Manufacturing process of silicon steel grade magnesium oxide using dolomite

Abstract

To provide a method for producing silicon steel grade magnesium oxide, which has high purity, is low cost, and produces little residue. [Solution] Dolomite is used as a raw material and is crushed and calcined, and the resulting lightly calcined dolomite powder is sequentially subjected to primary hydration, secondary hydration, magnesium chloride washing, carbonization, and thermal decomposition, 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 production cost, and little residue.

Description

[Technical Field]

[0001] The present invention relates to the technical field of magnesium oxide production, and in particular to a process for producing silicon steel grade magnesium oxide using dolomite. [Background technology]

[0002] Silicon steel-grade magnesium oxide is a magnesium oxide coating material used in the production of oriented silicon steel sheet, and is a high-value-added magnesium oxide product. It is mainly used in the high-temperature annealing treatment stage of the oriented silicon steel sheet manufacturing process, where it acts as an isolating agent, dephosphorizing agent, and desulfurizing agent, and reacts with silicon oxide on the surface of the silicon steel to form magnesium silicate, an excellent insulating film layer. However, at present, China's demand for silicon steel-grade magnesium oxide is large, and the product supply does not meet market demand, so the country remains dependent on imports.

[0003] Currently, the raw materials used to produce silicon steel-grade magnesium oxide include magnesite, dolomite, bischofite, seawater or salt lake saponification, and magnesium-containing ores. Specific production methods include the saponification-ammonium carbonate method, magnesium ore coalification method, ammonia method, and saponification-water pyrolysis method. However, each method has its own drawbacks. For example, the saponification-ammonium carbonate method is relatively mature and produces stable and reliable product quality, but consumes a large amount of raw materials and has high production costs. The magnesium ore coalification method has drawbacks such as high energy consumption and production costs, and its low purity makes industrial production difficult. The ammonia method is prone to magnesium oxide colloid formation, making process control relatively difficult, leading to localized sintering, reduced activity, and reduced recovery rates. Furthermore, it poses significant environmental issues. The saponification-water pyrolysis method requires high equipment, is prone to environmental pollution, and has a low raw material recovery rate.

[0004] In view of the above problems in the production of silicon steel grade magnesium oxide, it has become extremely important to explore a method for producing silicon steel grade magnesium oxide with high purity, low cost, and little residue. Summary of the Invention

[0005] The object of the present invention is to provide a process for producing electrical steel grade magnesium oxide using dolomite to solve the problems in the background art.

[0006] To achieve the above object, the present invention provides a process for producing silicon steel grade magnesium oxide using dolomite, which includes the following steps: S1: Dolomite raw material is crushed and fired to obtain lightly burned dolomite powder, and then the lightly burned dolomite powder is subjected to primary hydration treatment, and after hydration, the primary hydration product is obtained by filtering, washing and drying. S2: The primary hydrated product is subjected to secondary hydration according to the solid-liquid ratio, and the hydration temperature and time are controlled. After hydration, the secondary hydrated product is obtained by filtering, washing and drying. S3, the secondary hydration product is washed with magnesium chloride solution, and the washing temperature and washing time are controlled. After washing, the product is filtered, washed and dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4, the magnesium hydroxide obtained in S3 containing a small amount of impurity compounds is subjected to a carbonization reaction according to a solid-liquid ratio, and the carbonization temperature, carbonization time, and carbon dioxide flow rate are controlled. After the reaction is completed, the magnesium bicarbonate solution is obtained by filtration. S5. Pyrolyze the magnesium bicarbonate solution, controlling the pyrolysis temperature and time, and after completion, filter and dry to obtain magnesium carbonate. S6, the magnesium carbonate produced in S5 is calcined, and the calcination temperature and time are controlled to obtain silicon steel grade magnesium oxide.

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

[0008] Preferably, in S1, the solid-liquid ratio of the lightly burned dolomite powder is set to 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 set to 50 to 70°C, the hydration time is set to 20 to 40 minutes, and the hydration stirring speed is set to 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 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.

[0011] Preferably, in S4, 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 flow rate of carbon dioxide is 0.08 to 0.2 L min -1 Let's say.

[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 speed 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 is performed under nitrogen gas flow conditions.

[0014] Preferably, in the washing steps S1 to S3, washing is performed 5 to 8 times with deionized water, and the drying steps S1 to S3 and S5 are performed by vacuum drying.

