Method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate

Abstract

The invention relates to the field of chemical engineering and material engineering, and provides a method for preparing high-purity magnesium oxide through direct pyrolysis of magnesium sulfate. High-purity (hydrated) magnesium sulfate (MgSO4.nH2O, 0 < = n < = 7) is used as a raw material, the raw material is heated at 250-450 DEG C for 1-2 hours for dehydration and then ground into fine powder, high-temperature roasting is performed under the condition of no additive, and high-grade high-purity magnesium oxide (MgO > = 99.5 wt%) powder can be obtained. The magnesium oxide prepared by the method is high in purity, short in technological process and convenient for industrialization, SO2 gas generated by roasting can be recycled by lime water, and concentrated sulfuric acid by-products can be prepared by a traditional industrial method.

Description

Technical Field

[0001] The invention relates to the field of chemical engineering and material engineering, and in particular to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate. Background Art

[0002] As a commonly used chemical raw material, the purity of magnesium oxide determines its main application areas. High-purity magnesium oxide usually refers to magnesium oxide with a MgO mass percentage of more than 99%. It has a high melting point, good electrical insulation, thermal conductivity and alkali resistance, and good light transmittance. It is mainly used in high-temperature ceramics, electronics, national defense and aerospace fields.

[0003] Domestic high-purity magnesium oxide mainly uses brine or magnesium ore as raw materials, first prepares high-purity magnesium hydroxide, and then calcines it at high temperature to obtain high-purity magnesium oxide, or uses carbonate precipitation method to generate magnesium carbonate and then calcines it to obtain high-purity magnesium oxide. Other methods include gas phase method, inorganic acid dissolution method, soda ash method and carbonization method. my country urgently needs to develop a more advanced process to improve the product quality and international market competitiveness of magnesium oxide.

[0004] At present, there is no report on the use of magnesium sulfate pyrolysis to prepare high-purity magnesium oxide abroad, and domestic related reports are also very rare. Yang Hongzheng et al. disclose "Preparation and Production Technology of High-Purity Magnesium Oxide" (CN112661178A), and there are similarities between this technology and the present application, mainly in that the patent uses magnesium sulfate heptahydrate as raw material, dehydrates to generate anhydrous magnesium sulfate and then roasts, so that magnesium sulfate is decomposed to generate magnesium oxide. What is different from the present application is that its production process is complicated, and it is necessary to roast twice and wash twice, and the roasting raw material adopts a mixture consisting of anhydrous magnesium sulfate and activated carbon. Because the activated carbon does not react thoroughly at the roasting temperature, there is residue in the product, and the ash after the activated carbon is roasted is residual in the product, which is bound to affect the purity of the final product. Tian Jianhua et al. published the patent "A method for preparing high-purity magnesium oxide by pyrolyzing magnesium sulfate" (CN108862337A), which first synthesizes a P204 magnesium soap, then uses this magnesium soap to extract high-magnesium wastewater to prepare magnesium sulfate heptahydrate, and then dehydrates and roasts to prepare high-purity magnesium oxide. The method uses extraction to obtain magnesium sulfate with high purity, which is beneficial for the preparation of high-purity magnesium oxide, but the extraction method is expensive and has a poor operating environment. More importantly, this method also does not use a single magnesium sulfate as a roasting raw material, but mixes it with petroleum coke for roasting, thereby introducing more foreign impurities into the reaction system than activated carbon.

[0005] The method adopted by the present invention is different from the above method. The raw material is a single (hydrated) magnesium sulfate. No reagent is added before, during, or after the roasting process. The magnesium sulfate is directly roasted and decomposed to prepare high-purity magnesium oxide. The purity of the product is almost completely determined by the purity of the reactant high-purity magnesium sulfate, thereby ensuring the purity of the final product. The raw materials used in this technology are relatively wide, the process is very short, the operability is good, the production cost is low, the product has high added value, and it is convenient for industrial mass production. Summary of the invention

[0006] The invention provides a method for preparing high-purity magnesium oxide by directly pyrolyzing (hydrated) magnesium sulfate. The method uses (hydrated) magnesium sulfate as a raw material, dehydrates it and then roasts it without adding any reagent to prepare high-grade high-purity magnesium oxide powder.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate, comprising the following steps: anhydrous magnesium sulfate powder is loaded into a crucible, compacted, and directly placed in a high-temperature furnace for high-temperature roasting and pyrolysis to generate high-purity magnesium oxide powder. During high-temperature roasting, the raw material is only the dehydrated product of magnesium sulfate or hydrated magnesium sulfate, and no reducing agent, mineralizer, heat release agent, catalyst or other additives are added to prevent the introduction of impurities from the outside.

