System and method for comprehensive utilization of low-grade magnesite to produce magnesium oxide and calcium chloride

Abstract

The application provides a system and method for comprehensively utilizing low-grade magnesite to produce magnesium oxide and calcium chloride. The system comprises a crushing and screening assembly that gradually crushes and screens the low-grade magnesite to a set particle size; a first processing assembly connected to the crushing and screening assembly, which is used to obtain a treatment liquid by reacting the low-grade magnesite with a leaching liquid, and to obtain light-burned powder by washing and burning the solid residue; a second processing assembly connected to the first processing assembly, which is used to obtain a mother liquor and a precipitate residue by reacting the treatment liquid with a precipitant; the precipitate residue is washed, dried, and calcined to obtain magnesium oxide; and a concentration and crystallization assembly connected to the second processing assembly, which is used to obtain calcium chloride by concentrating and crystallizing the mother liquor. The application solves the technical problems of low comprehensive utilization rate of low-grade magnesite and difficulty in extracting magnesite products.

Description

Technical Field

[0001] This invention relates to the field of low-grade magnesite preparation technology, specifically to a system and method for comprehensively utilizing low-grade magnesite to produce magnesium oxide and calcium chloride. Background Technology

[0002] Magnesite is an important mineral resource playing a vital role in various fields, including building materials, refractories, chemicals, ceramics, and environmental protection. In refractories, it is used in the steel and glass industries; in building materials, it is used in the production of magnesite cement and the preparation of magnesia-based insulation materials. While magnesite reserves are abundant, high-quality, high-grade resources are scarce, with low-grade magnesite deposits being the majority. Low-grade magnesite typically contains only 20-40% magnesium oxide. With the increasing demand for magnesite products, how to comprehensively utilize low-grade magnesite to extract useful products is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0003] The purpose of this invention is to provide a system and method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite, so as to solve the technical problems of low comprehensive utilization rate of low-grade magnesite and difficulty in extracting magnesite products.

[0004] To achieve the above objectives, a system for the comprehensive utilization of low-grade magnesite to produce magnesium oxide and calcium chloride is proposed according to the first aspect of this application, comprising:

[0005] The crushing and screening assembly crushes and screens low-grade magnesite to a set particle size in stages.

[0006] The first processing component, which is connected to the crushing and screening component, is used to process the low-grade magnesite of a set particle size using a leaching solution to obtain a processing solution, and to wash the solid residue and calcine it into light-burned powder.

[0007] A second processing component, connected to the first processing component, is used to treat the processing liquid using a precipitant reaction to obtain mother liquor and precipitate residue; the precipitate residue is washed, dried, and then calcined to obtain magnesium oxide; and...

[0008] A concentration and crystallization assembly, connected to the second processing assembly, is used to concentrate and crystallize the mother liquor to obtain calcium chloride.

[0009] In some embodiments, the crushing and screening assembly includes a first abrasive element, a second abrasive element, and a third abrasive element connected in series according to the flow direction of the low-grade magnesite; wherein each of the first abrasive element, the second abrasive element, and the third abrasive element includes a crushing element and a screening element corresponding to each other; the crushing element crushes and grinds the incoming low-grade magnesite and then feeds it to the corresponding screening element for screening.

[0010] In some embodiments, a reflux pipe is provided between the crushing component and the screening component in the first abrasive component, the second abrasive component, and the third abrasive component, for returning the low-grade magnesite with a particle size that does not meet the set value screened out by the screening component to the corresponding screening component for further crushing and grinding.

[0011] In some embodiments, the first processing component includes a first reactor, a first filter, a first washer, and a firing machine; wherein the feed inlet of the first reactor is connected to the crushing and screening component; its liquid inlet is through which leachate is introduced; the discharge outlet of the first reactor is connected to the first filter; the liquid outlet of the first filter is connected to the second processing component, and its discharge outlet is connected to the first washer; the discharge outlet of the first washer is connected to the firing machine.

[0012] In some embodiments, the outlet of the first washing machine is connected to the second processing component for conveying magnesium-containing liquid to the second processing component.

[0013] In some embodiments, the second processing assembly includes a second reactor, a second filter, a second washer, and a calciner; wherein the inlet of the second reactor is connected to the outlet of the first filter and the outlet of the first washer; a precipitant is introduced into the inlet of the second reactor; the outlet of the second reactor is connected to the second filter; the outlet of the second filter is connected to the concentration and crystallization assembly, and its outlet is connected to the second washer; distilled water is introduced into the inlet of the second washer, and its outlet is connected to the calciner.

[0014] In some embodiments, a dryer is provided between the discharge port of the second washing machine and the firing machine.

[0015] In some embodiments, the concentration and crystallization assembly includes a concentration and crystallization machine, the inlet of which is connected to the outlet of the second filter.

