Synthesis process of small-particle-size basic cobalt carbonate

Abstract

The invention discloses a small-particle-size basic cobalt carbonate synthesis process in the technical field of inorganic functional materials, and the process is characterized in that firstly, surface-engineered gadolinium-doped cerium oxide nanoparticles are prepared as an inorganic modifier, and the modifier is prepared through the steps of coprecipitation, hydrothermal treatment, surface phosphorylation, reduction heat treatment and the like. In the synthesis of basic cobalt carbonate, the modifier is dispersed in water to form a turbid liquid, then cobaltous sulfate and a sodium bicarbonate solution are added into the turbid liquid in a parallel flow manner at a mild temperature to carry out a precipitation reaction, and nucleation and growth processes are regulated and controlled by accurately controlling the pH value of a reaction system; and finally, adjusting the terminal pH value by using a sodium carbonate solution, aging, separating, washing and drying to obtain a final product. Through the synergistic effect of the unique inorganic modifier and the double precipitants, high-yield preparation of the basic cobalt carbonate with small particle size, good sphericity degree and high purity under mild conditions is realized, the process is simple, and industrial production is easy to realize.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional materials technology, specifically to a process for synthesizing small-particle-size basic cobalt carbonate. Background Technology

[0002] Basic cobalt carbonate, as an important inorganic cobalt salt, is a key precursor for the preparation of high-performance cobalt-based functional materials such as cobalt tetroxide and lithium cobalt oxide. Its physicochemical properties, particularly particle size, uniformity of distribution, and microstructure, directly determine the core indicators of the resulting functional materials, such as tap density, specific surface area, and electrochemical performance. Therefore, the market demand for basic cobalt carbonate products with small particle size, narrow distribution, and regular morphology is increasingly urgent in many fields, including new energy batteries, high-end ceramic pigments, and catalysts. Traditional basic cobalt carbonate preparation processes typically involve a metathesis reaction between soluble cobalt salts (such as cobalt chloride and cobalt sulfate) and precipitants such as sodium carbonate or sodium bicarbonate. To control the product particle size, conventional technical routes often require the use of organic complexing agents (such as ammonia and citrate) to form intermediate complexes to slow down the precipitation rate, or complex processes requiring high temperature and high pressure, such as hydrothermal or solvothermal methods. While these methods can affect the product morphology to some extent, they inevitably introduce impurity ions that are difficult to remove completely, increasing the cost and difficulty of subsequent purification. Furthermore, the process conditions are relatively harsh and the energy consumption is high, which is not conducive to large-scale green industrial production.

[0003] However, achieving the controllable preparation of small-particle-size basic cobalt carbonate under mild conditions without relying on organic complexing agents still faces significant challenges. The core difficulty lies in effectively coordinating the formation of crystal nuclei and the growth rate of crystals during the precipitation reaction. To obtain fine particles, a high degree of supersaturation is needed to promote the instantaneous formation of numerous crystal nuclei; however, an excessively high reaction rate easily leads to localized concentration unevenness, causing particle agglomeration or excessively wide particle size distribution. Furthermore, to ensure the recovery rate of cobalt resources, sufficient alkalinity is required at the reaction endpoint to ensure complete precipitation of cobalt ions, but this accelerates the Ostwald ripening process of the grains, causing small particles to dissolve and redeposit on larger particles, thus coarsening the particle size. Existing improved precipitation methods, such as attempting to control the feeding rate, adjust the stirring intensity, or employ a dual-precipitant strategy, while simplifying the process, still lack sufficient fine control over the nanoscale of primary grains when completely abandoning the complexing agent, resulting in unsatisfactory product uniformity and batch stability.

