Dolomite roasting method, carbonization method, calcium-magnesium separation method and comprehensive utilization method

Abstract

The invention provides a dolomite roasting method, a carbonization method, a calcium-magnesium separation method and a comprehensive utilization method. The comprehensive utilization method of dolomite comprises the following steps: performing dolomite roasting on dolomite powder to obtain calcined powder; sequentially carrying out digestion treatment and aging treatment on the calcined white powder to obtain an aging solution; carrying out carbonization treatment on the aging solution to obtain a carbonization reaction solution; carrying out solid-liquid separation on the carbonization reaction liquid to obtain heavy magnesium water and a first solid isolate; carrying out pyrolysis treatment on the heavy magnesium water to obtain pyrolysis reaction liquid; carrying out solid-liquid separation on the pyrolytic reaction liquid to obtain decomposition liquid and a second solid isolate; carrying out magnesium carbonate roasting on the second solid isolate to obtain magnesium oxide; and carrying out reduction treatment on the magnesium oxide to obtain magnesium metal and magnesium aluminate spinel. According to the invention, comprehensive utilization of dolomite resources is realized, no waste residue or waste gas is discharged, a main product is magnesium metal, and byproducts are light calcium carbonate, magnesium aluminate spinel and solid carbon dioxide.

Description

Technical Field

[0001] The invention relates to resource utilization of dolomite and preparation of metallic magnesium, and in particular to a dolomite roasting method, a carbonization method, a calcium-magnesium separation method and a comprehensive utilization method. Background Art

[0002] The chemical composition of dolomite is CaMg(CO3)2, and its crystal belongs to the trigonal carbonate mineral. It is an important calcium and magnesium resource ore, which is often used to prepare magnesium metal. The Pidgeon process for magnesium refining refers to the thermal reduction method of reducing calcined dolomite (calcined white) into magnesium metal in a reduction furnace heated outside the tank by adding materials into the reduction tank. Although the Pidgeon process is a traditional magnesium refining process, it has industrial problems such as high energy consumption, low resource utilization, large slag volume, and high emissions.

[0003] The Chinese invention patent application with publication number CN115141941A discloses a method for comprehensive utilization of dolomite, which comprises 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 to carbonize until the pH value of the digestion solution reaches a preset value to complete carbonization, and then performing solid-liquid separation to obtain heavy magnesium water and a calcium carbonate filter cake; pyrolyzing the heavy magnesium water and then performing solid-liquid separation to obtain a basic magnesium carbonate filter cake; drying and calcining the basic magnesium carbonate filter cake to obtain magnesium oxide; mixing and pressing the magnesium oxide and a reducing agent to obtain a mass; vacuum reducing the mass to obtain metallic magnesium and magnesium-aluminum spinel; and drying the calcium carbonate filter cake to obtain light calcium carbonate. Although this patent application obtains metallic magnesium, magnesium-aluminum spinel and light calcium carbonate based on dolomite, it does not make any in-depth improvements on the calcination of dolomite, which makes it easy for recarbonization to occur and for unreacted carbonate to exist in the calcined dolomite. Moreover, it does not improve the carbonization process, and does not further improve the calcium-magnesium separation efficiency and the quality of the product.

[0004] In view of this, it is necessary to provide a dolomite roasting method, a carbonization method, a calcium-magnesium separation method and a comprehensive utilization method to solve or at least alleviate the technical defects of the above-mentioned dolomite being easily carbonized, having unreacted carbonate ions, and incomplete calcium-magnesium separation during the carbonization process. Summary of the invention

[0005] The main purpose of the present invention is to provide a dolomite roasting method, a carbonization method, a calcium-magnesium separation method and a comprehensive utilization method, aiming to solve the technical defects of the above-mentioned dolomite being easy to carbonize, having unreacted carbonate ions, and incomplete calcium-magnesium separation during the carbonization process.

[0006] To achieve the above object, the present invention provides a calcium and magnesium separation method, comprising the steps of:

[0007] S1, providing dolomite powder;

[0008] S2, calcining the dolomite powder to obtain calcined dolomite; and collecting carbon dioxide gas during the calcination of the dolomite;

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

[0010] S21, controlling the dolomite powder to be fluidized and roasted in a fluidized roasting main furnace to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h;

[0011] S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, thereby obtaining retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000° C., the retention time of the initially fired material in the high-temperature retention bin is 1-2 hours, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body;

[0012] S23, screening the retained material to obtain a first retained material and a second retained material; the first retained material contains a first-grade retained material, the second retained material contains a second-grade retained material, the particle size of the first-grade retained material is smaller than the particle size of the second-grade retained material and / or the mass of the first-grade retained material is smaller than the mass of the second-grade retained material;

[0013] S24, using the first retained material as the calcined white powder; performing cyclic roasting on the second retained material to obtain the calcined white powder, wherein the cyclic roasting temperature is 950-1100° C., and the cyclic roasting time is 5-10 min;

[0014] S3, digesting the calcined white powder to obtain a digestion liquid; separating the digestion liquid into solid and liquid, and then performing an aging treatment and solid-liquid separation in sequence to obtain an aged liquid;

[0015] S4, carbonizing the aged liquid to obtain a carbonized reaction liquid; performing solid-liquid separation on the carbonized reaction liquid to obtain heavy magnesium water and a first solid separator; the first solid separator contains calcium carbonate;

[0016] S5, pyrolyzing the heavy magnesium water to obtain a pyrolysis reaction liquid, and collecting carbon dioxide gas during the pyrolysis process; performing solid-liquid separation on the pyrolysis reaction liquid to obtain a decomposition liquid and a second solid separation; the second solid separation contains magnesium carbonate;

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

[0018] Furthermore, the sources of the dolomite powder include dolomite crushed materials and dolomite powder; the dolomite crushed materials and the dolomite powder are crushed to obtain the dolomite powder.

