Method for preparing high-purity magnesium oxide through low-temperature pyrolysis of magnesium sulfate

Abstract

The invention discloses a method for preparing high-purity magnesium oxide through low-temperature pyrolysis of magnesium sulfate. The method comprises the following steps: calcining and pyrolyzing anhydrous magnesium sulfate under the catalysis of noble metal to obtain high-purity magnesium oxide. According to the method provided by the invention, the pyrolysis temperature of magnesium sulfate can be obviously reduced on the premise of not adding a reducing agent, the energy consumption is reduced, and the pyrolysis efficiency is improved; and the magnesium sulfate pyrolysis process flow is simplified, and the purity of magnesium oxide is improved.

Description

Technical Field

[0001] The present invention belongs to the field of high-purity magnesium oxide production, and particularly relates to a method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate. Background Art

[0002] High-purity magnesium oxide (purity ≥ 98 wt%) has excellent acid and alkali resistance, electrical insulation, light transmittance and thermal conductivity, and is an important inorganic chemical product, widely used in industries such as medicine, ceramics, electronics, and electrical appliances. According to different production raw materials, the preparation methods of high-purity magnesium oxide can be divided into brine soda method and ammonium bicarbonate method, dolomite carbonization method, magnesite carbonization method, direct pyrolysis method and reduction pyrolysis method of magnesium sulfate, etc. Qinghai Province in China is rich in magnesium sulfate subtype salt lakes, and magnesium sulfate heptahydrate or magnesium sulfate hexahydrate will precipitate during the evaporation process of magnesium sulfate subtype salt lakes. Preparing magnesium oxide by pyrolysis using magnesium sulfate hydrate as raw material has the advantages of simple process flow, low cost and high magnesium yield.

[0003] At present, Patent CN119219036A discloses a method for preparing high-purity magnesium oxide by direct pyrolysis of magnesium sulfate. Using relatively high-purity hydrated magnesium sulfate as raw material, dehydrating at 250-450°C, and then pyrolyzing at 1250-1350°C for 1-2 h to prepare high-purity magnesium oxide. Patent CN110510644A discloses a method for rapidly pyrolyzing magnesium sulfate to prepare active submicron magnesium oxide. Dehydrating magnesium sulfate monohydrate or magnesium sulfate heptahydrate at a constant temperature of 300-500°C, and then roasting the ground magnesium sulfate at 1000-1500°C to obtain submicron magnesium oxide. Zhang Jingjing et al. (Inorganic Chemical Industry, 2010, 42(5)) found through experiments that the thermal decomposition reaction of anhydrous magnesium sulfate occurs in the range of 950-1150°C, and it can be completely decomposed only when the temperature is higher than 1100°C. The direct pyrolysis method of magnesium sulfate to prepare high-purity magnesium oxide has the advantages of simple process flow and high magnesium yield, but magnesium sulfate needs to be higher than 1100°C to be completely decomposed to obtain high-purity magnesium oxide, which has the problems of high energy consumption and low pyrolysis efficiency.

[0004] Patent CN112661178A discloses a preparation process of high-purity magnesium oxide. After drying and dehydrating magnesium sulfate heptahydrate and grinding it, the anhydrous magnesium sulfate powder and activated carbon are calcined at 800-1150°C to prepare magnesium oxide, and then the magnesium oxide is washed and calcined again to obtain high-purity magnesium oxide. Patent CN102173439A discloses a method for producing high-purity magnesium oxide by reducing and pyrolyzing magnesium sulfate with natural gas. Using magnesium sulfate heptahydrate as raw material, anhydrous magnesium sulfate is obtained by dehydration at 500-600°C, and anhydrous magnesium sulfate is reduced and pyrolyzed with natural gas at 900-1000°C to obtain magnesium oxide with a purity greater than 99%. Patent CN108862337A discloses a method for pyrolyzing magnesium sulfate to prepare high-purity magnesium oxide. First, magnesium sulfate heptahydrate is obtained by extracting high-magnesium wastewater, then anhydrous magnesium sulfate is obtained by dehydrating magnesium sulfate heptahydrate at 200-500°C, and the anhydrous magnesium sulfate powder and petroleum coke powder are mixed and pyrolyzed at 800-1100°C to obtain high-purity magnesium oxide. Adding substances such as activated carbon, natural gas, and petroleum coke during the pyrolysis of magnesium sulfate for reduction pyrolysis reaction can reduce the pyrolysis temperature of magnesium sulfate, but increases the preparation cost and process steps, and also reduces the purity of magnesium oxide. Summary of the Invention

[0005] The main object of the present invention is to provide a method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate, so as to overcome the problems of high pyrolysis temperature, high energy consumption, low pyrolysis efficiency when directly pyrolyzing magnesium sulfate to prepare high-purity magnesium oxide, low purity of magnesium oxide and complex process flow when adding a reducing agent for pyrolysis.