[0004] To address the shortcomings of existing technologies, this invention aims to provide an innovative, simple, and environmentally friendly solution for the synthesis of small-particle-size basic cobalt carbonate. The core concept of this invention lies in introducing a surface-engineered inorganic modifier, which is doped with specific rare earth elements and then surface-functionalized. In the synthesis process, this modifier is not a reactant but rather serves as a directional control center for the crystallization process. In a mild, room-temperature reaction system, through its unique surface physicochemical properties, this modifier can effectively adsorb metal ions, providing abundant heterogeneous nucleation sites, thereby significantly increasing the nucleation density and guiding the uniform formation of initial crystal nuclei. Simultaneously, combined with a stepwise, precisely controlled precipitant addition strategy, sodium bicarbonate is first used in a weakly alkaline environment to achieve initial precipitation of cobalt ions and lock in crystal nucleus size. Subsequently, sodium carbonate is used for final pH fine-tuning to ensure complete precipitation of cobalt ions. This synergistic mechanism enables the entire process to stably and efficiently produce basic cobalt carbonate products with fine primary particles, good secondary sphericity, and high cobalt recovery rate under simple conditions requiring no organic complexing agents and only conventional stirring and temperature control. All raw materials are commercially available and have good prospects for industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a small-particle-size basic cobalt carbonate synthesis process, which solves the technical problems of existing basic cobalt carbonate preparation processes that usually rely on organic complexing agents or harsh conditions to control particle size, resulting in high cost, complex process, easy introduction of impurities, and unsatisfactory cobalt recovery rate.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A process for synthesizing small-particle-size basic cobalt carbonate includes the following steps:

[0008] S1, by weight, add 800-1200 parts of deionized water to the reactor and heat to 28-32℃; add 0.5-1.5 parts of surface-engineered gadolinium-doped cerium oxide nanoparticles and stir at 28-32℃ to obtain a suspension;

[0009] S2, add 220-240 parts of cobalt sulfate aqueous solution and 95-110 parts of sodium bicarbonate aqueous solution to the suspension, adjust the pH to 7.7-7.9, and stir continuously to obtain a mixture;

[0010] S3, add 10-25 parts of sodium carbonate aqueous solution to the mixture, adjust the pH to 8.1-8.3, and age at 28-32℃ to obtain slurry;

[0011] S4. The slurry is centrifuged to obtain a filter cake. The filter cake is washed with deionized water at 60-70℃ to obtain a clean filter cake. The clean filter cake is dried at 110-130℃ and finally pulverized by airflow and sieved.

[0012] In this invention, the synthesis of small-particle-size basic cobalt carbonate relies on the heterogeneous nucleation microenvironment constructed by the aforementioned surface-engineered gadolinium-doped cerium oxide nanoparticles. In the weakly alkaline reaction system, the surface-phosphorylated gadolinium-doped cerium oxide nanoparticles are uniformly dispersed due to their negative charge, and their surface phosphate groups have a strong chelating effect on cobalt ions, allowing for the local enrichment of Co. 2+ This process lowers the nucleation energy barrier, thereby inducing the simultaneous generation of a large number of uniform crystal nuclei. By precisely controlling the rate of co-current addition of cobalt sulfate and sodium bicarbonate solutions, the pH of the system is stably maintained between 7.7 and 7.9, ensuring the coexistence of carbonate and hydroxide ions, which is beneficial for the preferential crystallization of basic cobalt carbonate rather than ordinary cobalt carbonate. After the addition is complete, sodium carbonate solution is further added dropwise to finely adjust the pH to 8.1-8.3, promoting the complete precipitation of residual cobalt ions and driving the initially formed nanocrystals to undergo limited Oswald ripening, forming a dense and highly spherical secondary microsphere structure. The entire precipitation and ripening process is carried out at a constant temperature, effectively suppressing disordered grain growth, and finally obtaining a small-particle-size basic cobalt carbonate product with uniform particle size and regular morphology, laying the structural foundation for its subsequent calcination preparation of high-performance battery-grade cobalt tetroxide.

[0013] According to a preferred embodiment of the present invention, in step S1, the stirring time at 28-32°C is 40-60 min.

[0014] According to a preferred embodiment of the present invention, in step S2, the stirring time is 2-4 hours.

[0015] According to a preferred embodiment of the present invention, in step S3, the aging time at 28-32°C is 1.5-2 hours.

[0016] According to a preferred embodiment of the present invention, in step S4, the washed filter cake is dried at 110-130°C for 24-48 hours.

