Low-carbon energy-saving process for preparing silicon steel grade magnesium oxide by carbonization method

Abstract

The present application relates to the technical field of inorganic chemical industry, and discloses a low-carbon energy-saving process for preparing silicon steel grade magnesium oxide by carbonization method.The process comprises the following steps: preparing magnesium hydroxide slurry; constructing a biological strengthening factor by using porous carriers to immobilize Bacillus mucilaginosus; mixing the slurry with the strengthening factor in a carbonization tower, pressurizing and feeding carbon dioxide into the carbonization tower for biochemical catalytic carbonization; and purifying, pyrolyzing, dehydrating and high-temperature calcining the obtained heavy magnesium water.The present application breaks through the carbon dioxide hydration kinetic bottleneck from the molecular level by introducing a biological enzyme catalytic mechanism, so that efficient mass transfer can be realized at low pressure, power consumption is reduced, the utilization rate of carbon dioxide is improved, and the product has high purity and consistent activity.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical technology, specifically relating to a low-carbon and energy-saving process for preparing silicon steel grade magnesium oxide by carbonization. Background Technology

[0002] As a core functional material in the oriented silicon steel manufacturing system, silicon steel grade magnesium oxide not only plays an isolating role in preventing steel strips from sticking together during the high-temperature annealing process, but also generates a magnesium silicate film underlayer with excellent insulation and magnetic properties through chemical reaction with silicon dioxide on the steel substrate surface.

[0003] The core rate-limiting step in existing carbonization processes lies in the hydration of carbon dioxide molecules in the liquid phase. This involves the chemical transformation of carbon dioxide from the gas phase through the gas-liquid interface into the liquid phase, where it combines with water molecules to form carbonic acid and subsequently dissociates into bicarbonate ions. Under natural operating conditions, the rate of this hydration reaction is extremely low, making it difficult to quickly establish a dissolution equilibrium of carbon dioxide in the slurry.

[0004] Current industrial practices maintain high carbon dioxide partial pressures (typically 0.2 MPa to 0.5 MPa or even higher) through large-scale compressor clusters, or utilize high-power mechanical stirring to reduce bubble size and increase mass transfer area through shear force. This strategy of compensating for low reaction rates with high energy consumption directly leads to a surge in electricity and coal consumption during the carbonization stage.

[0005] In actual production, due to the imperfect contact mechanism at the gas-liquid-solid three-phase interface, carbon dioxide bubbles are prone to coalescence during their ascent, leading to a sharp reduction in the reaction area. Simultaneously, the dynamic evolution of the viscosity of the magnesium hydroxide slurry during carbonization and the unevenness of the local concentration gradient result in a persistently low single-pass carbon dioxide utilization rate. A large amount of unreacted carbon dioxide is discharged with the exhaust gas, causing not only resource waste but also increasing the economic burden of end-of-pipe carbon capture and treatment. Summary of the Invention

[0006] This invention provides a low-carbon and energy-saving process for preparing silicon steel grade magnesium oxide by carbonization, aiming to solve the technical problems of low carbonization reaction rate, insufficient carbon dioxide utilization rate and poor system operating energy efficiency ratio in the prior art.

[0007] The present invention discloses a low-carbon and energy-saving process for preparing silicon steel grade magnesium oxide by carbonization, comprising the following steps:

[0008] The first step is the preparation and pretreatment of magnesium hydroxide slurry. Lightly calcined magnesium oxide powder with a magnesium oxide mass fraction greater than or equal to 90% is selected as the raw material. The lightly calcined magnesium oxide powder is conveyed into a digestion tank with multi-stage stirring function. Deionized water is added to the digestion tank; the resistivity of the deionized water must be greater than or equal to 1 megohm-cm. The solid-liquid mass ratio during digestion is controlled to be 1:10 to 1:15. The stirring mechanism in the digestion tank is a double-layer stirring structure consisting of upper and lower straight-blade turbine stirrers, with a rotation speed set to 150 to 200 rpm. The digestion reaction temperature is maintained at 90 to 95 degrees Celsius, and the reaction time lasts for 120 to 180 minutes. After digestion, the generated magnesium hydroxide slurry is sorted by a hydrocyclone classifier located at the outlet of the digestion tank to remove coarse particles larger than 50 micrometers and undigested slag. After sorting, the magnesium hydroxide slurry enters the slurry aging tank and is left to stand at room temperature for 12 hours to obtain magnesium hydroxide slurry with a median particle size distribution between 3 and 8 micrometers.

