Process method for preparing silicon steel grade magnesium oxide from dolomite

Abstract

The invention discloses a process method for preparing silicon-steel-grade magnesium oxide from dolomite, which belongs to the technical field of magnesium oxide preparation and comprises the following steps of: crushing and calcining the dolomite serving as a raw material, and sequentially performing primary hydration, secondary hydration, magnesium chloride cleaning, carbonization and pyrolytic reaction on the obtained lightly-calcined dolomite powder to obtain the silicon-steel-grade magnesium oxide. And calcining the obtained magnesium carbonate to obtain the silicon steel grade magnesium oxide. According to the method, dolomite is taken as a raw material, and silicon steel grade magnesium oxide with relatively high purity is extracted under specific hydration conditions and carbonization conditions; the silicon steel grade magnesium oxide prepared by the process has the advantages of high purity, low cost and few residues.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium oxide preparation, and in particular to a process for preparing silicon steel grade magnesium oxide from dolomite. Background Art

[0002] Silicon steel grade magnesium oxide is a magnesium oxide coating material used to manufacture oriented silicon steel sheets. It is a high value-added magnesium oxide product, mainly used in the high temperature annealing stage of the oriented silicon steel sheet manufacturing process, and plays the role of an isolating agent, dephosphorization and desulfurization agent. At the same time, it reacts with silicon oxide on the surface of silicon steel to form an excellent insulating film layer of magnesium silicate. However, at this stage, the demand for silicon steel grade magnesium oxide in my country is relatively large, and the product quantity cannot meet the market demand, and it still relies on imports.

[0003] At present, the raw materials for preparing silicon steel grade magnesium oxide mainly include magnesite, dolomite, bischofite, seawater or salt lake brine, magnesium-containing ore, etc. The specific preparation methods mainly include brine-ammonium carbonate method, magnesium ore carbonization method, ammonia method, brine pyrolysis method, etc. However, each method has its own shortcomings, such as brine-ammonium carbonate method: although the technology of this method is relatively mature and the product quality is stable and reliable, the raw material consumption is large and the production cost is high; magnesium ore carbonization method: there are disadvantages such as high energy consumption and high production cost, and the purity is low and cannot be industrialized; ammonia method: magnesium oxide is easy to form colloids and the process is difficult to control, resulting in local sintering, low activity and low recovery rate, and more prominent environmental protection problems; brine pyrolysis method: high equipment requirements, easy to cause greater pollution to the environment, and low raw material recovery rate.

[0004] Based on the above problems in the preparation of silicon steel grade magnesium oxide, it is of vital importance to find a method for preparing silicon steel grade magnesium oxide with high purity, low cost and less residue. Summary of the invention

[0005] The purpose of the present invention is to provide a process for preparing silicon steel grade magnesium oxide from dolomite to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides a process for preparing silicon steel grade magnesium oxide from dolomite, comprising the following steps: S1, crushing and calcining the dolomite raw material to obtain light-burned dolomite powder, and then performing a primary hydration treatment on the light-burned dolomite powder, and filtering, washing and drying after hydration to obtain a primary hydration product; S2, performing secondary hydration on the primary hydration product according to the solid-liquid ratio, controlling the hydration temperature and hydration time, filtering, washing and drying after hydration to obtain a secondary hydration product; S3, placing the secondary hydration product in a magnesium chloride solution for washing, controlling the washing temperature and washing time, filtering, washing, and drying after the washing is completed to obtain magnesium hydroxide with a small amount of impurity compounds; S4, subjecting the magnesium hydroxide with a small amount of impurity compounds obtained in S3 to a carbonization reaction according to the solid-liquid ratio, controlling the carbonization temperature, carbonization time and the flow rate of carbon dioxide, and filtering after the reaction is completed to obtain a magnesium bicarbonate solution; S5, pyrolyzing the magnesium bicarbonate solution, controlling the pyrolysis temperature and pyrolysis time, and filtering and drying to obtain magnesium carbonate after completion; S6. calcining the magnesium carbonate obtained in S5, controlling the calcination temperature and calcination time, to obtain silicon steel grade magnesium oxide.

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

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

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

[0010] Preferably, in S3, the mass concentration of the magnesium chloride solution is 3%~6%; the dosage is 200~400 mL, the cleaning temperature is 20~30°C, the cleaning time is 0.5~1 h, and the cleaning 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 min, and the carbon dioxide flow rate is 0.08-0.2 L·min -1 .

