Manufacturing process for silicon steel grade magnesium oxide using dolomite

Abstract

This invention provides a method for producing silicon steel grade magnesium oxide that is highly pure, low-cost, and produces minimal residue. [Solution] Dolomite is crushed and calcined as a raw material, and the resulting light-calcined dolomite powder is subjected to primary hydration, secondary hydration, magnesium chloride washing, carbonization, and thermal decomposition reactions in sequence, and the resulting magnesium carbonate is calcined to obtain silicon steel grade magnesium oxide. This invention uses dolomite as a raw material and extracts high-purity silicon steel grade magnesium oxide under specific hydration and carbonization conditions. The silicon steel grade magnesium oxide obtained by this process has the advantages of high purity, low manufacturing cost, and low residue.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium oxide production, and particularly to the production process of silicon steel grade magnesium oxide using dolomite.

Background Art

[0002] Silicon steel grade magnesium oxide is a magnesium oxide coating material used in the production of oriented silicon steel sheets, and is a high-value-added magnesium oxide product. It is mainly used in the high-temperature annealing treatment stage in the production process of oriented silicon steel sheets, serving as an isolation agent, dephosphorizing agent and desulfurizing agent, and reacting with silicon oxide on the surface of silicon steel to form magnesium silicate, which is an excellent insulating film layer. However, at present, the demand for silicon steel grade magnesium oxide in China is large, the supply volume of its products cannot meet the market demand, and it still depends on imports.

[0003] At present, the raw materials for producing silicon steel grade magnesium oxide mainly include magnesite, dolomite, bischofite, seawater or salt lake brine, magnesium-containing ores, etc. Specific production methods mainly include the brine-ammonium carbonate method, the magnesium ore carbonization method, the ammonia method, the brine thermal decomposition method, etc. However, each method has its own drawbacks. For example, the brine-ammonium carbonate method is relatively mature technically, the product quality is stable and reliable, but the consumption of raw materials is large and the production cost is high. The magnesium ore carbonization method has the drawbacks of high energy consumption and high production cost, and it is difficult for industrial production due to low purity. The ammonia method is relatively difficult to control the process because magnesium oxide is easy to form colloids, and local sintering, activity reduction and recovery rate reduction are likely to occur. Moreover, environmental problems are also prominent. The brine thermal decomposition method has high requirements for equipment, is likely to cause large environmental pollution, and has a low raw material recovery rate.

[0004] Given the problems in the production of silicon steel-grade magnesium oxide described above, it has become an extremely important task to explore methods for producing silicon steel-grade magnesium oxide that are highly pure, low-cost, and produce minimal residue. [Overview of the Initiative]

[0005] The objective of the present invention is to provide a manufacturing process for silicon steel grade magnesium oxide using dolomite in order to solve the problems in the background art.

[0006] To achieve the above objectives, the present invention provides a process for producing silicon steel grade magnesium oxide using dolomite, the process comprising the following steps. S1. Dolomite raw material is crushed and calcined to obtain light-calcined dolomite powder. Then, the light-calcined dolomite powder is subjected to primary hydration treatment, followed by filtration, washing, and drying to obtain the primary hydration product. S2. The primary hydrate product is subjected to secondary hydrate production according to the solid-liquid ratio, with controlled hydrate temperature and hydrate time. After hydrate production, the product is filtered, washed, and dried to obtain the secondary hydrate product. S3. The secondary hydration product is washed with magnesium chloride solution, controlling the washing temperature and washing time. After washing, it is filtered, washed, and dried to obtain magnesium hydroxide containing a small amount of impurity compounds. The magnesium hydroxide obtained in S4 and S3, containing small amounts of impurity compounds, is subjected to a carbonization reaction according to the solid-liquid ratio. The carbonization temperature, carbonization time, and carbon dioxide flow rate are controlled, and after the reaction is complete, the solution is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate solution is thermally decomposed, controlling the thermal decomposition temperature and time. After completion, the solution is filtered and dried to obtain magnesium carbonate. The magnesium carbonate produced in S6 and S5 is calcined, and the calcination temperature and time are controlled to obtain silicon steel grade magnesium oxide.