[0009] The preparation method of the anhydrous magnesium sulfate powder is to heat magnesium sulfate or hydrated magnesium sulfate at 250-450° C. for 1-2 hours to dehydrate to obtain anhydrous magnesium sulfate, and then grind it into fine powder. Whether to dehydrate affects the state of the material and the roasting environment, but does not affect the purity of the product.

[0010] The anhydrous magnesium sulfate powder has a particle size of ≤75 μm.

[0011] The molecular formula of the hydrated magnesium sulfate is MgSO4·nH2O, 0≤n≤7.

[0012] The purity of raw material (hydrated) magnesium sulfate (measured by mass percentage of MgSO4·nH2O) varies according to the amount of crystal water (n value) contained in the raw material, and the purity requirement for anhydrous magnesium sulfate is the lowest. The more crystal water the raw material magnesium sulfate has, the higher the purity requirement is. When anhydrous magnesium sulfate is used as the raw material, the purity should be above 99.67wt%, and when magnesium sulfate heptahydrate is used, the purity should be above 99.84wt%.

[0013] The pyrolysis temperature is ≥1200°C, and the high temperature calcination temperature is maintained for 0.5 to 3 hours.

[0014] The pyrolysis temperature is 1250-1350°C, and the high temperature roasting temperature is maintained for 1-2 hours. The selection of pyrolysis temperature and pyrolysis time is related to the roasting method, raw material state, and the volume of reactants, and can be flexibly adjusted in actual production.

[0015] Pyrolysis methods include static roasting, suspension roasting and fluidized roasting.

[0016] The pyrolysis tail gas is adsorbed by lime water, or is recycled in a similar way to the method of using the flue gas generated during the traditional roasting of sulfide ores to prepare concentrated sulfuric acid.

[0017] It is worth noting that the raw material high-purity magnesium sulfate required for the present invention can be selected from high-quality products produced domestically in the form of industrial-grade magnesium sulfate or purchased directly from a high-purity magnesium sulfate manufacturer, or can be obtained by recrystallizing and purifying the industrial-grade magnesium sulfate product. The preparation method is relatively simple and the raw material supply is very sufficient.

[0018] The advantages of the present invention are as follows:

[0019] 1. Under strict control of raw material purity and preparation process conditions, high-grade high-purity magnesium oxide can be produced. (Generally speaking, when the product MgO≧99%, it can be called high-purity magnesium oxide, and in the present invention, when the raw material purity and process parameters are strictly controlled, the product MgO≧99.5%).

[0020] 2. The process is short and easy to operate, has low requirements on equipment, high magnesium recovery rate, and high economic added value of products. It can be applied to many high-tech fields such as high-purity targets, substrates, high-performance ceramics, and electronic insulation devices.

[0021] 3. The pyrolysis temperature used is within the temperature range that can be easily reached by an industrial rotary kiln. No flux, mineralizer, heat agent, reducing agent or other substances are added during the pyrolysis process, ensuring that no foreign impurities are introduced into the reaction system, thereby achieving the goal of preparing high-purity magnesium oxide.

[0022] It needs to be further explained that: in addition to producing high-purity magnesium oxide, the thermal decomposition process of high-purity magnesium sulfate also produces SO2 and O2 gases. Due to the high SO2 concentration and extremely low impurity content in the gas, lime water adsorption can be used for small-scale production in the future, while in large-scale industrial production, the more mature industrial method of the current lead and zinc smelting industry can be used to produce concentrated sulfuric acid, and it is expected to obtain concentrated sulfuric acid with higher purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The process flow chart of the present invention for preparing high-purity magnesium oxide using magnesium sulfate is shown in FIG. Using high-purity (hydrated) magnesium sulfate as raw material, high-purity magnesium oxide is prepared mainly through three processes of dehydration, ball milling and roasting, and the tail gas is adsorbed by lime milk for harmless treatment.