[0017] According to a preferred embodiment of the present invention, the preparation steps of the surface-engineered gadolinium-doped cerium oxide nanoparticles include:

[0018] A1, by weight, mix an aqueous solution containing 75-85 parts of cerium nitrate hexahydrate and an aqueous solution containing 8-12 parts of gadolinium nitrate hexahydrate, and stir to obtain a mixed salt solution; under nitrogen protection and stirring, add the mixed salt solution and 15-25 parts of ammonia solution to deionized water at 58-62℃, adjust the pH to 9.9-10.1, and obtain a slurry; transfer the slurry to a high-pressure reactor and hydrothermally react at 178-182℃ to obtain a reaction mixture; after cooling the reaction mixture, centrifuge to collect the precipitate, wash the precipitate with deionized water, and obtain a gadolinium-doped cerium-based hydrated oxide wet filter cake;

[0019] A2, disperse the gadolinium-doped cerium-based hydrated oxide wet filter cake in an aqueous solution containing 5-15 parts of sodium pyrophosphate, stir at 78-82℃ to obtain a mixture; centrifuge the mixture to collect the solid product, wash the solid product with anhydrous ethanol to obtain the washed solid product;

[0020] A3. The washed solid product is placed in a tube furnace and heated to 495-505℃ under a hydrogen / argon reducing atmosphere and held thereto to obtain the calcined solid product.

[0021] A4. The calcined solid product is ground, dispersed in an ammonia-ammonium chloride buffer solution with a pH of 7.8-8.2, ultrasonically treated, and spray-dried.

[0022] In this invention, the formation mechanism of surface-engineered gadolinium-doped cerium oxide nanoparticles is based on a synergistic pathway of co-precipitation, hydrothermal treatment, in-situ phosphorylation, and reductive crystallization. First, trivalent cerium salt and trivalent gadolinium salt co-precipitate in an alkaline ammonia environment, generating an amorphous gadolinium-doped cerium-based hydrated oxide precursor rich in surface hydroxyl groups. This precursor undergoes high-temperature hydrothermal treatment, resulting in increased crystallinity and the formation of a high-specific-surface-area nanoframework while retaining a large number of active -OH groups. Subsequently, under mild heating conditions, sodium pyrophosphate hydrolyzes to generate hydrogen phosphate ions, which undergo strong chemisorption with the metal hydroxyl groups on the particle surface via ligand exchange reactions, forming stable Ce-OP covalent bonds and anchoring the surface phosphate groups. Finally, moderate heat treatment in a reducing atmosphere promotes the complete transformation of the hydrated oxide into gadolinium-doped cerium oxide with a cubic fluorite structure. Simultaneously, some tetravalent cerium is reduced to the trivalent state, introducing a high concentration of oxygen vacancies and dehydrating and solidifying the surface phosphate layer into an amorphous protective thin layer. The entire process avoids particle sintering caused by high-temperature pre-calcination, ensuring that the nano-modifier has high dispersibility, surface functionality and structural stability.

[0023] According to a preferred embodiment of the present invention, in step A1, the hydrothermal reaction time at 178-182°C is 36-40 hours.

[0024] According to a preferred embodiment of the present invention, in step A2, the stirring time at 78-82°C is 12-14 hours.

[0025] According to a preferred embodiment of the present invention, in step A3, the time for holding the temperature at 495-505°C is 2-4 hours.

[0026] According to a preferred embodiment of the present invention, in step A4, the ultrasonic treatment time is 1-2 hours.

[0027] The beneficial effects of this invention are as follows:

[0028] The technical solution provided by this invention, by combining an innovatively designed surface-engineered inorganic modifier with an optimized and simplified precipitation process, produces significant and multifaceted beneficial technical effects, effectively overcoming many bottlenecks in the prior art.

[0029] Firstly, regarding the core physicochemical properties of the product, this process achieves stable and controllable preparation of small-particle-size, highly uniform basic cobalt carbonate. Surface-functionalized gadolinium-doped cerium oxide nanoparticles act as efficient heterogeneous nucleation centers in the reaction system, significantly increasing the number of nuclei per unit volume, thus ensuring that the primary particle size of the obtained product reaches the nanometer level. Simultaneously, the dispersed presence of this modifier effectively prevents excessive aggregation of newly formed crystal nuclei. Combined with a stepwise, precisely controlled weakly alkaline precipitation environment, it guides the orderly growth and assembly of particles. The resulting basic cobalt carbonate product not only has fine primary particles but also exhibits excellent sphericity and a narrow particle size distribution in its secondary particle morphology. Furthermore, the unique dual-precipitant strategy and endpoint pH control ensure extremely high cobalt ion precipitation rates while achieving small particle sizes, greatly reducing metal loss. The product also has low impurity ion content and high purity, demonstrating excellent quality consistency as a precursor material.

