A continuous preparation process of high-purity magnesium oxide particles

Abstract

The application relates to the technical field of inorganic high-purity powder material preparation, in particular to a continuous preparation process of high-purity magnesium oxide particles, the purity of the magnesium oxide particles is not less than 99.95%, the D50 particle size is 1.8-2.1 mu m, the particle size distribution span is 0.70-0.85, the total content of trace metal impurities is 2.1-4.2 ppm, the thermal weight loss rate is 0.04%-0.08%, and the bulk density is 0.48-0.55 g / cm 3 3 . The application adopts a continuous production mode, replaces a traditional batch process, realizes whole-process continuous operation of raw material feeding, reaction, crystallization, washing, drying, calcination and grading, greatly improves the stability and uniformity of a production process, eliminates batch quality differences, and adapts to industrial large-scale production requirements.​

Description

Technical Field

[0001] This invention relates to the field of inorganic high-purity powder material preparation technology, specifically to a continuous preparation process for high-purity magnesium oxide particles. Background Technology

[0002] High-purity magnesium oxide, as a core inorganic high-purity powder material, is widely used in high-tech fields such as electronic devices, high-end ceramics, catalyst carriers, and optical materials. Downstream industries have put forward stringent requirements for its purity, particle morphology, particle size distribution, thermal stability, and bulk density.

[0003] Currently, there are still many technical problems in the industrial preparation of high-purity magnesium oxide. Traditional preparation processes mostly adopt batch production mode, making it difficult to achieve uniform control of the reaction process. There are batch differences in material mixing and reaction degree, resulting in insufficient product quality stability and failing to meet the industrial demand for continuous mass production.

[0004] Existing processes often employ a single precipitant system, which can lead to problems such as uneven crystallization and particle agglomeration during precursor generation, significantly increasing the difficulty of subsequent impurity removal and making it difficult to achieve deep removal of impurities.

[0005] Some continuous processes lack a hydrothermal crystallization modification step, resulting in inherent defects in the precursor grains. Surface and internal impurities cannot be effectively separated, leading to a natural upper limit on product purity and particle regularity. Furthermore, conventional calcination processes often employ a single isothermal calcination method, which is insufficiently matched to the thermal decomposition kinetics of the precursor, easily causing abnormal grain sintering and grain size differentiation, resulting in poor product thermal stability and density.

[0006] In addition, existing technologies generally lack a synergistic control mechanism for the entire process of raw material pretreatment, precipitation reaction, crystallization modification, and calcination classification. Under conditions of multi-raw material adaptation, high-concentration feeding, and continuous mass production, the process stability decreases significantly, and the overall performance of the product is difficult to meet the standards for high-end applications. Summary of the Invention

[0007] The primary objective of this invention is to provide a continuous preparation process for high-purity magnesium oxide particles.

[0008] A further objective of this invention is to provide high-purity magnesium oxide particles, wherein the magnesium oxide particles have a purity of not less than 99.95%, a D50 particle size of 1.8 μm to 2.1 μm, a particle size distribution range of 0.70 to 0.85, a total content of trace metal impurities of 2.1 ppm to 4.2 ppm, a thermal weight loss rate of 0.04% to 0.08%, and a bulk density of 0.48 g / cm³. 3 Up to 0.55 g / cm 3 .

[0009] Wherein, the purity refers to the MgO content, i.e. the main content of magnesium oxide, determined by chemical analysis (EDTA complexometric titration); the total content of trace metal impurities refers to the total amount of various trace metal impurities (including but not limited to Fe, Ca, Al, Si, Na, K, Mn, etc.) determined by inductively coupled plasma mass spectrometry (ICP-MS); the difference between purity and total content of trace metal impurities is composed of non-metallic impurities (including adsorbed water, residual carbonates, residual chlorides, etc.).

[0010] Preferably, the magnesium source of the magnesium oxide particles is magnesium chloride hexahydrate, or magnesium chloride hexahydrate and anhydrous magnesium sulfate in a mass ratio of 2:1, or magnesium chloride hexahydrate, anhydrous magnesium sulfate and magnesium nitrate hexahydrate in a mass ratio of 2:1:1.

[0011] Preferably, the magnesium oxide particles are obtained by a continuous composite precipitation, hydrothermal crystallization and gradient calcination process.