[0019] Furthermore, 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 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 treatment is carried out in a pressurized stirring shear carbonization tower; a gas distribution plate and a shear stirrer are provided in the tank body of the pressurized stirring shear carbonization tower, and the shear stirrer includes a stirring shaft, stirring blades, and a shear knife disk; the stirring shaft is vertically arranged and fixed in the tank body; the stirring blades and the shear knife disk are both installed on the stirring shaft, and the installation positions of the stirring blades and the shear knife disk are both higher than the gas distribution plate, and a shear blade is provided on the outer peripheral side of the shear knife disk, and the shear blade and the shear knife disk have an angle;

[0021] The carbonization treatment comprises: conveying the aged liquid into the tank body of the pressurized stirring shear carbonization tower, introducing carbon dioxide gas into the tank body through the gas distribution plate, and the carbon dioxide gas enters the tank body from bottom to top; controlling the stirring shaft of the shear stirrer to rotate at a preset speed, driving the stirring blades and the shear blade to rotate;

[0022] During the carbonization treatment, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is terminated.

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

[0024] 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 temperature of the pyrolysis treatment is 70-95° C., and the duration of the pyrolysis treatment is 0.5-2 hours;

[0025] The temperature of the magnesium carbonate roasting is 550-700° C., and the time of the magnesium carbonate roasting is 0.5-1 h.

[0026] The present invention also provides a dolomite comprehensive utilization method based on calcium and magnesium separation, comprising the steps of:

[0027] S01, obtaining magnesium oxide by any of the calcium and magnesium separation methods described above;

[0028] S02, performing a reduction treatment on the magnesium oxide 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] Further, the aluminum-based reducing agent comprises aluminum powder, and the particle size of the aluminum powder is 200-400 μm;

[0030] The reduction treatment 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 2-4h, and the vacuum degree of the vacuum reduction is controlled at 2-5Pa.

[0031] Furthermore, the step S2 further comprises: using the waste heat generated by the roasting of the dolomite as a heat source required for the pyrolysis treatment;

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

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

[0034] The step S6 further comprises: drying the second solid separation before roasting the magnesium carbonate; using the waste heat generated by roasting the magnesium carbonate and the heat of the magnesium oxide as a heat source for drying the second solid separation;

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

[0036] The step S02 further includes: using the waste heat generated by the vacuum reduction as a heat source for drying the first solid separation.

[0037] The present invention also provides a dolomite roasting method, comprising the steps of:

[0038] S21, controlling the dolomite powder to be fluidized and roasted in the fluidized roasting main furnace to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h;

[0039] S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, thereby obtaining retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000° C., the retention time of the initially fired material in the high-temperature retention bin is 1-2 hours, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body;

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

[0041] S24, the first retained material is used as calcined white powder; the second retained material is cyclically roasted in sequence to obtain calcined white powder, the temperature of the cyclic roasting is 950-1100°C, and the duration of the cyclic roasting is 5-10 minutes.

[0042] The present invention also provides a carbonization method, comprising: obtaining a calcined white powder body by any of the above-mentioned dolomite roasting methods, and obtaining an aging liquid after the calcined white powder body is subjected to a digestion treatment and an aging treatment; then the aging liquid is subjected to a carbonization treatment and a solid-liquid separation in sequence to obtain a heavy magnesium water and a solid separation containing calcium carbonate;

[0043] The carbonization treatment is carried out in a pressurized stirring shearing carbonization tower; a gas distribution plate and a shearing stirrer are arranged in the tank body of the pressurized stirring shearing carbonization tower, and the shearing stirrer comprises a stirring shaft, stirring blades, and a shearing knife disk; the stirring shaft is arranged vertically and fixed in the tank body; the stirring blades and the shearing knife disk are both installed on the stirring shaft, and the installation positions of the stirring blades and the shearing knife disk are both higher than the gas distribution plate, and a shearing blade is arranged on the outer peripheral side of the shearing knife disk, and the shearing blade and the shearing knife disk have an angle;

[0044] The carbonization treatment comprises: conveying the aged liquid into the tank body of the pressurized stirring shear carbonization tower, introducing carbon dioxide gas into the tank body through the gas distribution plate, and the carbon dioxide gas enters the tank body from bottom to top; controlling the stirring shaft of the shear stirrer to rotate at a preset speed, driving the stirring blades and the shear blade to rotate;

[0045] During the carbonization treatment, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is terminated.

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

[0047] The present invention can obtain fully reacted dolomite calcined white, and based on the dolomite calcined white, fully separate calcium and magnesium to obtain high-purity light calcium carbonate and magnesium oxide, and can further obtain high-quality metallic magnesium and magnesium-aluminum spinel; based on the dolomite roasting method and comprehensive utilization method of the invention, the present invention has a high comprehensive utilization rate of dolomite resources, low energy consumption, and does not generate waste slag or waste gas in the whole process, which fundamentally solves the current problem of low utilization rate of dolomite resources.

[0048] Specifically, the present invention adopts dolomite powder, and through fluidized roasting, efficient roasting of dolomite can be achieved, and carbon dioxide gas required for secondary carbonization is obtained, the surplus can be made into dry ice, and the heat exchange of calcination tail gas can provide heat source gas for midstream pyrolysis; by adopting a high-temperature retention method, the re-carbonization phenomenon can be avoided, and the sufficiency of the roasting reaction can be achieved; by screening the retained material and performing cyclic roasting, the sufficient roasting of the second-stage retained material can be achieved on the basis of saving energy consumption; thus, after completing the calcination of dolomite, the present invention can efficiently obtain high-activity and low-alkalinity calcined white powder in a low-energy consumption form, avoiding the re-carbonization phenomenon, and avoiding the presence of unreacted carbonate in the calcined dolomite.

[0049] After the calcination and digestion of dolomite are completed, the present invention controls the pressure in the tank body and controls the rotation of the stirring blade and the shearing blade during the carbonization process. Not only can the stirring blade promote mixing, but the shearing blade and the shearing blade have an angle, which has a force to push the medium to flow downward when the stirring shaft rotates, so that the floating speed of the gas is slowed down and the gas is fully in contact with the liquid; at the same time, the inclined shearing blade can also bevel the bubbles when rotating to break up the bubbles, so that the carbonization reaction can be fully carried out, and the formation of calcium carbonate is promoted, thereby improving the calcium-magnesium separation efficiency.