[0015] The principle of the process employed in the present invention is as follows. The products obtained by calcining dolomite are mainly magnesium oxide and calcium oxide. The reaction of magnesium oxide with water to produce magnesium hydroxide proceeds slowly, while the reaction of calcium oxide with water to produce calcium hydroxide proceeds rapidly. Therefore, in the process employed in the present invention, by controlling the hydration temperature and time appropriately 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 the form of a solution. After the primary hydration reaction is complete, the primary hydration product mainly consists of magnesium oxide, magnesium hydroxide, small amounts of calcium oxide, calcium hydroxide, and other impurity compounds. Magnesium oxide produces magnesium hydroxide under conditions of high reaction temperature and long reaction time, so in the secondary hydration step, the magnesium oxide and calcium oxide in the primary hydration product are converted into magnesium hydroxide and calcium hydroxide by controlling the appropriate hydration temperature and time. The secondary hydration product mainly consists of magnesium hydroxide, small amounts of calcium hydroxide, and other impurity compounds.

[0016] Magnesium chloride reacts with calcium hydroxide to produce calcium chloride and magnesium hydroxide. By washing a certain amount of the secondary hydration product with a magnesium chloride solution of a certain mass concentration, the small amount of calcium hydroxide in the secondary hydration product can be separated and removed from the secondary hydration product in the form of calcium chloride solution. After washing, the main components are magnesium hydroxide and a small amount of impurity compounds. This is mixed with a certain amount of ultrapure water according to a solid-liquid ratio and carbonized under appropriate carbonization conditions to produce a magnesium bicarbonate solution and a small amount of other impurity precipitate. After the carbonization reaction is complete, the precipitate is filtered and removed. The resulting carbonized liquid is then pyrolyzed to produce a magnesium carbonate precipitate. After the pyrolysis reaction is complete, the pyrolyzed liquid is filtered, dried, and calcined to obtain silicon steel-grade magnesium oxide with a mass fraction of 99.26%, a hydration rate of 4.16, and a citric acid activity of 56s.

[0017] Therefore, the process for producing silicon steel grade magnesium oxide using dolomite according to the present 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 production cost, and little residue.

[0018] The technical means of the present invention will be described in more detail below with reference to the drawings and examples. [Brief explanation of the drawings]

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

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

[0021] In order to clarify the objectives, technical means and advantages of the embodiments of the present invention, the technical means in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention, however, the described embodiments are only some of the embodiments of the present invention and do not include all the embodiments.

[0022] The present invention provides a process for producing silicon steel-grade magnesium oxide using dolomite. As shown in Figure 1, this process includes the following steps: dolomite is used as raw material. First, the dolomite is 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 at a calcination temperature of 900-1200°C for 2-5 hours to obtain lightly calcined dolomite powder. The calcination reaction in this process is as follows: CaCO3 MgCO3(s)→MgO(s)+CaO(s)+2CO2↑(high temperature) The resulting lightly burned dolomite powder is then subjected to primary hydration at a solid-liquid ratio of 0.5-1 g / L, while simultaneously adding 2-3 g of disodium ethylenediaminetetraacetate. The hydration temperature is 50-70°C, the hydration time is 20-40 minutes, and the stirring speed is 500-800 r / min. The primary hydration reaction 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 product is filtered to obtain magnesium oxide, magnesium hydroxide, and small amounts of calcium hydroxide and other impurity compounds. The primary hydration product is then dried in a vacuum dryer, after which the dried product is subjected to secondary hydration at a solid-liquid ratio of 1-2 g / L, with a hydration temperature of 90-110°C, a hydration time of 1-3 hours, and a hydration stirring speed of 500-800 r / min. The reaction formula for secondary hydration is as follows: 2MgO(s)+2H2O(aq)→2Mg(OH)2(s)↓, 2CaO(s)+2H2O(aq)→2Ca(OH)2(s)↓.

