Preparation process of high-purity active magnesium oxide

Abstract

The application relates to the technical field of magnesium oxide preparation, and discloses a high-purity active magnesium oxide preparation process, which comprises the following steps: S1, deep purification and membrane separation of a raw material solution: aiming at an industrial by-product magnesium source solution, first chemical pretreatment is carried out to remove heavy metal and silicon impurities; S2, controllable precipitation synthesis under the guidance of a biological template agent; S3, washing and instantaneous drying based on a membrane separation technology; and S4, dynamic program temperature-controlled calcination under the protection of an inert atmosphere: precursor powder obtained in step S3 is subjected to dynamic temperature program calcination of multi-stage temperature rising and falling and temperature holding platform under the protection of an inert atmosphere, the whole process integration of chemical pretreatment, nanofiltration membrane targeted purification, biological template agent guided precipitation, membrane separation washing and dynamic program temperature-controlled calcination is adopted, and the problems of insufficient purification of a complex industrial magnesium source, difficulty in precursor morphology and pore structure regulation and sintering inactivation caused by the calcination process in the traditional process are solved.

Description

Technical Field

[0001] This invention relates to the field of magnesium oxide preparation technology, specifically a process for preparing high-purity active magnesium oxide. Background Technology

[0002] Magnesium oxide, as an important inorganic chemical product, is widely used in refractory materials, adsorbents, catalysts, pharmaceuticals, environmental protection, and electronic materials. Its performance largely depends on purity and activity: high purity ensures its chemical stability and reliability in high-end applications, while high activity (typically manifested as high specific surface area, well-developed pore structure, and high iodine adsorption value) directly relates to its efficiency in catalysis and adsorption. Currently, industrial processes for producing magnesium oxide mainly include ore calcination, brine-lime, and brine-ammonia processes. However, these traditional methods generally suffer from the following problems: firstly, the raw materials largely rely on natural ores such as magnesite, resulting in high resource consumption; secondly, impurities such as calcium, silicon, and iron associated with the ores are difficult to completely remove, leading to limited product purity and difficulty in meeting the demands of high-purity applications. Secondly, in traditional precipitation processes, the imprecise control of precipitation conditions easily leads to coarse precursor grains, uneven morphology, and dense structure, resulting in low specific surface area and poor activity of calcined magnesium oxide. Thirdly, the calcination process often adopts simple procedures or constant temperature methods, which easily leads to excessive grain growth, pore structure collapse, and sintering, which is not conducive to the formation and retention of highly active structures. Fourthly, existing processes do not make sufficient use of industrial by-product magnesium sources (such as magnesium-rich brine after lithium extraction from salt lakes, boron mud acid leaching solution, etc.). These resources contain many types of impurities with large fluctuations in content, and conventional purification methods are difficult to achieve targeted and deep removal, especially the separation effect of key impurities such as calcium, sulfate, boron, and heavy metals is not good, which limits the low-cost and green preparation of high-purity active magnesium oxide. Therefore, we propose a high-purity active magnesium oxide preparation process. Summary of the Invention

[0003] The purpose of this invention is to provide a process for preparing high-purity active magnesium oxide to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing high-purity active magnesium oxide, comprising the following steps: S1: Deep purification and membrane separation of feed solution: For industrial by-product magnesium source solution, chemical pretreatment is first performed to remove heavy metals and silicon impurities, followed by deep separation using nanofiltration membrane to target and remove calcium ions and sulfate impurities, thereby obtaining a high-purity magnesium salt intermediate solution. S2: Controlled precipitation synthesis guided by biotemplate: The high-purity magnesium salt solution obtained in step S1 is mixed with a solution containing a specific ratio of biomass template agent and precipitant, and a co-precipitation reaction is carried out under the conditions of temperature, feeding method, stirring speed and pH to generate a basic magnesium carbonate precursor slurry with a uniform spherical and porous microstructure. S3: Washing and instant drying based on membrane separation technology: The precursor slurry obtained in step S2 is dialyzed and washed using a ceramic ultrafiltration membrane to completely remove chloride ions and ammonium ions soluble impurities. Then, the slurry is instantly solidified into a free-flowing microspherical precursor powder by spray drying to retain its microstructure. S4: Dynamic temperature-controlled calcination under inert atmosphere protection: The precursor powder obtained in step S3 is subjected to dynamic temperature-controlled calcination with multiple stages of heating, cooling and holding platforms under inert atmosphere protection, and finally the precursor is converted into a high-purity and high-activity magnesium oxide product.