[0050] In addition, the present invention obtains light calcium carbonate and magnesium oxide through the calcium-magnesium separation method. At the same time, the washing water of the carbonized calcium carbonate (the first solid separation) can be recycled as aging water (water replenishment to the digestion liquid), and the filtered hot water (decomposition liquid) after pyrolysis can be recycled as digestion hot water (hot water for digestion treatment). At the same time, the waste heat tail gas from the roasting of magnesium carbonate can be used as a heat source for drying the magnesium carbonate (the second solid separation) filtered out after pyrolysis after heat exchange, and the tail gas (carbon dioxide gas) after cooling can be purified together to prepare dry ice; high-purity metallic magnesium and magnesium-aluminum spinel can be produced by vacuum reduction of magnesium oxide and aluminum, and the waste heat of magnesium-aluminum spinel is used as a drying heat source gas for light calcium carbonate. The four products obtained by the present invention are light calcium carbonate, metallic magnesium, magnesium-aluminum spinel, and dry ice. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0052] Figure 1 It is a schematic diagram of the process of the dolomite comprehensive utilization method of the present invention;

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

[0054] Figure 3 It is a schematic diagram of the structure of the shearing cutter disc in the present invention.

[0055] Figure 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 blade; 9. feed pipe; 10. overflow pipe; 11. air inlet pipe; 12. pressure relief pipe; 13. shearing disc; 14. shearing blade.

[0056] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with the implementation methods and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0059] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0060] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0061] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any methods, equipment and materials of the prior art similar or equivalent to the methods, equipment and materials described in the embodiments of the present invention can also be used to implement the present invention.

[0062] See also Figure 1 As shown, the present invention provides a calcium and magnesium separation method, comprising the steps of:

[0063] S1, providing dolomite powder.

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

[0065] S2, calcining the dolomite powder to obtain calcined dolomite; and collecting carbon dioxide gas during the calcination of the dolomite.

[0066] In order to ensure that the alkalinity and activity of the dolomite roasting meet the high-quality standards, the dolomite roasting device is also equipped with a circulating roasting machine and a high-temperature retention bin to discharge carbonate roasting integrated device.

[0067] In the present invention, the tail gas (carbon dioxide gas) generated by the dolomite roasting can be used as a gas source in the subsequent carbonization treatment after purification, and the waste heat generated by the dolomite roasting can be used as a heat source for the pyrolysis treatment through a heat exchange process. Therefore, in this step, the waste heat generated by the dolomite roasting can be collected by heat exchange, and the waste heat generated by the dolomite roasting can be used as a heat source required for the pyrolysis treatment to save energy consumption.

[0068] In the present invention, the dolomite roasting is carried out in a fluidized roasting system, which includes a fluidized roasting main furnace body (suspension roasting furnace), a high-temperature retention bin and a circulating roasting machine; the fluidized roasting main furnace body, the high-temperature retention bin and the circulating roasting machine are connected in sequence; the circulating roasting machine includes a circulating fluidized bed.

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

[0070] S21, controlling the dolomite powder to be fluidized roasted in a fluidized roasting main furnace to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h.

[0071] S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, to obtain retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000°C, the retention time of the initially fired material in the high-temperature retention bin is 1-2h, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body.

[0072] S23, screening the retained material to obtain a first retained material and a second retained material; the first retained material contains a first-grade retained material, the second retained material contains a second-grade retained material, the particle size of the first-grade retained material is smaller than the particle size of the second-grade retained material and / or the mass of the first-grade retained material is smaller than the mass of the second-grade retained material; it should be noted that the retained material with sufficient reaction is usually smaller or lighter, and therefore can be screened by particle size and mass, and specifically, the retained materials of different levels of particle size and / or different levels of mass can be automatically screened by airflow.

[0073] S24, the first retained material is used as the calcined white powder; the second retained material is cyclically roasted in sequence to obtain the calcined white powder; during the cyclic roasting process, after each cycle, the qualified powder is collected according to the mass change and used as the calcined white powder; the temperature of the cyclic roasting is 950-1100°C, and the duration of the cyclic roasting (total roasting duration) is 5-10min; the cyclic roasting is carried out through a circulating fluidized bed, and the cyclic roasting refers to: the second retained material is cyclically roasted, and after each cycle, the qualified calcined white powder is collected according to the mass change; the number of cycles of the cyclic roasting is usually 2-3 times, and the cyclic process is positive pressure cyclic roasting; during the cyclic roasting process, the qualified calcined white powder can also be collected. In the present invention, the calcined white powder is transported to the fluidized roasting system for cyclone cooling to obtain a calcined white powder with high activity and low alkalinity.

[0074] In the present invention, 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 first retained material is basically the first-grade retained material, and the second retained material is basically the second-grade retained material; or 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 50-100 μm. In the present invention, since the dolomite that is not completely roasted is a minority, the amount of the second retained material will be much smaller than the amount of the first retained material. However, if screening is not performed, the roasting will not be complete. Therefore, the present invention performs cyclic roasting after screening, which can save energy and achieve sufficient roasting of dolomite. The first retained material is a small particle retained material, and the second retained material is a medium particle and a large particle retained material. Due to different screening methods and different batches of roasting, the definition of small particles is likely to have certain differences, and the boundary between the small particle retained material and the medium particle retained material is usually at 50-1 00μm; that is, the particle size of the small particle retention material is less than 100μm, and as a more stringent limitation, it can also be less than a value between 50-100μm; except for the small particle retention material, the rest are medium particle and large particle retention materials; the present invention preferably adopts airflow screening, and the first retention material and the second retention material are obtained after airflow screening. The first retention material belongs to qualified calcined white, which is basically a small particle retention material, and the second retention material is a retention material that needs to be cyclically roasted; the particle size and mass of the first retention material are smaller, so it can be determined by airflow screening.

[0075] In the present invention, the high-temperature retention bin can avoid the occurrence of anti-carbonization or the presence of a large amount of carbonate in the solid-gas separated powder, and can also increase the maximum decomposition time for large and medium particles that are not completely decomposed; the structure of the high-temperature retention bin is that the upper cylinder can store more powder, and the lower cone is used for discharging. The circulating roasting is carried out by the circulating fluidized bed, which can avoid the existence of incomplete decomposition of medium and large particles and affect the quality of the calcined white powder, and improve the utilization rate of dolomite raw materials and the magnesium output rate. The circulating fluidized bed is mainly composed of a fluidized bed roasting furnace body, a recycling air duct and a sealing groove. The medium and large particles (the second retention material) can increase the residence time and number of times in the furnace through circulation until the particles are completely decomposed and the weight becomes lighter and the material is automatically discharged.

