Method for preparing fine active magnesium oxide through one-step calcination of magnesium chloride solution

Abstract

The invention discloses a method for preparing fine active magnesium oxide through one-step calcination of a magnesium chloride solution, and relates to the technical field of active magnesium oxide preparation. The invention provides a method for preparing fine active magnesium oxide through one-step calcination of a magnesium chloride solution, the granularity of magnesium oxide is controlled by controlling the concentration of the magnesium chloride solution, the feeding speed and the gas introduction speed, and the activity of magnesium oxide is controlled by adjusting the calcination temperature; a dead-burnt magnesium oxide ball high-temperature bag type dust collector and a dry-type autogenous grinding-vibration screening process are adopted, so that the fine active magnesium oxide is efficiently separated from gas, and meanwhile, the fine active magnesium oxide is recycled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of active magnesium oxide preparation, and particularly relates to a method for preparing micro-fine active magnesium oxide by one-step calcination of magnesium chloride solution. BACKGROUND

[0002] Bittern is a mother liquor obtained after evaporation and concentration of seawater or salt lake water to obtain salt, and is a by-product of the salt industry. Bittern contains high concentrations of valuable elements such as potassium and magnesium, and is a liquid mineral resource that is both abundant and sustainable to develop and utilize. China has abundant bittern resources, which are currently mainly used to produce potassium fertilizer. After potassium extraction, the bittern contains a large amount of magnesium (mainly magnesium chloride). These magnesium resources are discharged on site or discharged into a salt lake at a long distance, which not only causes a large amount of magnesium resources to be wasted, but also occupies a large amount of land and causes environmental pollution. In addition, it also seriously affects the utilization of other resources in the salt lake. Therefore, high-value utilization of magnesium chloride in bittern has important significance for improving the economic benefits of bittern resources and improving the ecological environment.

[0003] Micro-fine active magnesium oxide is a fine chemical product of magnesium salt, and is widely used in rubber, high-grade cable, high-grade plastic, paint, ceramic, high-grade papermaking and pharmaceutical industries. The particle size and activity of magnesium oxide are important qualities that affect its application performance. China is a large producer of magnesium oxide. A large amount of low-purity and low-grade magnesium oxide primary products are exported. On the other hand, the production of high-technology and high-value products such as magnesium oxide with fine particle size and high reactivity is very small, which cannot meet the development requirements of China's industrial production, and long-term reliance on imports. Therefore, it is urgent to develop industrial production technology for producing micro-fine active magnesium oxide and other functional magnesium oxides. Preparing micro-fine active magnesium oxide from magnesium chloride in bittern, which is rich in resources and low in price, is conducive to completely solving the environmental pollution problem of bittern, and further realizing the high-value utilization of magnesium resources, and has broad application prospects.

[0004] At present, the method for preparing micro-fine active magnesium oxide from magnesium chloride mainly adopts a precipitation method, including an alkali method, a carbonization method, a calcination method and the like. The alkali method is to react magnesium chloride solution with an alkaline solution such as sodium hydroxide, potassium hydroxide, calcium hydroxide or ammonia water to generate magnesium hydroxide, and then to prepare magnesium oxide by calcination. A main problem of this method is that a large amount of by-products (sodium chloride, potassium chloride, calcium chloride or ammonium chloride) cannot be utilized, causing new pollution problems. At the same time, the raw material cost of sodium hydroxide and potassium hydroxide is high, which is not conducive to industrial production. The purity of calcium hydroxide is required to be high, which will affect the purity of magnesium oxide. Ammonia water is volatile, and a large amount of ammonium chloride is generated in the production process, which seriously affects the production environment and cannot be produced on a large scale. Patent CN200410019740.6 and the like adopt the above method.

[0005] Carbonization method is to mix magnesium chloride solution with soda solution or to pass ammonia gas and carbon dioxide mixture into magnesium chloride solution to generate intermediate magnesium carbonate or basic magnesium carbonate, and then to calcine to prepare active magnesium oxide. This method is difficult to control the intermediate magnesium carbonate or basic magnesium carbonate, resulting in uneven particle size distribution of the generated magnesium oxide, low activity, and seriously affecting the application performance. At the same time, the carbon ammonium method has high free ammonium concentration in the whole process reaction system, and the environmental pollution problem is serious. The patents CN200910194732.8 and the like use the above method. In order to solve the above problems, the patent CN201110372850.0 changes the preparation conditions of the basic magnesium carbonate by supergravity condition, and successfully prepares the active magnesium oxide product, but the supergravity condition is difficult to realize in actual production, and the environmental problem caused by high free ammonium concentration cannot be solved.