[0007] Preferably, in S1, the dolomite is first crushed and ball-milled, and the ball-milled dolomite powder is sieved to a mesh size of 100 to 200 mesh. Next, the sieved dolomite powder is calcined in a tubular furnace at a calcination temperature of 900 to 1200°C and a calcination time of 2 to 5 hours.

[0008] Preferably, in S1, the solid-liquid ratio of the light-calcined dolomite powder is 0.5 to 1 g / L, and in the primary hydration step, 2 to 3 g of disodium ethylenediaminetetraacetate is added, the hydration temperature is 50 to 70°C, the hydration time is 20 to 40 minutes, and the hydration stirring speed is 500 to 800 r / min.

[0009] Preferably, in S2, the solid-liquid ratio is 1 to 2 g / L, the hydration temperature is 90 to 110°C, the hydration time is 1 to 3 hours, and the hydration stirring speed is 500 to 800 r / min.

[0010] Preferably, in step S3, the mass concentration of the magnesium chloride solution is 3-6%, the amount used is 200-400 mL, the washing temperature is 20-30°C, the washing time is 0.5-1 hour, and the washing stirring speed is 500-800 r / min.

[0011] Preferably, in S4, the solid-liquid ratio is 5-8 g / L, the carbonization temperature is 10-20°C, the carbonization time is 40-60 minutes, and the carbon dioxide flow rate is 0.08-0.2 L·min. -1 Let's assume that.

[0012] Preferably, in S5, the thermal decomposition temperature is 80 to 100°C, the thermal decomposition time is 0.5 to 1 hour, and the thermal decomposition stirring rate is 500 to 800 r / min.

[0013] Preferably, in S6, the firing temperature is 900 to 1100°C, the firing time is 2 to 4 hours, and the firing conditions are firing under a nitrogen atmosphere.

[0014] Preferably, in steps S1 to S3, the washing process consists of 5 to 8 washes with deionized water. The drying process in steps S1 to S3 and S5 is vacuum drying.

[0015] The principle of the process method employed in the present invention is as follows. The products obtained by calcining dolomite are mainly magnesium oxide and calcium oxide. Of these, the reaction in which magnesium oxide reacts with water to produce magnesium hydroxide proceeds slowly, while the reaction in which calcium oxide reacts with water to produce calcium hydroxide proceeds rapidly. For this reason, in the process method employed in the present invention, by controlling the appropriate hydration temperature and hydration time in the primary hydration step and adding a certain amount of disodium ethylenediaminetetraacetate, most of the calcium oxide in the light-calcined dolomite powder can be separated and removed in solution form. After the primary hydration reaction is complete, the main components of the primary hydration product are magnesium oxide, magnesium hydroxide, small amounts of calcium oxide, calcium hydroxide, and other impurity compounds. Since magnesium oxide produces magnesium hydroxide under conditions of high reaction temperature and long reaction time, the secondary hydration step converts the magnesium oxide and calcium oxide in the primary hydration product into magnesium hydroxide and calcium hydroxide by controlling the appropriate hydration temperature and time. The main components of the secondary hydration product are magnesium hydroxide, small amounts of calcium hydroxide, and impurity compounds.

[0016] Magnesium chloride reacts with calcium hydroxide to produce calcium chloride and magnesium hydroxide. Therefore, by washing a certain amount of secondary hydration product with a magnesium chloride solution of a certain mass concentration, a small amount of calcium hydroxide in the secondary hydration product can be separated and removed from the secondary hydration product in the form of a calcium chloride solution. After washing, the main components are magnesium hydroxide and a small amount of impurity compounds. These are mixed with a certain amount of ultrapure water according to the solid-liquid ratio and subjected to a carbonization reaction, producing a magnesium bicarbonate solution and a small amount of other impurity precipitates under appropriate carbonization conditions. After the carbonization reaction is complete, the precipitate is filtered off, and the resulting carbonized liquid is subjected to a thermal decomposition reaction to produce a magnesium carbonate precipitate. By filtering, drying, and calcining the thermally decomposed liquid after the thermal decomposition reaction is complete, silicon steel grade magnesium oxide with a mass fraction of 99.26%, a hydration rate of 4.16, and a citric acid activity value of 56s is obtained.