[0030] Secondly, in terms of process and production cost, this invention demonstrates significant simplification and economic benefits. The entire synthesis process completely eliminates the organic complexing agents or template agents indispensable in traditional processes. This not only simplifies the raw material system but also thoroughly avoids the introduction of organic impurities that could affect product purity, as well as the increased costs associated with subsequent complex purification steps. The entire reaction is carried out under mild ambient temperature conditions, requiring no additional heating or cooling energy consumption, nor relying on complex equipment requiring high-pressure environments such as hydrothermal or solvothermal processes, significantly reducing equipment investment and production energy consumption. All chemical raw materials used, including rare earth salts required for modifier preparation, are conventionally available industrial or chemical-grade products, widely sourced and cost-controllable. The process steps are clear, the parameters are well-defined, and the repeatability is high, which is highly conducive to precise control and large-scale production.

[0031] Finally, in terms of environmental friendliness and industrialization potential, this invention aligns with the development direction of green manufacturing. By eliminating the use of any organic complexing agents, it reduces potential volatile organic compound emissions and the challenges of treating organic wastewater, making the production process cleaner and more environmentally friendly. The mild reaction conditions also mean lower energy consumption and reduced safety risks. The entire process chain, from modifier preparation to basic cobalt carbonate synthesis, utilizes an aqueous system, ensuring safe operation and simple waste treatment. In summary, this invention not only provides a method for preparing high-performance basic cobalt carbonate but also offers an industrially feasible path that combines excellent product performance, a simple process flow, lower production costs, and good environmental benefits. It has broad application prospects and market competitiveness in the supply of raw materials for new energy battery cathode material precursors and high-end catalyst supports. Detailed Implementation

[0032] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0033] Example 1

[0034] Preparation of surface-engineered gadolinium-doped cerium oxide nanoparticles

[0035] Step A1: Accurately weigh 80.0g of cerium nitrate hexahydrate and 8.8g of gadolinium nitrate hexahydrate, place them in a 2L beaker, add 500mL of deionized water, and stir at 500rpm magnetic stirring speed for 30min at room temperature until a completely clear mixed salt solution is obtained. Place a 5L three-necked flask in a constant temperature water bath, add 1000mL of deionized water and heat to 60.0℃, start the mechanical stirrer inside the flask at 300rpm, and begin continuously introducing high-purity nitrogen gas into the flask. Using two precision peristaltic pumps, simultaneously and uniformly pump the above mixed salt solution and a dilute ammonia solution prepared by mixing 20.0g of 25% ammonia water with 200mL of deionized water into the three-necked flask in a parallel flow. The entire feeding process lasts for 60min, and the pH value of the reaction system is precisely controlled at 10.0 throughout by adding a trace amount of ammonia water dropwise. After the feed was completed, the mixture was stirred and aged for 60 minutes at 60°C under nitrogen protection to obtain a milky white slurry. All the slurry was transferred to a 2L polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in a forced-air drying oven for hydrothermal reaction at 180°C for 38 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. All the product in the reactor was transferred to a centrifuge cup and centrifuged at 8000 rpm for 10 minutes. The supernatant was discarded, and the precipitate was redispersed with 500 mL of deionized water and centrifuged again. This washing process was repeated three times to finally obtain a gadolinium-doped cerium-based hydrated oxide wet filter cake.

[0036] Step A2: Accurately weigh 10.0 g of sodium pyrophosphate, dissolve it in 400 mL of deionized water, stir to dissolve, transfer to a 500 mL volumetric flask and dilute to volume to obtain a 0.1 mol / L sodium pyrophosphate solution. Transfer all the wet filter cake obtained in step A1 to a 1 L beaker, and add the above 500 mL sodium pyrophosphate solution. Place the beaker in a constant temperature oil bath at 80 °C and react continuously for 13 h with mechanical stirring at 400 rpm. After the reaction is complete, centrifuge the mixture at 8000 rpm for 10 min to collect the solid. Wash the solid with 200 mL of anhydrous ethanol with stirring, and centrifuge again. Repeat this ethanol washing process 3 times to obtain the surface phosphorylation modified precursor.

