 degrees Celsius for 1-3 hours. After calcination, it is ground into dolomite calcined powder with a particle size less than 100 mesh. The dolomite calcined powder is mixed with water at a weight ratio of 1:(2-6) and stirred to carry out a digestion reaction. The digestion temperature is controlled at 80-95℃, the time at 1-3 hours, and the stirring rate at 100-300 r / min. During calcination, the kiln gas generated from the dolomite calcination is used in the subsequent carbonization step. The kiln gas contains 25-40% carbon dioxide by volume.
[0021] Carbonization: Dilute the dolomite lime slurry to a liquid-to-solid volume ratio of 100:(5~15), and pump it into a carbonization reactor. Introduce the kiln gas to initiate the carbonization reaction. Control the carbonization reaction temperature at 30~50℃, and ensure the pH of the carbonization liquid is greater than 7, preferably 7~8, at the end of the reaction. This prevents over-carbonization, which could cause calcium carbonate to convert to calcium bicarbonate and dissolve into the carbonization liquid, resulting in excessive calcium content in the final product and affecting product quality. Simultaneously, continuous stirring is required during the carbonization reaction at a rate of 200~400 r / min. After the reaction is complete, filter the solution. The filtrate is the carbonization liquid, which mainly consists of magnesium bicarbonate. When diluting the dolomite lime slurry, use water, magnesium precipitate, or a mixture of both. The magnesium precipitate is the filtrate recovered in step S2. The liquid-to-solid volume ratio is the ratio of liquid volume to solid mass, expressed in mL / g.
[0022] In the carbonation reaction, diluted dolomite lime slurry reacts with carbon dioxide in the kiln gas, introducing bicarbonate ions to convert sparingly soluble magnesium hydroxide into relatively soluble magnesium bicarbonate, which then enters the carbonation solution. This achieves the effect of leaching magnesium and releasing it as ions in the solution. The reaction equation is as follows: Mg(OH)₂ + 2CO₂ = Mg(HCO₃)₂ (1); Ca(OH)2+CO2= CaCO3+H2O(2).
[0023] Step S2: Mix magnesium hydroxide with the carbonization liquid to obtain magnesium carbonate precipitate.
[0024] Specifically, the carbonized liquid from step S1 is added to a reaction tank, and magnesium hydroxide is added to carry out a magnesium precipitation reaction. The magnesium precipitation reaction time is controlled at 0.5~2 h, the amount of magnesium hydroxide added is 1~1.2 times the theoretical amount, and the stirring rate is 200~400 r / min. After the reaction is completed, the mixture is filtered. The filter residue is magnesium carbonate precipitate, part of which is used for calcination to generate magnesium oxide product, and the other part is used to regenerate magnesium hydroxide for recycling. The filtrate is magnesium precipitation liquid, which can be returned to step S1 to dilute dolomite lime milk.
[0025] The reaction equation for the magnesium precipitation reaction in this step is as follows: Mg(HCO3)2+Mg(OH)2= 2MgCO3+2H2O(3).
[0026] The theoretical amount of magnesium hydroxide in this step is the theoretical amount of magnesium hydroxide required to participate in the magnesium precipitation reaction: after detecting and calculating the total amount of magnesium bicarbonate in the carbonization solution, the theoretical amount of magnesium hydroxide required is calculated according to the reaction equation (3) above. The method for detecting the magnesium bicarbonate content in the carbonization solution is a conventional technique and will not be described in detail here.
[0027] Step S3: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.
[0028] Specifically, 40-60% of the magnesium carbonate precipitate obtained from filtration in step S2 is placed in an oven and 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.
[0029] Step S4: Regenerate magnesium hydroxide.
[0030] The remaining magnesium carbonate precipitate obtained in step S2 is mixed with a strong alkaline solution, preferably a sodium hydroxide and / or potassium hydroxide solution. The reaction temperature is 25-95℃, the reaction time is 0.5-3 h, and the stirring rate is 300-500 r / min. The amount of sodium hydroxide and / or potassium hydroxide in the strong alkaline solution is 1-3 times the theoretical amount. After the reaction is complete, the mixture is filtered. The filter residue is regenerated magnesium hydroxide, which is returned to step S2 to continue being used to convert magnesium bicarbonate into magnesium carbonate precipitate. The filtrate is a sodium carbonate or potassium carbonate solution.