[0016] To achieve the above objectives, a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite is proposed according to the second aspect of this application, utilizing the system described in any of the above embodiments, comprising the following steps:

[0017] Low-grade magnesite is crushed and screened in stages using crushing and screening components to a set particle size of no more than 74 micrometers.

[0018] The crushed low-grade magnesite and leaching solution are added at a ratio of 1:35-45 g / ml in the first treatment unit and stirred at 85-125°C for 1-3 hours. The reaction solution is then filtered to obtain a treatment solution and solid residue. The treatment solution is transported downstream, and the solid residue is washed and calcined into light calcined powder.

[0019] The treatment solution enters the second treatment component, where it reacts with a precipitant at a pH of 9-11, a temperature of 45-65℃, and a stirring rate of 100-300 r / min for 1-2 hours. After filtration, mother liquor and precipitate residue are obtained. The mother liquor is transported downstream, and the precipitate residue is washed, dried, and then calcined to obtain magnesium oxide.

[0020] The mother liquor is crystallized and concentrated in a concentration and crystallization component to obtain calcium chloride.

[0021] In some embodiments, the leachate comprises an ammonium salt solution with a mass percentage of 15%-20%, wherein the ammonium salt solution comprises ammonium chloride;

[0022] And / or, the precipitant is an alkaline solution comprising Ca(OH)2 with a concentration of 0.1-0.5 mol / L, and the addition ratio of Ca(OH)2 to the treatment solution is (1-2):1;

[0023] And / or, the solid residue is calcined at 750-1000℃ for 2-4 hours to obtain the lightly calcined powder;

[0024] And / or, the precipitate is calcined at 800-1000℃ for 2-4 hours.

[0025] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a system structure for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite in one embodiment of this application;

[0027] Figure 2 A schematic diagram of a system structure for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite in one embodiment of the application;

[0028] Figure 3 A flowchart of a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite in one embodiment of the application;

[0029] In the diagram: 1. Magnesite ore; 2. Jaw crusher; 3. First screening machine; 4. Cone crusher; 5. Second screening machine; 6. Ball mill; 7. Spiral classifier; 8. First reactor; 9. Leachate; 10. First filter; 11. Solid residue; 12. First washing machine; 13. Calcination machine; 14. Light calcined powder; 15. Magnesium-containing liquid; 16. Processing liquid; 17. Second reactor; 18. Precipitant; 19. Second filter; 20. Second washing machine; 21. Mother liquor; 22. Concentrated crystallizer; 23. Calcium chloride; 24. Distilled water storage tank; 25. Dryer; 26. Calcination machine; 27. Magnesium oxide. Detailed Implementation

[0030] The embodiments of this application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, the embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0031] To achieve the above objectives, a system for the comprehensive utilization of low-grade magnesite to produce magnesium oxide and calcium chloride is proposed according to the first aspect of this application, including a crushing and screening component, a first processing component, a second processing component, and a concentration and crystallization component; wherein the crushing and screening component crushes and screens the low-grade magnesite to a set particle size step by step.

[0032] Because low-grade magnesite contains many impurities and cannot be directly utilized, it must undergo leaching chemical reaction treatment before it can be used. This application can improve the utilization of low-grade magnesite and reduce resource waste. In this application, the crushing and screening component includes a first abrasive element, a second abrasive element, and a third abrasive element connected in series according to the flow direction of the low-grade magnesite (low-grade magnesite ore 1); wherein the first abrasive element, the second abrasive element, and the third abrasive element each include a corresponding crushing element and a screening element; the crushing element crushes and grinds the incoming magnesite ore 1 and then conveys it to its corresponding screening element for screening.

[0033] In other words, the crushing and screening assembly of this application includes a first abrasive element, a second abrasive element, and a third abrasive element connected in series. According to the flow direction of the magnesite ore 1, the magnesite ore 1 is sequentially crushed and screened through the first, second, and third abrasive elements. Each of the first, second, and third abrasive elements includes both crushing and screening components. Low-grade magnesite ore enters the crushing component of the first abrasive element, is crushed, and then enters the screening component of the first abrasive element for screening. Magnesite ore 1 with a suitable screening particle size enters the crushing component of the second abrasive element, is crushed, and then enters the screening component of the second abrasive element for screening. Magnesite ore 1 with a suitable screening particle size enters the crushing component of the third abrasive element, is crushed, and then enters the screening component of the third abrasive element for screening. The crushing of magnesite ore 1 with a suitable screening particle size is completed.