[0017] Therefore, the manufacturing process of silicon steel grade magnesium oxide using dolomite of the present invention uses dolomite as the raw material and extracts high-purity silicon steel grade magnesium oxide under specific hydration conditions and carbonation conditions. The silicon steel grade magnesium oxide obtained by this process has the advantages of high purity, low manufacturing cost, and few residues.

[0018] Hereinafter, the technical means of the present invention will be described in more detail with reference to the drawings and examples.

Brief Description of the Drawings

[0019] [Figure 1] Figure 1 is a flowchart in an embodiment of the present invention. [Figure 2] Figure 2 is an XRD diagram of the magnesium oxide obtained in Example 1 of the present invention. [Figure 3] Figure 3 is a scanning electron microscope photograph of the magnesium oxide obtained in Example 1 of the present invention, where (a) shows a 1μm scale and (b) shows a 500nm scale. [Figure 4] Figure 4 is a particle size distribution diagram of the magnesium oxide (untreated by ball milling) obtained in Example 1 of the present invention.

Modes for Carrying Out the Invention

[0020] Hereinafter, the technical means of the present invention will be described in more detail with reference to the drawings and examples.

[0021] To make the objectives, technical means, and advantages of the embodiments of the present invention clearer, while referring to the drawings attached to the embodiments of the present invention, the technical means in the embodiments of the present invention will be clearly and completely described. Note that the described embodiments are only a part of the embodiments of the present invention and do not include all the embodiments.

[0022] This invention provides a process for producing silicon steel grade magnesium oxide using dolomite. As shown in Figure 1, the method includes the following steps: Using dolomite as a raw material, the dolomite is first crushed and ball-milled, and the ball-milled dolomite powder is sieved through a 100-200 mesh sieve. The sieved dolomite powder is calcined in a tubular furnace to obtain lightly calcined dolomite powder under conditions of calcination temperature of 900-1200°C and calcination time of 2-5 hours. The calcination reaction equation in this process is as follows: CaCO3 MgCO3(s)→MgO(s)+CaO(s)+2CO2↑(high temperature) Next, the obtained light-calcined dolomite powder is subjected to primary hydration treatment at a solid-liquid ratio of 0.5-1 g / L, with 2-3 g of disodium ethylenediaminetetraacetate added simultaneously. The treatment is carried out under the conditions of hydration temperature of 50-70°C, hydration time of 20-40 minutes, and hydration stirring speed of 500-800 r / min. The reaction equation for primary hydration is as follows: 2MgO(s)+2CaO(s)+2H2O(aq)→MgO(s)+Mg(OH)2(s)↓+Ca(OH)2(s)↓, Ca(OH)2(s)+M gO(s)+Mg(OH)2(s)+EDTA-2Na(aq)→CaEDTA(aq)+MgO(s)+2NaOH(aq)+Mg(OH)2(s)↓ After hydration, the mixture is filtered to obtain magnesium oxide, magnesium hydroxide, and small amounts of calcium hydroxide and other elemental impurity compounds. The primary hydration product is dried in a vacuum dryer, and then subjected to secondary hydration at a solid-liquid ratio of 1-2 g / L under conditions of hydration temperature 90-110°C, hydration time 1-3 hours, and hydration stirring speed 500-800 r / min. The reaction equation for secondary hydration is as follows: 2MgO(s)+2H2O(aq)→2Mg(OH)2(s)↓, 2CaO(s)+2H2O(aq)→2Ca(OH)2(s)↓.