[0012] Preferably, in S5, the pyrolysis temperature is 80-100° C., the pyrolysis time is 0.5-1 h, and the pyrolysis stirring speed is 500-800 r / min.

[0013] Preferably, in S6, the calcination temperature is 900-1100° C., the calcination time is 2-4 h, and the calcination condition is calcination under nitrogen.

[0014] Preferably, in S1 to S3, the washing process is washing with deionized water for 5 to 8 times; and the drying process in S1 to S3 and S5 is vacuum drying.

[0015] The principle of the process method adopted by the present invention is that the products after calcining dolomite are mainly magnesium oxide and calcium oxide, wherein the process of magnesium oxide reacting with water to generate magnesium hydroxide is difficult, and the process of calcium oxide reacting with water to generate calcium hydroxide is violent, so the process method adopted by the present invention can separate most of the calcium oxide in the light-burned dolomite powder in the form of solution from the light-burned dolomite powder in a hydration process by controlling the appropriate hydration temperature and hydration time and adding a certain amount of disodium ethylenediaminetetraacetate; After the primary hydration reaction is completed, the main components of the primary hydration product are magnesium oxide, magnesium hydroxide, a small amount of calcium oxide, calcium hydroxide and other impurity compounds. Since magnesium oxide will generate magnesium hydroxide under a higher reaction temperature and a longer reaction time, in the secondary hydration process, 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 hydration time; the main components of the secondary hydration product are magnesium hydroxide, a small amount of calcium hydroxide and impurity compounds.

[0016] Since magnesium chloride reacts with calcium hydroxide to generate calcium chloride and magnesium hydroxide, a certain amount of secondary hydration products is washed with a magnesium chloride solution of a certain mass concentration, so that a small amount of calcium hydroxide in the secondary hydration products can be separated from the secondary hydration products in the form of a calcium chloride solution; the main components after washing are magnesium hydroxide and a small amount of impurity compounds, which are then mixed with a certain amount of ultrapure water according to the solid-liquid ratio for carbonization reaction, and a magnesium bicarbonate solution and other small amounts of impurity precipitates are generated under suitable carbonization conditions. After the carbonization reaction is completed, the precipitate is filtered to remove the precipitate, and the carbonized liquid is left for pyrolysis reaction to generate magnesium carbonate precipitate. The pyrolysis liquid after the pyrolysis reaction is filtered, dried, and calcined, thereby generating 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 56 s.

[0017] Therefore, the present invention provides a process for preparing silicon steel-grade magnesium oxide from dolomite, which uses dolomite as a raw material and extracts silicon steel-grade magnesium oxide with high purity under specific hydration conditions and carbonization conditions; the silicon steel-grade magnesium oxide prepared by this process has the advantages of high purity, low cost and less residue.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of an embodiment of the present invention; Figure 2 is the XRD pattern of magnesium oxide of Example 1 of the present invention; Figure 3This is a scanning electron microscope image of magnesium oxide in Example 1 of the present invention, wherein (a) is 1 μm, and (b) is 500 nm; Figure 4 This is a particle size distribution diagram of magnesium oxide (not ball-milled) in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0022] The present invention provides a process for preparing silicon steel grade magnesium oxide from dolomite, such as Figure 1 As shown, the method comprises the following steps: using dolomite as a raw material, firstly crushing and ball-milling the dolomite, and sieving the ball-milled dolomite powder through a 100-200 mesh sieve; calcining the sieved dolomite powder in a tubular furnace, the calcination temperature is 900-1200 ° C, the calcination time is 2-5 h, and light-burned dolomite powder is obtained; the calcination reaction equation in the process is: CaCO3·MgCO3(s)→MgO(s)+CaO(s)+2CO2↑(high temperature); Then the obtained light-burned dolomite powder is hydrated once at a solid-liquid ratio of 0.5-1 g / L, and 2-3 g of disodium ethylenediaminetetraacetate is added at the same time. The hydration temperature is controlled at 50-70 °C, the hydration time is 20-40 min, and the hydration stirring speed is 500-800 r / min. The reaction equation for the first hydration is: 2MgO(s)+2CaO(s)+2H2O(aq)→MgO(s)+Mg(OH)2(s)↓+Ca(OH)2(s)↓, Ca(OH)2(s)+MgO(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, a small amount of calcium hydroxide and impurity compounds of other elements; the primary hydration product is placed in a vacuum drying oven for drying, and the dried primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 1-2 g / L, the hydration temperature is controlled to be 90-110°C, the hydration time is 1-3 h, and the hydration stirring speed is 500-800 r / min. The reaction equation of the secondary hydration is: 2MgO(s)+2H2O(aq)→2Mg(OH)2(s)↓, 2CaO(s)+2H2O(aq)→2Ca(OH)2(s)↓.