[0009] The second step involves the construction and activation of bio-enhancing factors. This process introduces carbonic anhydrase-producing microorganisms as the core of the biocatalysis; these microorganisms are selected from *Bacillus mucilaginosus*. To ensure the microorganisms maintain their biological activity and physical stability in a strongly alkaline magnesium hydroxide slurry environment, a porous inert carrier is used for immobilization. The porous inert carrier consists of porous ceramic particles with an average pore size of 10 to 50 micrometers, a porosity of 65% to 80%, and a specific surface area of ​​30 to 60 square meters per gram. The material composition of the porous ceramic particles, by mass percentage, includes 60% to 70% alumina, 20% to 30% silica, and the remainder being flux components. Before immobilization, the porous ceramic particles undergo surface-active modification by immersing them in a 5% silane coupling agent solution for four hours to enhance their surface hydrophilicity and biocompatibility. The microbial loading process was carried out in a bioreactor, where *Bacillus mucilaginosus* was inoculated into a liquid culture medium containing 1% peptone, 0.5% yeast extract, 1% sodium chloride, and 0.02% magnesium sulfate by mass. The inoculum was loaded until the bacterial concentration reached 10-1 ppm. 9 When a colony-forming unit is reached, treated porous ceramic particles are introduced into the bioreactor. The reactor temperature is controlled at 30°C to 35°C, and the aeration rate is 50 to 80 kilometres per hour based on the volumetric oxygen transfer coefficient. Continuous circulation is maintained for 48 to 72 hours to allow biofilm formation. After biofilm formation, microorganisms form a stable biofilm structure within the pores of the porous ceramic particles, creating a bio-enhancing factor.

[0010] The third step is the pressurized biocarbonization reaction. This process is carried out in a dedicated biocarbonization tower. The biocarbonization tower is a vertical cylindrical pressure vessel with a length-to-diameter ratio of 8:1 to 10:1. The inner wall of the tower is lined with an alkali-resistant and corrosion-resistant coating. The prepared magnesium hydroxide slurry and the bio-enhancing agent are mixed at a volume ratio of 10:1 and then pumped into the biocarbonization tower. The bio-enhancing agent is in a suspended state inside the tower, and its spatial distribution is maintained uniformly by a slurry circulation pump at the bottom of the tower. A high-density microporous gas distribution system is installed at the bottom of the biocarbonization tower, and the gas distribution head is made of microporous metal membrane material with an average pore size of 3 to 5 micrometers. Industrial waste gas with a carbon dioxide concentration of ≥95% is treated by dust removal, desulfurization, and pressurization to a pressure of 0.2 MPa to 0.5 MPa, and then countercurrently blown into the slurry through the microporous gas distribution system.

[0011] During the biocarbonation reaction, carbon dioxide bubbles collide with and are adsorbed by suspended bio-enhancing factors as they rise. Carbon dioxide molecules enter the pores of the porous ceramic particles and come into contact with carbonic anhydrase secreted by Bacillus subtilis adhering to the pore walls. Carbonic anhydrase catalyzes the hydration reaction of carbon dioxide, converting it into bicarbonate ions and hydrogen ions. This biocatalytic process increases the hydration rate of carbon dioxide to more than ten thousand times the natural hydration rate. The generated bicarbonate ions rapidly diffuse to the interface between the carrier surface and the slurry, where they chemically react with magnesium hydroxide particles. The chemical reaction process is described as follows: solid magnesium hydroxide maintains a dissolution equilibrium in the aqueous solution; the generated magnesium ions combine with bicarbonate ions to form magnesium bicarbonate, which has higher solubility, thereby promoting the continuous dissolution and transformation of solid magnesium hydroxide. The temperature during the carbonation process is controlled between 20 and 30 degrees Celsius, and the heat of reaction is removed by a jacketed cooling water system located outside the carbonation tower.

[0012] During the carbonization reaction, pH and conductivity sensors installed at different heights within the tower monitor the reaction progress in real time. When the pH of the slurry drops from approximately 10.5 initially to a preset range of 7.2 to 7.5, and the conductivity value shows a significant plateau, the carbonization reaction is considered complete. At this point, the discharge system at the bottom of the tower is activated to send the reaction products to the subsequent processing section.

[0013] The fourth step is the clarification and impurity removal of the magnesium hydroxide solution. The carbonization reaction product is a mixed slurry containing magnesium bicarbonate, bio-enhancing agents, and unreacted solid impurities. This mixed slurry first enters a precision rotary filter. The filter screen of the rotary filter is set to a mesh size of 350 to 400 mesh, which can separate the bio-enhancing agents from the magnesium bicarbonate solution. The separated bio-enhancing agents are rinsed with a weakly alkaline washing solution and then returned to the storage tank of the second step for recycling through a return pipe. The magnesium bicarbonate solution obtained by filtration is the magnesium hydroxide solution. To meet the strict requirements for impurity content of silicon steel grade magnesium oxide, the magnesium hydroxide solution is sent to a deep purification tank, and an appropriate amount of impurity removal agent is added. The impurity removal agent includes a 0.5% (w / w) barium hydroxide solution to precipitate sulfate ions in the solution; and a 0.1% (w / w) sodium diethyldithiocarbamate to chelate and remove heavy metal ions such as iron, manganese, and copper. The purified magnesium hydroxide solution is then finely filtered through a microporous pleated filter element with a pore size of 0.22 micrometers to obtain a high-purity clarified magnesium hydroxide solution.

