Process for preparing silicon steel grade magnesium oxide from dolomite

Abstract

The application discloses a process method for preparing silicon steel grade magnesium oxide from dolomite, and belongs to the technical field of magnesium oxide preparation. Dolomite is used as raw material, and is crushed and calcined. Light-burned dolomite powder obtained is sequentially subjected to primary hydration, secondary hydration, magnesium chloride cleaning, carbonization and pyrolysis reaction. Magnesium carbonate obtained is calcined to obtain silicon steel grade magnesium oxide. The application extracts silicon steel grade magnesium oxide with high purity 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 present application relates to the technical field of magnesium oxide preparation, and particularly relates to a process method for preparing silicon steel grade magnesium oxide from dolomite. BACKGROUND

[0002] The silicon steel grade magnesium oxide is a magnesium oxide coating material for manufacturing oriented silicon steel sheets, is a high value-added magnesium oxide product, is mainly used in a high temperature annealing treatment stage in the manufacturing process of the oriented silicon steel sheets, plays a role of a separating agent, a dephosphorizing agent and a desulfurizing agent, and simultaneously reacts with silicon oxide on a surface of the silicon steel to form a good insulating film layer of magnesium silicate. However, at present, the demand for the silicon steel grade magnesium oxide is large in China, and the product quantity cannot meet the market demand, and still relies on import.

[0003] At present, raw materials for preparing the silicon steel grade magnesium oxide mainly include magnesite, dolomite, bischofite, seawater or salt lake brine, magnesium-containing ores and the like. Specific preparation methods mainly include a brine-ammonium carbonate method, a magnesite carbonization method, an ammonia method, a brine pyrolysis method and the like. However, each method has respective shortcomings, such as the brine-ammonium carbonate method: although the method is relatively mature, the product quality is stable and reliable, but raw material consumption is large, and the production cost is high; the magnesite carbonization method: has the shortcomings of high energy consumption, high production cost and the like, and low purity cannot be used for industrialized production; the ammonia method: the magnesium oxide is easy to form a colloid, and the process is difficult to control, causing local sintering, low activity, low recovery rate and prominent environmental protection problems; the brine pyrolysis method: has high requirements for equipment, causes great pollution to the environment, and has low raw material recovery rate.

[0004] Based on the problems existing in the preparation of the silicon steel grade magnesium oxide, it is a crucial problem to find a preparation method of the silicon steel grade magnesium oxide with high purity, low cost and few residues. SUMMARY

[0005] The present application aims to provide a process method for preparing silicon steel grade magnesium oxide from dolomite, so as to solve the problems in the background.

[0006] To achieve the above-mentioned purpose, the present application provides a process method for preparing silicon steel grade magnesium oxide from dolomite, comprising the following steps:

[0007] S1, crushing and calcining dolomite raw materials to obtain calcined dolomite powder, then performing primary hydration treatment on the calcined dolomite powder, and performing filtration, washing and drying on the hydrated product to obtain a primary hydration product;

[0008] S2, performing secondary hydration on the primary hydration product according to a solid-liquid ratio, controlling hydration temperature and hydration time, and performing filtration, washing and drying on the hydrated product to obtain a secondary hydration product;

[0009] S3, the secondary hydration product is placed in a magnesium chloride solution for cleaning, the cleaning temperature and cleaning time are controlled, and after the cleaning is completed, filtering, washing, and drying are performed to obtain magnesium hydroxide with a small amount of impurity compounds;

[0010] S4, the magnesium hydroxide with a small amount of impurity compounds obtained in S3 is subjected to a carbonation reaction according to a solid-liquid ratio, the carbonation temperature, carbonation time, and flow rate of carbon dioxide are controlled, and after the reaction is completed, filtering is performed to obtain a magnesium bicarbonate solution;

[0011] S5, the magnesium bicarbonate solution is subjected to pyrolysis, the pyrolysis temperature and pyrolysis time are controlled, and after the pyrolysis is completed, filtering and drying are performed to obtain magnesium carbonate;

[0012] S6, the magnesium carbonate prepared in S5 is subjected to calcination, the calcination temperature and calcination time are controlled, and silicon steel grade magnesium oxide is obtained.