[0006] To achieve the foregoing invention object, the technical solutions adopted by the present invention include: One aspect of the present invention provides a method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate, which includes: calcining and pyrolyzing anhydrous magnesium sulfate under the catalysis of a noble metal to obtain high-purity magnesium oxide.

[0007] Further, the method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate includes: Recrystallizing and grinding magnesium sulfate hydrate to obtain high-purity magnesium sulfate heptahydrate powder; Calcining and dehydrating the high-purity magnesium sulfate heptahydrate powder to obtain the anhydrous magnesium sulfate; Calcining and pyrolyzing the anhydrous magnesium sulfate under the catalysis of a noble metal to obtain high-purity magnesium oxide.

[0008] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate provided by the present invention can significantly reduce the pyrolysis temperature of magnesium sulfate and reduce energy consumption without adding a reducing agent; (2) Due to the catalytic effect of the noble metal, the method provided by the present invention improves the pyrolysis efficiency of magnesium sulfate; (3) The method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate provided by the present invention simplifies the process flow of magnesium sulfate pyrolysis and improves the purity of magnesium oxide. Specific Embodiments

[0009] In view of the problems existing in the above-mentioned prior art, through extensive and in-depth research by the inventors of the present invention, a method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate is provided. It mainly spreads the high-purity magnesium sulfate heptahydrate powder after recrystallization in a container made of precious metals (such as platinum, palladium, etc.) for pyrolysis reaction. The precious metals (such as platinum, palladium, etc.) have a catalytic effect on the magnesium sulfate pyrolysis reaction, which can reduce the pyrolysis temperature of magnesium sulfate and improve the pyrolysis efficiency of magnesium sulfate.

[0010] The following will further explain the technical solution, its implementation process, principle, etc.

[0011] As an aspect of the technical solution of the present invention, a method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate provided by it includes: calcining and pyrolyzing anhydrous magnesium sulfate under the catalysis of precious metals to obtain high-purity magnesium oxide.

[0012] In the above technical solution, its beneficial effect is mainly that anhydrous magnesium sulfate significantly reduces the pyrolysis temperature and energy consumption of magnesium sulfate under the catalysis of precious metals, and improves the pyrolysis rate and efficiency of magnesium sulfate.

[0013] In some embodiments, the method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate includes: Recrystallizing and grinding the magnesium sulfate hydrate salt to obtain high-purity magnesium sulfate heptahydrate powder; Calcining and dehydrating the high-purity magnesium sulfate heptahydrate powder to obtain the anhydrous magnesium sulfate; Calcining and pyrolyzing the anhydrous magnesium sulfate under the catalysis of precious metals to obtain high-purity magnesium oxide.

[0014] In some more specific embodiments, the method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate specifically includes: dissolving, evaporating, recrystallizing, and grinding the magnesium sulfate hydrate salt to obtain the high-purity magnesium sulfate heptahydrate powder.

[0015] Further, the particle size of the high-purity magnesium sulfate heptahydrate powder ≤ 0.1 mm.

[0016] In some more specific embodiments, the method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate specifically includes: spreading the high-purity magnesium sulfate heptahydrate powder in a precious metal container, heating up for calcining and dehydrating to obtain the anhydrous magnesium sulfate.

[0017] Further, the thickness of the high-purity magnesium sulfate heptahydrate powder spread in the precious metal container does not exceed 2 mm.

[0018] Further, the temperature for calcination dehydration is 300 - 600 °C, and the time is 2 - 4 h.

[0019] Further, the noble metal container includes a crucible.

[0020] Further, heat up to the temperature required for calcination dehydration at a rate of 2 - 20 °C / min.

[0021] In some embodiments, the temperature for calcination pyrolysis is 750 - 950 °C, and the time is 4 - 6 h.

[0022] In some embodiments, heat up to the temperature required for calcination pyrolysis at a rate of 2 - 20 °C / min.

[0023] In some embodiments, the magnesium sulfate hydrate salt includes at least any one of magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, magnesium sulfate monohydrate, etc., but is not limited thereto.

[0024] In some embodiments, the noble metal includes any one of platinum and palladium.