[0014] The fifth step is the pyrolysis reaction of the magnesium hydroxide solution. The purified magnesium hydroxide solution is pumped into a pyrolysis tower. The pyrolysis tower is equipped with multiple layers of staggered baffles and steam heating coils. The steam heating system is turned on, raising the temperature of the magnesium hydroxide solution from room temperature to 95-100 degrees Celsius. During heating, magnesium bicarbonate undergoes thermal decomposition. This reaction releases carbon dioxide gas and produces basic magnesium carbonate particles. The carbon dioxide gas generated during pyrolysis is collected by a condensation recovery system at the top of the tower. After condensation to remove moisture, it is sent to a controlled atmosphere tank and returned to the pressurized biocarbonation section of the third step for recycling. The pyrolysis reaction continues for 60-90 minutes until the magnesium ion concentration in the solution decreases to below 0.5 grams per liter.

[0015] The sixth step is the dehydration and washing of basic magnesium carbonate. The basic magnesium carbonate suspension generated by pyrolysis is sent to a plate and frame filter press for solid-liquid separation. The filter cake formed by pressing is washed in three stages of countercurrent washing with deionized water at 80 degrees Celsius, with the washing water volume controlled at a mass ratio of 5:1 to the filter cake. The washing process aims to remove chloride ions, sodium ions, and soluble organic matter entrained in the filter cake. The moisture content of the washed filter cake is controlled between 35% and 45%.

[0016] The seventh step is high-temperature calcination and post-processing of the finished product. The washed basic magnesium carbonate filter cake is fed into a continuous multi-layer calcination furnace with preheating function. The calcination process is divided into three stages: The first stage is the preheating and dehydration stage, with the temperature controlled at 200°C to 300°C and the residence time at 40 minutes. The residual heat of the furnace exhaust gas is used to remove physically adsorbed water and some crystal water. The second stage is the decomposition stage, with the temperature rising to 600°C to 700°C and the residence time at 60 minutes. In this stage, basic magnesium carbonate is completely decomposed into crude magnesium oxide, releasing carbon dioxide and water vapor. The third stage is the high-temperature crystal transformation stage, with the temperature rising to 950°C to 1100°C and the residence time at 120 minutes to 180 minutes. In this stage, by precisely controlling the temperature and time, the lattice defects and specific surface area of ​​magnesium oxide are adjusted to meet the activity requirements of silicon steel grade magnesium oxide. After calcination, the material enters an air-cooled cooler and is rapidly cooled to below 50°C. The cooled magnesium oxide is pulverized using an ultrafine pulverizer, with high-purity nitrogen gas introduced during the pulverization process to prevent moisture absorption and carbonization. Finally, an air classifier is used to control the particle size of the finished product, ensuring that the particle size distribution is between 0.5 micrometers and 2 micrometers, thus obtaining the final silicon steel grade magnesium oxide product.

[0017] In a preferred embodiment of the present invention, the digestion tank in the first step is equipped with an ultrasonic enhancement generator. During the digestion reaction, ultrasonic treatment with a frequency of 20 kHz to 40 kHz and a sound power density of 0.5 W to 1 W per square centimeter is activated. The cavitation effect of the ultrasound can break the passivation layer on the surface of the magnesium hydroxide particles, increase the solid-liquid contact area, thereby shortening the digestion time to less than 90 minutes and improving the uniformity of the slurry.

[0018] In a preferred embodiment of the present invention, during the construction of the bio-enhancing factor in the second step, an additional semi-permeable membrane structure is coated onto the surface of the porous ceramic particles. The semi-permeable membrane is composed of a gel layer formed by reacting 1% sodium alginate and 2% calcium chloride by mass. The pore size of this semi-permeable membrane allows carbon dioxide molecules, bicarbonate ions, and small nutrient molecules to pass freely, but blocks the direct mechanical abrasion of the microbial biofilm by large magnesium hydroxide particles, thereby extending the lifespan of the bio-enhancing factor to more than six months.

[0019] In a preferred embodiment of the present invention, the biocarbonization tower in the third step is equipped with multiple sets of symmetrical mechanical agitators arranged radially inside. The blades of the agitators are airfoil blades with low shear characteristics, and the rotational speed is set to 50 to 80 revolutions per minute. The combined flow field formed by mechanical agitation and bottom microporous aeration can enhance the mass transfer efficiency of the gas, liquid, and solid phases and prevent bio-enhancing factors from depositing at the bottom of the tower.