[0023] After the secondary hydration is completed, magnesium hydroxide, a small amount of calcium hydroxide and impurity compounds are obtained by filtering, washing and vacuum drying; Prepare a magnesium chloride solution with a mass concentration of 3%~6%, put an appropriate amount of secondary hydration product into 200~400 mL of magnesium chloride solution for cleaning, control the cleaning temperature to 20~30℃, the cleaning time to 0.5~1 h, and the cleaning stirring speed to 500~800 r / min; the reaction equation involved in this process is: 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 a small amount of impurity compounds; the secondary hydration product after washing is subjected to carbonization reaction at a solid-liquid ratio of 5-8 g / L to obtain a magnesium bicarbonate solution, and the carbonization temperature is controlled to be 10-20°C, the carbonization time is 40-60 min, and the carbon dioxide flow rate is 0.08-0.2 L·min -1 ; The reaction equation for carbonization is: Mg(OH)2(s)↓+2CO2↑→Mg(HCO3)2(aq); The magnesium bicarbonate solution filtered after the carbonization reaction is subjected to pyrolysis to obtain magnesium carbonate precipitation, and the pyrolysis temperature is controlled to be 80-100°C, the pyrolysis time is 0.5-1 h, and the pyrolysis stirring speed is 500-800 r / min; the pyrolysis reaction equation is: Mg(HCO3)2(aq) →MgCO3(s)↓+CO2↑+H2O(aq); The magnesium carbonate precipitate obtained by the pyrolysis reaction is calcined under nitrogen, the calcination temperature is controlled to be 900-1100°C, and the calcination time is 2-4 h to obtain silicon steel grade magnesium oxide. The calcination reaction equation is: MgCO3(s)↓→MgO(s)+ CO2↑ (high temperature).

[0024] The present process is described by means of the following specific examples.

[0025] Example 1 This embodiment 1 provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1. The dolomite is crushed and ball-milled, and then the ball-milled dolomite powder is sieved through a 200-mesh sieve, and then placed in a tube furnace at 900°C and calcined for 3 h to obtain light-burned dolomite powder; the light-burned dolomite powder is hydrated at a solid-liquid ratio of 1g / L, and 2.15 g of disodium ethylenediaminetetraacetate is added at the same time, the hydration temperature is controlled to be 50°C, the hydration time is 0.5h, and the stirring speed of the hydration is 750 r / min; after hydration, it is filtered, washed, and vacuum dried to obtain a primary hydration product; S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90°C, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtering, washing, and vacuum drying are performed to obtain a secondary hydration product; S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of the secondary hydration product and mix it with 200 mL of a 5% magnesium chloride solution for reaction, control the reaction temperature to 25°C, the reaction time to 1 h, and the stirring speed of the reaction to 750 r / min; after the reaction is completed, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds; S4, the obtained magnesium hydroxide with a small amount of impurity compounds was carbonized at a solid-liquid ratio of 5 g / L, and the carbonization temperature was controlled to be 21°C, the carbonization time was 1 h, and the carbon dioxide flow rate was 0.1 L·min -1 After the reaction is completed, the magnesium bicarbonate solution is filtered to obtain; S5, subjecting the magnesium bicarbonate filtrate to a pyrolysis reaction, controlling the pyrolysis temperature to 95°C, the pyrolysis time to 50 min, and the pyrolysis stirring speed to 750 r / min, and filtering and drying after completion to obtain magnesium carbonate; S6. The magnesium carbonate obtained in S5 is calcined with nitrogen, the calcination temperature is controlled to be 1100° C., and the calcination time is 3 h to obtain a silicon steel grade magnesium oxide product.

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

[0027] The product of Example 1 was tested and the test results were as follows Figure 2-4 shown.

