A method for roasting, carbonizing, separating calcium and magnesium from dolomite, and a method for comprehensive utilization.

Abstract

This invention provides a method for calcining dolomite, a carbonization method, a calcium-magnesium separation method, and a comprehensive utilization method. The comprehensive utilization method of dolomite includes: calcining dolomite powder to obtain calcined white powder; subjecting the calcined white powder to digestion and aging treatments sequentially to obtain an aging liquid; carbonizing the aging liquid to obtain a carbonization reaction liquid; performing solid-liquid separation on the carbonization reaction liquid to obtain heavy magnesium water and a first solid separate; pyrolyzing the heavy magnesium water to obtain a pyrolysis reaction liquid; performing solid-liquid separation on the pyrolysis reaction liquid to obtain a decomposition liquid and a second solid separate; calcining the second solid separate with magnesium carbonate to obtain magnesium oxide; and reducing the magnesium oxide to obtain metallic magnesium and magnesium aluminum spinel. This invention achieves comprehensive utilization of dolomite resources, with no waste residue or exhaust gas emissions. The main product is metallic magnesium, and the by-products are light calcium carbonate, magnesium aluminum spinel, and solid carbon dioxide.

Description

Technical Field

[0001] This invention relates to the resource utilization of dolomite and the preparation of metallic magnesium, and particularly to a method for roasting dolomite, a carbonization method, a calcium-magnesium separation method, and a comprehensive utilization method. Background Technology

[0002] Dolomite, with the chemical composition CaMg(CO3)2, is a trigonal carbonate mineral and an important source of calcium and magnesium. It is commonly used to produce metallic magnesium. The Pidgeon process for magnesium smelting refers to a thermal reduction method in which calcined dolomite (calcined white dolomite) is reduced to metallic magnesium using ferrosilicon as a reducing agent in a reduction furnace heated externally and fed into a reduction vessel. Although the Pidgeon process is a traditional magnesium smelting technology, it suffers from industrial problems such as high energy consumption, low resource utilization, large slag volume, and high emissions.

[0003] Chinese invention patent application CN115141941A discloses a comprehensive utilization method for dolomite. The method involves calcining dolomite to obtain calcined dolomite; digesting the calcined dolomite and then aging it to obtain a digestion solution; mixing the digestion solution with carbon dioxide and carbonizing it until the pH value of the digestion solution reaches a preset value to complete carbonation; then performing solid-liquid separation to obtain magnesium hydroxide and calcium carbonate filter cake; pyrolyzing the magnesium hydroxide and then performing solid-liquid separation to obtain basic magnesium carbonate filter cake; drying and calcining the basic magnesium carbonate filter cake to obtain magnesium oxide; mixing and pressing the magnesium oxide with a reducing agent to obtain lumps; vacuum reducing the lumps to obtain metallic magnesium and magnesium aluminum spinel; and drying the calcium carbonate filter cake to obtain light calcium carbonate. Although the patent application is based on dolomite to obtain metallic magnesium, magnesium aluminum spinel and light calcium carbonate, it does not make any in-depth improvements to the calcination of dolomite, which easily leads to recarbonation and the presence of unreacted carbonate ions in the calcined dolomite. Furthermore, it does not improve the carbonation process, nor does it further improve the calcium-magnesium separation efficiency or the quality of the product.

[0004] In view of this, it is necessary to provide a method for roasting dolomite, a method for carbonization, a method for separating calcium and magnesium, and a method for comprehensive utilization, so as to solve or at least alleviate the above-mentioned technical defects of dolomite calcination being prone to recarbonization, the presence of unreacted carbonate ions, and incomplete separation of calcium and magnesium during the carbonization process. Summary of the Invention

[0005] The main objective of this invention is to provide a method for roasting dolomite, a carbonization method, a calcium-magnesium separation method, and a comprehensive utilization method, aiming to solve the above-mentioned technical defects of dolomite calcination being prone to recarbonization, the presence of unreacted carbonate ions, and incomplete calcium-magnesium separation during the carbonization process.

[0006] To achieve the above objectives, the present invention provides a method for separating calcium and magnesium, comprising the following steps:

[0007] S1 provides dolomite powder;

[0008] S2, the dolomite powder is calcined to obtain calcined white powder; and carbon dioxide gas is collected during the dolomite calcination process.

[0009] The dolomite roasting process includes the following sub-steps:

[0010] S21, the dolomite powder is controlled to undergo fluidized bed roasting in the main furnace body to obtain the initial calcined material; the temperature of the fluidized bed roasting is 950-1100℃, and the duration of the fluidized bed roasting is 0.5-1.5h;

[0011] S22, control the initial calcined material to enter the high-temperature retention chamber before cooling, and obtain the retention material; the temperature of the initial calcined material in the high-temperature retention chamber is 900-1000℃, the retention time of the initial calcined material in the high-temperature retention chamber is 1-2h, and the high-temperature retention chamber is connected to the fluidized bed roasting main furnace.

[0012] S23, the retained material is screened to obtain a first retained material and a second retained material; the first retained material contains a first grade of retained material, and the second retained material contains two grades of retained material, wherein the particle size of the first grade of retained material is smaller than the particle size of the second grade of retained material and / or the mass of the first grade of retained material is smaller than the mass of the second grade of retained material.

[0013] S24, the first retained material is used as the calcined white powder; the second retained material is subjected to cyclic calcination to obtain the calcined white powder, the cyclic calcination temperature is 950-1100℃, and the cyclic calcination time is 5-10min;

[0014] S3, the calcined white powder is digested to obtain a digestion liquid; the digestion liquid is then separated into solid and liquid, and then subjected to aging treatment and solid-liquid separation in sequence to obtain an aged liquid;

[0015] S4, the aging liquid is subjected to carbonization treatment to obtain a carbonization reaction liquid; the carbonization reaction liquid is subjected to solid-liquid separation to obtain heavy magnesium water and a first solid separator; the first solid separator contains calcium carbonate;

[0016] S5, the magnesium hydroxide is subjected to pyrolysis to obtain a pyrolysis reaction solution, and carbon dioxide gas is collected during the pyrolysis process; the pyrolysis reaction solution is subjected to solid-liquid separation to obtain a decomposition liquid and a second solid separate; the second solid separate contains magnesium carbonate.

[0017] S6, the second solid separator is roasted with magnesium carbonate to obtain magnesium oxide; and carbon dioxide gas is collected during the roasting of the magnesium carbonate.

[0018] Furthermore, the source of the dolomite powder includes dolomite fragments and dolomite powder; the dolomite fragments and dolomite powder are crushed to obtain the dolomite powder.

[0019] Furthermore, the particle size of the first-grade retained material is smaller than the preset particle size value, and the particle size of the second-grade retained material is not smaller than the preset particle size value; the mass proportion of the first-grade retained material in the first retained material is greater than 90%, and the mass proportion of the second-grade retained material in the second retained material is greater than 90%; the preset particle size value is selected in the range of 50-100μm.

[0020] Furthermore, the carbonization process is carried out in a pressurized stirred shear carbonization tower; the pressurized stirred shear carbonization tower is equipped with a gas distribution plate and a shear agitator inside the tank, the shear agitator including a stirring shaft, stirring blades, and a shearing disc; the stirring shaft is vertically arranged and fixed inside the tank; the stirring blades and the shearing disc are both mounted on the stirring shaft, and the installation positions of the stirring blades and the shearing disc are both higher than the gas distribution plate; the outer periphery of the shearing disc is provided with shearing blades, and the shearing blades and the shearing disc form an angle;

[0021] The carbonization process includes: conveying the aging liquid into the tank of the pressurized stirring shearing carbonization tower; introducing carbon dioxide gas into the tank through the gas distribution plate, with the carbon dioxide gas entering the tank from bottom to top; controlling the stirring shaft of the shearing stirrer to rotate at a preset speed, thereby driving the stirring blades and the shearing disc to rotate;

[0022] During the carbonization process, the operating temperature of the pressurized stirring shear carbonization tower is controlled at 30-40℃, and the operating pressure of the pressurized stirring shear carbonization tower is controlled at 0.2-0.5MPa; when the pH value of the carbonization reaction solution reaches 7.3±0.3, the carbonization process is terminated.

