Method for preparing high-purity magnesium oxide product by carbonizing and purifying light burning powder and product

Abstract

The invention discloses a method for preparing a high-purity magnesium oxide product by carbonizing and purifying light burning powder and the high-purity magnesium oxide product. The method comprises the following steps: putting first light burning powder and process water into a first reaction device, introducing process gas into the first reaction device, and reacting to obtain the heavy magnesium water. The heavy magnesium water is pretreated to obtain purified heavy magnesium water. And introducing the purified heavy magnesium water into a second reaction device to obtain slurry containing magnesium carbonate. And performing post-treatment on the slurry to obtain a first pre-product containing high-purity magnesium carbonate. Mixing the first pre-product and the second light burning powder, and performing compression molding to obtain furnace charge; or calcining the first pre-product to obtain a second pre-product containing high-purity magnesium oxide, mixing the second pre-product with second light burning powder, and then carrying out compression molding to obtain the furnace charge. And smelting or sintering the furnace charge to respectively prepare high-purity magnesium oxide products such as high-purity fused magnesium or high-purity sintered magnesia.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology, and particularly relates to a method for preparing high-purity magnesium oxide products by carbonization and purification of lightly calcined powder, and the high-purity magnesium oxide products prepared by applying this method. Background Technology

[0002] Magnesium oxide products such as sintered magnesia and fused magnesia are important raw materials for refractory materials. They are obtained by sintering raw materials such as magnesite ore or light calcined powder in a sintering furnace or melting furnace. Their purity is an important factor that determines the refractory performance, erosion resistance and high-temperature structural strength of the products.

[0003] High-purity magnesia products, such as high-purity sintered magnesia with a magnesia content exceeding 98% and high-purity fused magnesia, are high-end products with higher added value. They are widely used in high-temperature industries such as steel, cement, glass, and ceramics, and are important basic raw materials for refractory materials and magnesia chemical products. Currently, the production of high-purity sintered magnesia and high-purity fused magnesia mainly relies on high-quality magnesite as raw material. my country has some of the world's largest reserves of magnesite and other magnesium ores. However, due to years of large-scale mining and utilization, my country's high-grade magnesite resources (magnesia content ≥46%) are becoming increasingly depleted, and the reserves of high-quality magnesite are decreasing sharply. This has led to a continuous rise in the production costs of high-purity sintered magnesia and high-purity fused magnesia, severely restricting the development of related industries and putting the increasingly urgent demand for high-purity magnesia products in a difficult situation.

[0004] On the other hand, the mining and processing of magnesite generates a large amount of low-grade magnesite (magnesium oxide content 30%–45%) and tailings powder. Due to their high impurity content and difficulty in purification, these low-grade magnesium resources are difficult to utilize effectively using traditional processes and are usually dumped or landfilled as waste. This not only causes serious resource waste and low resource utilization rate but also leads to severe environmental problems. Statistics show that in recent years, the amount of magnesite tailings stockpiled in my country has reached hundreds of millions of tons, with an annual increase of over ten million tons. The long-term stockpiling of these tailings not only occupies a large amount of land resources, but the dust, heavy metals, and other pollutants within them also cause serious pollution to the surrounding soil, water bodies, and atmospheric environment, posing a significant environmental safety hazard. Furthermore, the calcination and light-burned powder production processes of magnesite release large amounts of carbon dioxide. These carbon dioxide emissions not only contribute to the greenhouse effect but also waste valuable carbon resources. How to recycle the carbon dioxide generated during production as a resource and achieve "turning waste into treasure" has become an urgent need for the green development of the magnesite industry.

[0005] Currently, the production of high-purity sintered magnesia and high-purity fused magnesium oxide mainly employs traditional purification processes such as flotation, gravity separation, and chemical precipitation to further increase the magnesium oxide content in raw materials based on high-grade ore. While these methods can improve the purity of magnesium oxide products to some extent, they have significant limitations, mainly in the following aspects: First, the process flow is complex, requiring large equipment investment and high energy consumption; second, it requires the use of large amounts of chemical reagents, generating secondary pollution; and third, the purification effect is limited, with poor adaptability to low-grade mineral raw materials and an inability to effectively utilize valuable components in tailings, leading to the industry's perception that such low-grade mineral raw materials cannot be used for the production of high-purity sintered magnesia and high-purity fused magnesium oxide. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a method for preparing high-purity sintered magnesia and high-purity fused magnesia products through carbonization and purification of light-burned powder. The method uses low-grade light-burned powder from low-grade magnesium resources as the main raw material and carbon dioxide emitted during mineral processing as a purifying agent. This method economically and efficiently prepares high-purity sintered magnesia and high-purity fused magnesia that meet the needs of high-end applications, effectively solving the problem of resource utilization of low-grade magnesite and tailings, as well as carbon dioxide generated during production.

[0007] This invention provides a method for preparing high-purity magnesium oxide by carbonization and purification of light-burned powder, comprising: S1, feeding a first light-burned powder and process water into a first reaction device, and introducing process gas into the first reaction device, and obtaining heavy magnesium water through a carbonization reaction, wherein the process gas contains carbon dioxide; S2, pretreating the heavy magnesium water to remove impurities, thereby obtaining purified heavy magnesium water; S3, introducing the purified heavy magnesium water into a second reaction device, and obtaining a slurry containing magnesium carbonate through a pyrolysis reaction; S4, posttreating the slurry to obtain a first pre-product. The product contains high-purity magnesium carbonate; S5, the first preproduct and the second light calcined powder are mixed and then pressed into shape to obtain furnace charge, or the first preproduct is calcined to obtain the second preproduct, the second preproduct and the second light calcined powder are mixed and then pressed into shape to obtain furnace charge, the second preproduct contains high-purity magnesium oxide; S6, the furnace charge is charged into an electric melting furnace for smelting to produce a high-purity magnesium oxide product, the high-purity magnesium oxide product is high-purity fused magnesium, or the furnace charge is charged into a sintering furnace for sintering to produce a high-purity magnesium oxide product, the high-purity magnesium oxide product is high-purity sintered magnesia.