[0024] Figure 2 The XRD of the product prepared at different calcination temperatures of the present invention. When the calcination temperature is 1150°C, the pyrolysis temperature is insufficient, and a large amount of magnesium sulfate phase remains in the product. When the temperature reaches 1200°C, the magnesium sulfate is almost completely decomposed to form a magnesium oxide phase, but the magnesium oxide phase exists in the form of a mixed phase consisting of a cubic phase and a tetragonal phase. There is a very weak impurity phase in the low-angle area, which may be an intermediate phase produced by a very small amount of decomposition process. When the temperature reaches 1250°C, the magnesium sulfate is completely transformed into a single magnesium oxide cubic phase.

[0025] Figure 3 This is a SEM of high-purity magnesium oxide prepared by the present invention (final product of Example 1). The high-purity magnesium oxide is in a granular form with pores between the particles. The particles are agglomerated by many irregularly shaped crystal grains, and the crystal grain sizes vary from submicron to tens of microns. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.98wt%, comprising the following steps:

[0028] S1. Dehydration: 50.00 g of magnesium sulfate heptahydrate was heated at 350° C. for dehydration, kept at this temperature for 2 h, and then cooled to room temperature to obtain anhydrous magnesium sulfate.

[0029] S2, ball milling: the anhydrous magnesium sulfate obtained in step S1 is placed in an agate ball mill for 10 min, then ground into fine powder, and passed through a 200 mesh sieve to obtain anhydrous magnesium sulfate powder with a particle size of ≤75 μm.

[0030] S3, roasting: the anhydrous magnesium sulfate obtained in step S2 is placed in a corundum crucible and then placed in a resistance tube furnace for roasting at a temperature of 1250° C. for 2 hours to thermally decompose the reactants. The gas generated during the roasting process is adsorbed by lime emulsion and a neutralization reaction occurs to generate gypsum as a by-product.

[0031] Finally, 7.89 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2. The purity of the product MgO was 99.82 wt%. Figure 2 As shown, it is a single cubic phase of magnesium oxide. Figure 3 As shown, it is composed of many irregular blocky grains agglomerated together.

[0032] Example 2

[0033] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.98wt%, comprising the following steps:

[0034] S1. Dehydration: 50 g of magnesium sulfate heptahydrate was heated at 350° C. for dehydration, kept at this temperature for 1 hour, and then cooled to room temperature to obtain anhydrous magnesium sulfate.

[0035] S2, ball milling: This step is the same as in Example 1.

[0036] S3, roasting: the anhydrous magnesium sulfate obtained in step S2 is placed in a corundum crucible and then placed in a resistance tube furnace for roasting at a temperature of 1200° C. for 2 hours to thermally decompose the reactants. The gas generated during the roasting process is adsorbed by lime emulsion and a neutralization reaction occurs to generate gypsum as a by-product.

[0037] Finally, 7.87 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.61 wt%.

[0038] Example 3

[0039] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.98wt%, comprising the following steps:

[0040] S1. Dehydration: 50 g of magnesium sulfate heptahydrate was heated at 250° C. for dehydration, kept at this temperature for 2 h, and then cooled to room temperature to obtain anhydrous magnesium sulfate.

[0041] S2, ball milling: This step is the same as in Example 1.

[0042] S3, calcination: the anhydrous magnesium sulfate obtained in step S2 is placed in a corundum crucible and then placed in a resistance tube furnace for calcination at a temperature of 1350° C. for 2 hours to thermally decompose the reactants. The gas generated during the calcination process is adsorbed by lime emulsion and a neutralization reaction occurs to generate gypsum as a by-product.

[0043] Finally, 7.90 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2. The purity of MgO was 99.78 wt%.

[0044] Example 4

[0045] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.98wt%, comprising the following steps:

[0046] S1. Dehydration: 50 g of magnesium sulfate heptahydrate was heated at 450° C. for dehydration, kept at this temperature for 1 hour, and then cooled to room temperature to obtain anhydrous magnesium sulfate.