[0006] Calcination method is to prepare magnesium oxide by calcining magnesium chloride crystal or magnesium chloride solution as raw material. The whole process does not introduce other impurity ions. The patent CN200610071248.2 uses magnesium chloride crystal to directly calcine to generate magnesium oxide. The magnesium oxide prepared by this method is easy to be caked, resulting in coarse and uneven particle size of the magnesium oxide and poor activity. The magnesium chloride solution is prepared into magnesium oxide by spray method. The magnesium chloride solution is in the form of mist in the calcination furnace for rapid calcination. The particle size of the generated magnesium oxide is fine and the activity is high. However, the fine magnesium oxide generated in this method will overflow from the calcination furnace with the gas, greatly reducing the yield of magnesium oxide. It is found by experiment that the loss of this part of magnesium oxide accounts for 30% to 40% of the total amount of the generated magnesium oxide.

[0007] In order to solve this problem, the patent CN202410418035.0 discloses a magnesium oxide calcination device and use method. The magnesium oxide overflowing from the gas after calcination is recovered by a cyclone separation device. The cyclone classification device separates the magnesium oxide and the gas according to the density and particle size difference. However, since the particle size of the calcined magnesium oxide product is fine and the density is low, the difference between the magnesium oxide and the gas is small, and it is difficult to separate the magnesium oxide and the gas by this device. At the same time, the magnesium oxide has small particle size, strong adhesion and poor flowability, and the magnesium oxide product will adhere to the discharge port of the cyclone classification device, causing the discharge port to be blocked. At the same time, the HCL gas is easy to combine with water vapor in the environment below 300℃, and reacts with the magnesium oxide powder to generate impurities such as magnesium chloride or basic magnesium chloride, seriously affecting the purity of the fine magnesium oxide. Therefore, it is difficult to separate and recover the fine magnesium oxide by this method. SUMMARY

[0008] In view of the technical problems of poor activity of magnesium oxide, difficult recovery of fine particle size magnesium oxide, and low purity of magnesium oxide in the preparation process of fine active magnesium oxide at present, the present application provides a method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution,

[0009] To achieve the technical purpose, the application adopts the following scheme:

[0010] The method for preparing micro-fine active magnesium oxide by one-step calcination of magnesium chloride solution comprises the following steps:

[0011] S1, evaporate and concentrate the magnesium chloride solution, and control the mass fraction of magnesium chloride in the solution to be 20-40%;

[0012] S2, feed the concentrated magnesium chloride solution into the aerated calcination furnace, maintain the aerated state in the furnace, and calcine at a set temperature to obtain micro-fine active magnesium oxide I, HCl, water vapor, and a gas-solid mixture of magnesium oxide;

[0013] S3, feed the HCl, water vapor, and gas-solid mixture of magnesium oxide into a high-temperature bag-type dust collector of calcined magnesia balls to obtain a mixture of magnesium oxide and calcined magnesia balls and an HCl-water vapor mixture gas;

[0014] S4, perform dry self-milling-vibration screening operation on the mixture of magnesium oxide and calcined magnesia balls, and screen the micro-fine active magnesium oxide II under the screen and the calcined magnesia balls above the screen, return the calcined magnesia balls to the high-temperature bag-type dust collector of calcined magnesia balls for repeated use, and mix the micro-fine active magnesium oxide I and the micro-fine active magnesium oxide II to obtain micro-fine active magnesium oxide;

[0015] S5, cool the HCl-water vapor mixture gas in a gas collection bottle to generate dilute hydrochloric acid, and absorb the overflowed HCl in the gas collection bottle with lye.

[0016] Further, the feeding flow of the magnesium chloride solution in S2 is 0.5-0.8 L / min, the aerated flow of the aerated calcination furnace is 1-1.6 L / min, and the calcination temperature is 400-650 DEG C.