[0076] It should be pointed out that, compared with traditional dolomite roasting, the present invention performs fluidized roasting in dolomite roasting, uses a suspension roasting furnace, and is equipped with a cyclone preheating and cooling mechanism. Compared with rotary kiln calcination, it can reduce energy consumption by more than 20%, increase production capacity by more than 50%, and have better quality consistency; the present invention increases a high-temperature retention bin to prevent the recarbonization phenomenon and the maximum removal of carbonate ions; the present invention adds a circulating roasting fluidized bed for the circulating roasting, which can avoid the raw burning of medium and large particles (second-stage retention materials) and ensure that the activity of the calcined powder is more than 30% and the alkalinity is less than 0.9%; the present invention can purify the separated gas and exchange heat during the fluidized roasting process, provide a carbon dioxide gas source for the carbonization of the midstream calcium and magnesium separation, and provide a heat source for the thermal decomposition of heavy magnesium water.

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

[0078] S3, digesting the calcined white powder to obtain a digestion liquid; separating the digestion liquid into solid and liquid, and then subjecting the digestion liquid after solid-liquid separation to aging treatment and solid-liquid separation in sequence to obtain an aged liquid; the solid-liquid separation in this step is mainly for impurity removal, which can also be understood as an impurity removal treatment.

[0079] In the present invention, the digestion treatment is carried out in a collector-type digester. The digestion treatment process includes: mixing the calcined white powder and water at a temperature of 75-85°C for 1.5-6h, and the mass volume ratio of the calcined white powder and water is 1kg:30-60L; before the aging treatment, water is added to the digestion liquid after solid-liquid separation, and the concentration of magnesium oxide (derived from calcined white) is controlled to be 10-12g / L; the aging treatment time is 6-12h; the aging process is standing. Based on the fluidized roasting, digestion and aging processes, the present invention can obtain magnesium hydroxide with high crystallinity and excellent reaction activity.

[0080] S4, carbonizing the aged liquid to obtain a carbonized reaction liquid; performing solid-liquid separation on the carbonized reaction liquid to obtain heavy magnesium water and a first solid separator; the first solid separator contains calcium carbonate.

[0081] The carbonization treatment is carried out in a pressurized stirring shear carbonization tower; see Figure 2-Figure 3 As shown, a gas distribution plate 3 and a shear agitator are provided in the tank body 1 of the pressurized stirring shear carbonization tower, and the shear agitator includes a stirring shaft 6, stirring blades 8, and a shearing knife disk 13; the stirring shaft 6 is vertically arranged and fixed in the tank body 1; the stirring blades 8 and the shearing knife disk 13 are both installed on the stirring shaft 6, and the installation positions of the stirring blades 8 and the shearing knife disk 13 are both higher than the gas distribution plate 3, and a plurality of shearing blades 14 are provided on the outer peripheral side of the shearing knife disk 13, and the shearing knife disk 13 and the shearing blades 14 can be collectively referred to as a shearing assembly 7; the shearing blades 14 have an angle with the shearing knife disk 13, and the angle of the angle in the present invention is 45°, and the angle and angle direction of the plurality of shearing blades 14 are consistent with the shearing knife disk 13, and by controlling the angle direction and the rotation direction of the stirring shaft 6, the shearing blades 14 form a downward liquid pressure when rotating.

[0082] In the present invention, the stirring blades 8 and the shear blade discs 13 are usually arranged in multiple groups vertically along the stirring shaft 6, and the shear blade discs 13 are provided between two adjacent groups of the stirring blades 8. A group of shear blade discs 13 can also be provided above the stirring blades 8 farthest from the gas distribution plate 3; the rotation directions of the two adjacent groups of the stirring blades 8 are opposite, and the rotation direction of the stirring blades 8 close to the bottom is upward; the rotation direction is the stirring direction, which can be understood as the direction of the front of the stirring blades 8.

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

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

[0085] During the carbonization process, the shear blade 14 forms a downward liquid pressure when rotating, and the shearing direction is clockwise, specifically, the gas flow is upward and the liquid pressure is downward, and the center is 45° inclined and the horizontal rotation shearing is performed; during the carbonization process, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the digestion liquid reaches 7.3±0.3 (the end point pH affects the purity and recovery efficiency of the product, and the pH value of the digestion liquid is further 7.3-7.4), the carbonization process is terminated. In the carbonization process, the concentration of carbon dioxide used is controlled between 30% and 100%, and the time of the carbonization process is usually set to 0.5-2h, and can also be 0.8-1.2h.

[0086] The present invention adopts a pressurized stirring shearing 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 increase the reaction boundary line of calcium carbonate and magnesium bicarbonate products.

[0087] In the present invention, the pressurized stirring shearing carbonization tower mainly includes the double-headed sealed pressurized tank body 1, the mechanically driven stirring shaft 6, the stirring blade 8, the shearing blade 13, the shearing blade 14 and the gas distribution plate 3, as well as related air pipes, feed pipes 9, discharge valves, pressure safety valves and other components. The present invention performs pressurized carbonization and controls the operating pressure, so that all magnesium hydroxide can be carbonized to generate heavy magnesium water of magnesium bicarbonate, avoiding calcium carbonate from being dissolved into a mixture of aqueous solution and heavy magnesium water, and ensuring the quality of magnesium carbonate and the recovery rate of magnesium salt; the present invention sets the reverse gas distribution plate 3 at the bottom of the tank body 1, so that the carbon dioxide gas forms all tiny bubbles and rises from the bottom, and the absorption of the longitudinal reaction is faster; the present invention sets multiple groups of the stirring blades 8 and multiple groups of the shearing blades 14, so that the gas and solution can form a more complete multi-layer convection reaction, and the shearing blades 14 can also increase the specific gravity in the transverse carbonization effect; the present invention can prevent calcium carbonate precipitation from clogging the discharge valve through the stirring and breaking effect. The present invention, under the premise that the carbonization reaches the pH value standard, obtains a light calcium carbonate with a magnesium content of less than 2%, meets the "HG / T2226-2010" standard, and realizes calcium-magnesium separation; in the art, no matter what form the magnesium in the light calcium carbonate exists in, it is calculated as magnesium oxide. It should be pointed out that the traditional carbonization is not pressurized, it is difficult to separate completely, and the stirring and shearing carbonization is not performed, not only the carbonization efficiency is low and the time is long, but also it is easy to block the discharge valve and pipeline.