[0013] Preferably, in S1, the dolomite is first crushed and ball milled, the ball milled dolomite powder is sieved, the mesh size of the sieve is 100-200 mesh, and then the sieved dolomite powder is calcined in a tube furnace, the calcination temperature is 900-1200℃, and the calcination time is 2-5 h.

[0014] Preferably, in S1, the solid-liquid ratio of the lightly calcined 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℃, the hydration time is 20-40 min, and the hydration stirring speed is 500-800 r / min.

[0015] Preferably, in S2, the solid-liquid ratio is 1-2 g / L, the hydration temperature is 90-110℃, the hydration time is 1-3 h, and the hydration stirring speed is 500-800 r / min.

[0016] Preferably, in S3, the mass concentration of the magnesium chloride solution is 3%-6%, the amount used is 200-400 mL, the cleaning temperature is 20-30℃, the cleaning time is 0.5-1 h, and the cleaning stirring speed is 500-800 r / min.

[0017] Preferably, in S4, the solid-liquid ratio is 5-8 g / L, the carbonation temperature is 10-20℃, the carbonation time is 40-60 min, and the flow rate of carbon dioxide is 0.08-0.2 L·min -1 .

[0018] Preferably, in S5, the pyrolysis temperature is 80-100℃, the pyrolysis time is 0.5-1 h, and the pyrolysis stirring speed is 500-800 r / min.

[0019] Preferably, in the S6, the calcination temperature is 900-1100℃, the calcination time is 2-4 h, and the calcination condition is nitrogen gas calcination.

[0020] Preferably, in the S1-S3, the washing process is washing 5-8 times with deionized water; and in the S1-S3 and S5, the drying process is vacuum drying.

[0021] The principle of the process method adopted by the present application is that the product after calcination of dolomite is 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 in the first hydration process, by controlling the appropriate hydration temperature and hydration time, and adding a certain amount of disodium ethylenediaminetetraacetate, most of the calcium oxide in the calcined dolomite powder can be separated from the calcined dolomite powder in the form of a solution.

[0022] After the completion of the first hydration reaction, the main components in the first hydration product are magnesium oxide, magnesium hydroxide, a small amount of calcium oxide, calcium hydroxide and other impurity compounds. Because magnesium oxide will generate magnesium hydroxide at a higher reaction temperature and for a longer reaction time, in the second hydration process, by controlling the appropriate hydration temperature and hydration time, the magnesium oxide and calcium oxide in the first hydration product are generated into magnesium hydroxide and calcium hydroxide; the main components in the second hydration product are magnesium hydroxide, a small amount of calcium hydroxide and impurity compounds.

[0023] Because magnesium chloride reacts with calcium hydroxide to generate calcium chloride and magnesium hydroxide, so a certain amount of the second hydration product is washed with a magnesium chloride solution of a certain mass concentration, so that a small amount of calcium hydroxide in the second hydration product can be separated from the second hydration product 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 to perform a carbonization reaction, to generate a magnesium bicarbonate solution and other small amount of impurity precipitates under appropriate carbonization conditions. After the completion of the carbonization reaction, the precipitates are removed by filtration, and the carbonization liquid is left to perform a pyrolysis reaction to generate magnesium carbonate precipitates. The pyrolysis liquid after the completion of the pyrolysis reaction is filtered, dried and calcined, so that the 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 is generated.

[0024] Therefore, the process method for preparing silicon steel grade magnesium oxide from dolomite in the present application extracts silicon steel grade magnesium oxide with high purity 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 less residue.