[0023] Further, the digestion process includes: mixing the calcined white powder and water at a temperature of 75-85°C for 1.5-6 hours, wherein the mass-to-volume ratio of the calcined white powder to water is 1 kg: 30-60 L; before the aging process, adding water to the digestion liquid after solid-liquid separation, and controlling the concentration of magnesium oxide to be 10-12 g / L; the aging process lasts for 6-12 hours.

[0024] The pyrolysis treatment includes: placing the magnesium hydroxide in a negative pressure tank and pyrolyzing the magnesium hydroxide using an MVR evaporator; the temperature of the pyrolysis treatment is 70-95℃, and the duration of the pyrolysis treatment is 0.5-2h.

[0025] The magnesium carbonate is calcined at a temperature of 550-700℃ for a duration of 0.5-1h.

[0026] This invention also provides a method for the comprehensive utilization of dolomite based on calcium-magnesium separation, comprising the following steps:

[0027] S01, magnesium oxide is obtained by any of the calcium-magnesium separation methods described above;

[0028] S02, the magnesium oxide is reduced to obtain metallic magnesium and magnesium aluminum spinel; the reducing agent used in the reduction treatment includes an aluminum-based reducing agent, and the mass ratio of the magnesium oxide to the aluminum-based reducing agent is 2.9-3.1:1.

[0029] Furthermore, the aluminum-based reducing agent comprises aluminum powder, the particle size of which is 200-400 μm;

[0030] The reduction process includes: pressing the magnesium oxide and the aluminum powder into pellets, preheating the pellets to 400-600°C, and then performing vacuum reduction to obtain the metallic magnesium and the magnesium aluminum spinel; the temperature of the vacuum reduction is 1100-1200°C, the duration of the vacuum reduction is 2-4 hours, and the vacuum degree of the vacuum reduction is controlled at 2-5 Pa.

[0031] Furthermore, step S2 also includes: using the waste heat generated from roasting the dolomite as a heat source required for the pyrolysis treatment;

[0032] Step S4 further includes: washing the separation mechanism for solid-liquid separation in this step; washing and drying the first solid separated material in sequence to obtain light calcium carbonate; and using the washing water generated from washing the first solid separated material and washing the separation mechanism as cold water for replenishing water before the aging treatment.

[0033] Step S5 further includes: using the decomposition liquid obtained after the pyrolysis treatment as the hot water for the digestion treatment;

[0034] Step S6 further includes: drying the second solid separator before calcining the magnesium carbonate; using the residual heat generated from calcining the magnesium carbonate and the heat from the magnesium oxide as a heat source for drying the second solid separator;

[0035] The carbon dioxide gas produced by the roasting of magnesium carbonate and the carbon dioxide gas produced by the roasting of dolomite are collected, purified together, and used for the carbonization treatment. The excess carbon dioxide gas is used to prepare dry ice.

[0036] Step S02 further includes using the residual heat generated by the vacuum reduction as a heat source for drying the first solid separator.

[0037] The present invention also provides a method for calcining dolomite, comprising the following steps:

[0038] S21, control the dolomite powder to undergo fluidized bed roasting in the main furnace body to obtain the initial calcined material; the temperature of the fluidized bed roasting is 950-1100℃, and the duration of the fluidized bed roasting is 0.5-1.5h;

[0039] S22, control the initial calcined material to enter the high-temperature retention chamber before cooling, and obtain the retention material; the temperature of the initial calcined material in the high-temperature retention chamber is 900-1000℃, the retention time of the initial calcined material in the high-temperature retention chamber is 1-2h, and the high-temperature retention chamber is connected to the fluidized bed roasting main furnace.

[0040] S23, the retained material is screened to obtain a first retained material and a second retained material; the first retained material contains a first grade of retained material, and the second retained material contains two grades of retained material, wherein the particle size of the first grade of retained material is smaller than that of the second grade of retained material and / or the mass of the first grade of retained material is smaller than that of the second grade of retained material;

[0041] S24, the first retained material is used as calcined white powder; the second retained material is subjected to cyclic calcination in sequence to obtain calcined white powder, wherein the cyclic calcination temperature is 950-1100℃ and the cyclic calcination time is 5-10min.

[0042] The present invention also provides a carbonization method, comprising: obtaining calcined white powder by calcining dolomite as described above, wherein the calcined white powder is subjected to digestion and aging treatment to obtain aging liquid; and then the aging liquid is subjected to carbonization treatment and solid-liquid separation in sequence to obtain heavy magnesium water and solid separation containing calcium carbonate.

[0043] The carbonization process is carried out in a pressurized stirred shear carbonization tower. The pressurized stirred shear carbonization tower is equipped with a gas distribution plate and a shearing agitator inside the tank. The shearing agitator includes a stirring shaft, stirring blades, and a shearing disc. The stirring shaft is vertically arranged and fixed inside the tank. Both the stirring blades and the shearing disc are mounted on the stirring shaft, and their installation positions are higher than the gas distribution plate. Shearing blades are provided on the outer periphery of the shearing disc, and the shearing blades form an angle with the shearing disc.

[0044] The carbonization process includes: conveying the aging liquid into the tank of the pressurized stirring shearing carbonization tower; introducing carbon dioxide gas into the tank through the gas distribution plate, with the carbon dioxide gas entering the tank from bottom to top; controlling the stirring shaft of the shearing stirrer to rotate at a preset speed, thereby driving the stirring blades and the shearing disc to rotate;

[0045] During the carbonization process, the operating temperature of the pressurized stirring shear carbonization tower is controlled at 30-40℃, and the operating pressure of the pressurized stirring shear carbonization tower is controlled at 0.2-0.5MPa; when the pH value of the carbonization reaction solution reaches 7.3±0.3, the carbonization process is terminated.

[0046] Compared with the prior art, the present invention has at least the following advantages:

[0047] This invention can obtain fully reacted calcined dolomite and achieve complete separation of calcium and magnesium based on the calcined dolomite, resulting in high-purity light calcium carbonate and magnesium oxide. It can also further obtain high-quality metallic magnesium and magnesium aluminum spinel. Based on the dolomite roasting method and comprehensive utilization method in this invention, the invention has a high comprehensive utilization rate of dolomite resources, low energy consumption, and the entire process does not generate waste residue or waste gas, fundamentally solving the current problem of low utilization rate of dolomite resources.

[0048] Specifically, this invention uses dolomite powder and achieves efficient calcination of dolomite through fluidized bed calcination. This process also yields the carbon dioxide gas needed for secondary carbonization, with the excess being used to make dry ice and the calcination tail gas serving as a heat source for midstream pyrolysis. By employing a high-temperature retention method, re-carbonization is avoided, ensuring a complete calcination reaction. Through sieving and circulating calcination of the retained material, the second-stage retained material can be fully calcined while saving energy. Therefore, after completing the calcination of dolomite, this invention can efficiently obtain highly active, low-calcination-alkalinity calcined white powder with low energy consumption, avoiding re-carbonization and the presence of unreacted carbonate ions in the calcined dolomite.

[0049] After the dolomite is calcined and digested, this invention controls the pressure inside the tank and the rotation of the stirring and shearing blades during the carbonization process. This not only promotes mixing through the stirring blades, but also, because the shearing blades are at an angle to the shearing disc, they exert a downward force on the medium as they rotate with the stirring shaft, slowing down the upward velocity of the gas and ensuring sufficient contact with the liquid. At the same time, the inclined shearing blades can also cut the air bubbles at an angle during rotation, breaking them up so that the carbonization reaction can proceed fully and promoting the formation of calcium carbonate, thereby improving the calcium-magnesium separation efficiency.