[0037] Step A3: The solid product obtained in step A2 is evenly spread in a clean alumina boat and placed in the center of the isothermal zone of a tube furnace. The tube furnace is sealed, and a 5% (v / v) H2 / Ar mixture is introduced at a flow rate of 200 mL / min for 30 min to replace the air. Then, a programmed temperature rise is initiated: the temperature is increased from room temperature to 500℃ at a rate of 1℃ / min, and then held at 500℃ for 3 hours, maintaining a reducing atmosphere flow rate of 200 mL / min throughout. After heat treatment, the heating power is turned off, and the furnace is allowed to cool naturally to below 80℃ under continuous ventilation protection. The boat is then removed, yielding a calcined grayish-white solid.

[0038] Step A4: Gently grind the solid product obtained in step A3 in an agate mortar for 5 minutes. Weigh 1.07 g of ammonium chloride and dissolve it in 90 mL of deionized water. Add 0.62 mL of concentrated ammonia, calibrate and adjust the pH to 8.0 using a pH meter, and finally bring the volume to 100 mL to obtain an ammonia-ammonium chloride buffer solution. Weigh 5.0 g of the ground powder and slowly add it to 200 mL of the above buffer solution. Place the mixture in an ice-water bath and treat it for 1.5 h using an ultrasonic cell disruptor with a power of 300 W and a frequency of 40 kHz to form a uniform and stable milky white colloid. Dry the colloid using a spray dryer with an inlet temperature of 180 °C, an outlet temperature of 90 °C, and a feed pump speed of 10 mL / min. Collect the powder at the bottom of the drying tower to obtain the surface-engineered gadolinium-doped cerium oxide nanoparticles, and store them in a sealed container.

[0039] Synthesis of small-particle-size basic cobalt carbonate

[0040] Step S1: Add 1000g of deionized water to a 5L jacketed glass reactor. Turn on the circulating water bath to raise and stabilize the liquid temperature in the reactor to 30.0℃. Turn on the top mechanical stirrer and set the speed to 300rpm. Accurately add 0.8g of the modified agent powder prepared above to the reactor. Maintain the temperature of 30℃ and the stirring speed of 300rpm for 50 minutes to form a uniform and stable opalescent suspension.

[0041] Step S2: Weigh 220.0 g of cobalt sulfate heptahydrate, dissolve it in approximately 600 mL of deionized water, stir to dissolve, and then transfer it to a 1 L volumetric flask and dilute to volume to obtain a 1.0 mol / L cobalt sulfate solution (solution A). Weigh 95.0 g of sodium bicarbonate, dissolve it in approximately 500 mL of deionized water, stir to dissolve, and then transfer it to a 1 L volumetric flask and dilute to volume to obtain a 1.8 mol / L sodium bicarbonate solution (solution B). While maintaining the reaction vessel at 30°C and stirring at 300 rpm, use two high-precision peristaltic pumps to pump solutions A and B in a parallel flow at a uniform rate into the suspension from step S1. The total addition time is 150 min. Monitor the pH in real time with a pH meter and fine-tune the pump speed to ensure the pH of the reaction system remains constant at 7.8 throughout the addition process. After the addition is complete, continue stirring under the same conditions for 120 min.

[0042] Step S3: Weigh 15.0 g of anhydrous sodium carbonate, dissolve it in approximately 50 mL of deionized water, and bring the volume to 100 mL to obtain a 2.0 mol / L sodium carbonate solution. While continuously stirring, slowly add this sodium carbonate solution dropwise to the mixture obtained after step S2 using a dropping funnel. Monitor the pH with a pH meter and precisely adjust the final pH of the slurry to 8.2. Stop adding the slurry and maintain conditions of 30°C and 300 rpm for aging for 90 minutes.