[0005] Preferably, the magnesium source solution in step S1 has the following specific components: The magnesium-rich brine produced after lithium extraction from salt lakes is mainly composed of magnesium chloride hexahydrate, with magnesium ion concentration ranging from 150 g / L to 220 g / L. Typical impurity contents range from 300 mg / L to 800 mg / L for calcium ions, 500 mg / L to 1500 mg / L for sulfate ions, and 50 mg / L to 150 mg / L for boron. Boron mud, a solid waste produced during the production of boric acid from boromagnesite, is leached with inorganic acid to obtain the filtrate. The filtrate is then leached for 1-3 hours using 10%-20% sulfuric acid at a solid-liquid ratio of 1:2 to 1:4 and a temperature of 70℃ to 90℃. The main component of the filtrate is magnesium sulfate, with magnesium ion concentrations ranging from 120 g / L to 190 g / L. Typical impurities include: calcium ions from 200 mg / L to 600 mg / L, silica from 30 mg / L to 100 mg / L, and ferric ions from 5 mg / L to 20 mg / L.

[0006] Preferably, the chemical pretreatment in step S1 is specifically carried out as follows: The pH of the original magnesium source solution is precisely adjusted to the range of 9.5 to 11.5 using a sodium hydroxide and potassium hydroxide solution with a concentration of 5%-25%; a preferred embodiment is to adjust the pH to 10.5. A soluble sulfide is added as a precipitant, preferably sodium sulfide nonahydrate, at an amount of 105% to 150% of the theoretically calculated amount (based on the concentration of heavy metal ions in the solution). The mixture is placed in a constant temperature environment of 50°C to 70°C and stirred at a rate of 200 rpm to 400 rpm for aging reaction, with an aging time of 0.5 hours to 2 hours. After aging, solid-liquid separation is carried out using one of the following methods: plate and frame filter press, vacuum filtration, or centrifugation, and the clarified filtrate is collected.

[0007] Preferably, the nanofiltration membrane purification specifically includes: The nanofiltration membrane element is made of polyamide, polypiperazine amide, and their composite materials, with a nominal molecular weight cutoff ranging from 150 Da to 350 Da; the operating pressure is controlled between 1.0 MPa and 3.0 MPa; the operating temperature is maintained between 20°C and 35°C; the operating mode adopts a concentration and circulation mode, continuously collecting the permeate until the original liquid volume is concentrated to 5%-15% of the initial volume and then stopping; the collected permeate is a high-purity magnesium salt solution; after nanofiltration treatment, the calcium ion concentration in the permeate should be less than 100 mg / L.

[0008] Preferably, in step S2, the magnesium salt solution is divided into solution A and solution B. The specific preparation method is as follows: the nanofiltration permeate obtained in step S1 is diluted with deionized water and moderately concentrated by evaporation according to its actual magnesium ion concentration, and finally prepared into solution A with a magnesium ion concentration of 0.7 mol / L to 1.3 mol / L. The solution containing the biomass template agent and the precipitant is specifically as follows: The precipitant is either ammonium bicarbonate or ammonium carbonate, and the biomass template agent is sodium carboxymethyl cellulose, with a viscosity specification (1% aqueous solution, 25℃) between 500 mPa·s and 1500 mPa·s. In solution B, the ratio of the number of moles of precipitant to the number of moles of magnesium ions in solution A, i.e., precipitant / Mg 2+ The ratio should be within the range of 1.8:1 to 2.5:1, specifically 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, and 2.5:1. In solution B, the amount of sodium carboxymethyl cellulose, a biomass template agent, is calculated based on the final theoretical mass of magnesium oxide produced, and its addition ratio ranges from 0.2% to 5.0% of the theoretical magnesium oxide mass. When preparing solution B, first pre-disperse the calculated amount of sodium carboxymethyl cellulose in one-quarter of deionized water. Then, add the remaining aqueous solution containing the calculated amount of precipitant while stirring vigorously to ensure that the CMC is completely dissolved to form a homogeneous and transparent solution. Finally, bring the volume to the required level.