[0023] After secondary hydration is complete, the mixture is filtered, washed, and vacuum-dried to obtain magnesium hydroxide, a small amount of calcium hydroxide, and impurity compounds. Prepare a magnesium chloride solution with a mass concentration of 3-6%, and wash an appropriate amount of the secondary hydrate product in 200-400 mL of magnesium chloride solution. The washing temperature is 20-30°C, the washing time is 0.5-1 hour, and the washing stirring speed is 500-800 r / min. The reaction equation for this process is as follows: Ca(OH)2(s)+MgCl2(aq)→CaCl2(aq)+Mg(OH)2(s)↓; The main components of the secondary hydration product after washing are magnesium hydroxide and small amounts of impurity compounds. The secondary hydration product after washing is subjected to a carbonization reaction at a solid-liquid ratio of 5-8 g / L to obtain a magnesium bicarbonate solution. The carbonization temperature is 10-20°C, the carbonization time is 40-60 minutes, and the carbon dioxide flow rate is 0.08-0.2 L·min. -1 The process is carried out under the following conditions. The reaction equation for carbonization is as follows: Mg(OH)2(s)↓+2CO2↑→Mg(HCO3)2(aq) After the carbonization reaction is complete, the magnesium bicarbonate solution obtained by filtration is subjected to a thermal decomposition reaction to obtain a magnesium carbonate precipitate. The decomposition is carried out under the following conditions: thermal decomposition temperature 80-100°C, thermal decomposition time 0.5-1 hour, and thermal decomposition stirring speed 500-800 r / min. The reaction equation for thermal decomposition is as follows: Mg(HCO3)2(aq)→MgCO3(s)↓+CO2↑+H2O(aq) The magnesium carbonate precipitate obtained by the thermal decomposition reaction is subjected to calcination under a nitrogen atmosphere at a calcination temperature of 900-1100°C for 2-4 hours to obtain silicon steel grade magnesium oxide. The reaction equation for calcination is as follows: MgCO3(s)↓→MgO(s)+CO2↑(high temperature)

[0024] This process will be explained with the following specific examples.

[0025] Example 1 This first example provides a method for producing silicon steel grade magnesium oxide using dolomite, and is carried out in the following manner. S1. Dolomite is crushed and ball-milled. The ball-milled dolomite powder is sieved through a 200-mesh sieve and then calcined in a tubular furnace at 900°C for 3 hours to obtain light-calcined dolomite powder. The light-calcined dolomite powder is subjected to hydration treatment at a solid-liquid ratio of 1 g / L, with 2.15 g of disodium ethylenediaminetetraacetate added simultaneously. The treatment is carried out at a hydration temperature of 50°C, a hydration time of 0.5 hours, and a hydration stirring speed of 750 r / min. After hydration, the product is filtered, washed, and vacuum-dried to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrate treatment at a solid-liquid ratio of 2 g / L under the conditions of hydrate temperature 90°C, hydrate time 3 hours, and hydrate stirring speed 750 r / min. After hydrate, filtration, washing, and vacuum drying are performed to obtain the secondary hydrated product. S3. Prepare a 5% magnesium chloride solution by mass. Weigh an appropriate amount of secondary hydration product and mix it with 200 mL of the 5% magnesium chloride solution. The reaction is carried out at a temperature of 25°C, for a reaction time of 1 hour, and at a reaction stirring speed of 750 r / min. After the reaction is complete, filter, wash, and vacuum dry to obtain magnesium hydroxide containing a small amount of impurity compounds. S4. The obtained magnesium hydroxide containing a small amount of impurity compound was subjected to a carbonization reaction at a solid-liquid ratio of 5 g / L, at a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L·min. -1 The reaction is carried out under these conditions, and after the reaction is complete, the solution is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate filtrate is subjected to a thermal decomposition reaction under the following conditions: thermal decomposition temperature of 95°C, thermal decomposition time of 50 minutes, and thermal decomposition stirring speed of 750 r / min. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained in S6 and S5 is calcined under a nitrogen atmosphere at a calcination temperature of 1100°C for a calcination time of 3 hours to obtain a silicon steel grade magnesium oxide product.