[0031] The principle is as follows: Magnesium carbonate precipitate reacts when added to a solution of sodium hydroxide or potassium hydroxide. The solubility product constant of magnesium hydroxide is 1.8 × 10⁻⁶. -11 Magnesium carbonate precipitate mainly exists in the form of magnesium carbonate trihydrate, with a solubility product constant of 2.14 × 10⁻⁶. -5 The solubility product constant of magnesium hydroxide is several orders of magnitude smaller than that of magnesium carbonate trihydrate. Therefore, magnesium carbonate precipitate can react with sodium hydroxide or potassium hydroxide solution to form even less soluble magnesium hydroxide precipitate. The reaction equation for regenerating magnesium hydroxide is as follows: MgCO3 3H2O+2NaOH = Mg(OH)2+Na2CO3+3H2O(4); MgCO3 3H2O+2KOH = Mg(OH)2+K2CO3+3H2O(5).
[0032] The theoretical amount of sodium hydroxide and / or potassium hydroxide in the strong alkaline solution refers to the theoretical amount required for the reaction that converts the magnesium carbonate precipitate into magnesium hydroxide. This is calculated based on the specific type of the strong alkaline solution and the aforementioned reaction equations (4, 5) after determining the actual total magnesium carbonate content in the magnesium carbonate precipitate during this step. The method for detecting the actual total magnesium carbonate content in the magnesium carbonate precipitate is a conventional technique and will not be elaborated upon here.
[0033] Step S5: Regenerate the strong alkali.
[0034] Specifically, the filtrate obtained in step S4 is added to a reaction vessel, along with dolomite lime slurry; the amount of dolomite lime slurry used is 1 to 1.5 times the theoretical amount; the temperature is controlled at 50 to 95°C during the reaction, and the mixture is stirred for 0.5 to 3 hours. After the reaction, the mixture is filtered, and the filtrate is a regenerated sodium hydroxide and / or potassium hydroxide solution, which is returned to step S4 for the regeneration of magnesium hydroxide. In this regeneration reaction of the strong alkali, calcium hydroxide in the dolomite lime slurry reacts with the sodium carbonate and / or potassium carbonate generated in step S4 to generate a regenerated strong alkali. The specific components of the regenerated strong alkali correspond to the strong alkali solution used in step S4, which is a sodium hydroxide and / or potassium hydroxide solution. The reaction equation for the regeneration of the strong alkali in this step is as follows: Na2CO3+Ca(OH)2= CaCO3+2NaOH(6); K2CO3+Ca(OH)2= CaCO3+2KOH(7).
[0035] The theoretical amount of dolomite lime slurry in this step refers to the theoretical amount of dolomite lime slurry used in the regeneration of strong alkali. This is calculated based on the above-mentioned regeneration reaction equations (6, 7), after detecting the calcium hydroxide content in the dolomite lime slurry and detecting and calculating the total amount of target sodium carbonate or potassium carbonate, or sodium carbonate and potassium carbonate, in the filtrate from step S4 used for regenerating strong alkali. The methods for detecting the calcium hydroxide content in the dolomite lime slurry and the sodium carbonate or potassium carbonate content in the filtrate from step S4 used for regenerating strong alkali are conventional techniques and will not be elaborated upon here.
[0036] In addition, the filter residue produced in step S5 is a mixed residue mainly composed of magnesium hydroxide and calcium carbonate. This residue serves as a supplement to the raw material, dolomite lime slurry, and is returned to step S1 for dilution before undergoing a carbonation reaction with the kiln gas. Furthermore, since the calcium hydroxide in the original dolomite lime slurry has already been converted to calcium carbonate, during the carbonation reaction, carbon dioxide does not need to react 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 process time.
[0037] The present invention has the following advantages: (1) Achieving low-temperature magnesium precipitation. The addition of magnesium hydroxide to the carbonization liquid can achieve magnesium precipitation at low temperature, eliminating the need for high-temperature pyrolysis to precipitate magnesium carbonate, which greatly reduces production energy consumption and production costs.
[0038] (2) Magnesium hydroxide, sodium hydroxide, or potassium hydroxide can be regenerated, resulting in low reagent consumption and low production costs. Dolomite slurry can be used to regenerate sodium hydroxide or potassium hydroxide without the need for additional calcium hydroxide. The calcium hydroxide in the filter residue has already reacted and been converted into calcium carbonate, which can reduce carbon dioxide consumption and shorten carbonation time during carbonation.
[0039] (3) No wastewater is generated, resulting in good environmental benefits. Low-temperature magnesium precipitation allows the magnesium precipitation solution to be reused to dilute dolomite lime slurry at a relatively low temperature, and the entire process generates no wastewater.