[0020] In a preferred embodiment of the present invention, the pressurized biocarbonization section employs a two-stage series carbonization mode. The first-stage carbonization tower serves as the main reaction zone, with an inlet pressure set at 0.4 MPa to 0.5 MPa, achieving 80% carbonization conversion. The second-stage carbonization tower serves as the refining reaction zone, with an inlet pressure set at 0.2 MPa to 0.3 MPa, utilizing the exhaust gas from the first-stage tower for residual reactions. This two-stage series structure can improve the overall single-pass utilization rate of carbon dioxide.

[0021] In a preferred embodiment of the present invention, the deep purification tank in the fourth step is equipped with a high-intensity magnetic separation device. The magnetic separation device is activated simultaneously with the addition of the impurity removal agent, utilizing magnetic force to adsorb and remove any minute iron-containing magnetic impurities that may be present in the magnesium oxide solution, ensuring that the iron oxide mass fraction in the finished magnesium oxide is less than 0.01%.

[0022] In a preferred embodiment of the present invention, the pyrolysis reaction in the fifth step employs a multi-stage flash pyrolysis technique. The finely filtered magnesium hydroxide is first preheated to 80 degrees Celsius via a heat exchanger, and then sequentially enters flash chambers with decreasing pressure. By adjusting the vacuum level in each flash chamber, magnesium bicarbonate is induced to decompose rapidly at lower temperatures. This technique utilizes waste heat steam within the system, reducing pyrolysis energy consumption.

[0023] In a preferred embodiment of the present invention, an online infrared temperature measurement array is arranged inside the multi-layer calcining furnace in the seventh step. The infrared sensors monitor the real-time temperature of the material at different residence positions, and the central control system automatically adjusts the gas nozzle flow rate or electric heating power of each temperature zone based on the temperature feedback signal, ensuring that the temperature fluctuation in the calcining zone is controlled within ±5 degrees Celsius, thereby achieving precise control of the product activity.

[0024] The process of this invention achieves closed-loop recycling of wastewater throughout the entire operating cycle. The filtrate produced by pressure filtration in the sixth step, as well as the tertiary washing water, are returned to the first step as digested water for recycling after sedimentation, neutralization, and multi-media filtration. There is no process wastewater discharge throughout the entire process.

[0025] In another embodiment of the present invention, the carbonic anhydrase-producing microorganisms in the bio-enhancing factor can also be Bacteroides strains acclimated to an alkaline environment. The acclimation process involves continuous multi-generation transfer culture in a culture medium with progressively increasing pH (from pH 8.5 to pH 10.5). Through this acclimation process, the microorganisms maintain a high level of carbonic anhydrase secretion capacity while exhibiting stronger tolerance to high-concentration magnesium ion environments.

[0026] This invention establishes strict procedures for the replenishment and maintenance of bio-enhancing factors. During the carbonization cycle, the activity of the bio-enhancing factors in the system is sampled and analyzed every 120 hours. By measuring their enzyme activity index, if the activity decreases by more than 30% of the initial value, freshly prepared bio-enhancing factors are replenished into the carbonization tower via an online replenishment pump on the side line. Simultaneously, a small amount of trace element supplement solution containing 0.5% (w / w) zinc ions is added to the system to serve as the active center component of the carbonic anhydrase molecule, thereby maintaining enzyme catalytic efficiency.

[0027] At the automation control level, this process establishes a logic control system based on multivariate correlation. The inlet pressure of the carbonation tower, slurry flow rate, stirring speed, and pH value are set as interrelated control variables. When the pH detection module detects that the slurry acidity rise rate is lower than the preset threshold, the control system automatically increases the carbon dioxide inlet flow rate and increases the circulation pump pressure to enhance the mass transfer driving force. When the conductivity reaches the carbonation endpoint characteristic value, the system automatically closes the inlet valve and starts the discharge pump, achieving precise control of the carbonation cycle.

[0028] This invention discloses a low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide via carbonization. By introducing a bio-enzyme catalytic mechanism in the carbonization stage, it overcomes the bottleneck of carbon dioxide hydration kinetics at the molecular level. Combined with a three-phase microenvironment constructed using a porous support, it not only protects the biocatalyst but also enhances the reaction flux at the gas-liquid-solid interface through capillary action and diffusion enhancement of the porous structure.

[0029] Regarding product quality control, the biocarbonization process is completed in a near-neutral environment (pH 7.2-7.5) with mild reaction conditions, avoiding the synergistic precipitation of impurities such as calcium and silicon that may occur under strongly alkaline conditions, thus improving the purity of the heavy magnesium hydroxide. Through precise control of subsequent pyrolysis and high-temperature calcination, the resulting silicon steel-grade magnesium oxide not only has high chemical purity but also excellent particle size uniformity and activity consistency, fully meeting the stringent requirements of oriented silicon steel surface treatment.