[0009] Preferably, the specific control conditions for the co-precipitation reaction are as follows: Reaction temperature: controlled within the range of 40℃, 45℃, 50℃, 55℃, and 60℃; Feeding method: Liquid A and liquid B must be added in parallel and synchronously; the feeding rate should be kept constant so that the entire feeding process lasts for 30 minutes, 40 minutes, 50 minutes, 60 minutes, or 70 minutes. Stirring speed: Maintain between 300 rpm and 500 rpm to ensure uniform mixing of the reaction system and avoid excessively high local concentrations; pH at the reaction endpoint: By adjusting the concentrations and feeding ratio of solutions A and B, the pH of the system at the end of the reaction is stabilized between 7.2 and 8.5. Maturation process: After the material is added, continue the reaction for 15 minutes, 20 minutes, 30 minutes, 40 minutes and 45 minutes while maintaining the same temperature and stirring speed, so as to make the precursor crystal growth more complete.

[0010] Preferably, the washing of the ceramic ultrafiltration membrane in step S3 specifically includes: The ceramic ultrafiltration membrane is made of alumina, zirconium oxide, or a composite thereof, with an average pore size ranging from 10 nm to 100 nm. The operation mode is dialysis filtration, which involves continuously adding an equal amount of deionized water to the feed side while concentrating the solution. The transmembrane pressure is controlled between 0.4 MPa and 1.2 MPa. The washing endpoint is determined by real-time monitoring of the conductivity of the permeate. Washing can be stopped when the conductivity of the permeate decreases and stabilizes below 20 μS / cm, 30 μS / cm, 40 μS / cm, 50 μS / cm, and 60 μS / cm. The process parameters for the spray drying are as follows: Inlet air temperature: controlled within the range of 180℃, 200℃, 220℃, 240℃, and 260℃; Air outlet temperature: controlled within the range of 80℃, 90℃, 95℃, 100℃, and 110℃; Atomizer speed: Controlled between 15,000 rpm and 25,000 rpm to ensure that the slurry is atomized into uniform tiny droplets.

[0011] Preferably, in step S4, the inert atmosphere refers to one of nitrogen, argon, or a mixture thereof with a purity higher than 99.99%, which is introduced into the calcination furnace cavity at a flow rate of 0.5 L / min to 3 L / min throughout the calcination process to isolate air and prevent carbonation and sintering of the product. The temperature program of the dynamic programmed temperature-controlled calcination specifically includes: Low-temperature dehydration section: The temperature is increased from room temperature at rates of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, and 8℃ / min; after reaching 150℃, 180℃, 200℃, 220℃, and 250℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, 40 minutes, and 50 minutes, respectively. Intermediate-temperature decomposition and pore-forming section: The temperature is increased from the end temperature of the first section at a rate of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min; after increasing the temperature to 450℃, 480℃, 500℃, 520℃, and 550℃, a long-term holding time is performed; the holding time ranges are 60 minutes, 75 minutes, 90 minutes, 105 minutes, and 120 minutes. High-temperature annealing and structural stabilization stage: The temperature is rapidly reduced from the end temperature of the second stage at a rate greater than 5℃ / min; after cooling to 350℃, 380℃, 400℃, 420℃, and 450℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, and 40 minutes, respectively. Controlled cooling section: Under the condition of continuous inert atmosphere, heating is stopped, and the furnace body is allowed to cool naturally and under program control to below 60°C before being removed from the furnace.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention solves the problems of insufficient purification of complex industrial magnesium sources, difficulty in controlling the morphology and pore structure of precursors, and easy sintering deactivation during the calcination process by integrating chemical pretreatment, nanofiltration membrane targeted purification, biological template agent guided precipitation, membrane separation and washing, and dynamic programmed temperature-controlled calcination through the whole process integration. Specifically, for industrial by-product magnesium sources with high impurity content and fluctuating composition, such as old brine from salt lakes and acid leaching solutions from boron mud, the synergistic effect of chemical precipitation and nanofiltration membrane separation achieves deep removal of impurities such as calcium, sulfate, and heavy metals, ensuring that the calcium ion concentration in the permeate is below 100 mg / L, thus guaranteeing high product purity from the source. By introducing sodium carboxymethyl cellulose as a biological template agent, co-precipitation under strictly controlled conditions is carried out to prepare a precursor with a uniform spherical and porous structure. Combined with efficient washing and instantaneous curing by ceramic ultrafiltration membrane and spray drying, the active structure of the precursor is effectively preserved. Finally, by implementing multi-stage dynamic temperature-controlled calcination under an inert atmosphere, a mild and controllable transformation of the precursor into magnesium oxide is achieved, significantly inhibiting excessive grain growth and pore structure collapse. Attached Figure Description