[0025] The technical solutions of the present application are further described in detail below through the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Flow chart of the present application;

[0027] Figure 2 XRD pattern of magnesium oxide of Example 1 of the present application;

[0028] Figure 3 Scanning electron micrograph of magnesium oxide of Example 1 of the present application, where (a) is 1 μm and (b) is 500 nm;

[0029] Figure 4 Particle size distribution of magnesium oxide (not ball milled) of Example 1 of the present application. DETAILED DESCRIPTION

[0030] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0031] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0032] The present application provides a process for preparing silicon steel grade magnesium oxide from dolomite, as shown in the following scheme: Figure 1 The process comprises the following steps: taking dolomite as raw material, first crushing and ball milling the dolomite, and sieving the ball milled dolomite powder in a 100-200 mesh screen; calcining the sieved dolomite powder in a tube furnace, the calcination temperature being 900-1200 ℃ and the calcination time being 2-5 h, to obtain lightly calcined dolomite powder; the calcination reaction equation in this process is:

[0033] CaCO3·MgCO3(s)→MgO(s)+CaO(s)+2CO2↑(high temperature);

[0034] Then, the obtained lightly calcined dolomite powder is subjected to primary hydration at a solid-liquid ratio of 0.5-1 g / L, while adding 2-3 g of disodium ethylenediaminetetraacetate, the hydration temperature being controlled at 50-70 ℃, the hydration time being 20-40 min, and the hydration stirring speed being 500-800 r / min, and the primary hydration reaction equation is:

[0035] 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)↓;

[0036] After hydration, filtration is carried out, and magnesium oxide, magnesium hydroxide and a small amount of calcium hydroxide and other element impurity compounds are obtained; the first hydration product is placed in a vacuum drying box for drying treatment, and the dried first hydration product is subjected to secondary hydration according to a solid-liquid ratio of 1-2 g / L, the hydration temperature is controlled to be 90-110 ℃, the hydration time is controlled to be 1-3 h, and the hydration stirring speed is controlled to be 500-800 r / min, and the reaction equation of the secondary hydration is as follows:

[0037] 2MgO(s) + 2H2O(aq) → 2Mg(OH)2(s)↓, 2CaO(s) + 2H2O(aq) → 2Ca(OH)2(s)↓.

[0038] After the secondary hydration is completed, filtration, washing and vacuum drying are carried out to obtain magnesium hydroxide and a small amount of calcium hydroxide and impurity compounds;

[0039] A magnesium chloride solution with a mass concentration of 3%-6% is configured, and a proper amount of the secondary hydration product is placed in 200-400 mL of the magnesium chloride solution for cleaning, the cleaning temperature is controlled to be 20-30 ℃, the cleaning time is controlled to be 0.5-1 h, and the cleaning stirring speed is controlled to be 500-800 r / min; the reaction equation involved in the process is as follows:

[0040] Ca(OH)2(s) + MgCl2(aq) → CaCl2(aq) + Mg(OH)2(s)↓;

[0041] The main component of the secondary hydration product after cleaning is magnesium hydroxide and a small amount of impurity compounds; the secondary hydration product after cleaning is subjected to carbonation reaction according to a solid-liquid ratio of 5-8 g / L to obtain a magnesium bicarbonate solution, the carbonation temperature is controlled to be 10-20 ℃, the carbonation time is controlled to be 40-60 min, and the carbon dioxide flow rate is controlled to be 0.08-0.2 L·min -1 ; the reaction equation of the carbonation is as follows:

[0042] Mg(OH)2(s)↓ + 2CO2↑ → Mg(HCO3)2(aq);

[0043] The magnesium bicarbonate solution obtained after the carbonation reaction is filtered and pyrolyzed to obtain magnesium carbonate precipitate, the pyrolysis temperature is controlled to be 80-100℃, the pyrolysis time is controlled to be 0.5-1 h, and the pyrolysis stirring speed is controlled to be 500-800 r / min; the reaction equation of pyrolysis is:

[0044] Mg(HCO3)2(aq) → MgCO3(s)↓+ CO2↑+ H2O(aq);

[0045] The magnesium carbonate precipitate obtained by pyrolysis is calcined under a nitrogen atmosphere, the calcination temperature is controlled to be 900-1100℃, the calcination time is controlled to be 2-4 h, and the silicon steel grade magnesium oxide is obtained, and the reaction equation of calcination is:

[0046] MgCO3(s)↓→ MgO(s) + CO2↑(high temperature).