[0012] A continuous preparation process for the aforementioned high-purity magnesium oxide particles uses magnesium salts with an initial purity of not less than 99.5% as raw materials, and sequentially implements the following steps: raw material pretreatment, composite precipitation, hydrothermal crystallization, countercurrent washing, low-temperature drying, gradient calcination, and airflow classification. The composite precipitation involves simultaneously pumping a composite precipitant, consisting of magnesium salt raw material liquid, ammonium bicarbonate, and 25 wt% ammonia water, into a continuous dynamic reactor and conducting a continuous reaction at 55°C to 60°C. The mass ratio of ammonium bicarbonate to 25 wt% ammonia water in the composite precipitant is 1:1 to 1:3. The sum of the amount of ammonium bicarbonate in the composite precipitant and the amount of NH3 in the 25 wt% ammonia water, along with the amount of Mg in the magnesium source, is... 2+ The molar ratio of the substances is 1.2:1 to 2.2:1 to obtain a suspension of basic magnesium carbonate precursor; the entire process is a continuous operation.

[0013] Explanation of the principle of the composite precipitation reaction: In the composite precipitation reaction, ammonium bicarbonate provides CO3. 2- Source: Ammonia provides OH - The source, and the two work synergistically to affect Mg in magnesium salt solutions. 2+ This generates a basic magnesium carbonate precursor.

[0014] When magnesium chloride hexahydrate is used as the magnesium source, the representative reaction equation is: 5MgCl₂ + 4NH₄HCO₃ + 6NH₃·H₂O → 4MgCO₃·Mg(OH)₂·4H₂O↓ + 10NH₄Cl. According to this stoichiometry, the precipitant reacts with Mg… 2+ The theoretical molar ratio is 2:1. This invention specifies that the precipitant and Mg... 2+ The molar ratio is 1.2:1 to 2.2:1, with the lower limit of 1.2:1 being lower than the theoretical stoichiometric ratio. However, under these conditions, basic magnesium carbonate precipitate can still be formed, and unreacted Mg... 2+The precipitant remains in the liquid phase and is subsequently removed by countercurrent washing, without affecting product purity; a lower precipitant dosage helps obtain more uniform precursor nuclei and reduces co-precipitation of impurities. An upper limit of 2.2:1 provides excess precipitant to ensure complete precipitation.

[0015] Preferably, the raw material pretreatment involves drying the magnesium salt raw material at a constant temperature of 105°C for 2 hours, sieving it through an 80-mesh standard sieve, mixing it with deionized water at 200 r / min for 15 minutes to prepare a magnesium salt solution, and then obtaining a pure reaction raw material liquid through precision filtration.

[0016] Preferably, the mass ratio of ammonium bicarbonate to 25wt% ammonia in the composite precipitant is 1:1, 1:2, or 1:3.

[0017] Preferably, the stirring speed of the continuous dynamic reactor is 300 r / min, and the continuous reaction residence time of the material is 30 min; the mass concentration of the magnesium salt raw material solution is 15% to 32%, and the continuous feeding rate is 15 L / h to 30 L / h.

[0018] Preferably, the hydrothermal crystallization involves crystallizing the precursor suspension at a constant temperature of 160°C to 210°C for 2 to 3.5 hours under autogenous pressure.

[0019] Preferably, the countercurrent washing is performed by continuously washing three times in a countercurrent manner with deionized water, and the washing endpoint is when the conductivity of the washing liquid is ≤5μS / cm; the low-temperature drying is performed by continuously drying at 90℃ for 40 minutes using a drum dryer.

[0020] Preferably, the gradient calcination is a segmented holding calcination, with the first segment temperature at 800℃ to 850℃ and a holding time of 15 min to 20 min, and the second segment temperature at 1050℃ to 1180℃ and a holding time of 45 min to 70 min. The temperature is continuously increased at a rate of 5℃ / min from the initial temperature of entering the furnace to the holding temperature of the first segment and between the first and second segments.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention adopts a continuous production mode to replace the traditional intermittent process, realizing continuous operation of raw material feeding, reaction, crystallization, washing, drying, calcination and classification, which greatly improves the stability and uniformity of the production process, eliminates batch quality differences, and adapts to the needs of large-scale industrial production.