[0047] S2, ball milling: This step is the same as in Example 1.

[0048] S3, roasting: the anhydrous magnesium sulfate obtained in step S2 is placed in a corundum crucible and then placed in a resistance tube furnace for roasting at a temperature of 1400° C. for 0.5 h to thermally decompose the reactants. The gas generated during the roasting process is adsorbed by lime emulsion and a neutralization reaction occurs to generate gypsum as a by-product.

[0049] Finally, 7.85 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.73 wt%.

[0050] Example 5

[0051] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.98wt%, comprising the following steps:

[0052] S1, dehydration: This step is the same as that in Example 4.

[0053] S2, ball milling: This step is the same as in Example 1.

[0054] S3, roasting: the anhydrous magnesium sulfate obtained in step S2 is placed in a corundum crucible and then placed in a resistance tube furnace for roasting at a temperature of 1200° C. for 3 hours to thermally decompose the reactants. The gas generated during the roasting process is adsorbed by lime emulsion and a neutralization reaction occurs to generate gypsum as a by-product.

[0055] Finally, 7.88 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.53 wt%.

[0056] Example 6

[0057] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.95wt%. Except that the purity of the raw materials is different from that of Example 1, the remaining steps are exactly the same as those of Example 1.

[0058] Finally, 7.85 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.80 wt%.

[0059] Example 7

[0060] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.95wt%. Except that the purity of the raw materials is different from that of Example 2, the remaining steps are exactly the same as those of Example 2.

[0061] Finally, 7.84 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.75 wt%.

[0062] Example 8

[0063] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.95wt%. Except that the purity of the raw materials is different from that of Example 3, the remaining steps are exactly the same as those of Example 3.

[0064] Finally, 7.82 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.78 wt%.

[0065] Example 9

[0066] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.90wt%. Except that the purity of the raw materials is different from that of Example 1, the remaining steps are exactly the same as those of Example 1.

[0067] Finally, 7.81 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.55 wt%.

[0068] Example 10

[0069] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.90wt%. Except that the purity of the raw materials is different from that of Example 2, the remaining steps are exactly the same as those of Example 2.

[0070] Finally, 7.83 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.51 wt%.

[0071] Embodiment 11

[0072] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.90wt%. Except that the purity of the raw materials is different from that of Example 3, the remaining steps are exactly the same as those of Example 3.

[0073] Finally, 7.81 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.55 wt%.

[0074] Example 12

[0075] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate monohydrate (MgSO4·H2O) with a purity of 99.86%. Except that the raw materials are different from those in Example 1, the remaining steps are exactly the same as those in Example 1.

[0076] Finally, 14.04 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.52 wt%.

[0077] Embodiment 13

[0078] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of anhydrous magnesium sulfate (MgSO4·H2O) with a purity of 99.81%. Except that the raw materials are different from those in Example 1, the remaining steps are exactly the same as those in Example 1.

[0079] Finally, 14.02 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.50 wt%.

[0080] Embodiment 14

[0081] This embodiment relates to a method for preparing high-purity magnesium oxide by directly pyrolyzing a mixture of 99.98% magnesium sulfate heptahydrate (MgSO4·7H2O) and 99.86% magnesium sulfate monohydrate (MgSO4·H2O) (mixed in a mass ratio of 1:1). Except that the raw materials are different from those in Example 1, the remaining steps are exactly the same as those in Example 1.

[0082] Finally, 10.97 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.67 wt%.

[0083] Examples 15 to 17 can obtain high-purity magnesium oxide with a purity of not less than 99.0 wt%. The raw materials and main process parameters are shown in Table 1. The specific operating steps are as follows:

[0084] Embodiment 15

[0085] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.85wt%. Except that the purity of the raw materials is different from that of Example 1, the remaining steps are exactly the same as those of Example 1.

[0086] Finally, 7.85 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.37 wt%.

[0087] Example 16

[0088] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.85wt%. Except that the purity of the raw materials is different from that of Example 2, the remaining steps are exactly the same as those of Example 2.