[0023] After the secondary hydration is completed, 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%. Wash an appropriate amount of the secondary hydration product in 200-400 mL of magnesium chloride solution at a washing temperature of 20-30°C, for 0.5-1 hour, and at a stirring speed of 500-800 r / min. The reaction formula for this process is as follows: Ca(OH)2(s)+MgCl2(aq)→CaCl2(aq)+Mg(OH)2(s)↓; The main components of the secondary hydrated product after washing are magnesium hydroxide and a small amount of impurity compounds. The secondary hydrated product after washing is carbonized 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 carbonization reaction 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 thermal decomposition temperature is 80-100°C, the thermal decomposition time is 0.5-1 hour, and the thermal decomposition stirring speed is 500-800 r / min. The thermal decomposition reaction formula is as follows: Mg(HCO3)2(aq)→MgCO3(s)↓+CO2↑+H2O(aq) The magnesium carbonate precipitate obtained by the thermal decomposition reaction is calcined under a nitrogen atmosphere at a temperature of 900-1100°C for 2-4 hours to obtain silicon steel grade magnesium oxide. The calcination reaction is as follows: MgCO3(s)↓→MgO(s)+CO2↑(high temperature)

[0024] The following specific examples illustrate this process.

[0025] Example 1 Example 1 provides a method for producing silicon steel grade magnesium oxide using dolomite, which 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 lightly calcined dolomite powder. The lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L while simultaneously adding 2.15 g of disodium ethylenediaminetetraacetate. The hydration temperature is 50°C, the hydration time is 0.5 hours, and the agitation speed is 750 r / min. After hydration, the primary hydrated product is filtered, washed, and vacuum-dried. S2: The primary hydrated product is subjected to secondary hydration treatment at a solid-liquid ratio of 2 g / L under the conditions of a hydration temperature of 90°C, a hydration time of 3 hours, and a hydration stirring speed of 750 r / min. After hydration, the secondary hydrated product is obtained by filtration, washing, and vacuum drying. S3: Prepare a 5% magnesium chloride solution. Weigh out an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution. The reaction temperature is 25°C, the reaction time is 1 hour, and the stirring speed is 750 r / min. After the reaction is complete, the product is filtered, washed, and vacuum dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4: The obtained magnesium hydroxide containing a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, with a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L min -1 After the reaction is completed, the solution is filtered to obtain a magnesium hydrogen carbonate 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, the mixture is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained in S6 and S5 is calcined under a nitrogen stream at a calcination temperature of 1100°C for 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 is 56s, and the residue generation rate is 3.68%.

[0027] The results of testing the product of 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, which is carried out in the following manner. S1: Dolomite is calcined at a high temperature of 1000°C in a tubular furnace to obtain a mixture of magnesium oxide and calcium oxide. S2. The mixture of magnesium oxide and calcium oxide is mixed with water to obtain a mixture of magnesium hydroxide and calcium hydroxide. S3: Carbon dioxide is reacted with a mixture of magnesium hydroxide and calcium hydroxide to produce calcium carbonate and magnesium bicarbonate. S4: After the carbonization reaction is completed, the solution is filtered to obtain an aqueous magnesium bicarbonate solution, which is then heated (heating temperature 800°C) to obtain a magnesium carbonate product. S5: After the thermal decomposition, the magnesium carbonate is filtered to obtain solid magnesium carbonate, which is then calcined at a calcination temperature of 850°C to obtain magnesium oxide. S6: The magnesium oxide obtained by calcination is reacted with water at 65°C (mass concentration ratio of magnesium oxide to water is 1:8.5). Modification, purification, and impurity removal are carried out in water, and the solution after the reaction is filtered to obtain a magnesium hydroxide solid filter cake. The magnesium hydroxide filter cakes obtained in S7 and S6 are calcined at 950°C for 2 hours and 1000°C for 2 hours, respectively, to obtain magnesium oxides with different citric acid activities. The magnesium oxides with different properties obtained in S8 and S7 are crushed, and 70% of the product with 60S activity and 30% of the product with 200S activity 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 is 65s, and the residue generation rate is 50.4%.

[0030] The product and residue amounts of Example 1 and Comparative Example 1 were examined and compared. As a result, it was confirmed that the product obtained in Example 1 was similar in purity and hydration rate to the product obtained in Comparative Example 1, and that the amount of residue produced was small and the activity was high.