[0040] 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 lime slurry, and realizes green, pollution-free, and low-cost production of magnesium oxide.
[0041] Example 1 This embodiment produces magnesium oxide from dolomite lime slurry, including the following steps: Step S1: Dilute the dolomite lime slurry and then carbonize it to obtain carbonized liquid.
[0042] Preparation of dolomite lime slurry: 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 slurry.
[0043] Carbonization: Dilute dolomite lime slurry with water, control the liquid-to-solid volume ratio at 100:5, and pump it into the carbonization reactor. Introduce dolomite calcination kiln gas containing 25% carbon dioxide by volume to carry out the carbonization reaction. Control the temperature at 30℃, the final pH at 7, and the stirring rate at 400 r / min. After the reaction, filter the solution. The filtrate is a carbonization solution containing magnesium bicarbonate.
[0044] Step S2: Mix magnesium hydroxide with the carbonization liquid to obtain magnesium carbonate precipitate.
[0045] Add the carbonized liquid from step S1 to the reaction tank, add magnesium hydroxide to react, control the reaction time to 2 h, the amount of magnesium hydroxide added is 1.2 times the theoretical amount, the stirring speed is 300 r / min, filter after the reaction is completed, the filter residue is magnesium carbonate precipitate, and the filtrate is returned to step S1 to dilute dolomite lime milk.
[0046] Step S3: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.
[0047] 50% of the magnesium carbonate precipitate from step S2 was added to an oven and dried at 100°C for 4 hours, and then calcined at 800°C for 2 hours to obtain magnesium oxide product. The magnesium oxide content was tested to be 99.23%.
[0048] Step S4: Regenerate magnesium hydroxide.
[0049] Add 50% of the magnesium carbonate precipitate from step S2 to a sodium hydroxide or potassium hydroxide solution for reaction, controlling the temperature at 50℃, the time at 1 h, and the stirring rate at 500 r / min. The amount of sodium hydroxide or potassium hydroxide added is twice the theoretical amount. After the reaction is complete, filter the solution. The filter residue is magnesium hydroxide, which is returned to step S2 to precipitate magnesium bicarbonate. The filtrate is a sodium carbonate or potassium carbonate solution.
[0050] Step S5: Regenerate sodium hydroxide or potassium hydroxide: Add the filtrate obtained in step S4 to the reactor, add 1.2 times the theoretical amount of dolomite lime slurry, control the temperature at 80℃, stir and react for 2 h, filter after the reaction is completed, the filtrate is a regenerated sodium hydroxide or potassium hydroxide solution, return to step S4 to prepare magnesium hydroxide, and return the filter residue to step S1 for dilution and carbonization reaction with dolomite calcination kiln gas.
[0051] Example 2 This embodiment produces magnesium oxide from dolomite lime slurry, including the following steps: Step S1: Dilute the dolomite lime slurry and then carbonize it to obtain carbonized liquid.
[0052] The preparation method of dolomite lime slurry is the same as in Example 1. The dolomite lime slurry is diluted with water, and the liquid-to-solid volume-to-mass ratio is controlled at 100:10. It is then fed into a carbonization reactor, and dolomite calcination kiln gas containing 35% carbon dioxide by volume is introduced to carry out the carbonization reaction. The temperature is controlled at 40°C, the final pH is 7.5, and the stirring rate is 200 r / min. After the reaction, the mixture is filtered, and the filtrate is the carbonized liquid.
[0053] Step S2: Mix magnesium hydroxide with the carbonization liquid to obtain magnesium carbonate precipitate.
[0054] Add the carbonized liquid from step S1 to the reaction tank, add magnesium hydroxide to react, control the reaction time to 0.5 h, the amount of magnesium hydroxide added is the theoretical amount, the stirring rate is 200 r / min, filter after the reaction is completed, the filter residue is magnesium carbonate precipitate, and the filtrate is returned to step S1 to dilute dolomite lime milk.
[0055] Step S3: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.
[0056] The magnesium carbonate precipitate was added to an oven and dried at 120°C for 2 hours, and then calcined at 600°C for 4 hours to obtain magnesium oxide product. The magnesium oxide content was tested to be 99.52%.
[0057] Step S4: Regenerate magnesium hydroxide.