[0030] In terms of environmental protection and resource utilization, this process fully utilizes carbon dioxide from industrial waste gas and achieves closed-loop recycling of carbon dioxide within the system. Through efficient bioconversion and pyrolysis recovery, the total carbon dioxide emission reduction rate reaches over 90%. Simultaneously, the water resource recycling design throughout the entire process minimizes industrial water consumption. The successful implementation of this process provides an efficient, energy-saving, and environmentally friendly technological path for the industrial upgrading of the magnesium oxide industry.

[0031] As a supplementary explanation of the process of this invention, a high-efficiency demister is also installed at the top of the biocarbonization tower. This demister consists of multiple layers of polypropylene baffles and stainless steel wire mesh, designed to capture fine droplets escaping with the exhaust gas and any trace amounts of biological carrier debris that may be entrained, ensuring the cleanliness of the emitted exhaust gas. The trapped droplets are collected through a collection pipe and returned to the slurry aging tank.

[0032] In the finished product inspection and quality assurance system, this process employs an online particle size analyzer based on the principle of laser diffraction. During the seventh step, the ultrafine grinding and classification stage, the online analyzer monitors the powder particle size distribution in real time. If the D90 index exceeds the preset range of two micrometers, the rotor frequency of the classifier will automatically increase until the particle size returns to the acceptable range. This closed-loop control mechanism ensures zero defects in the finished products.

[0033] As a supplementary embodiment of the process of this invention, a low-temperature plasma treatment device is installed in the slurry aging tank in the first step. During the aging process, the plasma generator is turned on to generate a large number of active free radicals. These free radicals can oxidize and decompose the trace amounts of organic impurities remaining in the lightly calcined magnesium oxide, further improving the purity of the raw materials.

[0034] In a preferred embodiment of the present invention, the exhaust port of the carbonization tower in the third step is connected to a secondary bioadsorption column. This adsorption column is filled with moist honeycomb ceramic packing material loaded with the same carbonic anhydrase-producing microorganisms. Carbon dioxide that has not fully reacted within the tower is further captured and transformed by the biofilm on the surface of the packing material as it passes through the adsorption column, converting it into a bicarbonate solution which is then distilled into a magnesium hydroxide storage tank. This design further minimizes the system's carbon dioxide emissions.

[0035] In a preferred embodiment of the present invention, the washing solution for washing basic magnesium carbonate in the sixth step contains an additional surfactant with a mass fraction of 0.05%. The surfactant is sodium dodecylbenzenesulfonate. The application of this component reduces the surface tension of the capillary pores in the filter cake, making it easier for the washing water to penetrate and displace deep-seated ionic impurities. Simultaneously, it helps to inhibit excessive agglomeration of crystals during subsequent calcination.

[0036] In a preferred embodiment of the present invention, the high-temperature calcination stage of the seventh step employs a programmed temperature rise mode. The heating rate is controlled at 5 to 8 degrees Celsius per minute. Two holding platforms are set at 650 degrees Celsius and 850 degrees Celsius respectively, with each platform maintained for 30 minutes. This stepped heating process facilitates the slow escape of gases released from the decomposition of basic magnesium carbonate, preventing grain breakage or pore structure collapse caused by gas ejection, thereby obtaining active magnesium oxide with a specific pore distribution.

[0037] This process also fully considers the durability of the mechanical structure in its design. All pumps conveying slurries containing bio-enhancing agents are lined with rubber or polymer materials to reduce mechanical shear damage to the bioceramic particles. Simultaneously, large-radius elbows are used at critical bends in the pipeline to reduce local fluid velocity, thereby protecting the physical integrity of the biocarrier and ensuring its extended cycle life within the system.

[0038] In actual production operation, this process achieves full-process data monitoring through an integrated central control system. Sensor data from all key nodes (such as temperature, pressure, pH, flow rate, and material level) are transmitted to the control center in real time via fieldbus. The control system has a self-diagnostic function, automatically switching to a safe operating mode based on abnormal fluctuations in various parameters and prompting maintenance personnel to intervene. This highly automated control system reduces the intensity of manual operation and improves the stability of the process.

[0039] As an extended application of this invention, the porous carrier-microorganism-slurry three-phase microenvironment construction scheme adopted in this process also has strong potential for transfer and application in similar inorganic chemical processes involving gas-liquid-solid three-phase mass transfer (such as the carbonation process for the production of calcium carbonate and strontium carbonate). Its core biocatalytic logic and interface enhancement methods provide a universal technical platform for the green transformation of traditional chemical processes.