[0022] 2. This invention employs a composite precipitant system to optimize the uniformity of the precursor formation reaction, resulting in more regular crystallization of the basic magnesium carbonate precursor, laying the foundation for subsequent grain control and deep impurity removal. A dedicated raw material pretreatment process thoroughly removes moisture and mechanical impurities from the raw materials, ensuring the purity of the reaction system and reducing the risk of impurity introduction from the source. In-situ modification of the precursor is achieved through a hydrothermal crystallization process, realizing grain repair and structural optimization, effectively removing impurities encapsulated in the grains, and improving product purity and particle regularity.

[0023] 3. The gradient calcination process of this invention precisely matches the thermal decomposition kinetics of the precursor, avoiding abnormal sintering of grains, optimizing the crystal structure and density of the product, and improving the product's thermal stability and bulk density. The countercurrent washing and airflow classification work together to achieve efficient separation of soluble impurities and unqualified particles, further ensuring product purity and uniform particle size distribution.

[0024] 4. This invention achieves efficient adaptation of multi-element magnesium salt raw materials, maintaining process stability under high-concentration feeding and continuous mass production conditions. The resulting product has high purity, uniform particle size, excellent thermal stability and good density, which can meet the application requirements of high-end fields. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] All chemical raw materials used in this invention are commercially available high-purity industrial grade, with an initial purity of ≥99.5%, meeting the raw material standard requirements for the preparation of high-purity powders.

[0027] Explanation regarding purity and total content of trace metal impurities: The purity mentioned in this invention refers to the MgO content (i.e., the main magnesium oxide content), which is determined by chemical analysis (EDTA complexometric titration). The total content of trace metal impurities refers to the total amount of various trace metal impurities (including but not limited to Fe, Ca, Al, Si, Na, K, Mn, etc.) determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0028] The difference between purity and total trace metal impurities is due to non-metallic impurities (including adsorbed water, residual carbonates, residual chlorides, etc.). For example, a magnesium oxide product with a purity of 99.95% has an MgO content of 99.95% and a total non-MgO component of 0.05% (i.e., 500 ppm). The total amount of trace metal impurities is only 2.1-4.2 ppm, with the remainder being non-metallic impurities.

[0029] Explanation of the molar ratio of the composite precipitant: In the molar ratio of the composite precipitant to the magnesium source described in this invention, the amount of the composite precipitant is the sum of the amount of ammonium bicarbonate and the amount of NH3 in 25wt% ammonia water, and the amount of the magnesium source is the sum of the amounts of Mg in the magnesium source. 2+ The molar ratio is the ratio of the total precipitate equivalent of the composite precipitant to the magnesium source, wherein ammonium bicarbonate provides CO3. 2- Precipitation equivalent, ammonia water provides OH - Precipitation equivalents, the two work together to generate basic magnesium carbonate precursors.

[0030] General raw material pretreatment steps: Solid magnesium salt raw materials are placed in a constant temperature drying device, and the temperature is set at 105℃ for 2 hours to remove surface free moisture and solid mechanical impurities adsorbed during storage and transportation (the drying process does not involve the removal of crystal water from the magnesium salt salt structure; the raw materials retain their original hydrated structure after drying). After drying, the raw materials are sieved using an 80-mesh standard sieve to remove agglomerated particles and solid mechanical impurities, ensuring uniform particle size and consistent dissolution rate. The sieved high-purity magnesium salts were mixed with deionized water at room temperature with a stirring speed of 200 r / min and a stirring time of 15 min to prepare a uniform and transparent magnesium salt mixed solution. Finally, the magnesium salt solution was filtered using a precision filter to remove trace amounts of insoluble impurities, resulting in a pure reaction raw material solution for later use.

[0031] The general preparation process of this invention includes composite precipitation, hydrothermal crystallization, countercurrent washing, low-temperature drying, gradient calcination, and airflow classification. Unless otherwise specified, the general operating parameters and processes for each group are consistent, with differences only in the raw material ratio and core process parameters.

[0032] Example 1: In this embodiment, the reaction raw material is magnesium chloride hexahydrate, which is a commercially available high-purity industrial-grade raw material with a purity of 99.6% and no additional components are added.

[0033] The raw material pretreatment method is the same as the general pretreatment steps described above.