[0058] Half of the magnesium carbonate precipitate from step S2 is added to a sodium hydroxide or potassium hydroxide solution for reaction. The temperature is controlled at 30°C, the time is 3 h, and the stirring rate is 300 r / min. The amount of sodium hydroxide or potassium hydroxide added is 3 times the theoretical amount. After the reaction is completed, the mixture is filtered. The filter residue is magnesium hydroxide. The magnesium hydroxide is returned to step S2 to precipitate magnesium bicarbonate. The filtrate is a sodium carbonate or potassium carbonate solution.
[0059] Step S5: Regenerate sodium hydroxide or potassium hydroxide.
[0060] Add the filtrate obtained in step S4 to the reactor, add 1.5 times the theoretical amount of dolomite lime slurry, control the temperature at 95℃, stir and react for 0.5 h, filter after the reaction is completed, the filtrate is a regenerated sodium hydroxide or potassium hydroxide solution, return to step S4 to prepare magnesium hydroxide, and return the filter residue to step S1 for dilution and carbonization reaction with dolomite calcination kiln gas.
[0061] Example 3 This embodiment produces magnesium oxide from dolomite lime slurry, including the following steps: Step S1: Dilute the dolomite lime slurry and then carbonize it to obtain carbonized liquid.
[0062] The preparation method of the dolomite lime slurry is the same as in Example 1. The dolomite lime slurry is diluted with water, and the liquid-to-solid volume-to-mass ratio is controlled at 100:15. It is then fed into a carbonization reactor, and dolomite calcination kiln gas containing 35% carbon dioxide by volume is introduced to carry out the carbonization reaction. The temperature is controlled at 45°C, the final pH is 7.7, and the stirring rate is 300 r / min. After the reaction, the mixture is filtered, and the filtrate is a magnesium bicarbonate solution.
[0063] Step S2: Mix magnesium hydroxide with the carbonization liquid to obtain magnesium carbonate precipitate.
[0064] Add the magnesium bicarbonate solution from step (1) into the reaction tank, add magnesium hydroxide to react, control the reaction time to 3 h, add magnesium hydroxide at 1.1 times the theoretical amount, stir at 400 r / min, filter after the reaction is completed, the filter residue is magnesium carbonate precipitate, and the filtrate is returned to step (1) to dilute dolomite lime milk.
[0065] Step S3: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.
[0066] The magnesium carbonate precipitate described in the step was added to an oven and dried at 110°C for 3 hours, and then calcined at 750°C for 2 hours to obtain magnesium oxide product. The magnesium oxide content was tested to be 99.29%.
[0067] Step S4: Regenerate magnesium hydroxide.
[0068] Part of the magnesium carbonate precipitate from step S2 is added to a sodium hydroxide or potassium hydroxide solution for reaction. The temperature is controlled at 90℃, the time is 0.5 h, the stirring rate is 400 r / min, and the amount of sodium hydroxide or potassium hydroxide added is 1.2 times the theoretical amount. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium hydroxide. The magnesium hydroxide is returned to step S2 for precipitation of magnesium bicarbonate, and the filtrate is a sodium carbonate or potassium carbonate solution.
[0069] Step S5: Regenerate sodium hydroxide or potassium hydroxide.
[0070] The filtrate obtained in step S4 is added to the reactor, along with the theoretical amount of dolomite lime slurry. The temperature is controlled at 95°C, and the mixture is stirred for 0.5 h. After the reaction is complete, the mixture is filtered. The filtrate is a regenerated sodium hydroxide or potassium hydroxide solution, which is returned to step S4 for the preparation of magnesium hydroxide. The filter residue is returned to step S1, diluted, and then reacted with the dolomite calcination kiln gas for carbonization.
[0071] Example 4 This embodiment produces magnesium oxide from dolomite lime slurry, including the following steps: Step S1: Dilute the dolomite lime slurry and then carbonize it to obtain carbonized liquid.
[0072] The preparation method of dolomite lime slurry is the same as in Example 1. The dolomite lime slurry is diluted with water, and the liquid-to-solid volume-to-mass ratio is controlled at 100:10. It is then fed into a carbonization reactor, and dolomite calcination kiln gas containing 40% carbon dioxide by volume is introduced to carry out the carbonization reaction. The temperature is controlled at 35°C, the final pH is 7.8, and the stirring rate is 200 r / min. After the reaction, the mixture is filtered, and the filtrate is the carbonized liquid.
[0073] Step S2: Mix magnesium hydroxide with the carbonization liquid to obtain magnesium carbonate precipitate.