[0088] In the present invention, after the carbonization treatment is completed, a belt vacuum filter is used to separate the solid and liquid to obtain heavy magnesium water and a calcium carbonate filter cake (a first solid separation); the water filtered after washing the filter cake and the water used for cleaning the filter cloth of the belt vacuum filter are recycled as cold water for the subsequent replenishment of the digestate.

[0089] As a supplementary explanation to the step S4, the step S4 also includes: washing the separation mechanism (vacuum filter cloth) for solid-liquid separation in this step; washing the first solid separation, and then drying it at 200-400°C for 1.5-2h to obtain light calcium carbonate; using the washing water produced by washing the first solid separation and the separation mechanism as the cold water for the water replenishment before the aging treatment. In the present invention, before the pyrolysis treatment, heavy magnesium water can also be placed in the middle tank to precipitate fine particles of light calcium carbonate; and the present invention can completely remove the heavy magnesium water by adding water to the first solid separation for washing, thereby ensuring a high recovery rate of magnesium.

[0090] S5, pyrolyzing the heavy magnesium water to obtain a pyrolysis reaction liquid, and collecting carbon dioxide gas during the pyrolysis process; performing solid-liquid separation on the pyrolysis reaction liquid to obtain a decomposition liquid and a second solid separation; the second solid separation contains magnesium carbonate. The decomposition liquid can be directly used for digestion treatment, and its temperature meets the digestion requirements, thereby effectively reducing energy consumption.

[0091] The pyrolysis treatment comprises: placing the heavy magnesium water in a negative pressure tank after precipitation in the middle tank, using an MVR evaporator to pyrolyze the heavy magnesium water, while maintaining the vacuum degree in the negative pressure tank at 200±5Pa to reduce the pyrolysis temperature; the temperature of the pyrolysis treatment is 70-95°C, and the duration of the pyrolysis treatment is 0.5-2h.

[0092] That is, the heavy magnesium water is placed in an MVR evaporator for heating, and magnesium carbonate is precipitated under vacuum and low temperature conditions; then, a plate and frame filter is used for solid-liquid separation to obtain a decomposed liquid and a filter cake. In the present invention, the temperature of the pyrolysis treatment is 70-95°C, and the duration of the pyrolysis treatment is 0.5-2h. In combination with the pyrolysis temperature, the present invention uses an MVR evaporator to pyrolyze the heavy magnesium water and evacuates the heavy magnesium water, which can reduce the pyrolysis energy consumption.

[0093] Specifically, when the present invention performs pyrolysis reaction on the heavy magnesium water, a vacuum low-temperature pressurized evaporator is used for pyrolysis. The vacuum low-temperature pressurized evaporator includes a vacuum pump unit, a negative pressure tank, an MVR evaporator, an electrical control system and other devices. The heavy magnesium water is placed in the pyrolysis tower tank of the vacuum low-temperature pressurized evaporator during pyrolysis. The present invention utilizes the waste heat of the upstream fluidized roasting tail gas, and performs energy-saving pyrolysis through the matching low-temperature MVR evaporator, while reducing the pyrolysis temperature under vacuum state to further save energy consumption; the carbon dioxide precipitated during the pyrolysis process is collected and sent back to the solution before carbonization to achieve normal pressure pre-carbonization; after the pyrolysis is completed, solid-liquid separation is performed to obtain a basic magnesium carbonate filter cake. The hot water after pyrolysis is circulated back to the upstream as hot water for digestion. In this way, the step S5 also includes: using the decomposition liquid obtained after the pyrolysis treatment as hot water for the digestion treatment; collecting the carbon dioxide generated in the pyrolysis treatment and transporting it to the solution to be pre-carbonized after aging, so that normal pressure pre-carbonization can be performed before the pressurized carbonization treatment.

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

[0095] In the present invention, the temperature of the magnesium carbonate roasting is 550-700°C, and the duration of the magnesium carbonate roasting is 0.5-1h. If the temperature is too low or the roasting time is too short, the decomposition will be incomplete; if the temperature is too high or the roasting time is too long, the MgO grains will become larger and gradually lose activity; the present invention adopts a fluidized flash roasting furnace for the roasting.

[0096] In the present invention, the waste heat generated during the roasting of magnesium carbonate and the magnesium oxide after roasting can be used for heat exchange, and the heat obtained is used as a heat source for drying the basic magnesium carbonate filter cake; the carbon dioxide gas generated by the roasting of magnesium carbonate can be purified upstream together with the tail gas of the fluidized roasting of dolomite powder, and used as a gas source for carbonizing the digestion liquid, and the excess carbon dioxide can be used to prepare dry ice. That is, the step S6 also includes: before the roasting of magnesium carbonate, the second solid separation is dried at a temperature of 200-310°C and a duration of 1.5-2.5h; the waste heat generated by the roasting of magnesium carbonate and the heat of magnesium oxide are used as heat sources for drying the second solid separation; the carbon dioxide gas generated by the roasting of magnesium carbonate and the carbon dioxide gas generated by the roasting of dolomite are collected and purified together, and used as the digestion treatment after purification, and the excess carbon dioxide is used to prepare dry ice.

[0097] The present invention also provides a dolomite comprehensive utilization method based on calcium and magnesium separation, comprising the steps of:

[0098] S01, obtaining magnesium oxide by any of the calcium and magnesium separation methods described above.

[0099] S02, reducing the magnesium oxide 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. The selection of the 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 the economy is poor, but the aluminum oxide content may also exceed the standard, thereby affecting the quality and economic benefits of the final product.

[0100] In the present invention, the aluminum-based reducing agent includes aluminum powder, and the particle size of the aluminum powder is 200-400μm. 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 the magnesium oxide, thereby reducing the reaction efficiency. On the contrary, if the particle size is too small, the economy may be poor. Therefore, selecting this particle size range helps to balance the reaction effect and cost-effectiveness. In the present invention, the aluminum-based reducing agent includes aluminum powder made of secondary recycled aluminum, and the secondary recycled aluminum is mainly 1 series aluminum alloy, and the mass percentage of aluminum is ≥99%; the aluminum-containing reducing agent is stored in a closed environment before mixing with the magnesium oxide to prevent oxidation.