[0034] Prepare a 15% (w / w) magnesium chloride hexahydrate aqueous solution with a continuous feed rate of 15 L / h in the production line.

[0035] The composite precipitant used is composed of ammonium bicarbonate and 25 wt% industrial high-purity ammonia water, with a mass ratio of 1:1. The amount of ammonium bicarbonate in the precipitant is proportional to the amount of ammonia water in the 25 wt% ammonia water. The sum of the amounts of substances and the amount of Mg in the magnesium source 2+ The molar ratio of the substances is 1.2:1.

[0036] The prepared raw material solution and composite precipitant were simultaneously pumped into a continuous dynamic reactor. The stirring speed was set to 300 r / min, and the reaction was carried out continuously at a constant temperature of 55℃ for 30 min to prepare a homogeneous basic magnesium carbonate precursor suspension. Subsequent processes were as follows: the precursor suspension was transferred to a hydrothermal crystallization reactor and crystallized at 160℃ under self-generated pressure for 2 h. After crystallization, the mixture was washed three times continuously in countercurrent with deionized water until the conductivity of the washing solution was ≤5 μS / cm. The washed wet material was then sent to a drum dryer and dried continuously at 90℃ for 40 min. The dried powder was then sent to a gradient calcination furnace for segmented calcination. The temperature was increased from the initial furnace temperature at 5℃ / min to 800℃ and held for 20 min, followed by an increase at 5℃ / min to 1050℃ and held for 60 min. After calcination, the mixture was subjected to continuous airflow classification and sieved to obtain high-purity magnesium oxide granules.

[0037] Example 2: In this embodiment, the reaction raw materials are a two-component magnesium salt composite system, consisting of magnesium chloride hexahydrate and anhydrous magnesium sulfate. Both are commercially available high-purity industrial grade, with an initial purity of ≥99.5%, and a fixed mass ratio of 2:1.

[0038] The raw material pretreatment method is the same as the general pretreatment steps described above.

[0039] A 25% (w / w) aqueous solution of composite magnesium salts was prepared, with a continuous feed rate of 25 L / h in the production line. The composite precipitant used was composed of ammonium bicarbonate and 25 wt% industrial high-purity ammonia in a 1:2 mass ratio. The sum of the amounts of ammonium bicarbonate and NH3 in the 25 wt% ammonia solution, along with the amount of Mg in the magnesium source, was calculated. 2+ The molar ratio of the substances is 1.8:1.

[0040] The raw material solution and composite precipitant were simultaneously pumped into a continuous dynamic reactor. The stirring speed was set at 300 r / min, and the reaction was carried out continuously at a constant temperature of 60℃ for 30 min to prepare a precursor suspension. Subsequent hydrothermal, washing, and drying processes were performed as in Example 1, except that the hydrothermal crystallization temperature was 160℃ and the duration was 2 h, while the number of washings and the drying temperature and duration remained consistent. The gradient calcination process was set to increase the temperature from the initial furnace temperature to 800℃ at a rate of 5℃ / min and hold for 20 min, then increase the temperature to 1100℃ at a rate of 5℃ / min and hold for 70 min. Finally, high-purity magnesium oxide granules were obtained through airflow classification.

[0041] Example 3: The raw material composition, raw material ratio, raw material pretreatment method, raw material concentration, feed rate, precipitation reaction parameters, and washing and drying parameters in this embodiment are the same as those in Embodiment 2 above.

[0042] The differentiated process in this embodiment is hydrothermal crystallization. The precursor suspension is transported to a hydrothermal crystallization reactor and crystallized at a constant temperature of 190°C under self-generated pressure for 3 hours. After crystallization, closed-loop countercurrent washing and low-temperature drying are performed as in Embodiment 2.

[0043] The gradient calcination process parameters are the same as in Example 2, that is, the temperature is increased from the initial temperature of the furnace to 800℃ at 5℃ / min and held for 20min, and then increased to 1100℃ at 5℃ / min and held for 60min. After calcination, the product is subjected to airflow classification treatment to obtain high-purity magnesium oxide granules.

[0044] Example 4: In this embodiment, the raw material system, raw material pretreatment method, precipitation reaction process, hydrothermal crystallization process, and washing and drying process are all the same as those in Embodiment 3 above.