[0034] Examples such as Figure 1 As shown, the crushing and screening components of the first abrasive element are a jaw crusher 2 and a first screening machine 3, respectively; the crushing and screening components of the second abrasive element are a cone crusher 4 and a second screening machine 5, respectively; and the crushing and screening components of the third abrasive element are a ball mill 6 and a spiral classifier 7, respectively. Magnesite ore 1 is fed into the jaw crusher 2 for coarse crushing, so that the low-grade magnesite ore 1 can be crushed into coarse particles of 20-50 mm. The discharge port of the jaw crusher 2 is connected to the first screening machine 3, which screens the crushed magnesite ore 1 output from the jaw crusher 2. The qualified low-grade magnesite coarse powder with a particle size of 20-50 mm, screened out, is connected to the finished product discharge port of the first screening machine 3 through the inlet of the cone crusher 4. The low-grade magnesite coarse powder enters the cone crusher 4 and is easily and finely crushed. The cone crusher 4 crushes the 20-50 mm magnesite coarse powder into fine powder with a particle size between 5-10 mm, which facilitates faster and easier subsequent processing of low-grade magnesite. The discharge port of the cone crusher 4 is connected to the second screening machine 5, which screens the low-grade magnesite fine powder output from the cone crusher 4. The low-grade magnesite fine powder with a particle size between 5-10 mm, screened by the second screening machine 5, is fed into the ball mill 6 for further grinding. Therefore, the inclusion of the cone crusher 4 allows the ball mill 6 to process the magnesite more quickly during subsequent processing, reducing the grinding time and improving efficiency. The ball mill 6 further grinds the low-grade magnesite fine powder with a particle size between 5-10 mm into low-grade magnesite powder with a particle size not exceeding 74 micrometers (approximately 200 mesh). This powder is then fed into the spiral classifier 7 through the outlet of the ball mill 6. The spiral classifier 7 is connected to the first processing unit, where the low-grade magnesite powder with a particle size not exceeding 74 micrometers is further processed.

[0035] In some embodiments, a reflux pipe is provided between the crushing and screening components in the first, second, and third abrasive components to return low-grade magnesite with a particle size that does not meet the set value to its corresponding screening component for further crushing and grinding.

[0036] As can be seen, reflux pipes are provided between the crushing and screening components in the first, second, and third abrasive components. In other words, with Figure 1 For example, the crushing and screening components of the first abrasive element are a jaw crusher 2 and a first screening machine 3, respectively; the crushing and screening components of the second abrasive element are a cone crusher 4 and a second screening machine 5, respectively; and the crushing and screening components of the third abrasive element are a ball mill 6 and a spiral classifier 7, respectively. In this embodiment, a return pipe is provided between the jaw crusher 2 and the first screening machine 3, so that the filter end of the first screening machine 3 is connected to the feed inlet of the jaw crusher 2, allowing low-grade magnesite coarse particles that do not meet the 20-50 mm size to be sent back to the jaw crusher 2 for further crushing. In addition, another return pipe is provided between the cone crusher 4 and the second screening machine 5, so that the filter end of the second screening machine 5 is connected to the feed inlet of the cone crusher 4, allowing low-grade magnesite fine powder that does not meet the 5-10 mm size to be sent back to the cone crusher 4 for further crushing, so that the low-grade magnesite can maintain a particle size between 5-10 mm. Finally, another reflux pipe is also installed between the ball mill 6 and the spiral classifier 7, so that low-grade magnesite powder with a particle size greater than 74 micrometers can be separated and fed into the ball mill 6 for further grinding.

[0037] In this embodiment, low-grade magnesite is fed into a jaw crusher 2 for coarse crushing, and then screened by a first screening machine 3. Coarse low-grade magnesite particles with a particle size of 20-50 mm can be sent back to the jaw crusher 2 for further crushing. The coarse low-grade magnesite particles with a particle size of 20-50 mm can be sent to a cone crusher 4 for fine crushing, reducing the crushing difficulty and time of the cone crusher 4. The finely crushed low-grade magnesite powder is screened by the first screening machine 3, and the fine low-grade magnesite powder with a particle size of 5-10 mm is sent to a ball mill 6 for faster grinding and reduced processing time. The fine low-grade magnesite powder with a particle size of 5-10 mm is sent back to the cone crusher 4 for further crushing. Ball mill 6 mills low-grade magnesite powder with a particle size of 5-10 mm, and uses spiral classifier 7 for screening. Spiral classifier 7 conveys low-grade magnesite powder with a particle size not exceeding 74 micrometers downstream; low-grade magnesite powder with a particle size exceeding 74 micrometers is separated and fed back into ball mill 6 for further grinding. The scheme of this application can classify, grind, and screen low-grade magnesite, effectively improving the grinding efficiency of low-grade magnesite and resulting in low-grade magnesite powder with a small particle size, thereby increasing the contact area of ​​the low-grade magnesite powder and the efficiency of subsequent reactions.

[0038] In this application, the first processing component is connected to the crushing and screening component, and is used to process low-grade magnesite with a set particle size by reacting with leaching solution 9 to obtain processing solution 16, and wash the solid residue 11 and calcine it into light calcined powder 14.