[0050] Furthermore, this invention obtains light calcium carbonate and magnesium oxide through a calcium-magnesium separation method. Simultaneously, the washing water from the carbonized calcium carbonate (first solid fraction) can be recycled as aging water (to replenish the digestion solution), and the filtered hot water (decomposition liquid) after pyrolysis can be recycled as digestion hot water (hot water for digestion treatment). The waste heat from magnesium carbonate roasting can be used as a heat source to dry the filtered magnesium carbonate (second solid fraction) after pyrolysis. The cooled waste gas (carbon dioxide gas) can be purified together to prepare dry ice. Through vacuum reduction of magnesium oxide and aluminum, high-purity metallic magnesium and magnesium aluminum spinel can be produced. The waste heat from magnesium aluminum spinel is used as a drying heat source for light calcium carbonate. The four products obtained by this invention are light calcium carbonate, metallic magnesium, magnesium aluminum spinel, and dry ice. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0052] Figure 1 This is a flowchart illustrating the comprehensive utilization method of dolomite in this invention.

[0053] Figure 2 This is a schematic diagram of the pressurized stirring shear carbonization tower in this invention;

[0054] Figure 3 This is a schematic diagram of the shearing disc in this invention.

[0055] Reference numerals: 1. Tank body; 2. Discharge port; 3. Gas distribution plate; 4. Rotary drive mechanism; 5. Rotary output shaft; 6. Stirring shaft; 7. Shearing assembly; 8. Stirring blades; 9. Feed pipe; 10. Overflow pipe; 11. Air inlet pipe; 12. Pressure relief pipe; 13. Shearing disc; 14. Shearing blades.

[0056] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0059] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0060] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0061] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0062] See Figure 1 As shown, the present invention provides a method for separating calcium and magnesium, comprising the following steps:

[0063] S1 provides dolomite powder.

[0064] In this invention, the source of the dolomite powder may include: obtaining dolomite fragments and dolomite powder; then crushing the dolomite fragments and the dolomite powder to obtain the dolomite powder; the dolomite fragments and the dolomite powder are crushed using a vertical energy-saving grinding mill.

[0065] S2, the dolomite powder is calcined to obtain calcined white powder; and carbon dioxide gas is collected during the calcination process.

[0066] To ensure that the alkalinity and activity of the calcined dolomite meet the high-quality standards, the dolomite calcination device is also equipped with a circulating calciner and a high-temperature retention chamber for discharging carbonate ions and calcining.

[0067] In this invention, the exhaust gas (carbon dioxide gas) generated from the roasting of dolomite, after purification, can be used as a gas source in the subsequent carbonization process, while the waste heat generated from the roasting of dolomite is used as a heat source for the pyrolysis process through a heat exchange process. Therefore, in this step, the waste heat generated from the roasting of dolomite can be collected by heat exchange and used as a heat source for the pyrolysis process, thereby saving energy consumption.

[0068] In this invention, the dolomite calcination is carried out in a fluidized bed calcination system, which includes a fluidized bed calcination main furnace (suspension calcination furnace), a high-temperature retention chamber, and a circulating calciner; the fluidized bed calcination main furnace, the high-temperature retention chamber, and the circulating calciner are sequentially connected; the circulating calciner includes a circulating fluidized bed.

[0069] The dolomite roasting process includes the following sub-steps:

[0070] S21, control the dolomite powder to undergo fluidized roasting in the main furnace body to obtain the initial calcined material; the temperature of the fluidized roasting is 950-1100℃, and the duration of the fluidized roasting is 0.5-1.5h.

[0071] S22, control the initial calcined material to enter the high-temperature retention chamber before cooling, and obtain the retained material; the temperature of the initial calcined material in the high-temperature retention chamber is 900-1000℃, the retention time of the initial calcined material in the high-temperature retention chamber is 1-2h, and the high-temperature retention chamber is connected to the fluidized bed roasting main furnace.

[0072] S23, the retained material is sieved to obtain a first retained material and a second retained material; the first retained material contains a first grade of retained material, and the second retained material contains two grades of retained material, wherein the particle size of the first grade of retained material is smaller than the particle size of the second grade of retained material and / or the mass of the first grade of retained material is smaller than the mass of the second grade of retained material; it should be noted that the fully reacted retained material is usually small or light, so it can be sieved by particle size and mass, specifically by automatic sieving of the retained material of different particle sizes and / or different masses by airflow.

[0073] S24, the first retained material serves as the calcined white powder; the second retained material is sequentially subjected to cyclic calcination to obtain the calcined white powder; during the cyclic calcination process, after each cycle, qualified powder is collected based on mass change and used as the calcined white powder; the cyclic calcination temperature is 950-1100℃, and the cyclic calcination time (total calcination time) is 5-10 minutes; the cyclic calcination is carried out through a circulating fluidized bed, and the cyclic calcination refers to: cyclically calcining the second retained material, and collecting qualified calcined white powder based on mass change after each cycle; the number of cycles of the cyclic calcination is usually 2-3 times, and the cyclic process is positive pressure cyclic calcination; qualified calcined white powder can also be collected during the cyclic calcination process. In this invention, the calcined white powder is transported together to a fluidized bed calcination system for cyclone cooling to obtain highly active, low ignition alkalinity calcined white powder.

[0074] In this invention, the particle size of the first-grade retained material is smaller than a preset particle size value, and the particle size of the second-grade retained material is not smaller than the preset particle size value. The first-grade retained material is essentially the first-grade retained material, and the second-grade retained material is essentially the second-grade retained material; or the mass percentage of the first-grade retained material in the first-grade retained material is greater than 90%, and the mass percentage of the second-grade retained material in the second-grade retained material is greater than 90%. The preset particle size value is selected within the range of 50-100 μm. In this invention, since incompletely roasted dolomite is rare, the amount of the second retained material is much smaller than that of the first retained material. However, without sieving, incomplete roasting will occur. Therefore, this invention performs cyclic roasting after sieving, which saves energy and ensures thorough roasting of the dolomite. The first retained material is small-particle retained material, and the second retained material is medium- and large-particle retained material. Due to differences in sieving methods and different batches of roasting, the definition of small particles can vary. The boundary between small-particle and medium-particle retained material is usually between 50-100%. The particle size is between 0.00 μm; that is, the particle size of the small-particle retention material is less than 100 μm. As a more stringent limitation, it can also be less than a certain value between 50-100 μm. In addition to the small-particle retention material, the rest are medium-particle and large-particle retention materials. This invention preferentially uses airflow sieving to obtain the first retention material and the second retention material after airflow sieving. The first retention material is qualified calcined white material and is basically a small-particle retention material. The second retention material is a retention material that needs to be circulated and roasted. The particle size and mass of the first retention material are both smaller, so they can be determined by airflow sieving.

[0075] In this invention, the high-temperature retention chamber can avoid decarbonization or the presence of a large amount of carbonate ions in the solid-gas separation powder, and can also increase the maximum decomposition time for large and medium-sized particles that are not completely decomposed. The high-temperature retention chamber has an upper cylindrical structure to store more powder and a lower conical structure for discharge. The circulating calcination through the circulating fluidized bed can avoid the incomplete decomposition and under-calcination of medium and large particles, which affects the quality of the calcined white powder and improves the utilization rate of dolomite raw materials and magnesium yield. The circulating fluidized bed mainly consists of a fluidized bed calcination furnace, a recirculation air duct, and a sealing trough. The medium and large particles (secondary retention material) can have their residence time and frequency in the furnace increased through circulation until the particles are completely decomposed and become lighter, at which point they are automatically discharged.