[0045] The differentiated process in this embodiment is a gradient calcination process. After drying, the powder is continuously calcined in a segmented heating mode. The temperature is increased from the initial temperature at the furnace inlet to 850℃ at a rate of 5℃ / min and held for 15min. Then, the temperature is increased to 1180℃ at a rate of 5℃ / min and held for 45min. The heating rate is matched with the continuous discharge rate of the production line to ensure that the material is heated evenly.

[0046] After calcination, the product undergoes continuous airflow classification treatment to obtain high-purity magnesium oxide granules.

[0047] Example 5: In this embodiment, the reaction raw materials are a multi-component magnesium salt composite system, consisting of magnesium chloride hexahydrate, anhydrous magnesium sulfate, and magnesium nitrate hexahydrate. All three raw materials are commercially available high-purity industrial grade with an initial purity of ≥99.5% and a fixed mass ratio of 2:1:1.

[0048] The raw material pretreatment method is the same as the general pretreatment steps described above. A 32% (w / w) composite magnesium salt aqueous solution is prepared, with a continuous feed rate of 30 L / h on the production line. The composite precipitant used is composed of ammonium bicarbonate and 25 wt% industrial high-purity ammonia water, in a mass ratio of 1:3. The sum of the amount of ammonium bicarbonate in the precipitant and the amount of NH3 in the 25 wt% ammonia water, along with the amount of Mg in the magnesium source, is... 2+ The molar ratio of the substances is 2.2:1.

[0049] The raw material solution and the composite precipitant were simultaneously pumped into a continuous dynamic reactor, stirred at 300 r / min, and continuously reacted at a constant temperature of 60℃ for 30 min to prepare a precursor suspension.

[0050] The differentiated process parameters in this embodiment are as follows: hydrothermal crystallization, calcination, and grading processes; isothermal crystallization of the precursor suspension at 210°C under autogenous pressure for 3.5 hours; washing and drying processes are the same as the general steps described above; gradient calcination is set to increase the temperature from the initial furnace temperature at 5°C / min to 820°C and hold for 18 minutes, followed by increasing the temperature at 5°C / min to 1150°C and holding for 50 minutes; the airflow grading wind speed is adjusted to 10 m / s. 3 / h, high-purity magnesium oxide finished particles with regular particle size and optimal purity were obtained through screening.

[0051] Except for the preset comparison variables, the raw material pretreatment method, production equipment, environmental parameters, and auxiliary process parameters are all consistent with those in Example 5 to ensure that the test data are objective and accurate.

[0052] The test environment was 25℃ and 55% humidity. All test samples were finished granules that had been prepared and left to stand at room temperature and pressure for 24 hours to eliminate the interference of environmental factors and sample conditions on the test results.

[0053] Comparative Example 1: The raw material system, raw material component ratio, raw material pretreatment method, and precipitant ratio of this comparative example are the same as those in Example 5 above. A multi-component magnesium salt composite system is adopted, and the pretreatment follows the general pretreatment steps.

[0054] This comparative example employs a traditional batch preparation process, eliminating the core continuous processes of continuous feeding, continuous crystallization, closed-loop countercurrent washing, and gradient continuous calcination as described in this invention. The specific preparation steps are as follows: the prepared multi-component magnesium salt solution and the corresponding proportioned composite precipitant are added to a batch reactor in one step, reacted at a constant temperature of 60℃ and 300 r / min for 30 min, and then allowed to settle for 2 h; the supernatant is removed, and the mixture is washed and filtered once with ordinary deionized water; after washing, it is dried at 90℃ for 40 min, and finally, a constant temperature batch calcination process is used, calcining at 1050℃ for 60 min, followed by natural cooling to obtain the finished particles. All other environmental parameters and testing conditions remain consistent with those of Example 5.

[0055] Comparative Example 2: This comparative example aims to verify the necessity of the ammonia component in the composite precipitant system. The raw material system for this comparative example is the same as in Example 1, using single magnesium chloride hexahydrate, commercially available high-purity industrial grade, with a purity ≥99.5%. The raw material pretreatment method is the same as the general pretreatment steps described above. A 15% (w / w) magnesium chloride hexahydrate aqueous solution was prepared, with a continuous feed rate of 15 L / h.