[0031] Example 2 This example provides a method for producing silicon steel grade magnesium oxide using dolomite, which 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 lightly calcined dolomite powder. The lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L while simultaneously adding 2.15 g of disodium ethylenediaminetetraacetate. The hydration temperature is 50°C, the hydration time is 0.5 hours, and the agitation speed is 750 r / min. After hydration, the primary hydrated product is filtered, washed, and vacuum-dried. S2: The primary hydrated product is subjected to secondary hydration treatment at a solid-liquid ratio of 2 g / L under the conditions of a hydration temperature of 90°C, a hydration time of 3 hours, and a hydration stirring speed of 750 r / min. After hydration, the secondary hydrated product is obtained by filtration, washing, and vacuum drying. S3: Prepare a 5% magnesium chloride solution. Weigh out an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution. The reaction temperature is 25°C, the reaction time is 1 hour, and the stirring speed is 750 r / min. After the reaction is complete, the product is filtered, washed, and vacuum dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4: The obtained magnesium hydroxide containing a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, with a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L min -1 After the reaction is completed, the solution is filtered to obtain a magnesium hydrogen carbonate 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, the mixture is filtered and dried to obtain magnesium carbonate. The magnesium carbonate obtained by thermal decomposition in S6 and S5 is calcined under a nitrogen stream at a calcination temperature of 1100°C for 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 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, which 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 lightly calcined dolomite powder. The lightly calcined dolomite powder is then hydrated at a solid-liquid ratio of 1 g / L under the following conditions: hydration temperature: 50°C, hydration time: 0.5 hours, and hydration stirring speed: 750 r / min. After hydration, the product is filtered, washed, and vacuum dried to obtain the primary hydrated product. S2: The primary hydrated product is subjected to secondary hydration treatment at a solid-liquid ratio of 2 g / L under the conditions of a hydration temperature of 90°C, a hydration time of 3 hours, and a hydration stirring speed of 750 r / min. After hydration, the secondary hydrated product is obtained by filtration, washing, and vacuum drying. S3: Prepare a 5% magnesium chloride solution. Weigh out an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution. The reaction temperature is 25°C, the reaction time is 1 hour, and the stirring speed is 750 r / min. After the reaction is complete, the product is filtered, washed, and vacuum dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4: The obtained magnesium hydroxide containing a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, with a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L min -1 After the reaction is completed, the solution is filtered to obtain a magnesium hydrogen carbonate solution. S5: The magnesium bicarbonate filtrate is subjected to thermal decomposition reaction under the conditions of thermal decomposition temperature 95°C, thermal decomposition time 50 minutes, and thermal decomposition stirring speed 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 stream at a calcination temperature of 1100°C for 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 is 95s, and the residue generation rate is 8.75%.

[0035] Comparing the final products obtained in Example 2 and Comparative Example 2, it was confirmed that the purity of the product obtained in Example 1 was higher and the amount of residue generated was smaller than that in Comparative Example 1. This indicates that adding an appropriate amount of disodium ethylenediaminetetraacetate in the primary hydration step improves the purity of the obtained product and reduces the amount of residue generated.

[0036] Example 3 This example provides a method for producing silicon steel grade magnesium oxide using dolomite, which 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 lightly calcined dolomite powder. The lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L while simultaneously adding 2.15 g of disodium ethylenediaminetetraacetate. The hydration temperature is 50°C, the hydration time is 0.5 hours, and the agitation speed is 750 r / min. After hydration, the primary hydrated product is filtered, washed, and vacuum-dried. S2: The primary hydrated product is subjected to secondary hydration treatment at a solid-liquid ratio of 2 g / L under the conditions of a hydration temperature of 90°C, a hydration time of 3 hours, and a hydration stirring speed of 750 r / min. After hydration, the secondary hydrated product is obtained by filtration, washing, and vacuum drying. S3: Prepare a 5% magnesium chloride solution. Weigh out an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution. The reaction temperature is 25°C, the reaction time is 1 hour, and the stirring speed is 750 r / min. After the reaction is complete, the product is filtered, washed, and vacuum dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4: The obtained magnesium hydroxide containing a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, with a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.1 L min -1 After the reaction is completed, the solution is filtered to obtain a magnesium hydrogen carbonate solution. S5: The magnesium bicarbonate filtrate is subjected to thermal decomposition reaction under the conditions of thermal decomposition temperature 95°C, thermal decomposition time 50 minutes, and thermal decomposition stirring speed 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 stream at a calcination temperature of 1100°C for 3 hours to obtain a silicon steel grade magnesium oxide product.

[0037] The product was silicon steel grade magnesium oxide with a hydration rate of 4.16%, a mass fraction of 99.26%, and a citric acid activity value of 56s, and the residue generation rate was 3.68%.