[0026] The hydration rate of the product is 4.16%, the mass rate is 99.26%, the citric acid activity value is 56s, and the residue generation rate is 3.68%.

[0027] The results of the inspection of the product from Example 1 are shown in Figures 2-4.

[0028] Comparative Example 1 This comparative example provides a conventional method for producing silicon steel grade magnesium oxide using dolomite, and is carried out by the following method. S1, Dolomite is calcined at a high temperature in a tubular furnace at 1000°C to obtain a mixture of magnesium oxide and calcium oxide. S2, a mixture of magnesium oxide and calcium oxide is dissolved in water to obtain a mixture of magnesium hydroxide and calcium hydroxide. S3, carbon dioxide is subjected to a carbonization reaction with a magnesium hydroxide-calcium hydroxide mixture to obtain calcium carbonate and magnesium bicarbonate as products. S4. After the carbonization reaction is complete, the solution is filtered to obtain an aqueous magnesium bicarbonate solution. This aqueous magnesium bicarbonate solution is then heated (heating temperature 800°C) to obtain the magnesium carbonate product. In step S5, the magnesium carbonate after thermal decomposition is filtered to obtain solid magnesium carbonate. The magnesium carbonate is then calcined at a calcination temperature of 850°C to obtain magnesium oxide. S6. The magnesium oxide obtained from calcination is reacted with water at 65°C (mass concentration ratio of magnesium oxide to water: 1:8.5). Modification, purification, and impurity removal are performed in water, and the resulting solution is filtered to obtain a magnesium hydroxide solid filter cake. The magnesium hydroxide filtration cakes obtained in S7 and S6 were baked at 950°C for 2 hours and 1000°C for 2 hours, respectively, to obtain magnesium oxide with different citric acid activity. The magnesium oxides with different properties obtained in S8 and S7 are pulverized, and 70% of the product with activity 60S and 30% of the product with activity 200S are mixed to obtain a silicon steel grade magnesium oxide product.

[0029] The hydration rate of the product is 3.31%, the mass rate is 99.2%, the citric acid activity value is 65s, and the residue generation rate is 50.4%.

[0030] A comparative analysis of the product and residue amounts from Example 1 and Comparative Example 1 revealed that the product obtained in Example 1 had similar purity and hydration rate to the product obtained in Comparative Example 1, and also exhibited lower residue generation and higher activity.

[0031] Example 2 This example provides a method for producing silicon steel grade magnesium oxide using dolomite, and is carried out in the following manner. S1. Dolomite is crushed and ball-milled. The ball-milled dolomite powder is sieved through a 200-mesh sieve and then calcined in a tubular furnace at 900°C for 3 hours to obtain light-calcined dolomite powder. The light-calcined dolomite powder is subjected to hydration treatment at a solid-liquid ratio of 1 g / L, with 2.15 g of disodium ethylenediaminetetraacetate added simultaneously. The treatment is carried out at a hydration temperature of 50°C, a hydration time of 0.5 hours, and a hydration stirring speed of 750 r / min. After hydration, the product is filtered, washed, and vacuum-dried to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrate treatment at a solid-liquid ratio of 2 g / L under the conditions of hydrate temperature 90°C, hydrate time 3 hours, and hydrate stirring speed 750 r / min. After hydrate, filtration, washing, and vacuum drying are performed to obtain the secondary hydrated product. S3. Prepare a 5% magnesium chloride solution by mass. Weigh an appropriate amount of secondary hydration product and mix it with 200 mL of the 5% magnesium chloride solution. The reaction is carried out at a temperature of 25°C, for a reaction time of 1 hour, and at a reaction stirring speed of 750 r / min. After the reaction is complete, filter, wash, and vacuum dry to obtain magnesium hydroxide containing a small amount of impurity compounds. S4. The obtained magnesium hydroxide containing a small amount of impurity compound was subjected to a carbonization reaction at a solid-liquid ratio of 5 g / L, at a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L·min. -1 The mixture is processed under these conditions, and after the reaction is complete, it is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate filtrate is subjected to a thermal decomposition reaction under the following conditions: thermal decomposition temperature of 95°C, thermal decomposition time of 50 minutes, and thermal decomposition stirring speed of 750 r / min. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained by thermal decomposition in S6 and S5 is calcined under a nitrogen atmosphere at a calcination temperature of 1100°C for a calcination time of 3 hours to obtain a silicon steel grade magnesium oxide product.