[0008] In one possible implementation, the process gas includes at least one of the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering of carbonate minerals and the combustion exhaust gas generated during fuel combustion, so that the flue gas and combustion exhaust gas can be directly utilized as resources. In a preferred embodiment, the flue gas used is the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering of magnesium ores such as magnesite, magnesite tailings, or dolomite.

[0009] In one possible implementation, the process gas includes at least one of the following: calcination flue gas generated during the calcination preparation of the first light calcined powder and / or the second light calcined powder; flue gas generated during the pyrolysis reaction in S3; flue gas generated during the calcination of the first preproduct in S5; and flue gas generated during the melting or sintering of the furnace charge in S6.

[0010] In one possible implementation, the process gas is directly used as flue gas or combustion exhaust gas, and is directly introduced into the first reaction unit without any treatment.

[0011] In one possible implementation, the process gas is flue gas or combustion tail gas, which is then subjected to heat exchange and / or purification before being introduced into the first reaction unit.

[0012] The process gas used in this application can be the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering of carbonate minerals, or the combustion exhaust gas generated during fuel combustion. This transforms waste into valuable resources. While meeting the process gas requirements of this method, it also achieves the recovery and industrial reuse of large quantities of flue gas or exhaust gas generated in the chemical industry. It realizes the resource utilization of calcination flue gas and combustion exhaust gas from magnesite, dolomite, and other magnesium ores, and saves the significant energy consumption required for the emission reuse of calcination flue gas and combustion exhaust gas using traditional technologies. In one implementation of this application, the flue gas generated in the method step can even be used as the process gas in step S1, achieving closed-loop recycling of waste gas within the preparation process. This provides a practical and feasible integrated solution of "exhaust gas treatment - mineral processing" for carbon reduction and closed-loop product preparation in the chemical industry. Taking a magnesite plant as an example, using the technology of this application can reduce CO2 emissions by more than 90%, save energy by about 40%, achieve a solid waste comprehensive utilization rate of nearly 100%, and reduce the cost per ton of product by about 28%, demonstrating significant environmental and economic benefits.

[0013] In one possible implementation, the post-processing in S4 includes at least one of filtration and drying.

[0014] In one possible implementation, the second preproduct contains more than 98.5% magnesium oxide by mass.

[0015] In one possible implementation, the magnesium oxide content of the second light-burned powder is not less than 95%; the magnesium oxide content of the first light-burned powder is lower than that of the second light-burned powder. In a preferred embodiment, the magnesium oxide content of the first light-burned powder is 35% to 95%, preferably 70% to 85%.

[0016] In one possible implementation, the first lightly calcined powder is prepared from at least one of low-grade magnesite and tailings powder. In a preferred embodiment, the magnesium oxide content in the low-grade magnesite and tailings powder is in the range of 30% to 45%.

[0017] In one possible implementation, when the first preproduct and the second light calcined powder are mixed, the mass ratio between the first preproduct and the second light calcined powder is in the range of (7 to 10):1.

[0018] In one possible implementation, when the second preproduct and the second light calcined powder are mixed, the mass ratio between the second preproduct and the second light calcined powder is in the range of (3.5 to 5):1.

[0019] In one possible implementation, when the charge is loaded into an electric furnace for melting, the melting temperature of the charge in the electric furnace is 2800°C to 2850°C.

[0020] In one possible implementation, when the charge is loaded into the sintering furnace for sintering, the sintering temperature of the charge in the sintering furnace is 1800°C to 1850°C.

[0021] In one possible implementation, the high-purity magnesium oxide product prepared by this method has a magnesium oxide content of over 98.2%.

[0022] In one possible implementation, the pressure of the carbonization reaction is 0.05 MPa to 0.8 MPa, more preferably, the pressure of the carbonization reaction is 0.1 MPa to 0.5 MPa; the reaction temperature of the carbonization reaction is in the range of 10°C to 60°C, more preferably, the reaction temperature of the carbonization reaction is in the range of 20°C to 30°C; and the carbonization residence time is 15 min to 180 min, more preferably, the carbonization residence time is 20 min to 60 min.

[0023] In one possible implementation, the furnace charge is in the form of spheres or blocks.

[0024] In one possible implementation, the pyrolysis reaction in S3 is selected from either low-temperature vacuum pyrolysis or high-temperature atmospheric pressure pyrolysis.

[0025] In one possible implementation, the pyrolysis reaction is a low-temperature vacuum pyrolysis, the working vacuum degree in the second reaction device is 0.01MPa to 0.09MPa, preferably 0.01MPa to 0.06MPa, and the reaction temperature of the low-temperature vacuum pyrolysis reaction is in the range of 30℃ to 65℃, preferably 40℃ to 50℃.

[0026] In one possible implementation, in S2, the pretreatment includes coarse filtration and fine filtration. Coarse filtration removes large particulate insoluble impurities from the heavy magnesium hydroxide solution, while fine filtration removes colloidal impurities.