[0101] The reduction treatment comprises: pressing the magnesium oxide and the aluminum powder into pellets at a roller surface line pressure of 7-16 t / cm, preheating the pellets to 400-600°C, and then sending them into a vacuum high-resistance electric heating horizontal reduction furnace for 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 2-4h, and the vacuum degree of the vacuum reduction is controlled at 2-5Pa.

[0102] The reaction of the reduction treatment is as follows:

[0103] 4MgO+2Al=3Mg+MgO·Al2O3

[0104] Specifically, the present invention adopts a microwave drying and preheating integrated machine to preheat the pellets pressed from magnesium oxide and aluminum powder to 400-600°C, and then enters a vacuum high-resistance electric heating horizontal reduction furnace for reduction reaction, thereby obtaining metallic magnesium and magnesium-aluminum spinel; the waste heat in the process of magnesium-aluminum spinel generation is used as a heat source for drying the front-stage light calcium carbonate. In the present invention, the step S02 also includes: using the waste heat generated by the vacuum reduction as a heat source for drying the first solid separation.

[0105] The present invention also provides a dolomite roasting method, comprising the steps of:

[0106] S21, controlling the dolomite powder to be fluidized and roasted in the fluidized roasting main furnace body to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h.

[0107] S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, to obtain retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000°C, the retention time of the initially fired material in the high-temperature retention bin is 1-2h, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body.

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

[0109] S24, the first retained material is used as calcined white powder; the second retained material is cyclically roasted in sequence to obtain calcined white powder, the temperature of the cyclic roasting is 950-1100°C, and the duration of the cyclic roasting is 5-10 minutes.

[0110] In the present invention, the definition in the fluidized roasting method is equivalent to the definition of step S1-step S2 in the calcium-magnesium separation method, and the details remain consistent.

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

[0112] The carbonization treatment is carried out in a pressurized stirring shear carbonization tower; a gas distribution plate 3 and a shear agitator are arranged in a tank body 1 of the pressurized stirring shear carbonization tower, and the shear agitator comprises a stirring shaft 6, stirring blades 8, and a shear knife disk 13; the stirring shaft 6 is vertically arranged and fixed in the tank body 1; the stirring blades 8 and the shear knife disk 13 are both installed on the stirring shaft 6, and the installation positions of the stirring blades 8 and the shear knife disk 13 are both higher than the gas distribution plate 3, and a shear blade 14 is arranged on the outer peripheral side of the shear knife disk 13, and the shear blade 14 has an angle with the shear knife disk 13.

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

[0114] During the carbonization treatment, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is terminated.

[0115] In the present invention, the definition in the fluidized roasting method is equivalent to the definition of step S1 to step S4 in the calcium-magnesium separation method, and the details remain consistent.

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

[0117] Example 1

[0118] 1. Test steps:

[0119] 1. Provide dolomite powder; the dolomite powder has 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. Dolomite powder is roasted. The process of dolomite roasting is as follows:

[0121] The dolomite powder is controlled to be fluidized and roasted in the fluidized roasting main furnace to obtain the primary roasted material; the temperature of the fluidized roasting is 1100° C., and the duration of the fluidized roasting is 1.5 hours.

[0122] The initially fired material is controlled to enter the high-temperature retention bin from the fluidized bed roasting main furnace body and be retained for 1.5 hours to obtain the retained material; the temperature of the initially fired material in the high-temperature retention bin is between 900-1000°C, and the high-temperature retention bin and the fluidized bed roasting main furnace body are connected.

[0123] After the retained material is automatically screened by airflow, a first retained material and a second retained material are obtained; the first retained material obtained by automatic airflow screening is basically small particle retained material (less than 100 μm), and the second retained material is basically large and medium particle retained material.

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

[0125] 3. Mix the calcined white powder with water, set the solid-liquid ratio to 1kg:35L, and perform digestion (mixing reaction) at 75°C for 1.5 hours; after solid-liquid separation, obtain a digestion solution; based on a magnesium oxide concentration of 12g / L, mix the digestion solution and water, age for 8 hours, and then filter the aged liquid for solid-liquid separation to obtain an aged liquid.

[0126] 4. Carry out carbonization treatment (pressurized stirring and shear carbonization) on the aged liquid to obtain a carbonized reaction liquid; then, use a belt vacuum filter to separate the carbonized reaction liquid into solid and liquid to obtain heavy magnesium water and a filter cake; the filter cake is dried at 300° C. for 2 hours to obtain light calcium carbonate.

[0127] The carbonization treatment (pressurized stirring shear carbonization) is carried out in a pressurized stirring shear carbonization tower; a gas distribution plate and a shear agitator are arranged in the tank body of the pressurized stirring shear carbonization tower, and the shear agitator has a stirring shaft, two groups of stirring blades, and three groups of shear knife discs; the stirring shaft is arranged vertically and fixed in the tank body; the stirring blades and the shear knife disc are both installed on the stirring shaft, and the installation positions of the stirring blades and the shear knife disc are both higher than the gas distribution plate, and the stirring blades and the shear knife disc are both arranged vertically along the stirring shaft, and a shear knife disc is arranged between two adjacent groups of stirring blades (in this embodiment, one group of shear knife discs, one group of stirring blades, one group of shear knife discs, one group of shear knife discs, and one group of stirring blades are arranged in sequence from top to bottom), and the rotation directions of the two adjacent groups of stirring blades are opposite, the rotation direction of the stirring blade closest to the bottom is upward, and the rotation direction of the stirring blade farthest from the bottom is downward; a shear blade is arranged on the outer peripheral side of the shear knife disc, and the shear blade has an angle of 45° with the shear knife disc, and by controlling the angle direction and the rotation direction of the stirring shaft, the shear blade forms a downward liquid pressure when rotating.

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

[0129] During the carbonization treatment (pressurized stirring shear carbonization), the rotation speed of the stirring shaft is 200r / min, and the shearing mode formed by the shear blades is horizontal rotation shear at a 45° inclination angle from the center to the air flow upward, the liquid pressure downward, and the shearing direction is clockwise; the operating temperature of the pressurized stirring shear carbonization tower is controlled to be about 35°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.4MPa (the air intake of the pressurized stirring shear carbonization tower is controlled to perform pressurized carbonization operation); during the carbonization treatment, the concentration of carbon dioxide gas used is 45%; when the pH value of the digestate reaches 7.35, the carbonization treatment is ended, and the carbonization time is 1 hour.