[0032] The hydration rate of the product is 4.16%, the mass rate is 99.26%, the citric acid activity value is 56s, and the residue generation rate is 3.68%.

[0033] Comparative Example 2 This comparative example provides a method for producing silicon steel grade magnesium oxide using dolomite, and is carried out by the following method. S1. Dolomite is crushed and ball-milled. The ball-milled dolomite powder is sieved through a 200-mesh sieve, and then calcined in a tubular furnace at 900°C for 3 hours to obtain light-calcined dolomite powder. The light-calcined dolomite powder is subjected to hydration treatment at a solid-liquid ratio of 1 g / L under the conditions of hydration temperature of 50°C, hydration time of 0.5 hours, and hydration stirring speed of 750 r / min. After hydration, filtration, washing, and vacuum drying are performed to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrate treatment at a solid-liquid ratio of 2 g / L under the conditions of hydrate temperature 90°C, hydrate time 3 hours, and hydrate stirring speed 750 r / min. After hydrate, filtration, washing, and vacuum drying are performed to obtain the secondary hydrated product. S3. Prepare a 5% magnesium chloride solution by mass. Weigh an appropriate amount of secondary hydration product and mix it with 200 mL of the 5% magnesium chloride solution. The reaction is carried out at a temperature of 25°C, for a reaction time of 1 hour, and at a reaction stirring speed of 750 r / min. After the reaction is complete, filter, wash, and vacuum dry to obtain magnesium hydroxide containing a small amount of impurity compounds. S4. The obtained magnesium hydroxide containing a small amount of impurity compound was subjected to a carbonization reaction at a solid-liquid ratio of 5 g / L, at a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L·min. -1 The mixture is processed under these conditions, and after the reaction is complete, it is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate filtrate is subjected to a thermal decomposition reaction under the conditions of a thermal decomposition temperature of 95°C, a thermal decomposition time of 50 minutes, and a thermal decomposition stirring speed of 750 r / min. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained by thermal decomposition in S6 and S5 is calcined under a nitrogen atmosphere at a calcination temperature of 1100°C for a calcination time of 3 hours to obtain a silicon steel grade magnesium oxide product.

[0034] The hydration rate of the product is 4.3%, the mass rate is 84.77%, the citric acid activity value is 95s, and the residue generation rate is 8.75%.

[0035] A comparison of the final products obtained in Example 2 and Comparative Example 2 revealed that Example 1 produced a product with higher purity and less residue compared to Comparative Example 1. This indicates that adding an appropriate amount of disodium ethylenediaminetetraacetate in the primary hydration step improves the purity of the resulting product and reduces the amount of residue produced.