[0013] Figure 1 This is a structural flow diagram of a process for preparing high-purity active magnesium oxide. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0015] Please see Figure 1 As shown, the present invention provides a technical solution: a process for preparing high-purity active magnesium oxide, comprising the following steps: S1: Deep purification and membrane separation of feed solution: For industrial by-product magnesium source solution, chemical pretreatment is first performed to remove heavy metals and silicon impurities, followed by deep separation using nanofiltration membrane to target and remove calcium ions and sulfate impurities, thereby obtaining a high-purity magnesium salt intermediate solution. S2: Controlled precipitation synthesis guided by biotemplate: The high-purity magnesium salt solution obtained in step S1 is mixed with a solution containing a specific ratio of biomass template agent and precipitant, and a co-precipitation reaction is carried out under the conditions of temperature, feeding method, stirring speed and pH to generate a basic magnesium carbonate precursor slurry with a uniform spherical and porous microstructure. S3: Washing and instant drying based on membrane separation technology: The precursor slurry obtained in step S2 is dialyzed and washed using a ceramic ultrafiltration membrane to completely remove chloride ions and ammonium ions soluble impurities. Then, the slurry is instantly solidified into a free-flowing microspherical precursor powder by spray drying to retain its microstructure. S4: Dynamic temperature-controlled calcination under inert atmosphere protection: The precursor powder obtained in step S3 is subjected to dynamic temperature-controlled calcination with multiple stages of heating, cooling and holding platforms under inert atmosphere protection, and finally the precursor is converted into a high-purity and high-activity magnesium oxide product.

[0016] Furthermore, the magnesium source solution in step S1 has the following specific components: The magnesium-rich brine produced after lithium extraction from salt lakes is mainly composed of magnesium chloride hexahydrate, with magnesium ion concentration ranging from 150 g / L to 220 g / L. Typical impurity contents range from 300 mg / L to 800 mg / L for calcium ions, 500 mg / L to 1500 mg / L for sulfate ions, and 50 mg / L to 150 mg / L for boron. Boron mud, a solid waste produced during the production of boric acid from boromagnesite, is leached with inorganic acid to obtain the filtrate. The filtrate is then leached for 1-3 hours using 10%-20% sulfuric acid at a solid-liquid ratio of 1:2 to 1:4 and a temperature of 70℃ to 90℃. The main component of the filtrate is magnesium sulfate, with magnesium ion concentrations ranging from 120 g / L to 190 g / L. Typical impurities include: calcium ions from 200 mg / L to 600 mg / L, silica from 30 mg / L to 100 mg / L, and ferric ions from 5 mg / L to 20 mg / L.

[0017] Furthermore, the specific process of the chemical pretreatment in step S1 is as follows: The pH of the original magnesium source solution is precisely adjusted to the range of 9.5 to 11.5 using a sodium hydroxide and potassium hydroxide solution with a concentration of 5%-25%; a preferred embodiment is to adjust the pH to 10.5. A soluble sulfide is added as a precipitant, preferably sodium sulfide nonahydrate, at an amount of 105% to 150% of the theoretically calculated amount (based on the concentration of heavy metal ions in the solution). The mixture is placed in a constant temperature environment of 50°C to 70°C and stirred at a rate of 200 rpm to 400 rpm for aging reaction, with an aging time of 0.5 hours to 2 hours. After aging, solid-liquid separation is carried out using one of the following methods: plate and frame filter press, vacuum filtration, or centrifugation, and the clarified filtrate is collected.

[0018] Furthermore, the nanofiltration membrane purification specifically includes: The nanofiltration membrane element is made of polyamide, polypiperazine amide, and their composite materials, with a nominal molecular weight cutoff ranging from 150 Da to 350 Da; the operating pressure is controlled between 1.0 MPa and 3.0 MPa; the operating temperature is maintained between 20°C and 35°C; the operating mode adopts a concentration and circulation mode, continuously collecting the permeate until the original liquid volume is concentrated to 5%-15% of the initial volume and then stopping; the collected permeate is a high-purity magnesium salt solution; after nanofiltration treatment, the calcium ion concentration in the permeate should be less than 100 mg / L.