[0040] In the subsequent finished product packaging stage, the process of this invention recommends using vacuum packaging technology with a moisture-proof liner. Because silicon steel grade magnesium oxide has extremely strong hygroscopicity and reactivity, by filling the packaging bag with high-purity argon gas and performing vacuum sealing, the fluctuation of its activity value can be controlled within 5% during long-distance transportation and long-term storage, thereby ensuring the process stability of downstream silicon steel manufacturers.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] This invention introduces a bio-enhancing factor, utilizes carbonic anhydrase to catalyze the carbon dioxide hydration reaction, and combines pressurization and a composite flow field to enhance mass transfer, breaking through kinetic bottlenecks, significantly accelerating the carbonization rate, and shortening the reaction cycle.

[0043] Low-pressure operation reduces compressor energy consumption, carbon dioxide recovered by pyrolysis is recycled, wastewater is recycled in a closed loop with no external discharge, and bio-enhancing agents can be reused, significantly reducing energy consumption and resource waste.

[0044] The mild bio-carbonization environment reduces the precipitation of impurities. Through deep purification and precise calcination control, the product has high purity, uniform particle size, and consistent activity, meeting the requirements for silicon steel grade use.

[0045] The bio-enhancing factors are immobilized and protected by a semi-permeable membrane, making them resistant to strong alkaline environments and mechanical wear, resulting in a long service life; the entire process is automated and controlled, and the product performance fluctuates little during continuous operation.

[0046] It utilizes carbon dioxide from industrial waste gas to reduce carbon emissions; the process parameters are controllable, adaptable to different raw material purities, and the equipment has strong compatibility, making it easy to upgrade existing production lines. Detailed Implementation

[0047] This invention provides a low-carbon and energy-saving process for preparing silicon steel grade magnesium oxide by carbonization. The entire production process is divided into seven interconnected core process steps, including: precise preparation and physical property pretreatment of magnesium hydroxide slurry; construction and activation of bio-enhancing factors; pressurized bio-carbonization reaction; clarification and deep impurity removal of heavy magnesium water for the carbonization reaction products; pyrolysis reaction of heavy magnesium water; dehydration and washing process of basic magnesium carbonate; high-temperature calcination and post-processing of finished products.

[0048] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0049] Example 1: Lightly calcined magnesium oxide powder (magnesium oxide mass fraction 92%);

[0050] The magnesium hydroxide slurry had a solid-liquid mass ratio of 1:12 and a median particle size distribution of 5 μm.

[0051] Bio-enhancing factor (porous ceramic particles with an average pore size of 30 μm, porosity of 72%, and specific surface area of ​​45 m²) 2 / g, Bacillus subtilis loading 10 9 CFU / g, with a surface coated with a sodium alginate-calcium chloride semi-permeable membrane);

[0052] Industrial waste gas with a carbon dioxide concentration of 97%;

[0053] The impurity removal agent is 0.5% barium hydroxide solution and 0.1% sodium diethyldithiocarbamate;

[0054] Preparation steps: S1: Preparation and pretreatment of magnesium hydroxide slurry. Lightly calcined magnesium oxide powder was added to deionized water with a resistivity of 1.2 MΩ·cm at a solid-liquid ratio of 1:12. The mixture was stirred in a double layer at 92℃ (180 r / min) + ultrasonically at 28 kHz (0.8 W / cm). 2 Digest for 150 min; remove impurities larger than 50 μm using a hydrocyclone classifier; age the slurry in a aging tank at room temperature for 12 h; and remove organic impurities using low-temperature plasma treatment.

[0055] S2: Construction and activation of bio-enhancing factors: porous ceramic particles were treated with 5% silane coupling agent for 4 hours, and then... 9CFU / mL Bacillus mucilaginosus culture at 32℃ with a volumetric oxygen transfer coefficient of 65 h -1 Under the specified conditions, the membrane was attached for 60 hours, then covered with a semi-permeable membrane for later use.

[0056] S3: Pressurized biocarbonization reaction, magnesium hydroxide slurry and bio-enhancing agent are mixed at a volume ratio of 10:1 and injected into the biocarbonization tower (length-to-diameter ratio 9:1). 0.35MPa carbon dioxide gas is introduced into the microporous gas distribution system (pore size 4μm) at the bottom of the tower. A composite flow field is formed by airfoil stirring at 55r / min. The reaction is carried out at 25℃ until pH 7.3 and conductivity jump.

[0057] S4: Clarification and impurity removal of heavy magnesium water. The mixed slurry is separated from the bio-enhancing factor by a 380-mesh rotary filter (recycled). The filtrate enters the deep purification tank, where a purification agent and a magnetic separation device are added to adsorb magnetic impurities. Fine filtration is performed using a 0.22μm microporous pleated filter element.

[0058] S5: Heavy magnesium hydrothermal reaction, the clarified liquid is sent to the pyrolysis tower, heated to 98°C with steam, multi-stage flash pyrolysis for 75 minutes, release carbon dioxide and condense it back to the carbonization step.