[0039] The first processing component includes a first reactor 8, a first filter 10, a first washer 12, and a firing machine 13; the feed inlet of the first reactor 8 is connected to a crushing and screening component; its liquid inlet is through which leachate 9 is introduced; the discharge outlet of the first reactor 8 is connected to the first filter 10; the liquid outlet of the first filter 10 is connected to the second processing component, and its discharge outlet is connected to the first washer 12; the discharge outlet of the first washer 12 is connected to the firing machine 13. In other words, the feed inlet of the first reactor 8 is connected to the spiral classifier 7, which delivers low-grade magnesite powder with a particle size not exceeding 74 micrometers from the spiral classifier 7 to the first reactor 8. The inlet of the first reactor 8 is supplied with leachate 9, which can be an ammonium salt solution with a mass percentage of 15%-20%, such as an ammonium chloride solution. The leachate 9 and the low-grade magnesite powder are mixed in the first reactor 8 in a specific ratio. During the reaction, the slurry at the bottom of the first reactor 8 is lifted to the top, allowing the low-grade magnesite powder to fully mix and contact with the leachate 9. The leaching temperature is controlled between 85-125℃, and the reaction time is controlled between 1-3 hours, enabling the low-grade magnesite powder to undergo a metathesis reaction with the leachate 9. When the ammonium salt solution is an ammonium chloride solution, the chemical reaction is as follows: MgCO3 + 2NH4Cl → MgCl2 + 2NH3↑ + CO2↑ + H2O. This application utilizes the first reactor 8 to ensure sufficient stirring and contact between the magnesite ore powder and the leachate 9, enabling the magnesite ore powder to undergo a metathesis reaction with the leachate 9. This allows the magnesium ions in the magnesite ore powder to be rapidly decomposed into the leachate 9. Furthermore, in this embodiment, the leachate can also be an acidic solution such as dilute sulfuric acid, dilute hydrochloric acid, or dilute nitric acid. However, since concentrated acids such as sulfuric acid, hydrochloric acid, or nitric acid require dilution and are highly corrosive, ammonium chloride solution is chosen as the leachate. This solution can also be recycled, resulting in high economic efficiency.

[0040] Subsequently, the mixture in the first reactor 8 is connected to the first filter 10 through the outlet of the first reactor 8, and is filtered to produce solid residue 11 and processing liquid 16. Therefore, this application allows magnesium ions in low-grade magnesite powder to be rapidly decomposed into the leachate 9, and enables the separation of solid residue 11 and processing liquid 16. The outlet of the first filter 10 is connected to the second processing unit, outputting the processing liquid 16 to the downstream second processing unit for further processing. Simultaneously, the outlet of the first filter 10 is connected to the first washing machine 12, and the solid residue 11 is output to the first washing machine 12 for cleaning. Then, the outlet of the first washing machine 12 is connected to the calcining machine 13, where the solid residue 11 is calcined into light-burned powder 14, allowing the residue of the magnesite ore 1 to be utilized. The resulting light-burned powder 14 can be used to produce magnesite cement.

[0041] In some embodiments, the outlet of the first washing machine 12 is connected to a second processing component for conveying magnesium-containing liquid 15 to the second processing component.

[0042] In this embodiment, to maximize the recovery of magnesium from low-grade magnesite, the outlet of the first washing machine 12 is connected to the second processing component. In other words, the solid residue 11 carries a certain amount of magnesium ions, such as... Figure 2 As shown in this application, the magnesium-containing liquid 15 of the washed solid residue 11 is output to the second processing unit to process the magnesium ions, which can obtain a magnesium-containing product with a high yield, and recover the magnesium ions remaining in the solid residue 11 and the leachate 9.

[0043] In some embodiments, the magnesium-containing liquid 15 that has washed the solid residue 11 can be combined with the treatment liquid 16 output from the outlet of the first filter 10 and then introduced into the second treatment assembly. In this application, the magnesium-containing liquid 15 and the treatment liquid 16 will enter the second treatment assembly together, so that the treatment liquid 16 can combine with magnesium ions.

[0044] In this application, the second processing component is connected to the first processing component and is used to treat the processing liquid 16 by reacting with the precipitant 18 to obtain the mother liquor 21 and the precipitate residue; the precipitate residue is washed, dried and then calcined to obtain magnesium oxide 27.

[0045] The second processing component includes a second reactor 17, a second filter 19, a second washer 20, and a calciner 26. The inlet of the second reactor 17 is connected to the outlet of the first filter 10 and the outlet of the first washer 12. A precipitant 18 is introduced into the inlet of the second reactor 17. The outlet of the second reactor 17 is connected to the second filter 19. The outlet of the second filter 19 is connected to a concentration and crystallization component, and its outlet is connected to the second washer 20. Distilled water is introduced into the inlet of the second washer 20, and its outlet is connected to the calciner 26.