[0036] Example 3 This example provides a method for producing silicon steel grade magnesium oxide using dolomite, and is carried out in the following manner. S1. Dolomite is crushed and ball-milled. The ball-milled dolomite powder is sieved through a 200-mesh sieve and then calcined in a tubular furnace at 900°C for 3 hours to obtain light-calcined dolomite powder. The light-calcined dolomite powder is subjected to hydration treatment at a solid-liquid ratio of 1 g / L, with 2.15 g of disodium ethylenediaminetetraacetate added simultaneously. The treatment is carried out at a hydration temperature of 50°C, a hydration time of 0.5 hours, and a hydration stirring speed of 750 r / min. After hydration, the product is filtered, washed, and vacuum-dried to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrate treatment at a solid-liquid ratio of 2 g / L under the conditions of hydrate temperature 90°C, hydrate time 3 hours, and hydrate stirring speed 750 r / min. After hydrate, filtration, washing, and vacuum drying are performed to obtain the secondary hydrated product. S3. Prepare a 5% magnesium chloride solution by mass. Weigh an appropriate amount of secondary hydration product and mix it with 200 mL of the 5% magnesium chloride solution. The reaction is carried out at a temperature of 25°C, for a reaction time of 1 hour, and at a reaction stirring speed of 750 r / min. After the reaction is complete, filter, wash, and vacuum dry to obtain magnesium hydroxide containing a small amount of impurity compounds. S4. The obtained magnesium hydroxide containing a small amount of impurity compound was subjected to a carbonization reaction at a solid-liquid ratio of 5 g / L, at a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L·min. -1 The mixture is processed under these conditions, and after the reaction is complete, it is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate filtrate is subjected to a thermal decomposition reaction under the conditions of a thermal decomposition temperature of 95°C, a thermal decomposition time of 50 minutes, and a thermal decomposition stirring speed of 750 r / min. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained by thermal decomposition in S6 and S5 is calcined under a nitrogen atmosphere at a calcination temperature of 1100°C for a calcination time of 3 hours to obtain a silicon steel grade magnesium oxide product.

[0037] The product is silicon-steel grade magnesium oxide with a water content of 4.16%, a mass content of 99.26%, and a citrate activity value of 56s, and the residue generation rate is 3.68%.

[0038] Comparative Example 3 This comparative example provides a method for producing silicon steel grade magnesium oxide using dolomite, and is carried out by the following method. S1. Dolomite is crushed and ball-milled. The ball-milled dolomite powder is sieved through a 200-mesh sieve and then calcined in a tubular furnace at 900°C for 3 hours to obtain light-calcined dolomite powder. The light-calcined dolomite powder is subjected to hydration treatment at a solid-liquid ratio of 1 g / L, with 2.15 g of disodium ethylenediaminetetraacetate added simultaneously. The treatment is carried out at a hydration temperature of 50°C, a hydration time of 0.5 hours, and a hydration stirring speed of 750 r / min. After hydration, the product is filtered, washed, and vacuum-dried to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrate treatment at a solid-liquid ratio of 2 g / L under the conditions of hydrate temperature 90°C, hydrate time 3 hours, and hydrate stirring speed 750 r / min. After hydrate, filtration, washing, and vacuum drying are performed to obtain the secondary hydrated product. S3. Prepare a 5% magnesium chloride solution by mass. Weigh an appropriate amount of secondary hydration product and mix it with 200 mL of the 5% magnesium chloride solution. The reaction is carried out at a temperature of 25°C, for a reaction time of 1 hour, and at a reaction stirring speed of 750 r / min. After the reaction is complete, filter, wash, and vacuum dry to obtain magnesium hydroxide containing a small amount of impurity compounds. S4. The obtained magnesium hydroxide containing a small amount of impurity compound was subjected to a carbonization reaction at a solid-liquid ratio of 5 g / L, at a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.5 L·min. -1The mixture is processed under these conditions, and after the reaction is complete, it is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate filtrate is subjected to a thermal decomposition reaction under the conditions of a thermal decomposition temperature of 95°C, a thermal decomposition time of 50 minutes, and a thermal decomposition stirring speed of 750 r / min. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained by thermal decomposition in S6 and S5 is calcined under a nitrogen atmosphere at a calcination temperature of 1100°C for a calcination time of 3 hours to obtain a silicon steel grade magnesium oxide product.

[0039] The product is silicon-steel grade magnesium oxide with a water content of 4.54%, a mass content of 98.76%, and a citrate activity value of 75s, and the residue generation rate is 2.97%.

[0040] A comparison of the final products obtained in Example 3 and Comparative Example 3 revealed that the purity of the product obtained in Example 3 was higher than that of Comparative Example 3. This indicates that a high yield of the product can only be ensured under appropriate carbon dioxide flow rate conditions during the carbonization process. The reason why the residue generation rate in Comparative Example 3 was lower than that of Example 3 is that if the carbon dioxide flow rate is too high during the carbonization process, there is an excess of carbon dioxide, and the calcium carbonate precipitate formed by the reaction of calcium hydroxide and carbon dioxide is converted into a calcium bicarbonate solution due to the excess carbon dioxide. As a result, the amount of calcium carbonate precipitate produced decreases, and the residue generation rate decreases.