[0038] Comparative Example 3 This comparative example provides a method for producing silicon steel grade magnesium oxide using dolomite, which 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 lightly calcined dolomite powder. The lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L while simultaneously adding 2.15 g of disodium ethylenediaminetetraacetate. The hydration temperature is 50°C, the hydration time is 0.5 hours, and the agitation speed is 750 r / min. After hydration, the primary hydrated product is filtered, washed, and vacuum-dried. S2: The primary hydrated product is subjected to secondary hydration treatment at a solid-liquid ratio of 2 g / L under the conditions of a hydration temperature of 90°C, a hydration time of 3 hours, and a hydration stirring speed of 750 r / min. After hydration, the secondary hydrated product is obtained by filtration, washing, and vacuum drying. S3: Prepare a 5% magnesium chloride solution. Weigh out an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution. The reaction temperature is 25°C, the reaction time is 1 hour, and the stirring speed is 750 r / min. After the reaction is complete, the product is filtered, washed, and vacuum dried to obtain magnesium hydroxide containing a small amount of impurity compounds. S4: The obtained magnesium hydroxide containing a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, with a carbonization temperature of 21°C, a carbonization time of 1 hour, and a carbon dioxide flow rate of 0.5 L min -1After the reaction is completed, the solution is filtered to obtain a magnesium hydrogen carbonate solution. S5: The magnesium bicarbonate filtrate is subjected to thermal decomposition reaction under the conditions of thermal decomposition temperature 95°C, thermal decomposition time 50 minutes, and thermal decomposition stirring speed 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 stream at a calcination temperature of 1100°C for 3 hours to obtain a silicon steel grade magnesium oxide product.

[0039] The product was silicon steel grade magnesium oxide with a hydration rate of 4.54%, a mass fraction of 98.76%, and a citric acid activity value of 75s, and the residue generation rate was 2.97%.

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

[0041] Therefore, the process for producing silicon steel grade magnesium oxide using dolomite of the present invention uses dolomite as a raw material and extracts silicon steel grade magnesium oxide under specific hydration and complexation conditions, and the obtained silicon steel grade magnesium oxide has the advantages of high purity, low production costs, and little residue.

[0042] It should be noted that the above-mentioned embodiments are for explaining the technical means of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still make modifications or equivalent substitutions to the technical means of the present invention, and it is clear that even after such modifications or substitutions, the modified technical means still fall within the technical scope of the present invention.

Claims

1. 1. A process for producing silicon steel grade magnesium oxide using dolomite, comprising: S1: crushing and calcining dolomite raw material to obtain lightly calcined dolomite powder, and then subjecting the lightly calcined dolomite powder to primary hydration treatment, filtering, washing and drying the resulting primary hydration product; S2, subjecting the primary hydration product to secondary hydration according to a solid-liquid ratio, controlling the hydration temperature and time, and filtering, washing and drying the resulting secondary hydration product; S3. Washing the secondary hydration product with magnesium chloride solution, controlling the washing temperature and washing time, filtering, washing and drying after washing to obtain magnesium hydroxide containing a small amount of impurity compounds; S4: The magnesium hydroxide containing a small amount of impurity compounds obtained in S3 is subjected to a carbonization reaction according to a solid-liquid ratio, and the carbonization temperature, carbonization time, and carbon dioxide flow rate are controlled. After the reaction is completed, the magnesium bicarbonate solution is obtained by filtering. S5. Pyrolyzing the magnesium bicarbonate solution, controlling the pyrolysis temperature and time, and then filtering and drying to obtain magnesium carbonate; S6: Calcining the magnesium carbonate produced in S5, and controlling the calcination temperature and calcination time to obtain silicon steel grade magnesium oxide; In the step S1, the solid-liquid ratio of the lightly burned dolomite powder is set to 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 set to 50 to 70°C, the hydration time is set to 20 to 40 minutes, and the hydration stirring speed is set to 500 to 800 r / min, In the step S4, the flow rate of the carbon dioxide is set to 0.08 to 0.2 L min-1.

2. 2. The process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, wherein 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.

3. 2. The process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, wherein 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.

4. The process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, characterized in that in S4, the solid-liquid ratio is 5 to 8 g / L, the carbonization temperature is 10 to 20°C, and the carbonization time is 40 to 60 minutes.

5. 2. The process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, wherein 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 speed is 500 to 800 r / min.

6. 2. The process for producing silicon steel grade magnesium oxide using dolomite according to claim 1, wherein in S6, the firing temperature is 900 to 1100°C, the firing time is 2 to 4 hours, and the firing is performed under nitrogen gas flow conditions.

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