[0019] Furthermore, in step S2, the magnesium salt solution is divided into solution A and solution B. The specific preparation method is as follows: the nanofiltration permeate obtained in step S1 is diluted with deionized water and moderately concentrated by evaporation according to its actual magnesium ion concentration, and finally prepared into solution A with a magnesium ion concentration of 0.7 mol / L to 1.3 mol / L. The solution containing the biomass template agent and the precipitant is specifically as follows: The precipitant is either ammonium bicarbonate or ammonium carbonate, and the biomass template agent is sodium carboxymethyl cellulose, with a viscosity specification (1% aqueous solution, 25℃) between 500 mPa·s and 1500 mPa·s. In solution B, the ratio of the number of moles of precipitant to the number of moles of magnesium ions in solution A, i.e., precipitant / Mg 2+ The ratio should be within the range of 1.8:1 to 2.5:1, specifically 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, and 2.5:1. In solution B, the amount of sodium carboxymethyl cellulose (CMC), a biomass template agent, was calculated based on the final theoretical mass of magnesium oxide produced, with an addition ratio ranging from 0.2% to 5.0% of the theoretical magnesium oxide mass. The specific impact of the amount of biomass template agent added on product performance is as follows: As shown in the table above, the product performance is optimal when the addition amount is 1.5%. When preparing solution B, first pre-disperse the calculated amount of sodium carboxymethyl cellulose in one-quarter of the deionized water. Then, add the remaining aqueous solution containing the calculated amount of precipitant while stirring vigorously to ensure that the CMC is completely dissolved to form a homogeneous and transparent solution. Finally, bring the volume to the required level.

[0020] Furthermore, the specific control conditions for the co-precipitation reaction are as follows: Reaction temperature: controlled within the range of 40℃, 45℃, 50℃, 55℃, and 60℃; Feeding method: Liquid A and liquid B must be added in parallel and synchronously; the feeding rate should be kept constant so that the entire feeding process lasts for 30 minutes, 40 minutes, 50 minutes, 60 minutes, or 70 minutes. Stirring speed: Maintain between 300 rpm and 500 rpm to ensure uniform mixing of the reaction system and avoid excessively high local concentrations; pH at the reaction endpoint: By adjusting the concentrations and feeding ratio of solutions A and B, the pH of the system at the end of the reaction is stabilized between 7.2 and 8.5. Curing process: After the material is added, continue the reaction for 15 minutes, 20 minutes, 30 minutes, 40 minutes and 45 minutes while maintaining the same temperature and stirring speed, so as to make the precursor crystal growth more perfect.

[0021] Furthermore, the washing of the ceramic ultrafiltration membrane in step S3 specifically includes: The ceramic ultrafiltration membrane is made of alumina, zirconium oxide, or a composite thereof, with an average pore size ranging from 10 nm to 100 nm. The operation mode is dialysis filtration, which involves continuously adding an equal amount of deionized water to the feed side while concentrating the solution. The transmembrane pressure is controlled between 0.4 MPa and 1.2 MPa. The washing endpoint is determined by real-time monitoring of the conductivity of the permeate. Washing can be stopped when the conductivity of the permeate decreases and stabilizes below 20 μS / cm, 30 μS / cm, 40 μS / cm, 50 μS / cm, and 60 μS / cm. The process parameters for the spray drying are as follows: Inlet air temperature: controlled within the range of 180℃, 200℃, 220℃, 240℃, and 260℃; Air outlet temperature: controlled within the range of 80℃, 90℃, 95℃, 100℃, and 110℃; Atomizer speed: Controlled between 15,000 rpm and 25,000 rpm to ensure that the slurry is atomized into uniform tiny droplets.

[0022] Furthermore, in step S4, the inert atmosphere refers to the use of one of nitrogen, argon, or a mixture thereof with a purity higher than 99.99%, which is introduced into the calcination furnace cavity at a flow rate of 0.5 L / min to 3 L / min throughout the calcination process to isolate air and prevent carbonation and sintering of the product. The temperature program of the dynamic programmed temperature-controlled calcination specifically includes: Low-temperature dehydration section: The temperature is increased from room temperature at rates of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, and 8℃ / min; after reaching 150℃, 180℃, 200℃, 220℃, and 250℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, 40 minutes, and 50 minutes, respectively. Intermediate-temperature decomposition and pore-forming section: The temperature is increased from the end temperature of the first section at a rate of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min; after increasing the temperature to 450℃, 480℃, 500℃, 520℃, and 550℃, a long-term holding time is performed; the holding time ranges are 60 minutes, 75 minutes, 90 minutes, 105 minutes, and 120 minutes. High-temperature annealing and structural stabilization stage: The temperature is rapidly reduced from the end temperature of the second stage at a rate greater than 5℃ / min; after cooling to 350℃, 380℃, 400℃, 420℃, and 450℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, and 40 minutes, respectively. Controlled cooling section: Under the condition of continuous inert atmosphere, heating is stopped, and the furnace body is allowed to cool naturally and under program control to below 60°C before being removed from the furnace; The impact of dynamic temperature-controlled calcination versus traditional processes on product performance (with a fixed CMC addition of 1.5%). As shown in the table above, the product calcined using dynamic program temperature control is the best.