[0028] Comparative Example 1 This comparative example provides a traditional method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1, placing dolomite in a tube furnace at 1000°C for high temperature calcination to obtain a mixture of magnesium oxide and calcium oxide; S2, digesting and hydrating the mixture of magnesium oxide and calcium oxide with water to obtain a mixture of magnesium hydroxide and calcium hydroxide; S3, carbonizing the mixture of carbon dioxide, magnesium hydroxide and calcium hydroxide to produce calcium carbonate and magnesium bicarbonate; S4, after the carbonization reaction is completed, filtering is performed to obtain a magnesium bicarbonate aqueous solution, and then the magnesium bicarbonate aqueous solution is heated at a heating temperature of 800° C. to obtain a magnesium carbonate product; S5, filtering the pyrolyzed magnesium carbonate to obtain magnesium carbonate solid, and then calcining the magnesium carbonate at a calcination temperature of 850° C. to obtain magnesium oxide; S6, reacting the magnesium oxide obtained after calcination with water at 65° C., with the mass concentration ratio of magnesium oxide to water being 1:8.5, modifying, purifying and removing impurities in water, filtering the solution after the reaction to obtain a magnesium hydroxide solid filter cake; S7, calcining the magnesium hydroxide filter cake obtained in S6 at 950° C. for 2 hours and at 1000° C. for 2 hours, respectively, to obtain magnesium oxide with different citric acid activities; S8. The magnesium oxide with different characteristics obtained in S7 is crushed, and 70% of the product with activity 60 S and 30% of the product with activity 200 S are mixed to obtain silicon steel grade magnesium oxide product.

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

[0030] By comparing the products and residue amounts of Example 1 and Comparative Example 1, the product obtained in Example 1 has similar purity and hydration rate to the product obtained in Comparative Example 1, and has less residue generated and higher activity.

[0031] Example 2 This embodiment provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1. The dolomite is crushed and ball-milled, and then the ball-milled dolomite powder is sieved through a 200-mesh sieve, and then placed in a tube furnace at 900°C and calcined for 3 h to obtain light-burned dolomite powder; the light-burned dolomite powder is hydrated at a solid-liquid ratio of 1g / L, and 2.15 g of disodium ethylenediaminetetraacetate is added at the same time, the hydration temperature is controlled to be 50°C, the hydration time is 0.5h, and the stirring speed of the hydration is 750 r / min; after hydration, it is filtered, washed, and vacuum dried to obtain a primary hydration product; S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90°C, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtering, washing, and vacuum drying are performed to obtain a secondary hydration product; S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of the secondary hydration product and mix it with 200 mL of a 5% magnesium chloride solution for reaction, control the reaction temperature to 25°C, the reaction time to 1 h, and the stirring speed of the reaction to 750 r / min; after the reaction is completed, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds; S4. Then, the obtained magnesium hydroxide with a small amount of impurity compounds is carbonized at a solid-liquid ratio of 5 g / L, and the carbonization temperature is controlled to be 21°C, the carbonization time is 1 h, and the carbon dioxide flow rate is 0.1 L·min -1 After the reaction is completed, the magnesium bicarbonate solution is filtered to obtain; S5, subjecting the filtrate of the magnesium bicarbonate solution to a pyrolysis reaction, controlling the pyrolysis temperature to 95°C, the pyrolysis time to 50min, and the pyrolysis stirring speed to 750 r / min, and filtering and drying after completion to obtain magnesium carbonate; S6. The magnesium carbonate obtained by pyrolysis of S5 is calcined with nitrogen, the calcination temperature is controlled to be 1100° C., and the calcination time is 3 h to obtain a silicon steel grade magnesium oxide product.

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

[0033] Comparative Example 2 This comparative example provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1. The dolomite is crushed and ball-milled, and then the ball-milled dolomite powder is sieved through a 200-mesh sieve, and then placed in a tube furnace at 900°C for calcination for 3 h to obtain light-burned dolomite powder; the light-burned dolomite powder is hydrated at a solid-liquid ratio of 1g / L, the hydration temperature is controlled to be 50°C, the hydration time is 0.5 h, and the hydration stirring speed is 750 r / min; after hydration, it is filtered, washed, and vacuum dried to obtain a primary hydration product; S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90°C, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtering, washing, and vacuum drying are performed to obtain a secondary hydration product; S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of the secondary hydration product and mix it with 200 mL of a 5% magnesium chloride solution for reaction, control the reaction temperature to 25°C, the reaction time to 1 h, and the stirring speed of the reaction to 750 r / min; after the reaction is completed, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds; S4. Then, the obtained magnesium hydroxide with a small amount of impurity compounds is carbonized at a solid-liquid ratio of 5 g / L, and the carbonization temperature is controlled to be 21°C, the carbonization time is 1 h, and the carbon dioxide flow rate is 0.1 L·min -1 After the reaction is completed, the magnesium bicarbonate solution is filtered to obtain; S5, subjecting the filtrate of the magnesium bicarbonate solution to a pyrolysis reaction, controlling the pyrolysis temperature to 95°C, the pyrolysis time to 50min, and the pyrolysis stirring speed to 750 r / min, and filtering and drying after completion to obtain magnesium carbonate; S6. The magnesium carbonate obtained by pyrolysis of S5 is calcined with nitrogen, the calcination temperature is controlled to be 1100° C., and the calcination time is 3 h to obtain a silicon steel grade magnesium oxide product.