[0056] This comparative example uses a different precipitant system: the ammonia-water mixture system is omitted, and only ammonium bicarbonate is used as the precipitant. The molar ratio of ammonium bicarbonate to magnesium source is set to 1.2:1, as in Example 1. All other process parameters and operating steps, including precipitation reaction temperature (55℃), stirring speed (300 r / min), residence time (30 min), hydrothermal crystallization (160℃ / 2 h), washing and drying, and calcination and classification, are the same as in Example 1 above, to achieve a comparison focusing on the single variable of the precipitant system.

[0057] Comparative Example 3: The raw material composition, proportions, pretreatment methods, raw material concentrations, feed rates, precipitant systems, precipitation reaction parameters, washing and drying, and all pre- and post-process parameters for calcination and classification in this comparative example are the same as those in Example 5 above.

[0058] The comparative example is differentiated by eliminating the continuous hydrothermal crystallization in-situ modification process. After the material completes the precipitation reaction in the continuous dynamic reactor to generate a precursor suspension, it is directly sent to the closed-loop countercurrent washing equipment for washing, skipping the hydrothermal high-temperature and high-pressure crystallization modification process. The remaining processes remain unchanged.

[0059] Comparative Example 4: All raw material systems, pretreatment methods, precipitation reactions, hydrothermal crystallization, washing and drying pre-process parameters and operating steps in this comparative example are the same as those in Example 5 above.

[0060] The comparative example is differentiated by eliminating the gradient temperature control continuous calcination mode and replacing it with a conventional constant temperature calcination process. The dried powder is directly fed into the calcination furnace and continuously calcined at a single constant temperature of 1000℃ for 60 minutes without segmented heating or segmented heat preservation. After calcination, the finished particles are obtained by the same airflow classification process.

[0061] Comparative Example 5: The raw material composition, proportions, pretreatment methods, complete process flow, and equipment system of this comparative example are all the same as those in Example 5 above.

[0062] The comparative example was set to be differentiating the raw material concentration and precipitant ratio from the limits of this invention. The mass concentration of the ternary composite magnesium salt aqueous solution was adjusted to 40%, and the molar ratio of precipitant to magnesium source was adjusted to 3:1. The remaining reaction temperature, stirring rate, crystallization parameters, washing and drying, calcination and classification steps remained unchanged. This was used to verify the adaptation boundary of the process parameters and the stability of the process synergy of this invention.

[0063] In the continuous preparation process described in this invention, the ammonia water used is commercially available 25wt% industrial high-purity ammonia water. The mass ratio of ammonium bicarbonate to ammonia water recorded in the claims and specification refers to the mass ratio of solid ammonium bicarbonate to 25wt% ammonia water. The precision filtration employs a precision filter equipped with a 0.22μm microporous membrane, filtered at a conventional industrial pressure of 0.1MPa-0.3MPa to remove trace amounts of insoluble impurities from the magnesium salt solution. The continuous dynamic reaction vessel is a continuous stirred tank reactor (CSTR), and its effective volume is determined based on the continuous feed rate of the magnesium salt raw material solution of 15L / h. The flow rate is 30L / h, and the continuous reaction residence time of the material is 30min, matched with a range of 7.5L-15L to ensure a stable continuous reaction residence time of 30min. The continuous countercurrent washing uses a liquid-to-solid ratio of 5:1, with the washing water flow rate matched to the material feed rate at a 1:1 ratio. Deionized water is used for three consecutive countercurrent washes until the conductivity of the washing liquid is ≤5μS / cm, achieving deep removal of soluble impurities. The resistivity of the deionized water used throughout the process is ≥18.2MΩ·cm, preventing the introduction of external impurities. The airflow classification uses a horizontal airflow classifier, with the classification wind speed controlled at 8m. 3 / h-12m 3 / h, the grading particle size cut point is set to 3μm to accurately screen out unqualified large particles; The particle size distribution span is defined as span=(D90-D10) / D50 according to the GB / T19077-2016 standard; the material conveying throughout the process adopts peristaltic pump to precisely control the feeding rate and raw material ratio, ensuring the stable operation of the continuous process of raw material feeding, reaction, crystallization, washing, drying, calcination and classification.