[0027] Through pretreatment, the impurity content in the purified magnesium hydroxide solution is controlled to be ≤45mg / L for calcium oxide, ≤10mg / L for iron oxide, and ≤20mg / L for chloride ions. The purified magnesium hydroxide solution is clear and transparent. Using the pretreated purified magnesium hydroxide solution as raw material, the content of several major impurities in the first preproduct obtained through steps S3 and S4 is controlled to be within an ultra-low level range of less than 0.2% for calcium oxide, less than 0.01% for iron oxide, and less than 0.1% for chloride ions. In the first preproduct, the purity of high-purity magnesium carbonate is above 98.5%.

[0028] Based on the first preproduct with high purity and low impurity content, the high-purity magnesium oxide product obtained has a magnesium oxide content of over 98.2%, and the contents of several major impurities are controlled within an ultra-low range: calcium oxide below 0.6%, iron oxide below 0.35%, aluminum oxide below 0.3%, and silicon dioxide below 0.3%.

[0029] In one possible implementation, the post-processing in S4 includes drying at a temperature above 100°C.

[0030] Lightly calcined powder refers to magnesium ore such as magnesite, magnesite tailings, or dolomite obtained through calcination, with magnesium oxide as its main component. The calcination process can be calcination in a suspension kiln, a direct-fired rotary kiln, or an indirect-fired rotary kiln. In a preferred embodiment, calcination in a suspension kiln is used.

[0031] Magnesium bicarbonate solution refers to an aqueous solution of magnesium bicarbonate (Mg(HCO3)2).

[0032] This invention uses low-grade light-burned powder from low-grade magnesite and tailings powder as the main raw material, and creatively adopts a hydrometallurgical approach to purify it. Through a unique dissolution-purification-pyrolysis process, magnesium elements in the solid light-burned powder are efficiently transferred to the liquid phase. Then, impurities in the liquid phase are removed by filtration to obtain purified heavy magnesium water. Based on the purified heavy magnesium water, a pre-product containing high-purity magnesium carbonate and / or high-purity magnesium oxide is prepared to achieve purification. Furthermore, high-purity fused magnesium and high-purity sintered magnesia products such as high-purity fused magnesium and high-purity sintered magnesia are then prepared. This method completely overturns the industry's perception that low-grade mineral raw materials such as low-grade ore and tailings powder cannot be used in the production of high-purity sintered magnesia and high-purity fused magnesium. It overcomes the technical difficulties such as high energy consumption and high pollution in the purification and utilization of low-grade mineral raw materials, breaks through the traditional model and concept of "high energy consumption, high pollution, and low added value" in the purification of low-grade mineral raw materials, and provides a new path for the efficient utilization of low-grade magnesium ore. It enables the large accumulation of low-grade ore and tailings to regain higher-end industrial utilization value, greatly improves the added value of magnesite resources, and is conducive to improving the unbalanced utilization of magnesium resources in my country and increasing the comprehensive utilization rate of magnesium resources in my country.

[0033] During its research and development, the applicant discovered through microscopic testing and analysis that if the purity of electrofused or sintered raw materials such as lightly calcined powder does not reach a certain level, it will not only ultimately limit the purity of high-purity magnesium oxide products but also cause an increase in melt viscosity. Furthermore, impurities such as aluminum, calcium, and iron entering the grain boundaries will hinder the full growth of periclase (MgO) crystals, thus affecting the performance of the magnesia products. Therefore, although existing technologies for preparing high-purity sintered magnesia and high-purity electrofused magnesium achieve a certain level of purity, their refractoriness, erosion resistance, and high-temperature structural strength are always difficult to further approach theoretical levels, thus creating a subtle technical bottleneck in the preparation of high-purity magnesium oxide products with superior performance. In addition, although magnesium carbonate, as a high-purity magnesium source, can yield high-purity active magnesium oxide after decomposition, the applicant found that if magnesium carbonate is sintered or electrofused alone, its low bulk density leads to severe foaming and intense gas escape during melting, making it difficult to stably implement the process and obtain dense, high-purity magnesium oxide products. To address the aforementioned two issues, the applicant, through research and development, solved the purification problem of raw materials for electrofusion and sintering by adopting a hydrometallurgical approach. Furthermore, it addressed the challenge of stable implementation when using high-purity magnesium carbonate as a single raw material for sintering and electrofusion by mixing and briquetting the first or second pre-product with a second light-burned powder of over 95% purity. Ultimately, this approach achieved complementary advantages among multiple raw materials, including low-grade light-burned powder, high-purity pre-products, and second light-burned powder, in the entire preparation method. While ensuring the high purity of the pre-products, it also solved the process stability problem of high-purity magnesium carbonate and high-purity magnesium oxide in sintering and electrofusion, significantly reducing overall energy consumption. This resulted in the production of high-quality, high-purity electrofused magnesium and high-purity sintered magnesia products, possessing a purity of over 98.2% and performance closer to theoretical levels, making them more suitable for high-end applications. Because of the gradient differences in physical properties such as density and particle surface state between the second calcined powder and the first or second preproduct powder, a complementary coupling effect is formed between the second calcined powder and the preproduct powder when they are mixed. This improves the overall flowability of the powder during the pressing process, thereby increasing the bulk density of the mixed furnace charge, reducing micro-voids in the charge, and solving the problems of severe foaming and violent gas escape during the melting process, thus enabling the process to be implemented stably. The applicant has found that in order to achieve the best technical effect in the method of this application, the mixing ratio of the second calcined powder and the first or second preproduct needs to be within a certain range, and this range needs to have a specific matching relationship with the composition of the preproduct.For example, for the first preproduct whose main component is high-purity magnesium carbonate, the mass ratio between the first preproduct and the second light calcined powder needs to be in the range of (7-10):1; for the second preproduct whose main component is high-purity magnesium oxide, the mass ratio between the second preproduct and the second light calcined powder needs to be in the range of (3.5-5):1.