[0076] It should be noted that, compared with traditional dolomite calcination, this invention uses fluidized bed calcination in dolomite calcination, employing a suspension calcination furnace and equipped with a cyclone preheating and cooling mechanism. Compared with rotary kiln calcination, this can reduce energy consumption by more than 20%, increase production capacity by more than 50%, and achieve better quality consistency. This invention adds a high-temperature retention chamber, which can prevent re-carbonization and remove the maximum amount of carbonate ions. This invention adds a circulating calcination fluidized bed for the aforementioned circulating calcination, which can avoid under-burning of medium and large particles (second-stage retention material), ensuring that the activity of the calcined powder is above 30% and the basicity on ignition is below 0.9%. During the fluidized bed calcination process, this invention can purify and exchange the separated gas, providing a carbon dioxide gas source for the carbonization of calcium and magnesium separation in the midstream and a heat source for the hydrothermal decomposition of heavy magnesium.

[0077] It should be noted that if only conventional fluidized bed roasting is used for dolomite, the conventional fluidized bed roasting system only has the main furnace body and cyclone preheating and cooling device. If the raw material powder does not have a uniform particle size distribution, it is difficult to control the under-burning and over-burning of calcined white powder, and thus the physicochemical properties of the produced calcined white powder are difficult to meet the downstream digestion conditions.

[0078] S3, the calcined white powder is digested to obtain a digestion liquid; after solid-liquid separation of the digestion liquid, the digestion liquid after solid-liquid separation is subjected to aging treatment and solid-liquid separation in sequence to obtain an aged liquid; the solid-liquid separation in this step is mainly for the purpose of removing impurities, which can also be understood as impurity removal treatment.

[0079] In this invention, the digestion process is carried out in a heat-collecting box-type digester. The digestion process includes: mixing the calcined white powder and water at 75-85°C for 1.5-6 hours, with a mass-to-volume ratio of calcined white powder to water of 1 kg: 30-60 L; before the aging process, adding water to the digested liquid after solid-liquid separation, controlling the magnesium oxide concentration (based on magnesium oxide derived from calcined white powder) to be 10-12 g / L; the aging process lasts for 6-12 hours; and the aging process involves standing. Based on the fluidized bed roasting, digestion, and aging processes, this invention can obtain magnesium hydroxide with high crystallinity and excellent reactivity.

[0080] S4, the aging liquid is subjected to carbonization treatment to obtain a carbonization reaction liquid; the carbonization reaction liquid is subjected to solid-liquid separation to obtain magnesium hydroxide and a first solid separator; the first solid separator contains calcium carbonate.

[0081] The carbonization process is carried out in a pressurized, stirred, and sheared carbonization tower; see [link / reference] Figures 2-3 As shown, the tank 1 of the pressurized stirring shear carbonization tower is equipped with a gas distribution plate 3 and a shearing agitator. The shearing agitator includes a stirring shaft 6, stirring blades 8, and a shearing disc 13. The stirring shaft 6 is vertically arranged and fixed inside the tank 1. The stirring blades 8 and the shearing disc 13 are both mounted on the stirring shaft 6. The installation positions of the stirring blades 8 and the shearing disc 13 are both higher than the gas distribution plate 3. Multiple shearing blades 14 are provided on the outer periphery of the shearing disc 13. The shearing disc 13 and the shearing blades 14 can be collectively referred to as the shearing assembly 7. The shearing blades 14 and the shearing disc 13 have an angle. In this invention, the angle is 45°. The angle and direction of the multiple shearing blades 14 and the shearing disc 13 are consistent. By controlling the direction of the angle and the rotation direction of the stirring shaft 6, the shearing blades 14 generate downward liquid pressure when rotating.

[0082] In this invention, multiple sets of stirring blades 8 and shearing discs 13 are typically arranged vertically along the stirring shaft 6, and the shearing discs 13 are arranged between two adjacent sets of stirring blades 8. A set of shearing discs 13 may also be arranged above the stirring blades 8 furthest from the gas distribution disk 3. The rotation directions of two adjacent sets of stirring blades 8 are opposite, and the rotation direction of the stirring blades 8 near the bottom is upward. The rotation direction is the stirring direction, which can be understood as the orientation of the front of the stirring blades 8.

[0083] In this invention, the pressurized stirring shear carbonization tower is further provided with a discharge port 2, a rotary drive mechanism 4, a rotary output shaft 5, a feed pipe 9, an overflow pipe 10, an air inlet pipe 11, and a pressure relief pipe 12; wherein, the rotary drive mechanism 4 drives the stirring shaft 6 to rotate through the rotary output shaft 5, and the air inlet pipe 11 is used to supply gas to the gas distribution plate 3.

[0084] The carbonization process includes: transporting the aging liquid into the tank 1 of the pressurized stirring shearing carbonization tower; introducing carbon dioxide gas into the tank 1 through the gas distribution plate 3; and controlling the stirring shaft 6 of the shearing stirrer to rotate at a preset speed, thereby driving the stirring blades 8 and the shearing disc 13 to rotate.

[0085] During the carbonization process, the shear blades 14 generate downward liquid pressure as they rotate, with the shearing direction clockwise. Specifically, the airflow is upward while the liquid pressure is downward, resulting in a lateral rotational shearing at a 45° angle to the center. During the carbonization process, the operating temperature of the pressurized stirring shearing carbonization tower is controlled at 30-40℃, and the operating pressure is controlled at 0.2-0.5MPa. When the pH value of the digestate reaches 7.3±0.3 (the final pH affects the purity and recovery efficiency of the product; the pH value of the digestate is further set to 7.3-7.4), the carbonization process ends. In the carbonization process, the concentration of carbon dioxide is controlled between 30% and 100%, and the carbonization time is typically set to 0.5-2 hours, but can also be 0.8-1.2 hours.

[0086] This invention employs a pressurized stirring shear carbonization tower for carbonization, which has the advantages of easy control, sufficient gas-liquid contact and uniform reaction, low energy consumption, significantly improved carbon dioxide utilization efficiency, and can also enhance the reaction boundary between calcium carbonate and magnesium bicarbonate products.

[0087] In this invention, the pressurized stirring shearing carbonization tower mainly includes a double-sealed, pressurized tank 1, a mechanically driven stirring shaft 6, stirring blades 8, a shearing disc 13, shearing blades 14, and a gas distribution disc 3, as well as related components such as gas pipes, feed pipes 9, discharge valves, and pressure safety valves. This invention performs pressurized carbonization, controlling the operating pressure to ensure that all magnesium hydroxide is carbonized to generate magnesium bicarbonate solution, avoiding the conversion of calcium carbonate into calcium bicarbonate, which dissolves into a mixture of aqueous solution and magnesium bicarbonate solution, thus guaranteeing the quality of magnesium carbonate and the recovery rate of magnesium salts. The invention features a reverse-oriented gas distribution disc 3 at the bottom of the tank 1, causing carbon dioxide gas to form microbubbles that rise from the bottom, resulting in faster absorption of the longitudinal reaction. By setting multiple sets of stirring blades 8 and shearing blades 14, this invention enables more complete multi-layered convection reactions between gas and solution, and also increases the specific gravity of the shearing blades 14 in the transverse carbonization effect. The stirring and dispersing action of this invention prevents calcium carbonate precipitation from clogging the discharge valve. This invention, under the premise of achieving the required pH value during carbonation, yields light calcium carbonate with a magnesium content of less than 2%, meeting the standard of HG / T2226-2010, thus achieving calcium-magnesium separation. In this field, regardless of the form in which magnesium exists in light calcium carbonate, it is calculated as magnesium oxide. It should be noted that traditional carbonation does not involve pressurization, making complete separation difficult. Furthermore, the lack of stirring and shearing during carbonation results in low carbonation efficiency, long processing time, and a high risk of clogging the discharge valve and pipelines.