[0017] Further, the working temperature of the high-temperature bag-type dust collector of calcined magnesia balls in S3 is maintained at 300-350 DEG C, the hardness of the calcined magnesia balls reaches Mohs hardness 6 or above, and the MgO content is greater than 98%.

[0018] Further, the particle size composition of the calcined magnesia balls in the high-temperature bag-type dust collector of calcined magnesia balls in S3 is that the mass percentage of the calcined magnesia balls with a diameter of 8-12 mm is 30%, the mass percentage of the calcined magnesia balls with a diameter of 4-6 mm is 30%, and the mass percentage of the calcined magnesia balls with a diameter of 2-4 mm is 40%.

[0019] Further, the self-milling machine liner plate used in the dry self-milling-vibration screening operation in S4 is made of ceramic material, the dry self-milling time is 20-30 min, and the size of the vibration screen hole is 1-1.5 mm.

[0020] Further, the lye in S5 is sodium hydroxide solution with a concentration of 1-3 mol / L.

[0021] Compared with the prior art, the present application has the beneficial effects that: the present application realizes the control of the particle size of magnesium oxide by controlling the concentration, feeding speed and gas feeding speed of the magnesium chloride solution, and controls the activity of the magnesium oxide by adjusting the calcination temperature; the high-temperature bag-type dust collector for the calcined magnesium oxide balls and the dry self-milling-vibration screening process are adopted to realize the high-efficiency separation of the fine active magnesium oxide and the gas, and realize the recovery of the fine active magnesium oxide at the same time. The obtained magnesium oxide product has excellent performance, the particle size D 50 is less than 2 μm, the iodine absorption value is greater than 180 mg / g, and the morphology is uniform short rod. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The process flow chart of the one-step calcination preparation of the fine active magnesium oxide from the magnesium chloride solution provided by the present application is shown in the figure.

[0023] Figure 2 The schematic diagram of the high-temperature bag-type dust collector for the calcined magnesium oxide balls is shown in the figure.

[0024] Figure 3 The SEM diagram of the product magnesium oxide of Example 1 is shown in the figure.

[0025] Figure 4 The XRD diagram of the product magnesium oxide of Example 1 is shown in the figure.

[0026] Figure 5 The SEM diagram of the product magnesium oxide of Example 2 is shown in the figure.

[0027] Figure 6 The XRD diagram of the product magnesium oxide of Example 2 is shown in the figure.

[0028] Figure 7 The SEM diagram of the product of Comparative Example 1 is shown in the figure.

[0029] Figure 8 The XRD diagram of the product of Comparative Example 1 is shown in the figure.

[0030] Figure 9 The SEM diagram of the product of Comparative Example 2 is shown in the figure.

[0031] Figure 10 The XRD diagram of the product of Comparative Example 2 is shown in the figure. DETAILED DESCRIPTION

[0032] In order to fully understand the objects, features and effects of the present application, the present application is described in detail by the following specific embodiments, but the present application is not limited to this.

[0033] As shown in the figure, the method for preparing the fine active magnesium oxide by one-step calcination of the magnesium chloride solution comprises the following steps: Figures 1-2

[0034] ​S1, evaporate and concentrate the magnesium chloride solution, control the mass fraction of magnesium chloride in the solution at 20-40%.

[0035] S2, feed the concentrated magnesium chloride solution into the aerated calcination furnace, the feeding flow rate of the magnesium chloride solution is 0.5-0.8 L / min; at this time, the aerated calcination furnace is kept in an aerated state, the aerated flow rate is 1-1.6 L / min, and the calcination temperature of the aerated calcination furnace is 400-650℃, to obtain fine active magnesium oxide I, HCl, water vapor, and a gas-solid mixture of magnesium oxide.