[0034] This application also provides a high-purity magnesium oxide product, which is prepared by the above-mentioned method of carbonization and purification of light-burned powder to prepare high-purity magnesium oxide.

[0035] In one possible implementation, the magnesium oxide content of high-purity magnesium oxide products such as high-purity fused magnesium and high-purity sintered magnesia is above 98.2%.

[0036] The beneficial effects of this invention are: This invention proposes a novel method for carbonizing and purifying low-grade lightly calcined magnesite powder using carbon dioxide emitted during mineral processing as a purifying agent to produce high-purity magnesite and high-purity fused magnesium. This method not only effectively solves the resource utilization problem of low-grade magnesite and tailings, but also recycles the carbon dioxide emitted during the production process as a purifying agent, achieving the green circular development goal of "treating waste with waste and turning waste into treasure," resulting in significant economic, environmental, and social benefits.

[0037] (1) "Turning waste into treasure" and making efficient use of low-grade resources This invention creatively uses low-grade lightly calcined magnesite powder (magnesium oxide content 30%–45%) from low-grade magnesium resources as the main raw material, and purifies and utilizes it through a hydrometallurgical approach. This breaks through the dependence of traditional processes on high-grade mineral raw materials, realizes the efficient utilization of low-grade magnesite and tailings powder, greatly improves the added value of low-grade magnesium resources, and effectively solves the problem of resource waste.

[0038] (2) Carbon dioxide as a purification agent Using carbon dioxide emitted during mineral processing as a purifying agent, magnesium oxide in low-grade light-burned powder is converted into high-purity magnesium carbonate through a carbonation reaction, thereby separating and purifying impurities. This not only solves the carbon dioxide emission problem but also reduces purification costs and realizes the recycling of carbon dioxide resources.

[0039] (3) Product purity has been significantly improved Through a unique dissolution-purification-pyrolysis process, magnesium is effectively separated from most insoluble impurities such as Si, Ca, Fe, and Al, resulting in a high purity magnesium carbonate of over 98.5%. Consequently, the purity of the high-purity magnesium oxide product obtained is significantly higher than that of magnesia sand prepared solely using lightly calcined powder, allowing the magnesium oxide content in high-purity sintered magnesia sand and high-purity fused magnesium products to easily reach over 98.2%.

[0040] (4) The process is simple and the energy consumption cost is controllable. The main raw materials for this preparation method are inexpensive low-grade light calcined powder and process gas containing carbon dioxide. The process gas can utilize industrial waste gas. Furthermore, the process route is short, energy consumption is low, and operation is simple, which significantly reduces production costs.

[0041] (5) Environmentally friendly The entire process features a closed-loop circulation system, generating no large amounts of high-salt wastewater. Filtered impurities can be used as raw materials for building materials, and waste gas can be internally recycled, achieving green and clean production. Carbon dioxide is effectively utilized as a purification agent, reducing greenhouse gas emissions and meeting the requirements of the national "dual-carbon" strategy.

[0042] (6) Significant economic advantages Compared with traditional processes, the method of this invention has lower raw material costs, lower energy consumption, and less equipment investment, and can reduce overall production costs by more than 30%, giving the product a significant economic competitive advantage.

[0043] (7) High degree of comprehensive utilization of resources The method of this invention not only recovers magnesium resources from low-grade magnesite, but also achieves complete utilization of tailings powder, with a comprehensive resource utilization rate of over 95%, truly realizing "making the most of everything".

[0044] (8) It has wide technical adaptability and broad prospects for industrial application. The method of this invention is applicable to magnesite raw materials of different grades, has strong adaptability to raw materials, high technical maturity, simple process equipment, and is easy to realize industrial production. It can provide the magnesite industry with a green, efficient, and low-cost high-purity magnesia production technology route, and can be widely applied to the technical transformation and upgrading of existing magnesite mining enterprises. It has good prospects for promotion and application, and promotes the transformation and upgrading of the industry.

[0045] (9) The final product has excellent performance. The high-purity magnesium oxide product of this invention is produced using the method of this invention. Its pre-products (high-purity magnesium carbonate and high-purity magnesium oxide) have extremely high purity, and the high-purity fused magnesium or high-purity sintered magnesia obtained after electrofusion or sintering has well-developed crystals, a denser structure, and a larger grain size. It can simultaneously possess stable high purity of over 98.2% and excellent performance closer to the theoretical level, resulting in higher quality and suitability for high-end applications such as high-end refractory products with stringent performance requirements.

[0046] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0047] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements, and the drawings do not constitute a limitation of scale. Wherein: Figure 1 This is a schematic flowchart of a method for preparing high-purity magnesium oxide products by carbonization and purification of lightly calcined powder, as provided in an embodiment of this application. Detailed Implementation

[0048] The specific embodiments of the present invention are further described below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the following description, for ease of explanation, several details are used to provide a full understanding of the invention. However, the invention can still be practiced without these details. In other instances, well-known structures and apparatuses may be shown in a simplified manner to simplify the drawings.

[0049] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein.