[0046] For example, magnesium-containing liquid 15 and processing liquid 16 are fed into a second reactor 17, with precipitant 18 added to the inlet of the second reactor 17. The magnesium-containing liquid 15, processing liquid 16, and precipitant 18 are moved upwards and thoroughly mixed in the second reactor 17. The chemical reaction occurring in the second reactor 17 includes: MgCl2 + 2NaOH → Mg(OH)2↓ + 2NaCl. The second reactor 17 ensures that the magnesium-containing liquid 15, processing liquid 16, and precipitant 18 are mixed uniformly from bottom to top, reducing processing time and improving efficiency.

[0047] After the reaction in the second reactor 17 is completed, the outlet of the second reactor 17 is connected to the second filter 19. The second filter 19 is used to separate the mother liquor 21 and the magnesium hydroxide precipitate. The outlet of the second filter 19 is connected to the concentration and crystallization component, and its outlet is connected to the second washing machine 20. The inlet of the second washing machine 20 is connected to the distilled water storage tank 24, allowing distilled water to flow through. Its outlet is connected to the calciner 26. In some embodiments, a dryer 25 is provided between the outlet of the second washing machine 20 and the calciner 26. That is, the second washing machine 20 is fixedly installed at the outlet of the second filter 19, and the outlet of the second washing machine 20 is connected to the dryer 25. The outlet of the dryer 25 is connected to the calciner 26, and the calciner 26 produces magnesium oxide 27.

[0048] In this embodiment, the magnesium hydroxide precipitate is washed multiple times with distilled water released from the distilled water storage tank 24 to remove adsorbed impurity ions. The washed magnesium hydroxide precipitate is dried by the dryer 25 and finally sent to the calciner 26 for calcination. The temperature of the calciner 26 is kept at 800-1000℃ and the calcination time is controlled at 2-4 hours. After calcination, magnesium oxide 27 is produced, which can be used in the manufacture of parts.

[0049] In this application, the concentration and crystallization assembly is connected to the second processing assembly for concentrating and crystallizing the mother liquor 21 to obtain calcium chloride 23. In some embodiments, the concentration and crystallization assembly includes a concentration crystallizer 22, the inlet of which is connected to the outlet of the second filter 19.

[0050] The mother liquor 21 output from the second filter 19 can be injected into the concentrator crystallizer 22 and heated. The mother liquor 21 is evaporated by the concentrator crystallizer 22, so that the mother liquor 21 can be concentrated. When it is saturated, the heating and evaporation are stopped and forced cooling is performed so that the mother liquor 21 can be cleanly produced to produce calcium chloride 23. Therefore, the by-product of mother liquor 21 can be recycled and reused to manufacture calcium chloride 23.

[0051] To achieve the above objectives, according to the second aspect of this application, a method for the comprehensive utilization of low-grade magnesite to produce magnesium oxide and calcium chloride is proposed, such as... Figure 3 As shown, the system using any of the above embodiments includes the following steps:

[0052] S1: Use crushing and screening components to crush and screen low-grade magnesite to a set particle size of no more than 74 micrometers.

[0053] S2: The crushed low-grade magnesite and leaching solution are added at a ratio of 1:35-45 g / ml in the first treatment unit at 85-125℃ and stirred for 1-3 hours; the reaction solution is filtered to obtain the treatment solution and solid residue; the treatment solution is transported downstream, and the solid residue is washed and calcined into light calcined powder;

[0054] S3: The treatment liquid enters the second treatment component, and reacts with a precipitant at a pH of 9-11, a temperature of 45-65℃ and a stirring rate of 100-300 r / min for 1-2 hours. After filtration, mother liquor and precipitate are obtained. The mother liquor is transported downstream, and the precipitate is washed, dried and calcined to obtain magnesium oxide.

[0055] In S1, the low-grade magnesite is crushed and screened step by step using a crushing and screening component to a set particle size of no more than 74 micrometers.

[0056] In step S2, crushed low-grade magnesite is mixed with a 5%-20% ammonium salt solution at an addition ratio of 1:35-45 g / ml. The addition ratio of low-grade magnesite to leachate can be 1:35 g / ml, 1:36 g / ml, 1:37 g / ml, 1:38 g / ml, 1:39 g / ml, 1:40 g / ml, 1:41 g / ml, 1:42 g / ml, 1:43 g / ml, or 1:45 g / ml. When the amount of leachate added is small, the low-grade magnesite powder cannot be fully wetted, resulting in insufficient solid-liquid contact area and preventing the full extraction of magnesium from the magnesite powder. When the amount of leachate added is large, the stirring resistance is high, which can easily lead to internal overheating, affecting the accuracy of the reaction and increasing wear and tear on mechanical components.