[0047] The process is described through the following specific examples.

[0048] Example 1

[0049] This example 1 provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following way:

[0050] S1, crush and ball mill the dolomite, then sieve the ball-milled dolomite powder in a 200 mesh sieve, and then place it in a tube furnace at 900℃ for calcination for 3 h to obtain lightly calcined dolomite powder; hydrate the lightly calcined dolomite powder at a solid-liquid ratio of 1 g / L, while adding 2.15 g of disodium ethylenediaminetetraacetate, controlling the hydration temperature to be 50℃, the hydration time to be 0.5 h, and the hydration stirring speed to be 750 r / min; after hydration, filter, wash, and vacuum dry to obtain a primary hydration product;

[0051] S2, hydrate the primary hydration product at a solid-liquid ratio of 2 g / L for secondary hydration, control the hydration temperature to be 90℃, the hydration time to be 3 h, and the hydration stirring speed to be 750 r / min; after hydration, filter, wash, and vacuum dry to obtain a secondary hydration product;

[0052] S3, prepare a magnesium chloride solution with a mass concentration of 5%; weigh an appropriate amount of secondary hydration product and mix it with 200 mL of 5% magnesium chloride solution for reaction, control the reaction temperature to be 25℃, the reaction time to be 1 h, and the reaction stirring speed to be 750 r / min; after reaction, filter, wash, and vacuum dry to obtain magnesium hydroxide with a small amount of impurity compounds;

[0053] S4, the obtained magnesium hydroxide with a small amount of impurity compounds is carbonized according to a solid-liquid ratio of 5 g / L, the carbonization temperature is controlled to be 21 ℃, the carbonization time is controlled to be 1 h, and the carbon dioxide flow rate is controlled to be 0.1 L·min -1 , and a magnesium bicarbonate solution is obtained after filtration;

[0054] S5, the magnesium bicarbonate filtrate is pyrolyzed, the pyrolysis temperature is controlled to be 95 ℃, the pyrolysis time is controlled to be 50 min, and the pyrolysis stirring speed is controlled to be 750 r / min, and after completion, filtration and drying are performed to obtain magnesium carbonate;

[0055] S6, the magnesium carbonate obtained in S5 is calcined by passing nitrogen, the calcination temperature is controlled to be 1100 ℃, and the calcination time is controlled to be 3 h, to obtain a silicon steel grade magnesium oxide product.

[0056] The product has a hydration rate of 4.16%, a mass fraction of 99.26%, a citric acid activity value of 56 s, and a residue generation rate of 3.68%.

[0057] The product of Example 1 is detected, and the detection results are shown in Table 1. Figures 2-4

[0058] Comparative Example 1

[0059] This comparative example provides a traditional method for preparing a silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner:

[0060] S1, the dolomite is placed in a tubular furnace at a high temperature of 1000 ℃ for calcination, to obtain a mixture of magnesium oxide and calcium oxide;

[0061] S2, the mixture of magnesium oxide and calcium oxide is digested with water to obtain a mixture of magnesium hydroxide and calcium hydroxide;

[0062] S3, carbonization is performed on the mixture of magnesium hydroxide and calcium hydroxide with carbon dioxide, and the products are calcium carbonate and magnesium bicarbonate, respectively;

[0063] S4, after the completion of the carbonization reaction, filtration is performed to obtain a magnesium bicarbonate aqueous solution, and then the magnesium bicarbonate aqueous solution is heated, the heating temperature is 800 ℃, to obtain a magnesium carbonate product;