[0036] S3, feed the HCl, water vapor, and the gas-solid mixture of magnesium oxide into a high-temperature bag-type dust collector of heavy-burned magnesium oxide balls for separation, to obtain a mixture of magnesium oxide and heavy-burned magnesium oxide balls and an HCl-water vapor mixture; the temperature in the high-temperature bag-type dust collector of heavy-burned magnesium oxide balls is kept at 300-350℃, the hardness of the heavy-burned magnesium oxide balls reaches Mohs hardness 6 or above, the MgO content is greater than 98%, and the particle size composition of the heavy-burned magnesium oxide balls is as follows: the mass percentage of heavy-burned magnesium oxide balls with a diameter of 8-12 mm is 30%, the mass percentage of heavy-burned magnesium oxide balls with a diameter of 4-6 mm is 30%, and the mass percentage of heavy-burned magnesium oxide balls with a diameter of 2-4 mm is 40%.

[0037] S4, the mixture of magnesium oxide and heavy-burned magnesium oxide balls is subjected to dry self-grinding-vibration screening operation, the fine active magnesium oxide II is obtained on the screen, the heavy-burned magnesium oxide balls are obtained above the screen, the self-grinding machine liner is made of ceramic material, the dry self-grinding time is 20-30 min, the vibration screen aperture size is 1-1.5 mm, the heavy-burned magnesium oxide balls are returned to the high-temperature bag-type dust collector of heavy-burned magnesium oxide balls for repeated use, and the fine active magnesium oxide I is mixed with the fine active magnesium oxide II to obtain fine active magnesium oxide.

[0038] S5, the HCl-water vapor mixture is cooled in a gas collection bottle to generate dilute hydrochloric acid, the overflowed HCl in the gas collection bottle is absorbed by lye, and the lye is sodium hydroxide solution with a concentration of 1-3 mol / L.

[0039] Example 1

[0040] The magnesium chloride solution with mass fraction of 15% is evaporated and concentrated into magnesium chloride solution with mass fraction of 35%, which is fed into the air calcination furnace at a flow rate of 0.6 L / min, and the calcination temperature is set to 600℃, and the air flow rate is 1.2 L / min, to obtain fine active magnesium oxide I; the HCl, water vapor and magnesium oxide gas-solid mixture generated in the calcination process are fed into the calcined magnesia ball high-temperature bag-type dust collector to obtain a mixture of magnesia and calcined magnesia balls and HCl-water vapor mixture, wherein the working temperature of the dust collector is 310℃, the hardness of the calcined magnesia ball is 6, the MgO content is 98%, and the particle size composition is: the mass of 10mm diameter magnesia balls accounts for 30%, the mass of 4mm diameter magnesia balls accounts for 30%, and the mass of 3mm diameter magnesia balls accounts for 40%; the magnesia-calcined magnesia ball mixture is ground in the self-grinding machine with ceramic lining for 22min, and is screened by the vibrating screen with screen size of 1.2mm, the screened upper part is the calcined magnesia ball which is returned to the calcined magnesia ball high-temperature bag-type dust collector for repeated use, and the screened lower part is fine active magnesium oxide II; the HCl-water vapor mixture is cooled by the gas collection bottle to generate dilute hydrochloric acid, and the overflowed HCl is absorbed by 2mol / L sodium hydroxide solution; the fine active magnesium oxide I and the fine active magnesium oxide II are mixed to obtain fine active magnesium oxide. The fine active magnesium oxide is subjected to SEM analysis, XRD analysis, laser particle size and activity determination, and the results show that the morphology of the fine active magnesium oxide is uniform short rod, the XRD analysis result is magnesium oxide, the D 50 is 1.55μm, and the iodine absorption value is 180.5mg / g, as shown in Figures 3-4 .