[0057] In this process, the reaction temperature is 85-125℃, for example, reaction temperatures of 85℃, 95℃, 105℃, 115℃, 125℃, etc. The reaction of ammonium salt leaching magnesium is an endothermic reaction. When the reaction temperature is too low, such as below 85℃, the movement of magnesium elements inside the low-grade magnesite powder is slow, the leaching rate decreases, and the process time is prolonged. When the reaction temperature is too high, such as above 125℃, the decomposition rate is accelerated, more raw materials are consumed, more by-reactants are precipitated, and the ammonium salt itself is easily decomposed in a high-temperature environment, causing the reaction to be unstable.

[0058] Meanwhile, in this process, the solid residue is calcined at 750-1000℃ for 2-4 hours to obtain lightly calcined powder; the calcination temperature of the solid residue is 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc. When the calcination temperature of the solid residue is too low, such as below 750℃, the residual magnesium carbonate and basic magnesium carbonate in the residue will not decompose completely; when the calcination temperature of the solid residue is too high, such as above 1000℃, the CaO in the residue will melt and clump on the inner wall of the equipment, which can easily cause safety hazards to the equipment.

[0059] In S3, the treatment liquid and magnesium-containing liquid enter the second reactor. Using a precipitant, the reaction is carried out for 1-2 hours at a pH of 9-11, a temperature of 45-65℃, and a stirring rate of 100-300 r / min. After filtration, mother liquor and precipitate are obtained. The mother liquor is transported downstream, and the precipitate is washed, dried, and calcined to obtain magnesium oxide.

[0060] The precipitant is an alkaline solution, which can be a Ca(OH)₂ solution with a concentration of 0.1-0.5 mol / L. The addition ratio of Ca(OH)₂ to the treatment solution is (1-2):1, resulting in higher reaction efficiency and lower raw material costs. The generated calcium ions are easily concentrated and crystallized into calcium chloride, facilitating discharge. Alternatively, sodium hydroxide or ammonia can be used as the alkaline solution, but the ammonia concentration needs to be increased to 15%-25%, and ammonia itself is volatile. Sodium ions generated from sodium hydroxide require further processing.

[0061] In this process, the reaction pH is 9, 10, or 11, and the temperature is 45℃, 48℃, 50℃, 52℃, 55℃, 60℃, or 65℃. When the reaction temperature is too low, such as below 45℃, the ionic reaction rate between magnesium ions and hydroxide ions decreases, and the magnesium ion reaction is incomplete, resulting in high residual levels. When the reaction temperature is too high, such as above 65℃, the precipitant calcium hydroxide precipitates, causing an increase in impurity precipitation.

[0062] In this application, the precipitated slag is calcined at 800-1000℃ for 2-4 hours, wherein the calcination temperature of the precipitated slag is 800℃, 850℃, 900℃, 950℃, 1000℃, etc. When the calcination temperature of the precipitated slag is too low, such as below 800℃, combustion is incomplete, and the residual magnesium hydroxide exists in the product in the form of Mg(OH)2, resulting in a decrease in the purity of magnesium oxide. When the calcination temperature of the precipitated slag is too high, such as above 1000℃, the reaction is too fast, and the magnesium oxide crystals grow rapidly, resulting in insufficient internal density and a decrease in overall hardness.

[0063] To facilitate a further understanding of this application, the solutions described below are further described in conjunction with embodiments. Those skilled in the art will understand that the embodiments described in this application are only some examples, and any other suitable specific embodiments are within the scope of this application.

[0064] Example 1

[0065] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are as follows: the low-grade magnesite is crushed and screened to a set particle size of no more than 74 micrometers; the crushed low-grade magnesite powder is added to ammonium chloride with a mass percentage of 20% at a ratio of 1:35 g / ml in the first processing unit and stirred at 85°C for 3 hours; the reaction solution is filtered to obtain a processing solution and solid residue; the processing solution is transported downstream, and the solid residue is washed and calcined at 750°C for 4 hours to obtain lightly calcined powder.

[0066] The treatment solution enters the second treatment unit, where 0.5 mol / L Ca(OH)2 is used as a precipitant at a ratio of 1:1 with the treatment solution. The treatment solution and precipitant react for 1 hour at a pH of 11, a temperature of 50°C, and a stirring rate of 300 r / min, and then are filtered to obtain mother liquor and precipitate residue. The mother liquor is transported downstream, and the precipitate residue is washed, dried, and calcined at 1000°C for 2 hours to obtain magnesium oxide.