[0064] S5, the pyrolyzed magnesium carbonate is filtered to obtain a magnesium carbonate solid, and then the magnesium carbonate is calcined at a calcination temperature of 850 ℃ to obtain magnesium oxide;

[0065] S6, the obtained magnesium oxide after calcination is reacted with water at 65 ℃, the mass concentration ratio of magnesium oxide to water is 1:8.5, and the reaction is carried out in water to modify, purify and remove impurities, and the solution after the reaction is filtered to obtain a magnesium hydroxide solid filter cake;

[0066] ​S7, the magnesium hydroxide filter cake obtained in S6 is calcined at 950 DEG C for 2 hours and at 1000 DEG C for 2 hours respectively to obtain magnesium oxide with different citric acid activities;

[0067] S8, the magnesium oxide with different properties obtained in S7 is crushed, and the product with an activity of 60 S is mixed with the product with an activity of 200 S at a ratio of 70% to 30% to obtain a silicon steel grade magnesium oxide product.

[0068] The product has a hydration rate of 3.31%, a mass fraction of 99.2%, a citric acid activity of 65 s, and a residue generation rate of 50.4%.

[0069] By detecting and comparing the product and residue amount 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 generation and higher activity.

[0070] Example 2

[0071] The example provides a method for preparing a silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner:

[0072] S1, the dolomite is crushed and ball milled, and then the ball milled dolomite powder is sieved through a 200 mesh screen, and then placed in a tube furnace at 900 DEG C for calcination for 3 h to obtain lightly calcined dolomite powder; the lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L, while 2.15 g of disodium ethylenediaminetetraacetate is added, the hydration temperature is controlled at 50 DEG C, the hydration time is 0.5 h, and the stirring speed during hydration is 750 r / min; after hydration, filtration, washing and vacuum drying are performed to obtain a primary hydration product;

[0073] S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled at 90 DEG C, the hydration time is 3 h, and the stirring speed during hydration is 750 r / min; after hydration, filtration, washing and vacuum drying are performed to obtain a secondary hydration product;

[0074] S3, a magnesium chloride solution with a mass concentration of 5% is prepared; an appropriate amount of the secondary hydration product is mixed with 200 mL of the 5% magnesium chloride solution for reaction, the reaction temperature is controlled at 25 DEG C, the reaction time is 1 h, and the stirring speed during reaction is 750 r / min; after reaction, filtration, washing and vacuum drying are performed to obtain magnesium hydroxide with a small amount of impurity compounds;

[0075] S4, then the magnesium hydroxide with a small amount of impurity compounds is subjected to carbonation reaction at a solid-liquid ratio of 5 g / L, the carbonation temperature is controlled at 21 DEG C, the carbonation time is 1 h, the carbon dioxide flow rate is 0.1 L·min -1 , and after reaction, filtration is performed to obtain a magnesium bicarbonate solution;

[0076] S5, the magnesium bicarbonate solution filtrate was pyrolyzed, the pyrolysis temperature was controlled at 95℃, the pyrolysis time was 50 min, and the pyrolysis stirring speed was 750 r / min, after completion, filtration and drying were performed to obtain magnesium carbonate;

[0077] S6, the magnesium carbonate obtained by pyrolysis in S5 was calcined by passing nitrogen, the calcination temperature was controlled at 1100℃, and the calcination time was 3 h to obtain a silicon steel grade magnesium oxide product.

[0078] The product has a hydration rate of 4.16%, a mass fraction of 99.26%, a citric acid activity value of 56 s, and a residue generation rate of 3.68%.