[0041] Example 2

[0042] The magnesium chloride solution with mass fraction of 15% is evaporated and concentrated into magnesium chloride solution with mass fraction of 35%, which is fed into the air calcination furnace at a flow rate of 0.6 L / min, and the calcination temperature is set to 500℃, and the air flow rate is 1.2 L / min, to obtain fine active magnesium oxide I; the HCl, water vapor and magnesium oxide gas-solid mixture generated in the calcination process are fed into the calcined magnesium oxide bag-type dust collector to obtain magnesium oxide-calcined magnesium oxide ball mixture and HCl-water vapor mixture, wherein the working temperature of the dust collector is 330℃, the hardness of the calcined magnesium oxide ball is 6, the MgO content is 98%, and the particle size composition is: the mass of magnesium oxide ball with diameter of 10 mm accounts for 30%, the mass of magnesium oxide ball with diameter of 4 mm accounts for 30%, and the mass of magnesium oxide ball with diameter of 3 mm accounts for 40%; the magnesium oxide-calcined magnesium oxide ball mixture is ground in the self-grinding machine with ceramic lining for 22 min, and is screened by the vibrating screen with screen hole size of 1.2 mm, and the calcined magnesium oxide ball on the screen is returned to the calcined magnesium oxide bag-type dust collector for repeated use, and the fine active magnesium oxide II is obtained under the screen; the HCl-water vapor mixture is cooled by the gas collection bottle to generate dilute hydrochloric acid, and the overflowed HCl is absorbed by 2 mol / L sodium hydroxide solution; the fine active magnesium oxide I and the fine active magnesium oxide II are mixed to obtain fine active magnesium oxide. The fine active magnesium oxide is subjected to SEM analysis, XRD analysis, laser particle size and activity determination, and the results show that the morphology of the fine active magnesium oxide is uniform short rod, the XRD analysis result is magnesium oxide, the D 50 is 1.62 μm, and the iodine absorption value is 181.6 mg / g, as shown in Figures 5-6 .

[0043] Comparative Example 1

[0044] The magnesium chloride solution with mass fraction of 15% is evaporated and concentrated into magnesium chloride solution with mass fraction of 35%, which is fed into the air calcination furnace at a flow rate of 0.6 L / min, and the calcination temperature is set to 300℃, and the air flow rate is 1.2 L / min, to obtain fine active magnesium oxide I; the HCl, water vapor and magnesium oxide gas-solid mixture generated in the calcination process are fed into the calcined magnesium oxide bag-type dust collector to obtain magnesium oxide-calcined magnesium oxide ball mixture and HCl-water vapor mixture, wherein the working temperature of the dust collector is 310℃, the hardness of the calcined magnesium oxide ball is 6, the MgO content is 98%, and the particle size composition is: the mass of magnesium oxide ball with diameter of 10 mm accounts for 30%, the mass of magnesium oxide ball with diameter of 4 mm accounts for 30%, and the mass of magnesium oxide ball with diameter of 3 mm accounts for 40%; the magnesium oxide-calcined magnesium oxide ball mixture is ground in the self-grinding machine with ceramic lining for 22 min, and is screened by the vibrating screen with screen size of 1.2 mm, the screened upper part is the calcined magnesium oxide ball which is returned to the calcined magnesium oxide bag-type dust collector for repeated use, and the screened lower part is fine active magnesium oxide II; the HCl-water vapor mixture is cooled by the gas collection bottle to generate dilute hydrochloric acid, and the overflowed HCl is absorbed by 2 mol / L sodium hydroxide solution; the fine active magnesium oxide I and the fine active magnesium oxide II are mixed to obtain fine active magnesium oxide. The fine active magnesium oxide is subjected to SEM analysis, XRD analysis, laser particle size and activity determination, and the results show that the morphology of the fine active magnesium oxide is agglomerated, and there is part of short rod-shaped morphology, the XRD analysis result is magnesium oxide and basic magnesium chloride, which indicates that the magnesium chloride is not completely decomposed, the D 50 The particle size is 5.17 μm, and the iodine absorption value is 80.1 mg / g, as shown in Figures 7-8 .