[0088] In this invention, after the carbonization process is completed, a belt vacuum filter is used for solid-liquid separation to obtain magnesium hydroxide and calcium carbonate filter cake (the first solid separation product); the water used to wash the filter cake and the water used to clean the filter cloth of the belt vacuum filter are recycled as cold water for subsequent replenishment of the digestion solution.

[0089] As a supplementary explanation to step S4, step S4 further includes: washing the separation mechanism (vacuum filter cloth) used for solid-liquid separation in this step; washing the first solid separator and then drying it at 200-400℃ for 1.5-2 hours to obtain light calcium carbonate; using the washing water generated from washing the first solid separator and the separation mechanism as cold water for replenishing water before the aging treatment. In this invention, before pyrolysis, heavy magnesium water can also be placed in an intermediate tank to precipitate fine-particle light calcium carbonate; and, by washing the first solid separator with water, the heavy magnesium water can be completely removed, thereby ensuring a high magnesium recovery rate.

[0090] S5, the magnesium hydroxide is subjected to pyrolysis to obtain a pyrolysis reaction solution, and carbon dioxide gas is collected during the pyrolysis process; the pyrolysis reaction solution is subjected to solid-liquid separation to obtain a decomposition liquid and a second solid separate; the second solid separate contains magnesium carbonate. The decomposition liquid can be directly used for digestion, and its temperature at this point meets the digestion requirements, thereby effectively reducing energy consumption.

[0091] The pyrolysis treatment includes: placing the magnesium hydroxide solution in a negative pressure tank after sedimentation in an intermediate tank, and using an MVR evaporator to pyrolyze the magnesium hydroxide solution while maintaining a vacuum degree of 200±5Pa in the negative pressure tank to reduce the pyrolysis temperature; the temperature of the pyrolysis treatment is 70-95℃, and the duration of the pyrolysis treatment is 0.5-2h.

[0092] Specifically, the hydrated magnesium hydroxide is heated in an MVR evaporator, and magnesium carbonate precipitates out under vacuum and low-temperature conditions. Then, a plate and frame filter press is used for solid-liquid separation to obtain a decomposed liquid and a filter cake. In this invention, the pyrolysis temperature is 70-95℃, and the pyrolysis duration is 0.5-2 hours. By using an MVR evaporator to pyrolyze the hydrated magnesium hydroxide and applying vacuum to the hydrated magnesium hydroxide, the energy consumption of pyrolysis can be reduced.

[0093] Specifically, in this invention, the pyrolysis of the magnesium hydroxide is performed using a vacuum low-temperature pressurized evaporator. This evaporator includes a vacuum pump unit, a negative pressure tank, an MVR evaporator, and an electrical control system. The magnesium hydroxide is placed in the pyrolysis tower tank of the vacuum low-temperature pressurized evaporator during pyrolysis. This invention utilizes the waste heat from the upstream fluidized bed roasting tail gas for energy-saving pyrolysis via a matching low-temperature MVR evaporator. Simultaneously, the pyrolysis temperature is lowered under vacuum to further save energy. The carbon dioxide released during pyrolysis is collected and returned to the solution before carbonization to achieve atmospheric pressure pre-carbonization. After pyrolysis, solid-liquid separation is performed to obtain a basic magnesium carbonate filter cake. The hot water from pyrolysis is recycled back upstream as hot water for digestion. Therefore, step S5 further includes: using the decomposed liquid obtained after pyrolysis as hot water for digestion; collecting the carbon dioxide generated during pyrolysis and transporting it to the solution to be pre-carbonized after aging, thereby enabling atmospheric pressure pre-carbonization before pressurized carbonization.

[0094] S6, the second solid separator is roasted with magnesium carbonate to obtain magnesium oxide; and carbon dioxide gas is collected during the roasting of the magnesium carbonate.

[0095] In this invention, the magnesium carbonate is calcined at a temperature of 550-700℃ for 0.5-1 hour. If the temperature is too low or the calcination time is too short, incomplete decomposition will occur; if the temperature is too high or the calcination time is too long, the MgO grains will become larger and gradually lose their activity. This invention uses a fluidized bed flash calciner for the calcination.

[0096] In this invention, the waste heat generated during the magnesium carbonate roasting process and the roasted magnesium oxide can be used for heat exchange, and the obtained heat is used as a heat source for drying the basic magnesium carbonate filter cake. The carbon dioxide gas generated during magnesium carbonate roasting can be purified upstream together with the tail gas from the fluidized bed roasting of dolomite powder, serving as a gas source for the carbonation digestion liquid. Excess carbon dioxide can be used to prepare dry ice. That is, step S6 further includes: drying the second solid separation before the magnesium carbonate roasting at a temperature of 200-310°C for 1.5-2.5 hours; using the waste heat generated during magnesium carbonate roasting and the heat from the magnesium oxide as a heat source for drying the second solid separation; collecting the carbon dioxide gas generated during magnesium carbonate roasting and the carbon dioxide gas generated during dolomite roasting, purifying them together, and using the purified gas for the digestion treatment; and using the excess carbon dioxide to prepare dry ice.

[0097] This invention also provides a method for the comprehensive utilization of dolomite based on calcium-magnesium separation, comprising the following steps:

[0098] S01, magnesium oxide is obtained by any of the calcium-magnesium separation methods described above.

[0099] S02, the magnesium oxide is reduced to obtain metallic magnesium and magnesium aluminum spinel; the reducing agent used in the reduction treatment includes an aluminum-based reducing agent, and the mass ratio of magnesium oxide to the aluminum-based reducing agent is 2.9-3.1:1. The selection of this mass ratio is crucial. If the ratio is too high, the magnesium oxide content may exceed the standard; if the ratio is too low, not only will the economic efficiency be poor, but the aluminum oxide content may also exceed the standard, thereby affecting the quality and economic benefits of the final product.

[0100] In this invention, the aluminum-based reducing agent comprises aluminum powder with a particle size of 200-400 μm. By controlling the particle size of the aluminum powder, the efficiency and economy of the reduction reaction are optimized. If the particle size of the reducing agent is too large, it will lead to insufficient contact with magnesium oxide, thereby reducing the reaction efficiency. Conversely, if the particle size is too small, it may result in poor economic efficiency. Therefore, selecting this particle size range helps to balance the reaction effect and cost-effectiveness. In this invention, the aluminum-based reducing agent comprises aluminum powder made from recycled aluminum, which is mainly 1-series aluminum alloys with an aluminum mass percentage content ≥99%. The aluminum-containing reducing agent is stored in a sealed environment before being mixed with the magnesium oxide to prevent oxidation.

[0101] The reduction process includes: pressing the magnesium oxide and aluminum powder into pellets under a roller surface pressure of 7-16 t / cm, preheating the pellets to 400-600℃, and then sending them into a vacuum high-resistance electric heating horizontal reduction furnace for vacuum reduction to obtain metallic magnesium and magnesium aluminum spinel; the temperature of the vacuum reduction is 1100-1200℃, the duration of the vacuum reduction is 2-4 hours, and the vacuum degree of the vacuum reduction is controlled at 2-5 Pa.

[0102] The reaction that occurs during the reduction treatment is as follows:

[0103] 4MgO + 2Al = 3Mg + MgO·Al₂O₃

[0104] Specifically, this invention employs a microwave drying and preheating integrated machine to preheat the pellets made from pressed magnesium oxide and aluminum powder to 400-600°C, and then introduces them into a vacuum high-resistance electric heating horizontal reduction furnace for reduction reaction, thereby obtaining metallic magnesium and magnesium-aluminum spinel; the residual heat from the magnesium-aluminum spinel formation process is used as a heat source for the initial drying of light calcium carbonate. In this invention, step S02 further includes: using the residual heat generated by the vacuum reduction as a heat source for drying the first solid separation.