[0074] The magnesium bicarbonate solution from step S1 was added to the reaction tank, and magnesium hydroxide was added to carry out the reaction. The reaction time was controlled at 1.5 h, and the amount of magnesium hydroxide added was the theoretical amount. The stirring rate was 250 r / min. After the reaction was completed, the mixture was filtered, and the filter residue was magnesium carbonate precipitate. The filtrate was returned to step S1 to dilute the dolomite lime milk.
[0075] Step S3: Calcining the magnesium carbonate precipitate to produce magnesium oxide product.
[0076] The magnesium carbonate precipitate was added to an oven and dried at 120°C for 2 hours, and then calcined at 700°C for 3 hours to obtain magnesium oxide product with a magnesium oxide content of 99.64%.
[0077] Step S4: Prepare magnesium hydroxide.
[0078] Part of the magnesium carbonate precipitate from step S2 is added to a sodium hydroxide or potassium hydroxide solution for reaction. The temperature is controlled at 30°C, the time is 3 h, the stirring rate is 450 r / min, and the amount of sodium hydroxide or potassium hydroxide added is 2.5 times the theoretical amount. After the reaction is completed, the mixture is filtered, and the filter residue is magnesium hydroxide. The magnesium hydroxide is returned to step S2 for precipitating magnesium bicarbonate, and the filtrate is a sodium carbonate or potassium carbonate solution.
[0079] Step S5: Regenerate sodium hydroxide or potassium hydroxide.
[0080] Add the filtrate obtained in step S4 to the reactor, add 1.4 times the theoretical amount of dolomite lime slurry, control the temperature at 60℃, stir and react for 1 h, filter after the reaction is completed, the filtrate is a regenerated sodium hydroxide or potassium hydroxide solution, return to step S4 to prepare magnesium hydroxide, and return the filter residue to step S1 for dilution and carbonization reaction with dolomite calcination kiln gas.
[0081] 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.
[0082] 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: Carbonize dolomite lime slurry to obtain carbonized liquid, wherein the carbonized liquid includes magnesium bicarbonate; Step S2: Magnesium hydroxide is mixed with the carbonation solution to carry out a magnesium precipitation reaction to obtain magnesium carbonate precipitate; Step S3: Calcining at least a portion of the magnesium carbonate precipitate to produce magnesium oxide product.
2. The method according to claim 1, characterized in that, In the magnesium precipitation reaction of step S2, the amount of magnesium hydroxide used is 1 to 1.2 times the theoretical amount; the theoretical amount of magnesium hydroxide is the theoretical amount of magnesium hydroxide used in the magnesium precipitation reaction.
3. The method according to claim 2, characterized in that, The reaction time for magnesium precipitation in step S2 is 0.5 to 2 hours. During the reaction, the mixture is stirred at a rate of 200 to 400 r / min.
4. The method according to claim 3, characterized in that, It also includes step S4, regenerating magnesium hydroxide: at least a portion of the magnesium carbonate precipitate from step S2 is mixed and reacted with a strong alkaline solution, filtered, and the filter residue is regenerated magnesium hydroxide.
5. The method according to claim 4, characterized in that, The strong alkaline solution in step S4 is a sodium hydroxide and / or potassium hydroxide solution.
6. The method according to claim 5, characterized in that, In step S4, the reaction temperature for regenerating magnesium hydroxide is 25~95℃, the reaction time is 0.5~3 hours, and the stirring rate is 300~500 r / min.
7. The method according to claim 6, characterized in that, It also includes step S5, regenerating strong alkali: the filtrate obtained from step S4 is mixed with dolomite lime milk and reacted, then filtered. The filtrate is a regenerated strong alkali solution, which is returned to step S4 for regenerating magnesium hydroxide.
8. The method according to claim 7, characterized in that, The filter residue obtained in step S5 is returned to step S1 as a supplement to the dolomite lime slurry and participates in the carbonization reaction.
9. The method according to claim 8, characterized in that, In step S5, the amount of dolomite lime slurry used is 1 to 1.5 times the theoretical amount, the reaction temperature is 50 to 95°C, and the reaction is stirred for 0.5 to 3 hours; the theoretical amount of dolomite lime slurry in step S5 is the theoretical amount of dolomite lime slurry used in the reaction of regenerating strong alkali.
10. The method according to claim 1, characterized in that, The specific steps of step S3 are as follows: take 40-60% of the magnesium carbonate precipitate obtained by filtration in step S2, put it in an oven and dry it at 100-120℃ for 2-4 hours, and then calcine it at 600-800℃ for 2-3 hours to obtain magnesium oxide product.