[0130] 5. Pyrolyze the heavy magnesium water to obtain a pyrolysis reaction liquid; the pyrolysis temperature is set to 93°C, the pyrolysis time is 2 hours, and the pyrolysis reaction liquid is obtained; during the pyrolysis process, the heavy magnesium water is placed in a negative pressure tank after precipitation in the middle tank, and the heavy magnesium water is pyrolyzed by an MVR evaporator, while the vacuum degree in the negative pressure tank is maintained at 200 Pa. Then, a plate and frame filter is used for solid-liquid separation to obtain a decomposition liquid and a filter cake; the filter cake is dried at 300°C for 2 hours to obtain basic magnesium carbonate.

[0131] 6. Calcine basic magnesium carbonate at 680°C for 1 hour (calcination of magnesium carbonate) to obtain magnesium oxide.

[0132] 7. Process the secondary recycled aluminum into aluminum powder, obtain aluminum powder of different particle sizes through powder classification, and select aluminum powder with a particle size of 220μm for subsequent processing.

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

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

[0135] 2. Test results:

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

[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 following table:

[0139] MgO CaO Example 1 95.74％ 0.78％

[0140] 3. The composition of magnesium-aluminum spinel was analyzed by mass percentage, and the results are shown in the following table:

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

[0142] 4. The composition of magnesium metal was analyzed by mass percentage, and the results are shown in the following table:

[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. The results are shown in the following table:

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

[0146] Comparative Example 1

[0147] 1. Test process:

[0148] 1. Obtain calcined white powder in the same manner as in Example 1.

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

[0150] 3. Mix the calcined white powder, ferrosilicon and fluorite powder, and press them into pellets under a roller surface line pressure of 11 t / cm; the mass ratio of calcined white powder, ferrosilicon and fluorite powder is 83.4:15.7:1.8.

[0151] The pellets are preheated at 650°C and then placed in a vacuum high-resistance electric heating horizontal reduction furnace for vacuum reduction treatment to obtain metallic magnesium and reduced slag; the temperature during the reduction process is set at 1260°C, the reduction time is 9 hours, and the vacuum degree is controlled at 3-5Pa.

[0152] 2. Test results:

[0153] 1. The components of the reduced slag were analyzed by mass percentage, and the results are shown in the following table:

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

[0155] 2. The composition of magnesium metal was analyzed by mass percentage, and the results are shown in the following table:

[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] 1. Test process:

[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 endpoint pH of the subsequent carbonization reaction liquid was 7.38, and the carbonization time was 1 hour), and other conditions remained unchanged.

[0160] 2. Test results:

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

[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 following table:

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

[0165] 3. The composition of magnesium-aluminum spinel was analyzed by mass percentage, and the results are shown in the following table:

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

[0167] 4. The composition of magnesium metal was analyzed by mass percentage, and the results are shown in the following table:

[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] 1. Test process:

[0171] Compared with Example 1, in this comparative example, the pressurized stirring shear carbonization was adjusted to normal pressure bubbling carbonization, and other conditions remained unchanged.

[0172] During the atmospheric pressure bubbling carbonization process, no pressurization is performed, and no stirring shaft, stirring blades and shear blades are set; specifically, the atmospheric pressure bubbling carbonization in this comparative example is carried out in a atmospheric pressure bubbling carbonization tower; in this comparative example, carbon dioxide gas with a concentration of 45% is introduced into the gas distribution plate (located at the bottom of the tank body) of the atmospheric pressure bubbling carbonization tower, and bubbling carbonization operation is performed; during the carbonization treatment, the operating temperature of the atmospheric pressure bubbling carbonization tower is controlled to be around 35°C; when the pH value of the carbonization reaction liquid reaches 7.85 and can no longer drop, the carbonization treatment is terminated, and the carbonization time is 3 hours.

[0173] 2. Test results:

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

[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 following table:

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

[0178] Comparative Example 4

[0179] 1. Test process:

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

[0181] 2. Test results:

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

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

[0184] 2. The composition of magnesium-aluminum spinel was analyzed by mass percentage, and the results are shown in the following table:

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

[0186] 3. The composition of magnesium metal was analyzed by mass percentage, and the results are shown in the following table:

[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 only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied 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 in that: Includes steps: S1, providing dolomite powder; S2, calcining the dolomite powder to obtain calcined dolomite; and collecting carbon dioxide gas during the calcination of the dolomite; The process of dolomite roasting includes the following sub-steps: S21, controlling the dolomite powder to be fluidized and roasted in a fluidized roasting main furnace to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h; S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, thereby obtaining retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000° C., the retention time of the initially fired material in the high-temperature retention bin is 1-2 hours, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body; S23, screening the retained material to obtain a first retained material and a second retained material; the first retained material contains a first-grade retained material, the second retained material contains a second-grade retained material, the particle size of the first-grade retained material is smaller than the particle size of the second-grade retained material and / or the mass of the first-grade retained material is smaller than the mass of the second-grade retained material; S24, using the first retained material as the calcined white powder; The second retained material is subjected to cyclic roasting to obtain the calcined white powder, wherein the temperature of the cyclic roasting is 950-1100° C., and the duration of the cyclic roasting is 5-10 minutes; S3, digesting the calcined white powder to obtain a digestion solution; After the digestion liquid is separated into solid and liquid, aging treatment and solid-liquid separation are sequentially performed to obtain an aged liquid; S4, carbonizing the aged liquid to obtain a carbonized reaction liquid; performing solid-liquid separation on the carbonized reaction liquid to obtain heavy magnesium water and a first solid separator; the first solid separator contains calcium carbonate; S5, pyrolyzing the heavy magnesium water to obtain a pyrolysis reaction liquid, and collecting carbon dioxide gas during the pyrolysis process; performing solid-liquid separation on the pyrolysis reaction liquid to obtain a decomposition liquid and a second solid separation; the second solid separation contains magnesium carbonate; S6, roasting the second solid separator with magnesium carbonate to obtain magnesium oxide; and collecting carbon dioxide gas during the roasting of magnesium carbonate.

2. The calcium and magnesium separation method according to claim 1, characterized in that: The sources of the dolomite powder include dolomite crushed materials and dolomite powder; the dolomite crushed materials and the dolomite powder are crushed to obtain the dolomite powder.

3. The calcium and magnesium separation method according to claim 1, characterized in that: 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.