[0067] Example 2

[0068] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters differ from those in Example 1 as follows: Crushed low-grade magnesite powder and ammonium chloride (15% by mass) are added in a first processing unit at a ratio of 1:40 g / ml. The processing solution enters a second processing unit, where 0.1 mol / L Ca(OH)₂ is used as a precipitant, with an addition ratio of 2:1 to the processing solution. The reaction is carried out for 2 hours at pH 9, temperature 65°C, and stirring speed 100 r / min, followed by filtration.

[0069] Example 3

[0070] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters differ from those in Example 1 as follows: Crushed low-grade magnesite powder and ammonium chloride (18% by mass) are added in a first processing unit at a ratio of 1:45 g / ml; the processing solution enters a second processing unit, where 0.3 mol / L Ca(OH)₂ is used as a precipitant, with an addition ratio of 2:1 to the processing solution; the reaction is carried out for 1 hour at a pH of 10, a temperature of 60°C, and a stirring rate of 200 r / min, followed by filtration.

[0071] Example 4

[0072] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the crushed low-grade magnesite powder and ammonium chloride with a mass percentage of 18% are added in the first processing component at an addition ratio of 1:39 g / ml, and the mixture is stirred and reacted at 125°C for 1 hour.

[0073] Example 5

[0074] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the crushed low-grade magnesite powder and ammonium chloride with a mass percentage of 16% are added in the first processing component at an addition ratio of 1:40 g / ml, and the mixture is stirred and reacted at 100°C for 2 hours.

[0075] Example 6

[0076] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: after washing the solid residue, it is calcined at 1000°C for 2 hours to obtain lightly calcined powder.

[0077] The treatment solution enters the second treatment unit, where 0.3 mol / L Ca(OH)₂ is used as a precipitant at a ratio of 2:1 to the treatment solution; the pH of the treatment solution and precipitant is 10. The precipitate is washed, dried, and then calcined at 800℃ for 4 hours to obtain magnesium oxide.

[0078] Example 7

[0079] This embodiment provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: after washing the solid residue, it is calcined at 1000°C for 2 hours to obtain lightly calcined powder.

[0080] The treatment solution enters the second treatment component, where 0.3 mol / L Ca(OH)2 is used as a precipitant at a ratio of 2:1 to the treatment solution. The precipitate is washed, dried, and then calcined at 800℃ for 4 hours to obtain magnesium oxide.

[0081] Comparative Example 1

[0082] This comparative example provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the low-grade magnesite is crushed and screened to a set particle size of 500 mesh.

[0083] Comparative Example 2

[0084] This comparative example provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the crushed low-grade magnesite powder and ammonium chloride with a mass percentage of 15% are added in the first processing unit at an addition ratio of 1:50 g / ml.

[0085] Comparative Example 3

[0086] This comparative example provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the treatment liquid enters the second treatment component, and 0.1 mol / L Ca(OH)2 is used as a precipitant with an addition ratio of 2:1 to the treatment liquid; the reaction is carried out for 2 hours at a pH of 12, a temperature of 80°C, and a stirring rate of 100 r / min, and then filtered.

[0087] Comparative Example 4

[0088] This comparative example provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the crushed low-grade magnesite powder and ammonium chloride with a mass percentage of 20% are added in a first processing unit at an addition ratio of 1:35 g / ml, and the mixture is stirred and reacted at 50°C for 5 hours.

[0089] Comparative Example 5

[0090] This comparative example provides a method for producing magnesium oxide and calcium chloride by comprehensively utilizing low-grade magnesite. The process and parameters are different from those in Example 1 as follows: the crushed low-grade magnesite powder and ammonium chloride with a mass percentage of 20% are added in a first processing unit at an addition ratio of 1:35 g / ml, and the mixture is stirred and reacted at 150°C for 1 hour.

[0091] Experimental Example

[0092] The yields and purity of magnesium oxide and calcium chloride obtained in each example and comparative example were tested. The purity of magnesium oxide was tested by EDTA complexometric titration (GB / T 9853-2008), and its yield was the ratio of magnesium oxide to low-grade magnesite powder.

[0093] The purity of calcium chloride was determined by argentometric titration (Mohr method, GB / T 26520-2011), and the yield was the ratio of calcium chloride to low-grade magnesite powder. The results are shown in Table 1.

[0094] Table 1. Results of yield and purity of magnesium oxide and calcium chloride obtained in each example and comparative example.