[0059] S6: Basic magnesium carbonate dehydration and washing, pyrolysis suspension plate and frame filter press, 80℃ deionized water three-stage countercurrent washing (solid-liquid ratio 1:5), washing water contains 0.05% sodium 12-alkylbenzene sulfonate, filter cake moisture content 40%;

[0060] S7: High-temperature calcination and post-processing of finished products. The filter cake is fed into a multi-layer calcination furnace and the temperature is programmed to rise (6℃ / min): 250℃ preheating for 40min, 650℃ holding for 30min, and 1000℃ crystal transformation for 150min. After cooling, it is ultra-finely pulverized under the protection of high-purity nitrogen, and the airflow is classified to a particle size of 0.5-2μm. It is then vacuum-packed and filled with argon.

[0061] Example 2: Same as Example 1;

[0062] Preparation steps: Carbonization reaction pressure 0.2 MPa, the remaining steps are the same as in Example 1.

[0063] Example 3: Same as Example 1;

[0064] Preparation steps: Carbonization reaction pressure 0.5 MPa, the remaining steps are the same as in Example 1.

[0065] Example 4: The porous ceramic particles have an average pore size of 10 μm, and the remaining components and proportions are the same as in Example 1;

[0066] Preparation steps: Same as in Example 1.

[0067] Example 5: The porous ceramic particles have an average pore size of 50 μm, and the remaining components and proportions are the same as in Example 1;

[0068] Preparation steps: Same as in Example 1.

[0069] Example 6: Same as Example 1;

[0070] Preparation steps: The pyrolysis reaction temperature is 95℃, the pyrolysis time is 90min, and the remaining steps are the same as in Example 1.

[0071] Example 7: Same as Example 1;

[0072] Preparation steps: The pyrolysis reaction temperature is 100℃, the pyrolysis time is 60min, and the remaining steps are the same as in Example 1.

[0073] Example 8: The bio-enhancing factor microorganism was replaced with an alkaline-acclimated Bacteroides species, and the remaining components and proportions were the same as in Example 1;

[0074] Preparation steps: Same as in Example 1.

[0075] Comparative Example 1: The bio-enhancing factor was removed, and the remaining components were the same as in Example 1;

[0076] Preparation steps: The carbonization reaction does not involve bio-enhancing factors, and the remaining process parameters and steps are the same as in Example 1.

[0077] Comparative Example 2: Same as Example 1;

[0078] Preparation steps: Atmospheric pressure carbonization (0.1MPa) was used, without stirring and microporous gas distribution system. The remaining process parameters and steps were the same as in Example 1.

[0079] Test method:

[0080] Carbonization rate test: Record the time from the carbonization reaction to the endpoint and calculate the carbonization rate per unit volume of slurry;

[0081] Carbon dioxide utilization rate test: Determine the total consumption and recovery of carbon dioxide in the carbonization-pyrolysis cycle, and calculate the utilization rate;

[0082] Energy consumption test: Statistically measure the power consumption per unit mass of product and compare it with the energy-saving ratio of traditional processes;

[0083] Purity testing: Inductively coupled plasma mass spectrometry was used to determine the purity of magnesium oxide and the content of iron impurities.

[0084] Particle size testing: Particle size distribution was determined using a laser particle size analyzer;

[0085] Bio-enhancing factor lifespan test: After 1200 hours of cyclic use, the enzyme activity retention rate was measured.

[0086] The test data comparisons are shown in Table 1 and Table 2.

[0087] Table 1. Comparison of carbonization rate, carbon dioxide utilization rate, magnesium oxide purity, and median particle size.

[0088]

[0089] Table 2 Comparison of Iron Impurity Content, Unit Product Power Consumption, and Enzyme Activity Retention Rate

[0090]

[0091] Examples 1 to 8 utilize carbonic anhydrase in bio-enhancing factors to accelerate carbon dioxide hydration, construct a three-phase reaction microenvironment using a porous carrier, and enhance mass transfer through pressurization and stirring to achieve efficient carbonization under low pressure. Pyrolysis recovers carbon dioxide and wastewater is recycled, achieving low-carbon and energy-saving results. Comparative Example 1, lacking bio-enhancing factors, experienced a carbonization rate decrease of over 62%, resulting in reduced carbon dioxide utilization. Comparative Example 2, lacking pressurization and flow field enhancement, suffered a decline in reaction efficiency and product purity.

[0092] The carbonization rate and carbon dioxide utilization are optimal when the carbonization reaction pressure is 0.35 MPa to 0.5 MPa, the carrier pore size is 30 μm to 50 μm, and the pyrolysis temperature is 98℃ to 100℃. Among these factors, pressure directly affects carbon dioxide solubility and mass transfer driving force, carrier pore size determines microbial loading and enzyme catalytic efficiency, and pyrolysis temperature controls the decomposition rate of magnesium bicarbonate. These three factors work synergistically to ensure the high efficiency and stability of the process.