[0105] The present invention also provides a method for calcining dolomite, comprising the following steps:

[0106] S21, control the dolomite powder to undergo fluidized roasting in the main furnace body to obtain the initial calcined material; the temperature of the fluidized roasting is 950-1100℃, and the duration of the fluidized roasting is 0.5-1.5h.

[0107] S22, control the initial calcined material to enter the high-temperature retention chamber before cooling, and obtain the retained material; the temperature of the initial calcined material in the high-temperature retention chamber is 900-1000℃, the retention time of the initial calcined material in the high-temperature retention chamber is 1-2h, and the high-temperature retention chamber is connected to the fluidized bed roasting main furnace.

[0108] S23, the retained material is screened to obtain a first retained material and a second retained material; the first retained material contains a first grade of retained material, and the second retained material contains two grades of retained material, wherein the particle size of the first grade of retained material is smaller than that of the second grade of retained material and / or the mass of the first grade of retained material is smaller than that of the second grade of retained material.

[0109] S24, the first retained material is used as calcined white powder; the second retained material is subjected to cyclic calcination in sequence to obtain calcined white powder, wherein the cyclic calcination temperature is 950-1100℃ and the cyclic calcination time is 5-10min.

[0110] In this invention, the limitations in the fluidized bed roasting method are equivalent to the limitations in steps S1-S2 of the calcium-magnesium separation method, and the details are consistent.

[0111] The present invention also provides a carbonization method, comprising: obtaining calcined white powder by calcining dolomite as described above, wherein the calcined white powder is subjected to digestion and aging treatment to obtain a digestion liquid; and then the digestion liquid is subjected to carbonization treatment and solid-liquid separation in sequence to obtain heavy magnesium water and a solid separation containing calcium carbonate.

[0112] The carbonization process is carried out in a pressurized stirring shear carbonization tower. The tank 1 of the pressurized stirring shear carbonization tower is equipped with a gas distribution plate 3 and a shearing agitator. The shearing agitator includes a stirring shaft 6, stirring blades 8, and a shearing disc 13. The stirring shaft 6 is vertically arranged and fixed inside the tank 1. The stirring blades 8 and the shearing disc 13 are both mounted on the stirring shaft 6. The installation positions of the stirring blades 8 and the shearing disc 13 are both higher than the gas distribution plate 3. Shearing blades 14 are provided on the outer periphery of the shearing disc 13, and the shearing blades 14 and the shearing disc 13 have an angle.

[0113] The carbonization process includes: transporting the aging liquid into the tank 1 of the pressurized stirring shearing carbonization tower; introducing carbon dioxide gas into the tank 1 through the gas distribution plate 3; and controlling the stirring shaft 6 of the shearing stirrer to rotate at a preset speed, thereby driving the stirring blades 8 and the shearing disc 13 to rotate.

[0114] During the carbonization process, the operating temperature of the pressurized stirring shear carbonization tower is controlled at 30-40℃, and the operating pressure of the pressurized stirring shear carbonization tower is controlled at 0.2-0.5MPa; when the pH value of the carbonization reaction solution reaches 7.3±0.3, the carbonization process is terminated.

[0115] In this invention, the limitations in the fluidized bed roasting method are equivalent to the limitations in steps S1-S4 of the calcium-magnesium separation method, and the details are consistent.

[0116] The following are specific examples of the present invention:

[0117] Example 1

[0118] I. Experimental Procedure:

[0119] 1. Provide dolomite powder; the dolomite powder contains the following components (by mass fraction): 22.75% MgO, 30.19% CaO, 0.67% SiO2, 0.089% Al2O3, 0.061% Fe2O3, and 45.89% CO2.

[0120] 2. The dolomite powder is calcined. The dolomite calcination process is as follows:

[0121] Dolomite powder is controlled to undergo fluidized bed roasting in the main furnace body to obtain initial calcined material; the fluidized bed roasting temperature is 1100℃ and the fluidized bed roasting time is 1.5h.

[0122] The initial calcined material is controlled to enter the high-temperature retention chamber from the fluidized bed roasting main furnace and remain there for 1.5 hours to obtain the retained material. The temperature of the initial calcined material in the high-temperature retention chamber is between 900-1000℃. The high-temperature retention chamber and the fluidized bed roasting main furnace are connected.

[0123] After the retained material is automatically screened by airflow, the first retained material and the second retained material are obtained. The first retained material obtained by automatic airflow screening is mainly composed of small particles (less than 100μm), while the second retained material is mainly composed of large and medium particles.

[0124] The first retained material is used as calcined white powder; the second retained material is subjected to cyclic calcination (in a circulating fluidized bed) to obtain calcined white powder. The cyclic calcination temperature is 1000℃, the total calcination time is 10min, the number of cycles is 3, and the cyclic process is positive pressure cyclic calcination; the above calcined white powder is cooled together by cyclone to obtain calcined white powder with high activity and low ignition alkalinity.

[0125] 3. Mix calcined white powder with water, with a solid-liquid ratio of 1 kg: 35 L, and digest (mixed reaction) at 75 °C for 1.5 hours. After solid-liquid separation, the digestion liquid is obtained. Based on a magnesium oxide concentration of 12 g / L, mix the digestion liquid with water and age it for 8 hours. Then, separate the aged liquid from the solid liquid by filtration to obtain the aged liquid.

[0126] 4. Carbonize the aging liquid (pressure stirring shear carbonization) to obtain carbonization reaction liquid; then, use a belt vacuum filter to separate the solid and liquid of the carbonization reaction liquid to obtain heavy magnesium water and filter cake; dry the filter cake at 300℃ for 2 hours to obtain light calcium carbonate.

[0127] Carbonization treatment (pressurized stirring shear carbonization) is carried out in a pressurized stirring shear carbonization tower. The tank of the pressurized stirring shear carbonization tower is equipped with a gas distribution plate and a shear agitator. The shear agitator has a stirring shaft, two sets of stirring blades, and three sets of shear blades. The stirring shaft is vertically arranged and fixed in the tank. The stirring blades and shear blades are both installed on the stirring shaft. The installation positions of the stirring blades and shear blades are higher than the gas distribution plate. The stirring blades and shear blades are both arranged vertically along the stirring shaft, and a shear blade is provided between two adjacent sets of stirring blades (in this embodiment, one set of shear blades, one set of stirring blades, one set of shear blades, one set of shear blades, and one set of stirring blades are arranged from top to bottom). The rotation directions of two adjacent sets of stirring blades are opposite. The stirring blades closest to the bottom rotate upwards, and the stirring blades furthest from the bottom rotate downwards. Shear blades are provided on the outer periphery of the shear blades. The shear blades have a 45° angle with the shear blades. By controlling the direction of the angle and the rotation direction of the stirring shaft, the shear blades generate downward liquid pressure when rotating.

[0128] The carbonization process (pressurized stirring shear carbonization) is as follows: the digestion liquid is transported to the tank of the pressurized stirring shear carbonization tower, and carbon dioxide gas is introduced into the tank through the gas distribution plate. The carbon dioxide gas is introduced into the tank from bottom to top; the stirring shaft of the shearing stirrer is controlled to rotate at a preset speed, which drives the stirring blades and shearing disc to rotate.

[0129] During the carbonization process (pressurized stirring shearing carbonization), the stirring shaft rotates at 200 r / min. The shearing method formed by the shearing blades is upward airflow and downward liquid pressure with a 45° tilt angle at the center, rotating laterally in a clockwise direction. The operating temperature of the pressurized stirring shearing carbonization tower is controlled at approximately 35℃, and the operating pressure is controlled at 0.4 MPa (the air intake of the pressurized stirring shearing carbonization tower is controlled for pressurized carbonization operation). During the carbonization process, the concentration of carbon dioxide gas used is 45%. When the pH value of the digestate reaches 7.35, the carbonization process ends, and the carbonization time is 1 hour.