[0079] Comparative Example 2

[0080] This comparative example provides a method for preparing a silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner:

[0081] S1, the dolomite was crushed and ball milled, and then the ball milled dolomite powder was sieved through a 200 mesh screen, and then placed in a tube furnace at 900℃ for calcination for 3 h to obtain lightly calcined dolomite powder; the lightly calcined dolomite powder was hydrated at a solid-liquid ratio of 1 g / L, the hydration temperature was controlled at 50℃, the hydration time was 0.5 h, and the stirring speed during hydration was 750 r / min; after hydration, filtration, washing, and vacuum drying were performed to obtain a primary hydration product;

[0082] S2, the primary hydration product was subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature was controlled at 90℃, the hydration time was 3 h, and the stirring speed during hydration was 750 r / min; after hydration, filtration, washing, and vacuum drying were performed to obtain a secondary hydration product;

[0083] S3, a magnesium chloride solution with a mass concentration of 5% was prepared; an appropriate amount of the secondary hydration product was mixed with 200 mL of the 5% magnesium chloride solution for reaction, the reaction temperature was controlled at 25℃, the reaction time was 1 h, and the stirring speed during reaction was 750 r / min; after reaction, filtration, washing, and vacuum drying were performed to obtain magnesium hydroxide with a small amount of impurity compounds;

[0084] S4, then the magnesium hydroxide with a small amount of impurity compounds was subjected to carbonation reaction at a solid-liquid ratio of 5 g / L, the carbonation temperature was controlled at 21℃, the carbonation time was 1 h, the carbon dioxide flow rate was 0.1 L·min -1 , and after reaction, filtration was performed to obtain a magnesium bicarbonate solution;

[0085] S5, the magnesium bicarbonate solution filtrate is subjected to pyrolysis reaction, the pyrolysis temperature is controlled to be 95 DEG C, the pyrolysis time is controlled to be 50 min, and the pyrolysis stirring speed is controlled to be 750 r / min, after completion, filtration and drying are carried out to obtain magnesium carbonate;

[0086] S6, the magnesium carbonate obtained by pyrolysis in S5 is subjected to nitrogen calcination, the calcination temperature is controlled to be 1100 DEG C, and the calcination time is controlled to be 3 h, to obtain a silicon steel grade magnesium oxide product.

[0087] The product has a hydration rate of 4.3%, a mass fraction of 84.77%, a citric acid activity value of 95 s, and a residue generation rate of 8.75%.

[0088] The final products obtained in Example 2 and Comparative Example 2 are compared, and the product obtained in Example 1 has higher purity and less residue than the product obtained in Comparative Example 1, indicating that adding an appropriate amount of disodium ethylenediaminetetraacetate in the first hydration process can ensure that the obtained product has higher purity and less residue.

[0089] Example 3

[0090] The example provides a method for preparing a silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner:

[0091] S1, the dolomite is crushed and ball milled, and then the ball milled dolomite powder is sieved through a 200 mesh screen, and then placed in a tube furnace at 900 DEG C for calcination for 3 h to obtain lightly calcined dolomite powder; the lightly calcined dolomite powder is hydrated at a solid-liquid ratio of 1 g / L, and 2.15 g of disodium ethylenediaminetetraacetate is added, the hydration temperature is controlled to be 50 DEG C, the hydration time is controlled to be 0.5 h, and the stirring speed of hydration is controlled to be 750 r / min; after hydration, filtration, washing and vacuum drying are carried out to obtain a first hydration product;

[0092] S2, the first hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled to be 90 DEG C, the hydration time is controlled to be 3 h, and the stirring speed of hydration is controlled to be 750 r / min; after hydration, filtration, washing and vacuum drying are carried out to obtain a secondary hydration product;

[0093] S3, a magnesium chloride solution with a mass concentration of 5% is prepared; an appropriate amount of secondary hydration product is mixed with 200 mL of 5% magnesium chloride solution for reaction, the reaction temperature is controlled to be 25 DEG C, the reaction time is controlled to be 1 h, and the stirring speed of reaction is controlled to be 750 r / min; after reaction, filtration, washing and vacuum drying are carried out to obtain magnesium hydroxide with a small amount of impurity compounds;