[0064] The magnesium salts, ammonium bicarbonate, ammonia, and other raw materials used in this invention are all commercially available high-purity industrial-grade products with an initial purity of not less than 99.5%. These materials can be obtained by those skilled in the art through conventional commercial channels. By combining the raw material pretreatment, process steps, parameter conditions, and the above-mentioned supplementary content described in this specification, the technical solution of this invention can be completely reproduced without creative effort, and the target high-purity magnesium oxide particles can be prepared.

[0065] Given the continuous production nature of this process, a unified sampling and sample pretreatment standard was established for this test. After the production line had been running stably for 2 hours, samples were collected at multiple points at equal time intervals at the air classifier outlet. After mixing, the samples were divided using the quartering method to ensure that the samples could objectively reflect the quality of the entire batch of materials. All samples to be tested were placed in a sealed environment at normal temperature and pressure for 24 hours, and agglomerated particles generated during collection and transportation were removed to ensure uniform powder state and avoid deviations in particle size, bulk density, impurity content, and other test items caused by powder agglomeration and fluctuations in environmental temperature and humidity.

[0066] The hydrothermal crystallization process of this invention adopts a closed hydrothermal reactor. The reactor volume filling rate is uniformly controlled at 60%-80% in all examples and comparative examples. This filling range can ensure material processing efficiency while reserving sufficient safety buffer space for system heating and pressurization. Combined with the precursor suspension system and the crystallization temperature range of 160℃-210℃, the self-generated pressure formed by the system during the reaction is stable at 0.6 MPa-2.0 MPa. No external pressurization is required throughout the process. The crystallization reaction is completed by relying on the saturated vapor pressure generated by the heating of the material, ensuring that the crystallization effect of each group of materials is uniform.

[0067] Based on the practical application needs of this product in high-end fields such as electronic devices, high-end ceramics, catalyst carriers, and optical materials, a complete testing index system covering main content, impurity components, particle characteristics, powder properties, and thermal stability has been established. All testing items are conducted using current and valid national and industry standards, and are carried out with dedicated testing equipment to comprehensively characterize the overall performance of the finished product. This not only determines whether the product meets the requirements for use in high-end fields but also visually distinguishes the quality differences of products under different process schemes.

[0068] Performance testing and results analysis: Product purity (MgO content) was determined according to HG / T2573 or GB / T1612 using EDTA complexometric titration; total content of trace metal impurities was determined using inductively coupled plasma mass spectrometry (ICP-MS); particle size and particle size distribution range were determined according to GB / T19077-2016 using a laser particle size analyzer; particle micromorphology was observed and statistically analyzed using scanning electron microscopy (SEM); powder bulk density was determined according to the bulk density determination method specified in HG / T2573; thermal stability was determined according to GB / T6425 using a simultaneous thermal analyzer to measure the thermal weight loss rate in the temperature range of 800℃-1300℃; and soluble anion residue was determined according to GB / T31197-2014 using an ion chromatograph.

[0069] All tests were conducted in a constant environment of 25°C and 55% humidity to avoid interference from environmental factors and sample conditions on the test data.

[0070] The performance test results of each embodiment and comparative example are shown in Table 1 below.

[0071] Table 1:

[0072] Results analysis: This invention overcomes the limitations of existing technologies by synergistically adapting the entire process of raw material pretreatment, composite precipitation, hydrothermal modification, and gradient calcination. Under the industry-recognized unfavorable conditions of multi-component magnesium salt compounding, high-concentration raw material feeding, and high-speed continuous mass production, it can stably prepare ultra-high purity magnesium oxide particles with a purity of ≥99.95%. The product features smaller particle size, more uniform particle size distribution, lower residual amount of trace metal impurities, better thermal stability, and higher bulk density, significantly improving particle regularity and product compactness.

[0073] Traditional intermittent processes lack a continuous synergistic control system, resulting in poor reaction uniformity, incomplete impurity removal, and significant batch fluctuations. Conventional single-raw-material continuous processes lack a composite buffer synergistic mechanism, making them unsuitable for multi-raw-material systems, and limiting the inherent limits of product purity and uniformity. The absence of a hydrothermal modification process directly leads to the loss of the synergistic effect of grain repair and deep impurity removal, resulting in the inability to remove impurities encapsulated in the grains and a surge in product defects. Conventional isothermal calcination cannot match the thermal decomposition kinetics of precursors, making it impossible to avoid grain sintering and particle size differentiation defects. When the process parameters exceed the range defined by this invention, the precise synergistic balance of each process is disrupted, causing the entire system of this invention to fail completely and product performance to deteriorate.