4. The calcium and magnesium separation method according to claim 1, characterized in that: The carbonization treatment is carried out in a pressurized stirring shearing carbonization tower; a gas distribution plate and a shearing stirrer are arranged in the tank body of the pressurized stirring shearing carbonization tower, and the shearing stirrer comprises a stirring shaft, stirring blades, and a shearing knife disk; the stirring shaft is arranged vertically and fixed in the tank body; the stirring blades and the shearing knife disk are both installed on the stirring shaft, and the installation positions of the stirring blades and the shearing knife disk are both higher than the gas distribution plate, and a shearing blade is arranged on the outer peripheral side of the shearing knife disk, and the shearing blade and the shearing knife disk have an angle; The carbonization treatment comprises: conveying the aged liquid into the tank body of the pressurized stirring shear carbonization tower, introducing carbon dioxide gas into the tank body through the gas distribution plate, and the carbon dioxide gas enters the tank body from bottom to top; controlling the stirring shaft of the shear stirrer to rotate at a preset speed, driving the stirring blades and the shear blade to rotate; During the carbonization treatment, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is terminated.

5. The calcium and magnesium separation method according to claim 1, characterized in that: The digestion treatment process includes: mixing the calcined white powder and water at a temperature of 75-85° C. for 1.5-6 hours, wherein the mass volume ratio of the calcined white powder and water is 1 kg:30-60 L; before the aging treatment, adding water to the digestion liquid after solid-liquid separation, and controlling the concentration of magnesium oxide to 10-12 g / L in terms of magnesium oxide; and the aging treatment lasts for 6-12 hours; 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 temperature of the pyrolysis treatment is 70-95° C., and the duration of the pyrolysis treatment is 0.5-2 hours; The magnesium carbonate is calcined at a temperature of 550-700° C. and is calcined for a time of 0.5-1 h.

6. A method for comprehensive utilization of dolomite based on calcium and magnesium separation, characterized in that: Includes steps: S01, obtaining magnesium oxide by the calcium-magnesium separation method as described in any one of claims 1 to 5; S02, performing a reduction treatment on the magnesium oxide 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.

7. The dolomite comprehensive utilization method according to claim 6, characterized in that: The aluminum-based reducing agent includes aluminum powder, and the particle size of the aluminum powder is 200-400 μm; The reduction treatment 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 2-4h, and the vacuum degree of the vacuum reduction is controlled at 2-5Pa.

8. The dolomite comprehensive utilization method according to claim 6 or 7, characterized in that: The step S2 further comprises: using the waste heat generated by the roasting of the dolomite as a heat source required for the pyrolysis treatment; The step S4 further includes: washing the separation mechanism for solid-liquid separation in this step; washing and drying the first solid separation in sequence to obtain light calcium carbonate; using the washing water produced by washing the first solid separation and the separation mechanism as cold water for replenishing water before the aging treatment; The step S5 further comprises: using the decomposition liquid obtained after the pyrolysis treatment as hot water for the digestion treatment; The step S6 further comprises: drying the second solid separation before roasting the magnesium carbonate; using the waste heat generated by roasting the magnesium carbonate and the heat of the magnesium oxide as a heat source for drying the second solid separation; The carbon dioxide gas generated by the roasting of magnesium carbonate and the carbon dioxide gas generated by the roasting of dolomite are collected and purified together, and used for the carbonization treatment after purification, and the excess carbon dioxide gas is used to prepare dry ice; The step S02 further includes: using the waste heat generated by the vacuum reduction as a heat source for drying the first solid separation.

9. A dolomite roasting method, characterized in that: Includes steps: S21, controlling the dolomite powder to be fluidized and roasted in the fluidized roasting main furnace to obtain a primary roasted material; the temperature of the fluidized roasting is 950-1100° C., and the duration of the fluidized roasting is 0.5-1.5 h; S22, controlling the initially fired material to enter the high-temperature retention bin for retention before cooling, thereby obtaining retained material; the temperature of the initially fired material in the high-temperature retention bin is 900-1000° C., the retention time of the initially fired material in the high-temperature retention bin is 1-2 hours, and the high-temperature retention bin is connected to the fluidized bed roasting main furnace body; S23, screening the retained material to obtain a first retained material and a second retained material; the first retained material contains a first-grade retained material, the second retained material contains a second-grade retained material, the particle size of the first-grade retained material is smaller than that of the second-grade retained material and / or the mass of the first-grade retained material is smaller than that of the second-grade retained material; S24, the first retained material is used as calcined white powder; The second retained material is cyclically roasted in sequence to obtain calcined white powder. The temperature of the cyclic roasting is 950-1100° C. and the duration of the cyclic roasting is 5-10 minutes.

10. A carbonization method, characterized in that: include: The dolomite roasting method according to claim 9 is used to obtain calcined white powder, and the calcined white powder is subjected to digestion treatment and aging treatment to obtain an aging liquid; then the aging liquid is subjected to carbonization treatment and solid-liquid separation in sequence to obtain heavy magnesium water and a solid separation containing calcium carbonate; The carbonization treatment is carried out in a pressurized stirring shearing carbonization tower; a gas distribution plate and a shearing stirrer are arranged in the tank body of the pressurized stirring shearing carbonization tower, and the shearing stirrer comprises a stirring shaft, stirring blades, and a shearing knife disk; the stirring shaft is arranged vertically and fixed in the tank body; the stirring blades and the shearing knife disk are both installed on the stirring shaft, and the installation positions of the stirring blades and the shearing knife disk are both higher than the gas distribution plate, and a shearing blade is arranged on the outer peripheral side of the shearing knife disk, and the shearing blade and the shearing knife disk have an angle; The carbonization treatment comprises: conveying the aged liquid into the tank body of the pressurized stirring shear carbonization tower, introducing carbon dioxide gas into the tank body through the gas distribution plate, and the carbon dioxide gas enters the tank body from bottom to top; controlling the stirring shaft of the shear stirrer to rotate at a preset speed, driving the stirring blades and the shear blade to rotate; During the carbonization treatment, the operating temperature of the pressurized stirring shear carbonization tower is controlled to be 30-40°C, and the operating pressure of the pressurized stirring shear carbonization tower is controlled to be 0.2-0.5MPa; when the pH value of the carbonization reaction liquid reaches 7.3±0.3, the carbonization treatment is terminated.

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