[0130] 5. The magnesium hydroxide solution was pyrolyzed to obtain a pyrolysis reaction solution. The pyrolysis temperature was set at 93℃, and the pyrolysis time was 2 hours. During the pyrolysis process, the magnesium hydroxide solution was placed in a negative pressure tank after sedimentation in the intermediate tank, and an MVR evaporator was used to pyrolyze the magnesium hydroxide solution while maintaining a vacuum of 200 Pa in the negative pressure tank. Then, a plate and frame filter press was used for solid-liquid separation to obtain a decomposition liquid and a filter cake. The filter cake was dried at 300℃ for 2 hours to obtain basic magnesium carbonate.

[0131] 6. Calcining basic magnesium carbonate at 680℃ for 1 hour (calcination of magnesium carbonate) yields magnesium oxide.

[0132] 7. The recycled aluminum is processed into aluminum powder, and aluminum powder of different particle sizes is obtained through powder classification. Aluminum powder with a particle size of 220μm is selected for subsequent processing.

[0133] 8. Mix magnesium oxide and aluminum powder at a mass ratio of 2.9:1, and press the mixture into pellets under high pressure of 8t / cm roller surface pressure.

[0134] 9. Preheat the pellets to 600℃, then reduce the pellets under vacuum. The reaction process is carried out at 1200℃, the reduction time is set to 3 hours, and the vacuum degree is maintained at 2-5 Pa to obtain metallic magnesium and magnesium aluminum spinel.

[0135] II. Experimental Results:

[0136] 1. The composition of light calcium carbonate was analyzed by mass percentage, and the results are shown in the table below:

[0137] <![CDATA[CaCO3]]> MgO Example 1 98.17％ 0.82％

[0138] 2. The composition of magnesium oxide was analyzed by mass percentage, and the results are shown in the table below:

[0139] MgO CaO Example 1 95.74％ 0.78％

[0140] 3. Compositional analysis of magnesium aluminum spinel was performed based on its mass percentage, and the results are shown in the table below:

[0141] <![CDATA[Al2O3]]> MgO CaO <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> Example 1 67.25％ 30.13％ 0.81％ 0.38％ 0.09％

[0142] 4. Compositional analysis of metallic magnesium by mass percentage is shown in the table below:

[0143] Mg Fe Si Al Mn Ni Cu Example 1 99.95％ 0.002％ 0.009％ 0.006％ 0.0015％ 0.001％ 0.005％

[0144] 5. The composition of the calcined white powder was analyzed by mass percentage, and the results are shown in the table below:

[0145] MgO CaO <![CDATA[R2O3(Al2O3+Fe2O3)]]> <![CDATA[SiO2]]> <![CDATA[K2O+Na2O]]> Burn-off rate Example 1 20.58％ 32.85％ 0.48％ 0.36％ 0.037％ 46.5％

[0146] Comparative Example 1

[0147] I. Experimental Procedure:

[0148] 1. Calcined white powder was obtained in the same manner as in Example 1.

[0149] 2. The ferrosilicon is crushed and then the crushed small particles are fed into a ball mill for grinding using a dry ball mill. After powder classification, ferrosilicon of different particle sizes is obtained. Ferrosilicon powder with a particle size of 160μm (containing 75% silicon by mass) is selected.

[0150] 3. The calcined white powder, ferrosilicon, and fluorite powder are mixed and formulated, and then pressed into pellets under a roller surface linear pressure of 11t / cm; the mass ratio of calcined white powder, ferrosilicon, and fluorite powder is 83.4:15.7:1.8.

[0151] After preheating the pellets at 650℃, they were placed in a vacuum high-resistance electric heating horizontal reduction furnace for vacuum reduction treatment to obtain metallic magnesium and reduction slag. The temperature during the reduction process was set at 1260℃, the reduction time was 9 hours, and the vacuum degree was controlled at 3-5 Pa.

[0152] II. Experimental Results:

[0153] 1. The composition of the reduction slag was analyzed by mass percentage, and the results are shown in the table below:

[0154] <![CDATA[Al2O3]]> MgO CaO <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> Comparative Example 1 1.27％ 8.06％ 54.72％ 32.95％ 2.42％

[0155] 2. Compositional analysis of metallic magnesium by mass percentage is shown in the table below:

[0156] Mg Fe Si Al Mn Ni Cu Comparative Example 1 99.68％ 0.005％ 0.005％ 0.005％ 0.0018％ 0.002％ 0.005％

[0157] Comparative Example 2

[0158] I. Experimental Procedure:

[0159] 1. Compared with Example 1, the digestion temperature in this comparative example was adjusted from 75°C to 50°C, and the aging time was adjusted from 8 hours to 4 hours (correspondingly, the final pH of the subsequent carbonization reaction solution was 7.38, and the carbonization time was 1 hour), while other conditions remained unchanged.

[0160] II. Experimental Results:

[0161] 1. The composition of light calcium carbonate was analyzed by mass percentage, and the results are shown in the table below:

[0162] <![CDATA[CaCO3]]> MgO Comparative Example 2 96.37％ 2.16％

[0163] 2. The composition of magnesium oxide was analyzed by mass percentage, and the results are shown in the table below:

[0164] MgO CaO Comparative Example 2 94.84％ 4.69％

[0165] 3. Compositional analysis of magnesium aluminum spinel was performed based on its mass percentage, and the results are shown in the table below:

[0166] <![CDATA[Al2O3]]> MgO CaO <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> Comparative Example 2 64.25％ 28.23％ 4.81％ 0.39％ 0.08％

[0167] 4. Compositional analysis of metallic magnesium by mass percentage is shown in the table below:

[0168] Mg Fe Si Al Mn Ni Cu Comparative Example 2 99.78％ 0.008％ 0.012％ 0.007％ 0.0025％ 0.003％ 0.009％

[0169] Comparative Example 3

[0170] I. Experimental Procedure:

[0171] Compared to Example 1, this comparative example changed the pressurized stirring shear carbonization to atmospheric pressure bubbling carbonization, while keeping other conditions unchanged.

[0172] During the atmospheric pressure bubbling carbonization process, no pressure was applied, and no stirring shaft, stirring blades, or shearing blades were installed. Specifically, the atmospheric pressure bubbling carbonization in this comparative example was carried out in an atmospheric pressure bubbling carbonization tower. In this comparative example, carbon dioxide gas with a concentration of 45% was introduced into the gas distribution plate (located at the bottom of the tank) of the atmospheric pressure bubbling carbonization tower, and bubbling carbonization was performed. During the carbonization process, the operating temperature of the atmospheric pressure bubbling carbonization tower was controlled at about 35°C. When the pH value of the carbonization reaction solution reached 7.85 and could not be lowered further, the carbonization process was terminated, and the carbonization time was 3 hours.

[0173] II. Experimental Results:

[0174] 1. The composition of light calcium carbonate was analyzed by mass percentage, and the results are shown in the table below:

[0175] <![CDATA[CaCO3]]> MgO Comparative Example 3 80.16％ 9.06％

[0176] 2. The composition of magnesium oxide was analyzed by mass percentage, and the results are shown in the table below:

[0177] MgO CaO Comparative Example 3 72.25％ 25.69％

[0178] Comparative Example 4

[0179] I. Experimental Procedure:

[0180] Compared to Example 1, the pyrolysis temperature in this comparative example was adjusted from 93°C to 100°C, while other conditions remained unchanged.