[0089] Finally, 7.90 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.32 wt%.

[0090] Embodiment 17

[0091] This embodiment relates to a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate heptahydrate (MgSO4·7H2O) with a purity of 99.78wt%. Except that the purity of the raw materials is different from that in Example 1, the remaining steps are exactly the same as those in Example 1.

[0092] Finally, 7.83 g of high-purity magnesium oxide powder was obtained, the main chemical components of which are shown in Table 2, and the purity of MgO was 99.08 wt%.

[0093] It can be seen from the above examples that: (1) Under the same process conditions, the higher the purity of the raw material, the purer the product magnesium oxide. When the raw material is magnesium sulfate heptahydrate, when the purity is above 99.90wt%, under suitable process conditions, it can be ensured that the purity of the generated magnesium oxide reaches 99.5wt%, and when the purity is above 99.78wt%, under suitable process conditions, it can be ensured that the purity of the generated magnesium oxide reaches above 99%, that is, high-purity magnesium oxide is produced. (2) When obtaining magnesium oxide of the same or similar purity, when the amount of crystal water in the hydrated magnesium sulfate raw material used is small, the purity requirement of the raw material is lower. (3) Regardless of the type of magnesium sulfate and their mixture, as long as the raw material purity is high enough and the process conditions are reasonable, high-purity magnesium oxide can be prepared by the technical route of the present invention. (4) Through quantitative calculation and analysis, the impurities in the high-purity magnesium oxide product in each embodiment are almost completely derived from the impurities in the raw material, but not all impurities in the raw material completely remain in the solid phase product of pyrolysis, that is, a small part of the impurities are volatilized during the roasting process. (5) During the preparation process, although there was a small amount of material loss during the ball milling process, the overall magnesium recovery rate was still above 96%.

[0094] Table 1. Raw materials, main preparation process parameters and product purity of high-purity magnesium oxide prepared in each embodiment

[0095]

[0096]

[0097] As can be seen from Table 1, from Example 1 to Example 14, the purity of the prepared magnesium oxide is above 99.5wt%, and from Example 15 to Example 17, it can still reach above 99wt%, that is, it meets the purity requirement of high-purity magnesium oxide.

[0098] Table 2. Main chemical components of high-purity magnesium oxide prepared in various examples

[0099]

[0100]

[0101] As can be seen from Table 2, the main chemical component of the high-purity magnesium oxide prepared in each embodiment is MgO, and its purity is above 99.5wt%. The impurity content of the product is very low, mainly oxides of elements such as Al, Fe, Si, and Ca.

[0102] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate, characterized in that: The steps are as follows: anhydrous magnesium sulfate powder is loaded into a crucible, and after compaction, it is placed in a high-temperature furnace for direct high-temperature roasting and pyrolysis to generate high-purity magnesium oxide powder.

2. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1, characterized in that: The preparation method of the anhydrous magnesium sulfate powder is to heat magnesium sulfate or hydrated magnesium sulfate at 250-450° C. for 1-2 hours to dehydrate to obtain anhydrous magnesium sulfate, and then grind it into fine powder.

3. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: The anhydrous magnesium sulfate powder has a particle size of ≤75 μm.

4. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 2, characterized in that: The molecular formula of the hydrated magnesium sulfate is MgSO4·nH2O, 0≤n≤7.

5. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: The more crystal water the raw material magnesium sulfate has, the higher the purity requirement is. When anhydrous magnesium sulfate is used as the raw material, the purity should be above 99.67wt%, and when magnesium sulfate heptahydrate is used, the purity should be above 99.84wt%.

6. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: The pyrolysis temperature is ≥1200°C, and the high temperature calcination temperature is maintained for 0.5 to 3 hours.

7. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: The pyrolysis temperature is 1250-1350°C, and the high temperature calcination temperature is maintained for 1-2 hours.

8. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: Pyrolysis methods include static roasting, suspension roasting and fluidized roasting.

9. The method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate according to claim 1 or 2, characterized in that: The pyrolysis tail gas is adsorbed by lime water, or is recycled in a similar way to the method of using the flue gas generated during the traditional roasting of sulfide ores to prepare concentrated sulfuric acid.

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