[0050] In this invention, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this invention and are not intended to limit the indicated device, element, or component to having a specific orientation, or to require it to be constructed and operated in a specific orientation. Furthermore, some of the aforementioned terms may have other meanings besides indicating orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0051] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] like Figure 1 As shown in the embodiments of this application, a method for preparing high-purity magnesium oxide products by carbonization and purification of lightly calcined powder is provided. The method includes: S1, the first light calcined powder and process water are put into the first reaction device, and process gas containing carbon dioxide is introduced into the first reaction device. After carbonization reaction, heavy magnesium water is obtained.

[0053] S2, pretreatment of the magnesium hydroxide solution to remove impurities and obtain purified magnesium hydroxide solution.

[0054] S3, purified magnesium hydroxide solution is passed into the second reaction device, and a slurry containing magnesium carbonate is obtained through pyrolysis reaction.

[0055] S4. The slurry is post-processed to obtain a first pre-product containing high-purity magnesium carbonate.

[0056] S5, the first preproduct and the second light calcined powder are mixed and then pressed into shape to obtain the furnace charge; or, the first preproduct is calcined to obtain a second preproduct containing high-purity magnesium oxide, the second preproduct and the second light calcined powder are mixed and then pressed into shape to obtain the furnace charge.

[0057] S6, the furnace charge is loaded into an electric melting furnace for smelting to produce high-purity fused magnesium; or, the furnace charge is loaded into a sintering furnace for sintering to produce high-purity sintered magnesia.

[0058] In one implementation, the process gas includes at least one of the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering of carbonate minerals and the combustion exhaust gas generated during the fuel combustion process, so that the flue gas and combustion exhaust gas can be directly utilized as resources.

[0059] In a preferred embodiment, the flue gas used is the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering process of magnesium ores such as magnesite, magnesite tailings, or dolomite.

[0060] In one implementation, the process gas includes at least one of the following: calcination flue gas generated during the calcination preparation of the first light calcined powder and / or the second light calcined powder; flue gas generated during the pyrolysis reaction in S3; flue gas generated during the calcination of the first preproduct in S5; and flue gas generated during the melting or sintering of the furnace charge in S6.

[0061] In one implementation, the process gas is directly flue gas or combustion exhaust gas, which is introduced directly into the first reaction unit without any treatment.

[0062] In one implementation, the process gas is flue gas or combustion exhaust gas, which is then subjected to heat exchange and / or purification before being introduced into the first reaction unit.

[0063] The process gas used in this application can be the flue gas generated during the calcination, pyrolysis, electrofusion, or sintering of carbonate minerals, or the combustion exhaust gas generated during fuel combustion. This transforms waste into valuable resources. While meeting the process gas requirements of this method, it also achieves the recovery and industrial reuse of large quantities of flue gas or exhaust gas generated in the chemical industry. It realizes the resource utilization of calcination flue gas and combustion exhaust gas from magnesite, dolomite, and other magnesium ores, and saves the significant energy consumption required for the emission reuse of calcination flue gas and combustion exhaust gas using traditional technologies. In one implementation of this application, the flue gas generated in the method step can even be used as the process gas in step S1, achieving closed-loop recycling of waste gas within the preparation process. This provides a practical and feasible integrated solution of "exhaust gas treatment - mineral processing" for carbon reduction and closed-loop product preparation in the chemical industry. Taking a magnesite plant as an example, using the technology of this application can reduce CO2 emissions by more than 90%, save energy by about 40%, achieve 100% comprehensive utilization of solid waste, and reduce the cost per ton of product by about 28%, demonstrating significant environmental and economic benefits.

[0064] In one implementation, the post-processing in S4 includes at least one of filtration and drying.

[0065] In one implementation, the second preproduct contains at least 98.5% magnesium oxide by mass.

[0066] In one implementation, the magnesium oxide content of the second light-burned powder is not less than 95%; the magnesium oxide content of the first light-burned powder is lower than that of the second light-burned powder.

[0067] In a preferred embodiment, the magnesium oxide content of the first lightly calcined powder is 35% to 95%, preferably 70% to 85%.

[0068] In one implementation, the first lightly calcined powder is prepared from at least one of low-grade magnesite and tailings powder.

[0069] In a preferred embodiment, the magnesium oxide content in the low-grade magnesite and tailings powder is in the range of 30% to 45%.

[0070] In one implementation, when the first preproduct and the second light calcined powder are mixed, the mass ratio between the first preproduct and the second light calcined powder is in the range of (7 to 10):1.

[0071] In one implementation, when the second preproduct and the second light calcined powder are mixed, the mass ratio between the second preproduct and the second light calcined powder is in the range of (3.5 to 5):1.

[0072] In one implementation, when the charge is loaded into an electric furnace for melting, the melting temperature of the charge in the electric furnace is 2800°C to 2850°C.

[0073] In one implementation, when the charge is loaded into a sintering furnace for sintering, the sintering temperature of the charge in the sintering furnace is 1800°C to 1850°C.

[0074] In one implementation, the high-purity magnesium oxide product prepared by this method has a magnesium oxide content of over 98.2%.

[0075] In one implementation, the carbonization reaction pressure is 0.05 MPa to 0.8 MPa, more preferably, the carbonization reaction pressure is 0.1 MPa to 0.5 MPa; the carbonization reaction temperature is in the range of 10°C to 60°C, more preferably, the carbonization reaction temperature is in the range of 20°C to 30°C; and the carbonization residence time is 15 min to 180 min, more preferably, the carbonization residence time is 20 min to 60 min.

[0076] In one implementation, the furnace charge is in spherical or block form.