[0094] S4, then the magnesium hydroxide obtained with a small amount of impurity compounds is subjected to carbonization reaction at a solid-liquid ratio of 5 g / L, the carbonization temperature is controlled at 21 ℃, the carbonization time is 1 h, and the carbon dioxide flow rate is 0.1 L·min -1 , and a magnesium bicarbonate solution is obtained after filtration;

[0095] S5, the magnesium bicarbonate solution filtrate is subjected to pyrolysis reaction, the pyrolysis temperature is controlled at 95 ℃, the pyrolysis time is 50 min, and the pyrolysis stirring speed is 750 r / min, and after completion, filtration and drying are performed to obtain magnesium carbonate;

[0096] S6, the magnesium carbonate obtained by pyrolysis in S5 is subjected to nitrogen calcination, the calcination temperature is controlled at 1100 ℃, and the calcination time is 3 h, to obtain a silicon steel grade magnesium oxide product.

[0097] The product has a hydration rate of 4.16%, a mass fraction of 99.26%, a citric acid activity value of 56 s of silicon steel grade magnesium oxide, and a residue generation rate of 3.68%.

[0098] Comparative Example 3

[0099] This comparative example provides a method for preparing silicon steel grade magnesium oxide from dolomite, which is carried out in the following manner:

[0100] S1, the dolomite is crushed and ball milled, and then the ball milled dolomite powder is sieved through a 200 mesh screen, and then placed in a tube furnace at 900 ℃ for calcination for 3 h to obtain lightly calcined dolomite powder; the lightly calcined dolomite powder is subjected to hydration at a solid-liquid ratio of 1 g / L, while 2.15 g of disodium ethylenediaminetetraacetate is added, the hydration temperature is controlled at 50 ℃, the hydration time is 0.5 h, and the hydration stirring speed is 750 r / min; after hydration, filtration, washing, and vacuum drying are performed to obtain a primary hydration product;

[0101] S2, the primary hydration product is subjected to secondary hydration at a solid-liquid ratio of 2 g / L, the hydration temperature is controlled at 90 ℃, the hydration time is 3 h, and the hydration stirring speed is 750 r / min; after hydration, filtration, washing, and vacuum drying are performed to obtain a secondary hydration product;

[0102] S3, a magnesium chloride solution with a mass concentration of 5% is prepared; an appropriate amount of secondary hydration product is mixed with 200 mL of the 5% magnesium chloride solution for reaction, the reaction temperature is controlled at 25 ℃, the reaction time is 1 h, and the reaction stirring speed is 750 r / min; after reaction, filtration, washing, and vacuum drying are performed to obtain magnesium hydroxide with a small amount of impurity compounds;

[0103] S4, then the magnesium hydroxide obtained with a small amount of impurity compound is carbonized according to a solid-liquid ratio of 5 g / L, the carbonization temperature is controlled to be 21 DEG C, the carbonization time is controlled to be 1 h, and the carbon dioxide flow rate is controlled to be 0.5 L·min -1 , and after the reaction is completed, the magnesium bicarbonate solution is obtained by filtering;

[0104] S5, the magnesium bicarbonate solution is pyrolyzed, the pyrolysis temperature is controlled to be 95 DEG C, the pyrolysis time is controlled to be 50 min, and the pyrolysis stirring speed is controlled to be 750 r / min, and after the pyrolysis is completed, the magnesium carbonate is obtained by filtering and drying;

[0105] S6, the magnesium carbonate obtained by pyrolysis in S5 is calcined by passing nitrogen, the calcination temperature is controlled to be 1100 DEG C, and the calcination time is controlled to be 3 h, and the silicon steel grade magnesium oxide product is obtained.

[0106] The product has a hydration rate of 4.54%, a mass fraction of 98.76%, a citric acid activity value of 75 s of the silicon steel grade magnesium oxide, and a residue generation rate of 2.97%.