[0023] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing high-purity active magnesium oxide, characterized in that, Includes the following steps: S1: Deep purification and membrane separation of feed solution: For industrial by-product magnesium source solution, chemical pretreatment is first performed to remove heavy metals and silicon impurities, followed by deep separation using nanofiltration membrane to target and remove calcium ions and sulfate impurities to obtain magnesium salt intermediate solution. S2: Controlled precipitation synthesis guided by biotemplate: The magnesium salt solution obtained in step S1 is mixed with a solution containing a specific ratio of biomass template agent and precipitant, and a co-precipitation reaction is carried out under the conditions of temperature, feeding method, stirring speed and pH to generate a basic magnesium carbonate precursor slurry with a uniform spherical and porous microstructure. S3: Washing and instant drying based on membrane separation technology: The precursor slurry obtained in step S2 is dialyzed and washed using a ceramic ultrafiltration membrane to completely remove chloride ions and ammonium ions soluble impurities. Then, the slurry is instantly solidified into a free-flowing microspherical precursor powder by spray drying to retain its microstructure. S4: Dynamic temperature-controlled calcination under inert atmosphere protection: The precursor powder obtained in step S3 is subjected to dynamic temperature-controlled calcination with multiple stages of heating, cooling and holding platforms under inert atmosphere protection, and finally the precursor is converted into magnesium oxide product.

2. The process for preparing high-purity active magnesium oxide according to claim 1, characterized in that: The magnesium source solution in step S1 has the following specific components: The magnesium-rich brine produced after lithium extraction from salt lakes is mainly composed of magnesium chloride hexahydrate, with magnesium ion concentration ranging from 150 g / L to 220 g / L. Typical impurity contents range from 300 mg / L to 800 mg / L for calcium ions, 500 mg / L to 1500 mg / L for sulfate ions, and 50 mg / L to 150 mg / L for boron. Boron mud, a solid waste produced during the production of boric acid from boromagnesite, is leached with inorganic acid to obtain the filtrate. The filtrate is then leached for 1-3 hours using 10%-20% sulfuric acid at a solid-liquid ratio of 1:2 to 1:4 and a temperature of 70℃ to 90℃. The main component of the filtrate is magnesium sulfate, with magnesium ion concentrations ranging from 120 g / L to 190 g / L. Typical impurities include: calcium ions from 200 mg / L to 600 mg / L, silica from 30 mg / L to 100 mg / L, and ferric ions from 5 mg / L to 20 mg / L.

3. The process for preparing high-purity active magnesium oxide according to claim 2, characterized in that: The specific process of the chemical pretreatment in step S1 is as follows: The pH of the original magnesium source solution is precisely adjusted to the range of 9.5 to 11.5 using a sodium hydroxide and potassium hydroxide solution with a concentration of 5%-25%; a preferred embodiment is to adjust the pH to 10.

5. Add a soluble sulfide as a precipitant, preferably sodium sulfide nonahydrate, at an amount of 105% to 150% of the theoretically calculated amount. Place the mixture in a constant temperature environment of 50°C to 70°C and stir at a rate of 200 rpm to 400 rpm for aging reaction. The aging time is 0.5 hours to 2 hours. After aging, solid-liquid separation is carried out using one of the following methods: plate and frame filter press, vacuum filtration, or centrifugation, and the clarified filtrate is collected.

4. The process for preparing high-purity active magnesium oxide according to claim 3, characterized in that: The nanofiltration membrane purification specifically includes: The nanofiltration membrane element is made of polyamide, polypiperazine amide, and their composite materials, with a nominal molecular weight cutoff ranging from 150 Da to 350 Da; the operating pressure is controlled between 1.0 MPa and 3.0 MPa; the operating temperature is maintained between 20°C and 35°C; the operating mode adopts a concentration and circulation mode, continuously collecting the permeate until the original liquid volume is concentrated to 5%-15% of the initial volume and then stopping.