[0077] In one implementation, the pyrolysis reaction in S3 is selected from either low-temperature vacuum pyrolysis or high-temperature atmospheric pressure pyrolysis.

[0078] In one implementation, the pyrolysis reaction is a low-temperature vacuum pyrolysis, the working vacuum degree in the second reaction device is 0.01MPa to 0.09MPa, preferably 0.01MPa to 0.06MPa, and the reaction temperature of the low-temperature vacuum pyrolysis reaction is in the range of 30℃ to 65℃, preferably 40℃ to 50℃.

[0079] In one implementation, in step S2, the pretreatment includes coarse filtration and fine filtration. Coarse filtration removes large particulate insoluble impurities from the magnesium hydroxide solution, while fine filtration removes colloidal impurities from the magnesium hydroxide solution.

[0080] Through pretreatment, the impurity content in the purified magnesium hydroxide solution is controlled to be ≤45mg / L for calcium oxide, ≤10mg / L for iron oxide, and ≤20mg / L for chloride ions. The purified magnesium hydroxide solution is clear and transparent. Using the pretreated purified magnesium hydroxide solution as raw material, the content of several major impurities in the first preproduct obtained through steps S3 and S4 is controlled to be within an ultra-low level range of less than 0.2% for calcium oxide, less than 0.01% for iron oxide, and less than 0.1% for chloride ions. In the first preproduct, the purity of high-purity magnesium carbonate is above 98.5%.

[0081] Based on the first preproduct with high purity and low impurity content, the high-purity magnesium oxide product obtained has a magnesium oxide content of over 98.2%, and the contents of several major impurities are controlled within an ultra-low range: calcium oxide below 0.6%, iron oxide below 0.35%, aluminum oxide below 0.3%, and silicon dioxide below 0.3%.

[0082] In one implementation, the post-processing in S4 includes drying at a temperature above 100°C.

[0083] Lightly calcined powder refers to magnesium ore such as magnesite, magnesite tailings, or dolomite obtained through calcination, with magnesium oxide as its main component. The calcination process can be calcination in a suspension kiln, a direct-fired rotary kiln, or an indirect-fired rotary kiln. In a preferred embodiment, calcination in a suspension kiln is used.

[0084] Magnesium bicarbonate solution refers to an aqueous solution of magnesium bicarbonate (Mg(HCO3)2).

[0085] This invention uses low-grade light-burned powder from low-grade magnesite and tailings powder as the main raw material, and creatively adopts a hydrometallurgical approach to purify it. Through a unique dissolution-purification-pyrolysis process, magnesium elements in the solid light-burned powder are efficiently transferred to the liquid phase. Then, impurities in the liquid phase are removed by filtration to obtain purified heavy magnesium water. Based on the purified heavy magnesium water, a pre-product containing high-purity magnesium carbonate and / or high-purity magnesium oxide is prepared to achieve purification. Furthermore, high-purity fused magnesium and high-purity sintered magnesia products such as high-purity fused magnesium and high-purity sintered magnesia are then prepared. This method completely overturns the industry's perception that low-grade mineral raw materials such as low-grade ore and tailings powder cannot be used in the production of high-purity sintered magnesia and high-purity fused magnesium. It overcomes the technical difficulties such as high energy consumption and high pollution in the purification and utilization of low-grade mineral raw materials, breaks through the traditional model and concept of "high energy consumption, high pollution, and low added value" in the purification of low-grade mineral raw materials, and provides a new path for the efficient utilization of low-grade magnesium ore. It enables the large accumulation of low-grade ore and tailings to regain higher-end industrial utilization value, greatly improves the added value of magnesite resources, and is conducive to improving the unbalanced utilization of magnesium resources in my country and increasing the comprehensive utilization rate of magnesium resources in my country.

[0086] During its research and development, the applicant discovered through microscopic testing and analysis that if the purity of electrofused or sintered raw materials such as lightly calcined powder does not reach a certain level, it will not only ultimately limit the purity of high-purity magnesium oxide products but also cause an increase in melt viscosity. Furthermore, impurities such as aluminum, calcium, and iron entering the grain boundaries will hinder the full growth of periclase (MgO) crystals, thus affecting the performance of the magnesia products. Therefore, although existing technologies for preparing high-purity sintered magnesia and high-purity electrofused magnesium achieve a certain level of purity, their refractoriness, erosion resistance, and high-temperature structural strength are always difficult to further approach theoretical levels, thus creating a subtle technical bottleneck in the preparation of high-purity magnesium oxide products with superior performance. In addition, although magnesium carbonate, as a high-purity magnesium source, can yield high-purity active magnesium oxide after decomposition, the applicant found that if magnesium carbonate is sintered or electrofused alone, its low bulk density leads to severe foaming and intense gas escape during melting, making it difficult to stably implement the process and obtain dense, high-purity magnesium oxide products. To address the aforementioned two issues, the applicant, through research and development, solved the purification problem of raw materials for electrofusion and sintering by adopting a hydrometallurgical approach. Furthermore, it addressed the challenge of stable implementation when using high-purity magnesium carbonate as a single raw material for sintering and electrofusion by mixing and briquetting the first or second pre-product with a second light-burned powder of over 95% purity. Ultimately, this approach achieved complementary advantages among multiple raw materials, including low-grade light-burned powder, high-purity pre-products, and second light-burned powder, in the entire preparation method. While ensuring the high purity of the pre-products, it also solved the process stability problem of high-purity magnesium carbonate and high-purity magnesium oxide in sintering and electrofusion, significantly reducing overall energy consumption. This resulted in the production of high-quality, high-purity electrofused magnesium and high-purity sintered magnesia products, possessing a purity of over 98.2% and performance closer to theoretical levels, making them more suitable for high-end applications. Because of the gradient differences in physical properties such as density and particle surface state between the second calcined powder and the first or second preproduct powder, a complementary coupling effect is formed between the second calcined powder and the preproduct powder when they are mixed. This improves the overall flowability of the powder during the pressing process, thereby increasing the bulk density of the mixed furnace charge, reducing micro-voids in the charge, and solving the problems of severe foaming and violent gas escape during the melting process, thus enabling the process to be implemented stably. The applicant has found that in order to achieve the best technical effect in the method of this application, the mixing ratio of the second calcined powder and the first or second preproduct needs to be within a certain range, and this range needs to have a specific matching relationship with the composition of the preproduct.For example, for the first preproduct whose main component is high-purity magnesium carbonate, the mass ratio between the first preproduct and the second light calcined powder needs to be in the range of (7-10):1; for the second preproduct whose main component is high-purity magnesium oxide, the mass ratio between the second preproduct and the second light calcined powder needs to be in the range of (3.5-5):1.