[0043] Step S4: Transfer all the aged slurry to a centrifuge and centrifuge at 4000 rpm for 15 minutes. Discard the supernatant to obtain a pink filter cake. Transfer the filter cake to a washing tank, add hot deionized water at 65°C, stir to disperse, and centrifuge again. Repeat this hot washing process 5 times until the final washing liquid is tested with 5% barium chloride solution, and no white precipitate is produced within 5 minutes. Place the washed filter cake in a vacuum drying oven and dry it at 120°C and -0.095 MPa for 36 hours. Crush the dried lumpy material using an air jet mill at a working pressure of 0.7 MPa, and then pass it through a 400-mesh standard sieve. Collect the sieve-passing material to obtain a small-particle-size basic cobalt carbonate product.

[0044] Example 2

[0045] The specific implementation method is the same as in Example 1, except that the surface-engineered gadolinium-doped cerium oxide nanoparticles are prepared...

[0046] Step A1: Accurately weigh 75.0 g of cerium nitrate hexahydrate and 12.0 g of gadolinium nitrate hexahydrate, place them in a 2 L beaker, add 450 mL of deionized water, and stir until completely dissolved. Heat a 5 L three-necked flask to 60.0 °C in a water bath, add 800 mL of deionized water, and under nitrogen protection and stirring at 300 rpm, pump the mixed salt solution and a dilute solution prepared with 15.0 g of 25% ammonia water in a co-current pump, controlling the pH of the addition process to 10.0. After addition, age for 60 min, transfer the slurry to an autoclave, and hydrothermally react at 180 °C for 36 h. After cooling, centrifuge and wash the precipitate three times with deionized water to obtain a wet filter cake.

[0047] Step A2: Add all the wet filter cake obtained in A1 to a solution prepared with 5.0 g sodium pyrophosphate and 500 mL deionized water, and stir the mixture in an oil bath at 80 °C for 12 h. After the reaction, collect the solid by centrifugation and wash it three times with anhydrous ethanol.

[0048] Step A3: Place the washed solid in a tube furnace and heat it to 500°C at a rate of 1°C / min under a 5% H2 / Ar atmosphere at a flow rate of 200 mL / min, and hold for 2 hours. Then cool it to below 80°C under a protective atmosphere and remove it.

[0049] Step A4: Grind the calcined product and disperse it in 200 mL of ammonia-ammonium chloride buffer solution with pH=8.0. Sonicate for 1.0 h to form a colloid, and then spray dry to obtain the modifier powder.

[0050] Synthesis of small-particle-size basic cobalt carbonate

[0051] Step S1: Add 800g of deionized water to the reactor and heat to 28℃. Add 1.5g of the above modifier and stir at 28℃ and 300rpm for 40min to form a suspension.

[0052] Step S2: A 1.0 mol / L solution containing 240.0 g of cobalt sulfate heptahydrate and a 1.8 mol / L solution containing 110.0 g of sodium bicarbonate are pumped into the suspension in a co-current flow, with the total addition time controlled at 240 min, during which the pH is maintained at 7.8. Stirring continues for 240 min after addition.

[0053] Step S3: Add dropwise a 2.0 mol / L solution prepared with 10.0 g of anhydrous sodium carbonate to the mixture, adjust the pH to 8.2, and age at 28°C for 120 min.

[0054] Step S4: After centrifugation and washing five times with hot water at 65℃, the filter cake is vacuum dried at 110℃ for 48 hours. The dried product is then subjected to air jet milling and passed through a 400-mesh sieve to obtain the final product with a D50 of 1.8μm.

[0055] Example 3

[0056] The specific implementation method is the same as in Example 1, except that the surface-engineered gadolinium-doped cerium oxide nanoparticles are prepared...

[0057] Step A1: Accurately weigh 85.0 g of cerium nitrate hexahydrate and 8.0 g of gadolinium nitrate hexahydrate, and dissolve them in 500 mL of deionized water. Under nitrogen protection at 60 °C, add this mixed salt solution and a solution prepared with 25.0 g of 25% ammonia water in parallel streams to 1200 mL of deionized water, controlling the pH to 10.0. After aging, transfer the slurry to an autoclave and hydrothermally react at 182 °C for 40 h. After cooling, centrifugation, and washing three times with water, a wet filter cake is obtained.