[0107] The final products obtained in Example 3 and Comparative Example 3 are compared, the product obtained in Example 3 has higher purity than that in Comparative Example 3, which indicates that only under the suitable carbon dioxide flow rate in the carbonization process, the product can have higher yield. The reason why the residue generation rate of Comparative Example 3 is lower than that of Example 3 is that in the carbonization process, if the carbon dioxide flow rate is too fast, the carbon dioxide will be excessive in the carbonization process, the calcium carbonate precipitate generated by the reaction of calcium hydroxide and carbon dioxide will be converted into calcium bicarbonate solution due to the excessive carbon dioxide, so that the amount of the generated calcium carbonate precipitate is reduced, and the residue generation rate is reduced.

[0108] Therefore, the process method for preparing the silicon steel grade magnesium oxide from dolomite has the advantages of high purity, low cost and less residue of the prepared silicon steel grade magnesium oxide.

[0109] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A process for the preparation of silicon steel grade magnesia from dolomite, characterized by, It comprises the following steps: S1, crushing and calcining dolomite raw material to obtain lightly calcined dolomite powder, specifically: firstly, crushing and ball milling dolomite, sieving the ball-milled dolomite powder, the mesh number of the sieve is 100-200 mesh; then calcining the sieved dolomite powder in a tube furnace, the calcining temperature is 900-1200℃, and the calcining time is 2-5h; Then, the lightly calcined dolomite powder is subjected to a first hydration treatment, and after hydration, filtration, washing and drying, a first hydration product is obtained; the solid-liquid ratio of the lightly calcined dolomite powder is 0.5-1g / L, and during the first hydration process, 2-3g of disodium ethylenediaminetetraacetate is added; the hydration temperature is controlled at 50-70℃, the hydration time is 20-40min, and the hydration stirring speed is 500-800r / min; S2, the first hydration product is subjected to a second hydration according to the solid-liquid ratio, the hydration temperature and time are controlled, and after hydration, filtration, washing and drying, a second hydration product is obtained; the solid-liquid ratio is 1-2g / L, the hydration temperature is 90-110℃, the hydration time is 1-3h, and the hydration stirring speed is 500-800r / min; S3, the second hydration product is placed in a magnesium chloride solution for cleaning, the cleaning temperature and time are controlled, and after cleaning, filtration, washing and drying, magnesium hydroxide with a small amount of impurity compounds is obtained; S4, carbonizing the magnesium hydroxide with a small amount of impurity compounds obtained in S3 according to the solid-liquid ratio, controlling the carbonization temperature, carbonization time and flow rate of carbon dioxide, and after the reaction is completed, filtering to obtain a magnesium bicarbonate solution; the flow rate of carbon dioxide is 0.08-0.2 L·min -1 ; S5, the magnesium bicarbonate solution is pyrolyzed, the pyrolysis temperature and time are controlled, and after completion, filtration and drying are performed to obtain magnesium carbonate; S6, the magnesium carbonate prepared in S5 is calcined, the calcination temperature and time are controlled, and silicon steel grade magnesium oxide is obtained.

2. A process for the production of silicon steel grade magnesia from dolomite as claimed in claim 1 wherein: In S3, the mass concentration of the magnesium chloride solution is 3%-6%, the amount used is 200-400mL, the cleaning temperature is 20-30℃, the cleaning time is 0.5-1h, and the cleaning stirring speed is 500-800r / min.

3. A process for the preparation of silicon steel grade magnesia from dolomite as claimed in claim 1 wherein: In S4, the solid-liquid ratio is 5-8g / L, the carbonization temperature is 10-20℃, and the carbonization time is 40-60min.

4. A process for the production of silicon steel grade magnesia from dolomite as claimed in claim 1 wherein: In S5, the pyrolysis temperature is 80-100℃, the pyrolysis time is 0.5-1h, and the pyrolysis stirring speed is 500-800r / min.

5. A process for the production of silicon steel grade magnesia from dolomite as claimed in claim 1 wherein: In S6, the calcination temperature is 900-1100℃, the calcination time is 2-4h, and the calcination condition is nitrogen gas calcination.

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