[0087] This application also provides a high-purity magnesium oxide product, which is prepared by the above-mentioned method of carbonization and purification of light-burned powder to prepare high-purity magnesium oxide.

[0088] In one implementation, the magnesium oxide content of high-purity magnesium oxide products such as high-purity fused magnesium and high-purity sintered magnesia is above 98.2%.

[0089] The following are specific examples of the present invention: Example 1

[0090] (1) 400 kg of low-grade light calcined powder with a magnesium oxide content of 80% and an appropriate amount of process water are added to the first reaction device, and CO2 gas is introduced into the first reaction device at 0.3 MPa until the solution is saturated. After the carbonization reaction is complete, heavy magnesium water is obtained.

[0091] (2) The magnesium hydroxide solution is first coarsely filtered by means of plate and frame filter press to remove large insoluble impurities in the magnesium hydroxide solution, and then finely filtered by means of precision filter to obtain clear and transparent purified magnesium hydroxide solution.

[0092] (3) The purified heavy magnesium water is introduced into the second reaction device and carried out a low-temperature vacuum pyrolysis reaction under the conditions of pressure of 0.03MPa, reaction temperature of 45℃, stirrer speed of 100rpm and reaction time of 3h to obtain a slurry containing magnesium carbonate.

[0093] (4) After the reaction was completed, the resulting white slurry containing magnesium carbonate was filtered and then dried at 105°C for 5 hours to obtain high-purity magnesium carbonate. Chemical analysis showed that the purity of the high-purity magnesium carbonate reached 99%.

[0094] (5) The high-purity magnesium carbonate and lightly calcined powder with a magnesium oxide content of 95% are mixed at a mass ratio of 10:1 and pressed into spherical furnace charge.

[0095] (6) The furnace charge is placed in an electric melting furnace and smelted at 2850°C for 5 hours. After cooling, a high-purity fused magnesium product is obtained.

[0096] Chemical analysis revealed that the obtained high-purity fused magnesium product contained 98.5% magnesium oxide. The main impurities were: silicon dioxide 0.25%, iron oxide 0.25%, calcium oxide 0.4%, and aluminum oxide 0.2%, with a total impurity content below 1.3%. The product exhibited a dense and uniform particle structure with a bulk density of 3.55 g / cm³. 3 The average grain size is approximately 450 μm. The product meets the industrial application requirements for high-purity fused magnesium. Example 2

[0097] Steps (1) to (4) are the same as in Example 1.

[0098] (5) High-purity magnesium carbonate is calcined to obtain high-purity magnesium oxide. Chemical analysis shows that the magnesium oxide content in the high-purity magnesium oxide reaches 99%. The high-purity magnesium oxide is mixed with light-burned powder with a magnesium oxide content of 95% at a mass ratio of 5:1 and pressed into spherical furnace charge.

[0099] (6) The furnace charge is placed in an electric melting furnace and smelted at 2850°C for 5 hours. After cooling, a high-purity fused magnesium product is obtained.

[0100] Chemical analysis revealed that the obtained high-purity fused magnesium product contained 98.8% magnesium oxide. The main impurities were: silicon dioxide 0.2%, iron oxide 0.2%, calcium oxide 0.35%, and aluminum oxide 0.15%, with a total impurity content below 1%. The product exhibited a dense and uniform particle structure with a bulk density of 3.57 g / cm³. 3 The average grain size is approximately 470 μm. The product meets the industrial application requirements for high-purity fused magnesium. Example 3

[0101] Steps (1) to (5) are the same as in Example 1.

[0102] (6) The furnace charge is placed in a sintering furnace and sintered at 1850°C for 2 hours. After cooling, a high-purity sintered magnesia product is obtained.

[0103] Chemical analysis revealed that the obtained high-purity sintered magnesia product contained 98.3% magnesium oxide. The main impurities were: silicon dioxide 0.15%, iron oxide 0.35%, calcium oxide 0.35%, and aluminum oxide 0.3%, with a total impurity content below 1.4%. The product exhibited a dense and uniform particle structure with a bulk density of 3.45 g / cm³. 3 The average grain size is approximately 180 μm. The product meets the industrial application requirements for high-purity sintered magnesia. Example 4

[0104] Steps (1) to (5) are the same as in Example 2.

[0105] (6) The furnace charge is placed in a sintering furnace and sintered at 1850°C for 2 h. After cooling, a high-purity sintered magnesia product is obtained.