[0095]

[0096] As shown in Table 1, this application has achieved a magnesium oxide yield of 88–92% and a purity of 96–98% after precipitation-calcination, which can directly meet the requirements of industrial-grade high-purity magnesium oxide and is significantly better than the traditional calcination method.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A system for producing magnesium oxide and calcium chloride from low-grade magnesite, characterized in that, include: The crushing and screening assembly crushes and screens low-grade magnesite in stages to a particle size of no more than 74 micrometers. The first processing component, connected to the crushing and screening component, is used to react the low-grade magnesite of a set particle size with a leaching solution at 85-125°C with stirring for 1-3 hours. The leaching solution includes an ammonium salt solution with a mass percentage of 15%-20%, and the low-grade magnesite is reacted with the leaching solution at a ratio of 1:35-45 g / ml. After the reaction, a processed solution is obtained, and the solid residue is washed and calcined into lightly calcined powder. The second processing component, connected to the first processing component, is used to lift and move the processing liquid from bottom to top using a precipitant, and to fully mix and stir it to obtain mother liquor and precipitate residue. The precipitant is an alkaline solution comprising Ca(OH)2 with a concentration of 0.1-0.5 mol / L, and its addition ratio to the processing liquid is (1-2):

1. The precipitate residue is washed, dried, and then calcined to obtain magnesium oxide. The purity of the magnesium oxide is 96-98%, and the yield is 88-92%. as well as A concentration and crystallization assembly, connected to the second processing assembly, is used to concentrate and crystallize the mother liquor to obtain calcium chloride.

2. The system of claim 1, wherein, The crushing and screening assembly includes a first abrasive element, a second abrasive element, and a third abrasive element connected in series according to the flow direction of the low-grade magnesite; wherein each of the first abrasive element, the second abrasive element, and the third abrasive element includes a corresponding crushing element and a screening element; the crushing element crushes and grinds the incoming low-grade magnesite and then feeds it to the corresponding screening element for screening.

3. The system of claim 2, wherein, A reflux pipe is provided between the crushing component and the screening component in the first abrasive component, the second abrasive component, and the third abrasive component. This pipe is used to return the low-grade magnesite that is screened out by the screening component but whose particle size does not meet the set value to the corresponding screening component for further crushing and grinding.

4. The system according to any of claims 1-3, characterized in that, The first processing assembly includes a first reactor, a first filter, a first washer, and a firing machine; wherein the feed inlet of the first reactor is connected to the crushing and screening assembly; its liquid inlet is through which leachate is introduced; the discharge outlet of the first reactor is connected to the first filter; the liquid outlet of the first filter is connected to the second processing assembly, and its discharge outlet is connected to the first washer; the discharge outlet of the first washer is connected to the firing machine.

5. The system of claim 4, wherein, The outlet of the first washing machine is connected to the second processing component for conveying magnesium-containing liquid to the second processing component.

6. The system of claim 5, wherein, The second processing assembly includes a second reactor, a second filter, a second washer, and a calciner; wherein the inlet of the second reactor is connected to the outlet of the first filter and the outlet of the first washer; a precipitant is introduced into the inlet of the second reactor; the outlet of the second reactor is connected to the second filter; the outlet of the second filter is connected to the concentration and crystallization assembly, and its outlet is connected to the second washer; distilled water is introduced into the inlet of the second washer, and its outlet is connected to the calciner.

7. The system of claim 6, wherein, A dryer is installed between the discharge port of the second washing machine and the firing machine.

8. The system of claim 6, wherein, The concentration and crystallization assembly comprises a concentration and crystallization machine, and a liquid inlet of the concentration and crystallization machine is connected with a liquid outlet of the second filter.

9. A method for producing magnesium oxide and calcium chloride from low-grade magnesite, characterized in that, The system according to any one of claims 1-8, comprising the following steps: The low-grade magnesite is crushed and screened to a particle size of not more than 74 microns by using the crushing and screening assembly; The crushed low-grade magnesite is added to the leaching liquid at an addition ratio of 1:35-45 g / ml in the first treatment assembly at 85-125 ℃, and the reaction is stirred for 1-3 h; the reaction liquid is filtered to obtain a treatment liquid and a solid residue; the treatment liquid is sent to the downstream, and the solid residue is washed and calcined into light calcined powder; The treatment liquid is sent to the second treatment assembly, and a precipitant is used to react at a pH value of 9-11, a temperature of 45-65 ℃, and a stirring rate of 100-300 r / min for 1-2 h, and then the treatment liquid is filtered to obtain a mother liquor and a precipitate residue; the mother liquor is sent to the downstream, and the precipitate residue is washed, dried, and calcined into magnesium oxide; The mother liquor is concentrated and crystallized in the concentration and crystallization assembly to obtain calcium chloride.

10. The method of claim 9, wherein, The leaching liquid comprises an ammonium salt solution with a mass percentage of 15%-20%, and the ammonium salt solution comprises ammonium chloride; The precipitant is an alkali solution, and the alkali solution comprises Ca(OH)2 with a concentration of 0.1-0.5 mol / L, and the addition ratio of the alkali solution to the treatment liquid is (1-2):1; The solid residue is calcined at a temperature of 750-1000 ℃ for 2-4 h to obtain the light calcined powder; The precipitate residue is calcined at a temperature of 800-1000 ℃ for 2-4 h.

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