[0045] Comparative Example 2

[0046] The magnesium chloride solution with mass fraction of 15% is used as raw material, and is evaporated and concentrated into magnesium chloride solution with mass fraction of 50%, which is fed into the air calcination furnace at a flow rate of 0.6L / min, and the calcination temperature is set to 500℃, and the air flow rate is 1.2L / min, to obtain fine active magnesium oxide I; the HCl, water vapor and magnesium oxide gas-solid mixture generated in the calcination process are fed into the calcined magnesium bag-type dust collector, to obtain magnesium oxide-calcined magnesium ball mixture and HCl-water vapor mixed gas, wherein the working temperature of the dust collector is 300℃, the hardness of the calcined magnesium ball is 6, the MgO content is 98%, and the particle size composition is: the mass of the 10mm diameter magnesium oxide ball accounts for 30%, the mass of the 4mm diameter magnesium oxide ball accounts for 30%, and the mass of the 3mm diameter magnesium oxide ball accounts for 40%; the magnesium oxide-calcined magnesium ball mixture is ground in the self-grinding machine with ceramic lining for 22min, and is screened by the vibrating screen with a screen hole size of 1.2mm, and the screened upper part is the calcined magnesium ball which is returned to the calcined magnesium bag-type dust collector for repeated use, and the screened lower part is fine active magnesium oxide II; the HCl-water vapor mixed gas is cooled by the gas collection bottle to generate dilute hydrochloric acid, and the overflowed HCl in the gas collection bottle is absorbed by the 2mol / L sodium hydroxide solution; the fine active magnesium oxide I and the fine active magnesium oxide II are mixed to obtain fine active magnesium oxide. The fine active magnesium oxide is subjected to SEM analysis, XRD analysis, laser particle size and activity determination, and the results show that part of the product appears short rod structure, but is aggregated together as a whole, the XRD analysis result is magnesium oxide and basic magnesium chloride, the D 50 is 10.31μm, and the iodine absorption value is 91.2mg / g, as shown in Figures 9-10 .

[0047] Finally, it should be noted that: the above enumeration is only the preferred embodiments of the present application, of course, the person skilled in the art can modify and change the present application, provided that these modifications and changes are within the scope of the claims of the present application and its equivalent technology, should be considered as the protection scope of the present application.

Claims

1. A method for preparing finely active magnesium oxide by one-step calcination of magnesium chloride solution, characterized in that, Includes the following steps: S1. Evaporate and concentrate the magnesium chloride solution to control the mass fraction of magnesium chloride in the solution to be between 20% and 40%. S2. The concentrated magnesium chloride solution is fed into an aerated calcining furnace. The furnace is kept aerated and calcined at a set temperature to obtain a mixture of fine active magnesium oxide I, HCl, water vapor, and magnesium oxide gas-solid mixture. S3, HCl, water vapor, and magnesium oxide gas-solid mixture are fed into a high-temperature bag filter for reburned magnesium oxide balls to obtain a magnesium oxide-reburned magnesium oxide ball mixture and an HCl-water vapor mixture. S4. The mixture of magnesium oxide and calcined magnesium oxide balls is subjected to dry autogenous milling and vibrating sieving. The underside of the screen is fine active magnesium oxide II, and the overside is calcined magnesium oxide balls. The calcined magnesium oxide balls are returned to the high-temperature bag filter for reuse. Fine active magnesium oxide I and fine active magnesium oxide II are mixed to form fine active magnesium oxide. The S5 and HCl-water vapor mixture is cooled in the gas collecting bottle to generate dilute hydrochloric acid, and the HCl overflowing from the gas collecting bottle is absorbed by the alkaline solution.

2. The method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution according to claim 1, characterized in that, The flow rate of the magnesium chloride solution in S2 is 0.5-0.8 L / min, the gas flow rate of the gas-filled calcining furnace is 1-1.6 L / min, and the calcination temperature is between 400℃ and 650℃.

3. The method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution according to claim 1, characterized in that, The high-temperature bag filter for reburned magnesium oxide balls described in S3 maintains an operating temperature of 300–350°C, and the reburned magnesium oxide balls have a Mohs hardness of 6 or higher and an MgO content greater than 98%.

4. The method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution according to claim 1, characterized in that, The high-temperature bag filter for reburned magnesium oxide balls described in S3 has the following particle size distribution: 30% by mass of reburned magnesium oxide balls with a diameter of 8-12 mm, 30% by mass of reburned magnesium oxide balls with a diameter of 4-6 mm, and 40% by mass of reburned magnesium oxide balls with a diameter of 2-4 mm.

5. The method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution according to claim 1, characterized in that, The autogenous grinding mill liner used in the dry autogenous grinding-vibrating screening operation described in S4 is made of ceramic material. The dry autogenous grinding time is between 20 and 30 minutes, and the screen aperture size of the vibrating screen is 1 to 1.5 mm.

6. The method for preparing fine active magnesium oxide by one-step calcination of magnesium chloride solution according to claim 1, characterized in that, The alkaline solution in S5 is a sodium hydroxide solution with a concentration of 1–3 mol / L.

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