[0025] In some more specific embodiments, the method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate may specifically include the following steps: (1) Dissolve the magnesium sulfate hydrate salt in water, evaporate, recrystallize, and grind it to obtain high-purity magnesium sulfate heptahydrate powder with a particle size ≤ 0.1 mm; (2) Spread the high-purity magnesium sulfate heptahydrate powder in a noble metal crucible, heat up to 300 - 600 °C at a rate of 2 - 20 °C / min for calcination dehydration for 2 - 4 h to obtain anhydrous magnesium sulfate; (3) Under the catalysis of the noble metal, heat up the anhydrous magnesium sulfate to 750 - 950 °C at a rate of 2 - 20 °C / min for calcination pyrolysis for 4 - 6 h to obtain high-purity magnesium oxide.

[0026] In some embodiments, the mass fraction of magnesium oxide in the high-purity magnesium oxide ≥ 99.5 wt%.

[0027] Specifically, in the present invention, the reaction mechanism of the noble metal (such as platinum, palladium, etc.) having a catalytic effect on the pyrolysis reaction of magnesium sulfate is as follows: The noble metal (such as platinum, palladium, etc.) can provide highly active surface sites, promote the adsorption of magnesium sulfate and the cleavage of chemical bonds. When anhydrous magnesium sulfate adsorbs on the surface of the noble metal crucible to form an activated adsorbed state, the d-orbital electrons of the noble metal participate in the polarization of chemical bonds, weaken the S - O bond and Mg - O bond, thereby reducing the energy barrier and required temperature of the pyrolysis reaction and promoting the thermal decomposition of magnesium sulfate.

[0028] In summary, the method provided by the present invention can significantly reduce the pyrolysis temperature of magnesium sulfate, reduce energy consumption, improve pyrolysis efficiency, simplify the magnesium sulfate pyrolysis process flow, and improve the purity of magnesium oxide without adding a reducing agent.

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent substitutions on the basis of understanding the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, shall all be covered within the protection scope of the present invention.

[0030] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For those reagents or instruments not specifying the manufacturer, they can all be obtained through commercial purchase. The remaining raw materials not mentioned and the commercial purchase selections of the instruments are all conventional selections and do not involve the core technical means of the present invention.

[0031] Example 1 Add magnesium sulfate heptahydrate to distilled water for dissolution, and then evaporate and recrystallize. Measure the impurity ion content in the recrystallized magnesium sulfate heptahydrate, and the purity of magnesium sulfate heptahydrate is ≥99.9 wt%.

[0032] Grind the recrystallized magnesium sulfate heptahydrate to a particle size of ≤0.1 mm. Spread the magnesium sulfate heptahydrate powder evenly in a platinum crucible, and the thickness of the powder layer is 0.2 mm.

[0033] Put the platinum crucible carrying the magnesium sulfate heptahydrate powder into a muffle furnace for calcination. Heat it at 300 °C for 4 h to obtain anhydrous magnesium sulfate. Then continue to heat it at 750 °C for 6 h to obtain high-purity magnesium oxide, and the purity of the magnesium oxide obtained in this example is ≥99.5 wt%.

[0034] Example 2 Add magnesium sulfate heptahydrate to distilled water for dissolution, and then evaporate and recrystallize. Measure the impurity ion content in the recrystallized magnesium sulfate heptahydrate, and the purity of magnesium sulfate heptahydrate is ≥99.9 wt%.

[0035] Grind the recrystallized magnesium sulfate heptahydrate to a particle size of ≤0.1 mm. Spread the magnesium sulfate heptahydrate powder evenly in a palladium crucible, and the thickness of the powder layer is 0.1 mm.

[0036] Put the palladium crucible carrying the magnesium sulfate heptahydrate powder into a muffle furnace for calcination. Heat it at 600 °C for 2 h to obtain anhydrous magnesium sulfate. Then continue to heat it at 950 °C for 4 h to obtain high-purity magnesium oxide, and the purity of the magnesium oxide obtained in this example is ≥99.8 wt%.

[0037] Example 3 Dissolve magnesium sulfate heptahydrate in distilled water, and then evaporate and recrystallize. Determine the content of impurity ions in the recrystallized magnesium sulfate heptahydrate, and the purity of magnesium sulfate heptahydrate is ≥99.9 wt%.

[0038] Grind the recrystallized magnesium sulfate heptahydrate to a particle size of ≤0.1 mm. Spread the magnesium sulfate heptahydrate powder evenly in a platinum crucible, and the thickness of the powder layer is 0.2 mm.

[0039] Put the platinum crucible containing the magnesium sulfate heptahydrate powder into a muffle furnace and calcine it. After heating to 400 °C, heat for 3 h to obtain anhydrous magnesium sulfate. Continue to heat to 850 °C and heat for 5 h to obtain high-purity magnesium oxide, and the purity of magnesium oxide is ≥99.6 wt%.

[0040] Example 4 The operation steps are the same as those in Example 3, except that: the magnesium sulfate hydrate is magnesium sulfate hexahydrate; the purity of magnesium sulfate hexahydrate is ≥99.9 wt%.