[0181] II. Experimental Results:

[0182] 1. The composition of magnesium oxide was analyzed by mass percentage, and the results are shown in the table below:

[0183] MgO CaO Comparative Example 4 94.54％ 1.37％

[0184] 2. Compositional analysis of magnesium aluminum spinel by mass percentage is shown in the table below:

[0185] <![CDATA[Al2O3]]> MgO CaO <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> Comparative Example 4 65.55％ 29.73％ 1.21％ 0.37％ 0.08％

[0186] 3. Compositional analysis of metallic magnesium by mass percentage is shown in the table below:

[0187] Mg Fe Si Al Mn Ni Cu Comparative Example 4 99.93％ 0.003％ 0.008％ 0.005％ 0.0015％ 0.001％ 0.006％

[0188] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for separating calcium and magnesium, characterized by, The method comprises the steps of: S1, providing dolomite powder; S2, calcining the dolomite powder to obtain calcined dolomite powder, and collecting carbon dioxide gas during the calcination process of the dolomite powder; The calcination process of the dolomite powder comprises the following steps: S21, controlling the dolomite powder to be fluidized calcined in a fluidized calcination main furnace body to obtain primary calcined material; the temperature of the fluidized calcination is 950-1100℃, and the time length of the fluidized calcination is 0.5-1.5h; S22, controlling the primary calcined material to be stored in a high-temperature storage bin without cooling to obtain stored material; the temperature of the primary calcined material in the high-temperature storage bin is 900-1000℃, the time length of the primary calcined material in the high-temperature storage bin is 1-2h, and the high-temperature storage bin is in communication with the fluidized calcination main furnace body; S23, screening the stored material to obtain first stored material and second stored material; the first stored material contains one-grade stored material, and the second stored material contains two-grade stored material; the particle size of the one-grade stored material is smaller than that of the two-grade stored material; The particle size of the one-grade stored material is smaller than a preset particle size value, and the particle size of the two-grade stored material is not smaller than the preset particle size value; the preset particle size value is selected in the range of 50-100μm; S24, taking the first stored material as the calcined dolomite powder; S25, performing cyclic calcination on the second stored material to obtain the calcined dolomite powder; the temperature of the cyclic calcination is 950-1100℃, and the time length of the cyclic calcination is 5-10min; S3, performing digestion treatment on the calcined dolomite powder to obtain a digestion liquid; After the digestion liquid is subjected to solid-liquid separation, aging treatment and solid-liquid separation are sequentially performed to obtain an aging liquid; S4, performing carbonation treatment on the aging liquid to obtain a carbonation reaction liquid; performing solid-liquid separation on the carbonation reaction liquid to obtain heavy magnesium water and a first solid separation product; the first solid separation product contains calcium carbonate; S5, performing pyrolysis treatment on the heavy magnesium water to obtain a pyrolysis reaction liquid, and collecting carbon dioxide gas during the pyrolysis treatment; performing solid-liquid separation on the pyrolysis reaction liquid to obtain a decomposition liquid and a second solid separation product; the second solid separation product contains magnesium carbonate; S6, performing magnesium carbonate calcination on the second solid separation product to obtain magnesium oxide, and collecting carbon dioxide gas during the magnesium carbonate calcination.

2. The calcium-magnesium separation method according to claim 1, characterized by, The source of the dolomite powder includes dolomite fragments and dolomite powder; the dolomite fragments and the dolomite powder are crushed to obtain the dolomite powder.

3. The calcium-magnesium separation method according to claim 1, characterized by, The carbonation treatment is performed in a pressurized stirring and shearing carbonation tower; a gas distribution disc and a shearing stirrer are arranged in the tank body of the pressurized stirring and shearing carbonation tower; the shearing stirrer comprises a stirring shaft, stirring blades and a shearing cutter disc; the stirring shaft is vertically arranged and fixed in the tank body; the stirring blades and the shearing cutter disc are both mounted on the stirring shaft; the mounting positions of the stirring blades and the shearing cutter disc are both higher than the gas distribution disc; a shearing blade is arranged on the outer circumferential side of the shearing cutter disc; the shearing blade and the shearing cutter disc have an included angle. The carbonization treatment comprises: conveying the aging liquid into a tank of the pressurized stirring and shearing carbonization tower, introducing carbon dioxide gas into the tank through the gas distribution plate, and the carbon dioxide gas entering the tank from bottom to top; and rotating the stirring shaft of the shearing stirrer at a preset rotating speed to drive the stirring blade and the shearing cutter to rotate. During the carbonization treatment, the operating temperature of the pressurized stirring and shearing carbonization tower is controlled to be 30-40℃, and the operating pressure of the pressurized stirring and shearing carbonization tower is controlled to be 0.2-0.5 MPa; and when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is ended.

4. The calcium-magnesium separation method according to claim 1, characterized by, The digestion treatment process comprises: mixing and reacting the calcined white powder and water at a temperature of 75-85℃ for 1.5-6h, and the mass-volume ratio of the calcined white powder and water is 1 kg: 30-60 L; before the aging treatment, water is added to the digestion liquid after solid-liquid separation, and the concentration of magnesium oxide is controlled to be 10-12 g / L; and the aging treatment time is 6-12h; The pyrolysis treatment comprises: placing the heavy magnesium water in a negative pressure tank, and using an MVR evaporator to pyrolyze the heavy magnesium water; the pyrolysis treatment temperature is 70-95℃, and the pyrolysis treatment time is 0.5-2h; The magnesium carbonate roasting temperature is 550-700℃, and the magnesium carbonate roasting time is 0.5-1h.

5. A method for calcining dolomite, characterized by, The method comprises the steps of: S21, controlling the dolomite powder to be fluidized and roasted in a fluidized roasting main furnace to obtain a primary roasted material; the fluidized roasting temperature is 950-1100℃, and the fluidized roasting time is 0.5-1.5h; S22, controlling the primary roasted material to enter a high-temperature holding bin when it is not cooled to hold, to obtain a holding material; the temperature of the primary roasted material in the high-temperature holding bin is 900-1000℃, the holding time of the primary roasted material in the high-temperature holding bin is 1-2h, and the high-temperature holding bin is in communication with the fluidized roasting main furnace; S23, screening the holding material to obtain a first holding material and a second holding material; the first holding material contains a first-grade holding material, and the second holding material contains a second-grade holding material; the particle size of the first-grade holding material is smaller than that of the second-grade holding material; The particle size of the first-grade holding material is smaller than a preset particle size value, and the particle size of the second-grade holding material is not smaller than the preset particle size value; the preset particle size value is selected in the range of 50-100 μm; S24, the first holding material is used as a calcined white powder; The second holding material is sequentially subjected to cyclic roasting to obtain a calcined white powder; the cyclic roasting temperature is 950-1100℃, and the cyclic roasting time is 5-10 min.

6. A carbonization method characterized by, The method comprises: The calcined white powder obtained by the dolomite roasting method of claim 5 is subjected to digestion treatment and aging treatment to obtain an aging liquid; and then the aging liquid is sequentially subjected to carbonization treatment and solid-liquid separation to obtain heavy magnesium water and a solid separation product containing calcium carbonate; The carbonization treatment is carried out in a pressurized stirring shearing carbonization tower; a gas distribution disc and a shearing stirrer are arranged in the tank body of the pressurized stirring shearing carbonization tower, the shearing stirrer comprises a stirring shaft, stirring blades and a shearing cutter disc; the stirring shaft is vertically arranged and fixed in the tank body; the stirring blades and the shearing cutter disc are both mounted on the stirring shaft, the mounting positions of the stirring blades and the shearing cutter disc are both higher than the gas distribution disc, and the outer circumferential side of the shearing cutter disc is provided with shearing blades, and the shearing blades have an included angle with the shearing cutter disc; The carbonization treatment comprises the following steps: conveying the aging liquid into the tank body of the pressurized stirring shearing carbonization tower, introducing carbon dioxide gas into the tank body through the gas distribution disc, and making the carbon dioxide gas enter the tank body from bottom to top; and rotating the stirring shaft of the shearing stirrer at a preset rotating speed to drive the stirring blades and the shearing cutter disc to rotate; During the carbonization treatment, the operating temperature of the pressurized stirring shearing carbonization tower is controlled to be 30-40℃, the operating pressure of the pressurized stirring shearing carbonization tower is controlled to be 0.2-0.5 MPa, and when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is ended.

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