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

[0035] Comparing the final products obtained in Example 2 and Comparative Example 2, the product obtained in Example 1 has higher purity and less residue generated than that in Comparative Example 1, indicating that adding an appropriate amount of disodium ethylenediaminetetraacetate during the primary hydration process can ensure that the obtained product has higher purity and less residue is generated.

[0036] Example 3 This embodiment provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1. The dolomite is crushed and ball-milled, and then the ball-milled dolomite powder is sieved through a 200-mesh sieve, and then placed in a tube furnace at 900°C and calcined for 3 h to obtain light-burned dolomite powder; the light-burned dolomite powder is hydrated at a solid-liquid ratio of 1g / L, and 2.15 g of disodium ethylenediaminetetraacetate is added at the same time, the hydration temperature is controlled to be 50°C, the hydration time is 0.5h, and the stirring speed of the hydration is 750 r / min; after hydration, it is filtered, washed, and vacuum dried to obtain a primary hydration product; S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90°C, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtering, washing, and vacuum drying are performed to obtain a secondary hydration product; S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of the secondary hydration product and mix it with 200 mL of a 5% magnesium chloride solution for reaction, control the reaction temperature to 25°C, the reaction time to 1 h, and the stirring speed of the reaction to 750 r / min; after the reaction is completed, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds; S4. Then, the obtained magnesium hydroxide with a small amount of impurity compounds is carbonized at a solid-liquid ratio of 5 g / L, and the carbonization temperature is controlled to be 21°C, the carbonization time is 1 h, and the carbon dioxide flow rate is 0.1 L·min -1 After the reaction is completed, the magnesium bicarbonate solution is filtered to obtain; S5, subjecting the filtrate of the magnesium bicarbonate solution to a pyrolysis reaction, controlling the pyrolysis temperature to 95°C, the pyrolysis time to 50min, and the pyrolysis stirring speed to 750 r / min, and filtering and drying after completion to obtain magnesium carbonate; S6. The magnesium carbonate obtained by pyrolysis of S5 is calcined with nitrogen, the calcination temperature is controlled to be 1100° C., and the calcination time is 3 h to obtain a silicon steel grade magnesium oxide product.

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

[0038] Comparative Example 3 This comparative example provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner: S1. The dolomite is crushed and ball-milled, and then the ball-milled dolomite powder is sieved through a 200-mesh sieve, and then placed in a tube furnace at 900°C and calcined for 3 h to obtain light-burned dolomite powder; the light-burned dolomite powder is hydrated at a solid-liquid ratio of 1g / L, and 2.15 g of disodium ethylenediaminetetraacetate is added at the same time, the hydration temperature is controlled to be 50°C, the hydration time is 0.5h, and the stirring speed of the hydration is 750 r / min; after hydration, it is filtered, washed, and vacuum dried to obtain a primary hydration product; S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90°C, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtering, washing, and vacuum drying are performed to obtain a secondary hydration product; S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of the secondary hydration product and mix it with 200 mL of a 5% magnesium chloride solution for reaction, control the reaction temperature to 25°C, the reaction time to 1 h, and the stirring speed of the reaction to 750 r / min; after the reaction is completed, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds; S4. Then, the obtained magnesium hydroxide with a small amount of impurity compounds is carbonized at a solid-liquid ratio of 5 g / L, and the carbonization temperature is controlled to be 21°C, the carbonization time is 1 h, and the carbon dioxide flow rate is 0.5 L·min -1 After the reaction is completed, the magnesium bicarbonate solution is filtered to obtain; S5, subjecting the filtrate of the magnesium bicarbonate solution to a pyrolysis reaction, controlling the pyrolysis temperature to 95°C, the pyrolysis time to 50min, and the pyrolysis stirring speed to 750 r / min, and filtering and drying after completion to obtain magnesium carbonate; S6. The magnesium carbonate obtained by pyrolysis of S5 is calcined with nitrogen, the calcination temperature is controlled to be 1100° C., and the calcination time is 3 h to obtain a silicon steel grade magnesium oxide product.