5. The process for preparing high-purity active magnesium oxide according to claim 1, characterized in that: In step S2, the magnesium salt solution is divided into solution A and solution B. The specific preparation method is as follows: the nanofiltration permeate obtained in step S1 is diluted with deionized water and moderately concentrated by evaporation according to its actual magnesium ion concentration, and finally prepared into solution A with a magnesium ion concentration of 0.7 mol / L to 1.3 mol / L. The solution containing the biomass template agent and the precipitant is specifically as follows: The precipitant is either ammonium bicarbonate or ammonium carbonate, and the biomass template agent is sodium carboxymethyl cellulose with a viscosity specification between 500 mPa·s and 1500 mPa·s. In solution B, the ratio of the number of moles of precipitant to the number of moles of magnesium ions in solution A, i.e., precipitant / Mg 2+ The ratio should be within the range of 1.8:1 to 2.5:1, specifically 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, and 2.5:

1. In solution B, the amount of sodium carboxymethyl cellulose, a biomass template agent, is calculated based on the final theoretical mass of magnesium oxide produced, and its addition ratio ranges from 0.2% to 5.0% of the theoretical magnesium oxide mass. When preparing solution B, first pre-disperse the calculated amount of sodium carboxymethyl cellulose in one-quarter of deionized water. Then, add the remaining aqueous solution containing the calculated amount of precipitant while stirring vigorously to ensure that the CMC is completely dissolved to form a homogeneous and transparent solution. Finally, bring the volume to the required level.

6. The process for preparing high-purity active magnesium oxide according to claim 5, characterized in that: The specific control conditions for the co-precipitation reaction are as follows: Reaction temperature: controlled within the range of 40℃, 45℃, 50℃, 55℃, and 60℃; Feeding method: Liquid A and liquid B must be added in parallel and synchronously; the feeding rate should be kept constant so that the entire feeding process lasts for 30 minutes, 40 minutes, 50 minutes, 60 minutes, or 70 minutes. Stirring speed: Maintain between 300 rpm and 500 rpm to ensure uniform mixing of the reaction system and avoid excessively high local concentrations; pH at the reaction endpoint: By adjusting the concentrations and feeding ratio of solutions A and B, the pH of the system at the end of the reaction is stabilized between 7.2 and 8.

5. Maturation process: After the material is added, continue the reaction for 15 minutes, 20 minutes, 30 minutes, 40 minutes and 45 minutes while maintaining the same temperature and stirring speed, so as to make the precursor crystal growth more complete.

7. The process for preparing high-purity active magnesium oxide according to claim 1, characterized in that: The washing of the ceramic ultrafiltration membrane in step S3 specifically includes: The ceramic ultrafiltration membrane is made of alumina, zirconium oxide, or a composite thereof, with an average pore size ranging from 10 nm to 100 nm. The operation mode is dialysis filtration. The transmembrane pressure is controlled between 0.4 MPa and 1.2 MPa.

8. The process for preparing high-purity active magnesium oxide according to claim 1, characterized in that: In step S4, the inert atmosphere refers to one of nitrogen, argon, or a mixture thereof with a purity higher than 99.99%, which is introduced into the calcination furnace cavity at a flow rate of 0.5 L / min to 3 L / min throughout the calcination process. The temperature program of the dynamic programmed temperature-controlled calcination specifically includes: Low-temperature dehydration section: The temperature is increased from room temperature at rates of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, and 8℃ / min; after reaching 150℃, 180℃, 200℃, 220℃, and 250℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, 40 minutes, and 50 minutes, respectively. Intermediate-temperature decomposition and pore-forming section: The temperature is increased from the end temperature of the first section at a rate of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min; after increasing the temperature to 450℃, 480℃, 500℃, 520℃, and 550℃, a long-term holding time is performed; the holding time ranges are 60 minutes, 75 minutes, 90 minutes, 105 minutes, and 120 minutes. High-temperature annealing and structural stabilization stage: The temperature is rapidly reduced from the end temperature of the second stage at a rate greater than 5℃ / min; after cooling to 350℃, 380℃, 400℃, 420℃, and 450℃, the temperature is held for 15 minutes, 20 minutes, 30 minutes, and 40 minutes, respectively. Controlled cooling section: Under the condition of continuous inert atmosphere, heating is stopped, and the furnace body is allowed to cool naturally and under program control to below 60°C before being removed from the furnace.

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