[0106] Chemical analysis revealed that the obtained high-purity sintered magnesia product contained 98.5% magnesium oxide. The main impurities were: silicon dioxide 0.15%, iron oxide 0.3%, calcium oxide 0.3%, and aluminum oxide 0.25%, with a total impurity content below 1.2%. The product exhibited a dense and uniform particle structure with a bulk density of 3.47 g / cm³. 3 The average grain size is approximately 185 μm. The product meets the industrial application requirements for high-purity sintered magnesia.

[0107] Comparative Example 1 Lightly calcined magnesium powder with a magnesium oxide content of 95% was directly smelted at 2850°C for 5 hours. After cooling, fused magnesium was obtained. The resulting fused magnesium contained only 96.5% magnesium oxide, and the contents of several major impurities were: silicon dioxide 1.0%, iron oxide 0.5%, calcium oxide 1.4%, and aluminum oxide 0.45%. The bulk density of the product was 3.28 g / cm³. 3 The average grain size is about 120 μm, and it contains a large amount of low-melting-point phases such as silicates. Its performance is far lower than that of the high-purity fused magnesium products obtained in Example 1 and Example 2.

[0108] Comparative Example 2 Lightly calcined powder with a magnesium oxide content of 95% was directly used and sintered at 1850°C for 2.5 hours. After cooling, sintered magnesia was obtained. The magnesium oxide content in the obtained sintered magnesia was only 96.2%, and the contents of several major impurities were: silicon dioxide 1.1%, iron oxide 0.5%, calcium oxide 1.5%, and aluminum oxide 0.6%. The bulk density of the product was 3.25 g / cm³. 3 The average grain size is about 125 μm, and it contains a large amount of low-melting-point phases such as silicates. Its performance is far lower than that of the high-purity sintered magnesia products obtained in Examples 3 and 4.

[0109] As can be seen from Examples 1 to 4 and Comparative Examples 1 and 2, the pre-products (high-purity magnesium carbonate and high-purity magnesium oxide) obtained by the method of the present invention have extremely high purity. Moreover, the crystals of the high-purity fused magnesium or high-purity sintered magnesia products obtained after electrofusion or sintering are better developed, have a denser structure, and larger grain size than the products obtained in the comparative examples. They can simultaneously possess stable high purity of over 98.2% and excellent performance closer to the theoretical level, resulting in higher quality products that can be used in high-end application fields such as high-end refractory products with stringent performance requirements.

[0110] The embodiments of the present invention are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing high-purity magnesium oxide products by carbonization and purification of lightly calcined powder, characterized in that, include: S1, the first light calcined powder and process water are put into the first reaction device, and process gas is introduced into the first reaction device. After carbonization reaction, heavy magnesium water is obtained; the process gas contains carbon dioxide. S2, pretreatment of the magnesium hydroxide solution to remove impurities and obtain purified magnesium hydroxide solution; S3, the purified magnesium hydroxide solution is passed into the second reaction device and a slurry containing magnesium carbonate is obtained through pyrolysis reaction; S4, the slurry is post-processed to obtain the first preproduct, which contains high-purity magnesium carbonate; S5, the first preproduct and the second light calcined powder are mixed and then pressed into shape to obtain the furnace charge; or, the first preproduct is calcined to obtain the second preproduct, the second preproduct and the second light calcined powder are mixed and then pressed into shape to obtain the furnace charge, wherein the second preproduct contains high-purity magnesium oxide. S6, the furnace charge is loaded into an electric melting furnace for smelting to produce high-purity magnesium oxide products, which are high-purity fused magnesium oxide products; or, the furnace charge is loaded into a sintering furnace for sintering to produce high-purity magnesium oxide products, which are high-purity sintered magnesia products.

2. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, Process gases include at least one of the flue gas generated during the calcination, pyrolysis, electrofusion or sintering of carbonate minerals and the combustion exhaust gas generated during the fuel combustion process.

3. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, The process gases include at least one of the following: calcination flue gas generated during the calcination preparation of the first light calcined powder and / or the second light calcined powder; flue gas generated during the pyrolysis reaction in S3; flue gas generated during the calcination of the first preproduct in S5; and flue gas generated during the melting or sintering of the furnace charge in S6.

4. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, The post-processing in S4 includes at least one of filtration and drying.

5. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, The magnesium oxide content of the second light-burned powder is not less than 95%; the magnesium oxide content of the first light-burned powder is lower than that of the second light-burned powder.

6. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, The first light calcined powder is prepared from at least one of low-grade magnesite and tailings powder.

7. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, When the first preproduct and the second light calcined powder are mixed, the mass ratio between the first preproduct and the second light calcined powder is in the range of (7 to 10):

1.

8. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, When the second preproduct and the second light calcined powder are mixed, the mass ratio between the second preproduct and the second light calcined powder is in the range of (3.5 to 5):

1.

9. The method for preparing high-purity magnesium oxide products by carbonization and purification of light-burned powder according to claim 1, characterized in that, The carbonization reaction pressure is 0.05MPa to 0.8MPa, the carbonization reaction temperature is in the range of 10℃ to 60℃, and the carbonization residence time is 15min to 180min.

10. A high-purity magnesium oxide product, characterized in that, The high-purity magnesium oxide product is prepared by the method described in any one of claims 1-9, which involves carbonization and purification of lightly calcined powder.

11. The high-purity magnesium oxide product according to claim 10, characterized in that, High-purity magnesium oxide products have a magnesium oxide content of over 98.2%.

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