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

[0040] The final product obtained in embodiment 3 and comparative example 3 is compared, and embodiment 3 is higher in purity than the product obtained in comparative example 3, showing that in carbonization process, only under suitable carbon dioxide flow rate, can guarantee that product has higher productive rate.The reason that the residue generation rate of comparative example 3 is lower than the residue generation rate of implementation 3 is because in carbonization process, if carbon dioxide flow rate is too fast, then can cause the excessive of carbon dioxide in carbonization process, cause the calcium carbonate precipitation generated by calcium hydroxide and carbon dioxide reaction, can make the calcium carbonate precipitation generated transform and generate calcium bicarbonate solution because of the excessive of passing into carbon dioxide.So cause the amount of generating calcium carbonate precipitation to reduce, the residue generation rate reduces.

[0041] Therefore, the process for preparing silicon steel grade magnesium oxide from dolomite of the present invention uses dolomite as raw material and extracts silicon steel grade magnesium oxide under specific hydration conditions and complexation conditions. The prepared silicon steel grade magnesium oxide has the advantages of high purity, low cost and less residue.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A process for preparing silicon steel grade magnesium oxide from dolomite, characterized in that: The following steps are involved: S1, crushing and calcining the dolomite raw material to obtain light-burned dolomite powder, and then performing a primary hydration treatment on the light-burned dolomite powder, and filtering, washing and drying after hydration to obtain a primary hydration product; S2, performing secondary hydration on the primary hydration product according to the solid-liquid ratio, controlling the hydration temperature and hydration time, filtering, washing and drying after hydration to obtain a secondary hydration product; S3, placing the secondary hydration product in a magnesium chloride solution for washing, controlling the washing temperature and washing time, filtering, washing, and drying after the washing is completed to obtain magnesium hydroxide with a small amount of impurity compounds; S4, subjecting the magnesium hydroxide with a small amount of impurity compounds obtained in S3 to a carbonization reaction according to the solid-liquid ratio, controlling the carbonization temperature, carbonization time and the flow rate of carbon dioxide, and filtering after the reaction is completed to obtain a magnesium bicarbonate solution; S5, pyrolyzing the magnesium bicarbonate solution, controlling the pyrolysis temperature and pyrolysis time, filtering and drying to obtain magnesium carbonate after completion; S6. calcining the magnesium carbonate obtained in S5, controlling the calcination temperature and calcination time, to obtain silicon steel grade magnesium oxide.

2. The process for preparing silicon steel grade magnesium oxide from dolomite according to claim 1, characterized in that: In the S1, the solid-liquid ratio of the light-burned dolomite powder is 0.5-1 g / L. During the primary hydration process, 2-3 g of disodium ethylenediaminetetraacetate is added, and the hydration temperature is controlled to be 50-70°C, the hydration time is 20-40 min, and the hydration stirring speed is 500-800 r / min.

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

4. The process for preparing silicon steel grade magnesium oxide from dolomite according to claim 1, characterized in that: In the S3, the mass concentration of the magnesium chloride solution is 3%~6%; the dosage is 200~400 mL, the cleaning temperature is 20~30°C, the cleaning time is 0.5~1 h, and the cleaning stirring speed is 500~800 r / min.

5. The process for preparing silicon steel grade magnesium oxide from dolomite according to claim 1, characterized in that: In the S4, the solid-liquid ratio is 5-8 g / L, the carbonization temperature is 10-20°C, the carbonization time is 40-60 min, and the carbon dioxide flow rate is 0.08-0.2 L·min -1 .

6. The process for preparing silicon steel grade magnesium oxide from dolomite according to claim 1, characterized in that: In the S5, the pyrolysis temperature is 80-100° C., the pyrolysis time is 0.5-1 h, and the pyrolysis stirring speed is 500-800 r / min.

7. The process for preparing silicon steel grade magnesium oxide from dolomite according to claim 1, characterized in that: In the S6, the calcination temperature is 900-1100° C., the calcination time is 2-4 h, and the calcination condition is calcination under nitrogen.

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