[0093] Compared to Comparative Example 1 without bio-enhancing agents, the carbonization rate of the example was increased by more than 166%, the purity of magnesium oxide was increased by more than 0.1%, and the power consumption per unit product was reduced by more than 48%. Compared to Comparative Example 2 without pressurization process, the carbonization rate was increased by more than 204%, the carbon dioxide utilization rate was increased by more than 20%, and the iron impurity content was reduced by more than 83%. Moreover, the wastewater was recycled in a closed loop and the bio-enhancing agents could be reused, which meets the needs of green chemical development.

[0094] In summary, this invention achieves simultaneous improvement in carbonization rate, product purity, and energy-saving effect by coupling biological enhancement factors with pressurized carbonization process. The carbon dioxide utilization rate exceeds 98%, and the product meets the stringent requirements of silicon steel production, demonstrating good potential for industrialization.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carburization, characterized in that, Includes the following steps: (1) Preparation and pretreatment of magnesium hydroxide slurry; (2) Construction and activation of bio-enhancing factors; (3) Pressurized biocarbonization reaction; (4) Clarification and impurity removal of magnesium hydroxide solution; (5) The pyrolysis reaction of magnesium hydroxide; (6) Dehydration and washing of basic magnesium carbonate; (7) High-temperature calcination and post-processing of finished products.

2. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 1, characterized in that, The specific steps of (1) are as follows: lightly calcined magnesium oxide powder is selected as raw material, the lightly calcined magnesium oxide powder is transported to a digestion tank with multi-stage stirring function, and deionized water is added to carry out digestion reaction; after digestion, the slurry is sorted by a hydrocyclone classifier to remove impurities, and then enters the slurry aging tank to stand and age at room temperature to obtain magnesium hydroxide slurry.

3. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 2, characterized in that, The specific steps of (2) are as follows: Bacillus mucilaginosus is selected as the carbonic anhydrase-producing microorganism, and the Bacillus mucilaginosus is immobilized using a porous inert carrier to prepare a bio-enhancing factor; wherein, the porous inert carrier is selected as porous ceramic particles.

4. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 3, characterized in that, The specific steps of (3) are as follows: in the biocarbonation tower, the magnesium hydroxide slurry and the bio-enhancing factor are mixed at a volume ratio of 10:1, and industrial waste gas with a carbon dioxide concentration of ≥95% is introduced through the microporous gas distribution system at the bottom of the tower to react and generate magnesium bicarbonate solution.

5. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 4, characterized in that, The specific steps of (4) are as follows: the mixed slurry after carbonization reaction is sent to a rotary filter for solid-liquid separation, the separated bio-enhancing factor is recycled, and the filtrate is sent to a deep purification tank as heavy magnesium water; a purification agent is added to the heavy magnesium water for precipitation and chelation reaction, and then it is finely filtered through a microporous pleated filter element to obtain a clear heavy magnesium water solution.

6. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 5, characterized in that, The specific steps of (5) are as follows: the clarified magnesium hydroxide solution is sent into the pyrolysis tower, and the magnesium bicarbonate is thermally decomposed by steam heating. The released carbon dioxide gas is condensed and recovered and returned to the third step for recycling. Basic magnesium carbonate particles are precipitated in the solution.

7. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carburization according to claim 6, characterized in that, The specific steps of (6) are as follows: the suspension generated by pyrolysis is separated into solid and liquid phases by a plate and frame filter press, and the resulting filter cake is subjected to three-stage countercurrent washing.

8. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 7, characterized in that, The specific steps of (7) are as follows: the washed filter cake is sent into a continuous multi-layer calcining furnace and successively undergoes a preheating and dehydration stage of 200℃~300℃, a decomposition stage of 600℃~700℃ and a high-temperature crystal transformation stage of 950℃~1100℃; the calcined material is cooled, ultra-finely pulverized and air-flow classified to obtain silicon steel grade magnesium oxide product.

9. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carbonization according to claim 2, characterized in that, The digester is equipped with a double-layer stirring structure consisting of two layers of straight-bladed turbine stirrers. During digestion, the stirring speed is set to 150 r / min to 200 r / min. Furthermore, during the digestion reaction, an ultrasonic enhancement generator is activated, controlling the ultrasonic frequency to 20 kHz to 40 kHz and the sound power density to be 0.5 W / cm². 2 ~1W / cm 2 .

10. The low-carbon and energy-saving process for preparing silicon steel-grade magnesium oxide by carburization according to claim 3, characterized in that, The slurry aging tank is equipped with a low-temperature plasma treatment device; and the carbonic anhydrase-producing microorganisms also include Bacteroides species that have been domesticated in an alkaline environment. The domestication process is carried out in a culture medium with a pH value increasing from 8.5 to 10.5 through continuous multi-generation transfer culture.

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