[0041] The purity of the magnesium oxide obtained in this example is ≥99.6 wt%.

[0042] Example 5 The operation steps are the same as those in Example 2, except that: the magnesium sulfate hydrate is magnesium sulfate monohydrate; the purity of magnesium sulfate monohydrate is ≥99.9 wt%.

[0043] The purity of the magnesium oxide obtained in this example is ≥99.7 wt%.

[0044] Comparative Example 1 The operation steps are the same as those in Example 2, except that: the thickness of the powder layer is 8 mm.

[0045] The purity of the magnesium oxide obtained in this comparative example is ≥96.8 wt%.

[0046] Comparative Example 2 The operation steps are the same as those in Example 2, except that: the magnesium sulfate heptahydrate powder is spread evenly in an alumina crucible.

[0047] The purity of the magnesium oxide obtained in this comparative example is ≥95.6 wt%.

[0048] Comparative Example 3 The operation steps are the same as those in Example 2, except that: the temperature of calcination and pyrolysis is 600 °C.

[0049] The purity of the magnesium oxide obtained in this comparative example is ≥94.3 wt%.

[0050] Comparative Example 4 The operation steps are the same as those in Example 2, except that: the temperature of calcination and pyrolysis is 1000 °C.

[0051] The purity of the magnesium oxide obtained in this comparative example is ≥ 99.8 wt%. Compared with Example 2, when the calcination pyrolysis temperature exceeds 950 °C, there is no obvious effect on improving the purity of the obtained magnesium oxide. However, too high a calcination pyrolysis temperature will increase energy consumption and economic costs.

[0052] All aspects, embodiments, features, and examples of the present invention should be considered illustrative in all respects and are not intended to limit the present invention, the scope of which is defined only by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will appreciate other embodiments, modifications, and uses.

[0053] In addition, the inventors of this case also referred to the foregoing embodiments and conducted tests using other raw materials, process operations, and process conditions described in this specification, and all obtained relatively ideal results.

[0054] Although the present invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the present invention, and elements of the embodiments can be replaced with substantial equivalents. Additionally, many modifications can be made without departing from the scope of the present invention to adapt a particular situation or material to the teachings of the present invention. Therefore, the present invention is not intended to be limited to the specific embodiments disclosed for carrying out the present invention, but is intended to cover all embodiments that fall within the scope of the appended claims.

Claims

1. A method for preparing high-purity magnesium oxide by low-temperature pyrolysis of magnesium sulfate, characterized in that, It includes: Calcining and pyrolyzing anhydrous magnesium sulfate under the catalysis of a noble metal to obtain high-purity magnesium oxide.

2. The method according to claim 1, wherein It includes: Recrystallizing and grinding a hydrated magnesium sulfate salt to obtain high-purity magnesium sulfate heptahydrate powder; Calcining and dehydrating the high-purity magnesium sulfate heptahydrate powder to obtain the anhydrous magnesium sulfate; Calcining and pyrolyzing the anhydrous magnesium sulfate under the catalysis of a noble metal to obtain high-purity magnesium oxide.

3. The method according to claim 2, wherein Specifically, it includes: Dissolving, evaporating, recrystallizing, and grinding the hydrated magnesium sulfate salt to obtain the high-purity magnesium sulfate heptahydrate powder.

4. The method according to claim 3, wherein: The particle size of the high-purity magnesium sulfate heptahydrate powder is ≤0.1 mm.

5. The method according to claim 2 or 3, characterized in that, Specifically, it includes: Laying the high-purity magnesium sulfate heptahydrate powder flat in a noble metal container, heating up for calcining and dehydrating to obtain the anhydrous magnesium sulfate.

6. The method according to claim 5, characterized in that: The thickness of the high-purity magnesium sulfate heptahydrate powder laid flat in the noble metal container does not exceed 2 mm; And / or, the temperature for calcining and dehydrating is 300 - 600 °C, and the time is 2 - 4 h; And / or, heating up to the temperature required for calcining and dehydrating at a rate of 2 - 20 °C / min.

7. The method according to claim 1, characterized in that: The temperature for calcining and pyrolyzing is 750 - 950 °C, and the time is 4 - 6 h; And / or, heating up to the temperature required for calcining and pyrolyzing at a rate of 2 - 20 °C / min.

8. The method according to claim 2, wherein: The hydrated magnesium sulfate salt includes at least any one of magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, and magnesium sulfate monohydrate.

9. The method according to claim 1 or 2, characterized in that: The noble metal includes any one of platinum and palladium.

10. The method according to claim 1, characterized in that: The purity of the high-purity magnesium oxide is ≥99.5 wt%.