[0041] Therefore, the silicon steel grade magnesium oxide production process using dolomite according to the present invention uses dolomite as a raw material and extracts silicon steel grade magnesium oxide under specific hydration and complexing conditions. The resulting silicon steel grade magnesium oxide has the advantages of high purity, low production cost, and low residue.

[0042] The above-described embodiments are for illustrative purposes only and do not limit the present invention. Although the invention has been described in detail with reference to embodiments, those skilled in the art can still modify or make equivalent substitutions of the technical means of the present invention, and it is clear that such modifications or substitutions will still fall within the technical scope of the present invention.

Claims

1. A process for manufacturing silicon steel grade magnesium oxide using dolomite, S1. After crushing and calcining the dolomite raw material to obtain light-calcined dolomite powder, the light-calcined dolomite powder is subjected to primary hydration treatment, and after hydration, it is filtered, washed and dried to obtain the primary hydration product. S2. The primary hydrated product is subjected to secondary hydrated hydrate according to the solid-liquid ratio, the hydrated temperature and hydrated time are controlled, and after hydrated hydrate, the product is filtered, washed and dried to obtain the secondary hydrated product. S3. The secondary hydration product is washed with a magnesium chloride solution, controlling the washing temperature and washing time. After washing, it is filtered, washed, and dried to obtain magnesium hydroxide containing a small amount of impurity compounds. In S4, the magnesium hydroxide containing the small amount of impurity compound obtained in S3 is subjected to a carbonization reaction according to the solid-liquid ratio, the carbonization temperature, carbonization time, and carbon dioxide flow rate are controlled, and after the reaction is complete, the solution is filtered to obtain a magnesium bicarbonate solution. S5. The magnesium bicarbonate solution is thermally decomposed, controlling the thermal decomposition temperature and time. After completion, it is filtered and dried to obtain magnesium carbonate. The magnesium carbonate produced in S6 and S5 is calcined, and the calcination temperature and calcination time are controlled to obtain silicon steel grade magnesium oxide. A manufacturing process for silicon steel grade magnesium oxide using dolomite, characterized by the following features.

2. A process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that, in S1, the solid-liquid ratio of the light-calcined dolomite powder is 0.5 to 1 g / L, 2 to 3 g of disodium ethylenediaminetetraacetate is added in the primary hydration step, the hydration temperature is 50 to 70°C, the hydration time is 20 to 40 minutes, and the hydration stirring speed is 500 to 800 r / min.

3. A process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that, in S2, the solid-liquid ratio is 1 to 2 g / L, the hydration temperature is 90 to 110°C, the hydration time is 1 to 3 hours, and the hydration stirring speed is 500 to 800 r / min.

4. A process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that, in S3, the mass concentration of the magnesium chloride solution is 3 to 6%, the amount used is 200 to 400 mL, the washing temperature is 20 to 30°C, the washing time is 0.5 to 1 hour, and the washing stirring speed is 500 to 800 r / min.

5. In S4 above, the solid-liquid ratio is 5 to 8 g / L, the carbonization temperature is 10 to 20°C, the carbonization time is 40 to 60 minutes, and the carbon dioxide flow rate is 0.08 to 0.2 L·min －１ A process for producing silicon steel grade magnesium oxide using dolomite as described in claim 1, characterized in that it is the process described in claim 1.

6. A process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that, in S5, the thermal decomposition temperature is 80 to 100°C, the thermal decomposition time is 0.5 to 1 hour, and the thermal decomposition stirring rate is 500 to 800 r / min.

7. A process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that, in S6, the firing temperature is 900 to 1100°C, the firing time is 2 to 4 hours, and the firing conditions are firing under a nitrogen atmosphere.

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