[0074] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A high-purity magnesium oxide granule, characterized in that, The magnesium oxide particles have a purity of not less than 99.95%, a D50 particle size of 1.8 μm to 2.1 μm, a particle size distribution range of 0.70 to 0.85, a total trace metal impurity content of 2.1 ppm to 4.2 ppm, a thermal weight loss rate of 0.04% to 0.08%, and a bulk density of 0.48 g / cm³. 3 Up to 0.55 g / cm 3 The purity refers to the MgO content, and the total content of trace metal impurities refers to the total amount of trace metal impurities determined by inductively coupled plasma mass spectrometry.

2. The high-purity magnesium oxide particles according to claim 1, characterized in that, The magnesium source for the magnesium oxide particles is magnesium chloride hexahydrate, or magnesium chloride hexahydrate and anhydrous magnesium sulfate in a mass ratio of 2:1, or magnesium chloride hexahydrate, anhydrous magnesium sulfate and magnesium nitrate hexahydrate in a mass ratio of 2:1:

1.

3. The high-purity magnesium oxide particles according to claim 1, characterized in that, The magnesium oxide particles were prepared by a continuous composite precipitation, hydrothermal crystallization and gradient calcination process.

4. A continuous preparation process for the high-purity magnesium oxide particles according to any one of claims 1 to 3, characterized in that, Magnesium salts with an initial purity of not less than 99.5% were used as raw materials. The process involved sequential steps of raw material pretreatment, composite precipitation, hydrothermal crystallization, countercurrent washing, low-temperature drying, gradient calcination, and airflow classification. The composite precipitation involved simultaneously pumping a composite precipitant, consisting of magnesium salt raw material solution, ammonium bicarbonate, and 25 wt% ammonia water, into a continuous dynamic reactor. The magnesium salt raw material solution had a mass concentration of 15% to 32%, and the reaction was carried out continuously at 55°C to 60°C. The mass ratio of ammonium bicarbonate to 25 wt% ammonia water in the composite precipitant was 1:1 to 1:

3. The sum of the amounts of ammonium bicarbonate and NH3 in the composite precipitant, and the amount of Mg in the magnesium source, were also considered. 2+ The molar ratio of the substances is 1.2:1 to 2.2:1 to obtain a suspension of basic magnesium carbonate precursor; the entire process is a continuous operation.

5. The continuous preparation process according to claim 4, characterized in that, The raw material pretreatment involves drying the magnesium salt raw material at a constant temperature of 105℃ for 2 hours, sieving it through an 80-mesh standard sieve, mixing it with deionized water at 200 r / min for 15 minutes to prepare a magnesium salt solution, and then obtaining a pure reaction raw material liquid through precision filtration.

6. The continuous preparation process according to claim 4, characterized in that, The mass ratio of ammonium bicarbonate to 25wt% ammonia in the composite precipitant is 1:1, 1:2, or 1:

3.

7. The continuous preparation process according to claim 4, characterized in that, The stirring speed of the continuous dynamic reactor is 300 r / min, the continuous reaction residence time of the material is 30 min, and the continuous feed rate is 15 L / h to 30 L / h.

8. The continuous preparation process according to claim 4, characterized in that, The hydrothermal crystallization involves crystallizing the precursor suspension at a constant temperature of 160°C to 210°C for 2 to 3.5 hours under autogenous pressure.

9. The continuous preparation process according to claim 4, characterized in that, The countercurrent washing is performed by continuously washing three times in a countercurrent manner with deionized water, and the washing endpoint is when the conductivity of the washing liquid is ≤5μS / cm; the low-temperature drying is performed by continuously drying at 90℃ for 40 minutes using a drum dryer.

10. The continuous preparation process according to claim 4, characterized in that, The gradient calcination is a segmented holding calcination. The first segment is at a temperature of 800℃ to 850℃ and is held for 15 min to 20 min. The second segment is at a temperature of 1050℃ to 1180℃ and is held for 45 min to 70 min. The temperature is continuously increased at a rate of 5℃ / min from the initial temperature of the furnace to the holding temperature of the first segment and between the first and second segments.

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