[0058] Step A2: Add the wet filter cake to a solution prepared by mixing 15.0 g of sodium pyrophosphate with 500 mL of water, and stir at 82 °C for 14 h. After centrifugation, wash the solid three times with anhydrous ethanol.

[0059] Step A3: Place the solid in a tube furnace and heat it to 495°C at a rate of 1°C / min under a 5% H2 / Ar atmosphere, holding it at that temperature for 4 hours. Remove it after cooling under a protective atmosphere.

[0060] Step A4: After grinding the product, disperse it in 200 mL of buffer solution with pH=8.2, sonicate for 2.0 h, and spray dry to obtain modifier powder.

[0061] Synthesis of small-particle-size basic cobalt carbonate

[0062] Step S1: Add 1200g of deionized water to the reactor and heat to 32℃. Add 0.5g of the above modifier and stir at 32℃ and 300rpm for 60min.

[0063] Step S2: A solution containing 230.0 g of cobalt sulfate heptahydrate and a solution containing 100.0 g of sodium bicarbonate are pumped in concurrently over a period of 180 min, maintaining the pH at 7.9. Stir for 180 min after adding the solutions.

[0064] Step S3: Add a solution prepared with 25.0g of anhydrous sodium carbonate, adjust the pH to 8.3, and age at 32℃ for 100min.

[0065] Step S4: The slurry is centrifuged, washed 5 times with 70℃ hot water, and the filter cake is dried at 130℃ for 24 hours. The product is obtained after pulverizing and sieving.

[0066] Comparative Example 1

[0067] The specific implementation method is the same as in Example 1, except that surface-engineered gadolinium-doped cerium oxide nanoparticles are not added in this comparative example. Step S1: Add 1000g of deionized water to the reaction vessel, heat to 30°C, and stir at 300rpm for 50min without adding surface-engineered gadolinium-doped cerium oxide nanoparticles. Steps S2-S4: are exactly the same as in Example 1, that is, 220.0g of cobalt sulfate heptahydrate, 95.0g of sodium bicarbonate and 15.0g of anhydrous sodium carbonate are used, and the pH control, aging, washing, drying and pulverizing conditions are the same.

[0068] Comparative Example 2

[0069] The specific implementation method is the same as in Example 1, except that this comparative example uses unengineered (unphosphorylated) gadolinium-doped cerium oxide nanoparticles. The preparation of the unengineered (unphosphorylated) gadolinium-doped cerium oxide nanoparticles only involves steps A1, A3, and A4: after preparing the wet filter cake according to step A1 of Example 1, step A3 (reduction calcination at 500℃ for 3 hours) is performed directly, followed by step A4 (dispersion, ultrasonication, and spray drying), without the sodium pyrophosphate modification step of A2. The main synthesis process is exactly the same as in Example 1: 0.8 g of unengineered (unphosphorylated) gadolinium-doped cerium oxide nanoparticles are used, and the amounts of other materials and operating parameters (such as 1000 g of water, 220.0 g of cobalt salt, pH control, drying conditions, etc.) are consistent with those in Example 1.

[0070] Comparative Example 3

[0071] The specific implementation method is the same as in Example 1, except that this comparative example uses a traditional ammonium salt precipitant system. Step S1 is the same as in Example 1: 0.8g of surface-engineered gadolinium-doped cerium oxide nanoparticles prepared in Example 1 are added. Step S2 is modified: 95.0g of sodium bicarbonate is replaced with an equimolar amount of ammonium bicarbonate (approximately 118.1g) to prepare a solution, which is added concurrently with the cobalt sulfate solution, controlling the pH to 7.8. Step S3 is modified: 15.0g of sodium carbonate is replaced with an equimolar amount of ammonium carbonate (approximately 23.6g) to prepare a solution, adjusting the final pH to 8.2. All other conditions, including aging, washing, drying, and pulverizing, are consistent with those in Example 1.

[0072] Performance testing

[0073] The small-particle-size basic cobalt carbonates prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following method, which included the following steps:

[0074] The performance test of the present invention was carried out in accordance with the general methods in the art. The specific steps are as follows: The particle size distribution of the sample was determined using a laser particle size analyzer. Before the test, about 0.1g of the sample was dispersed in 50mL of anhydrous ethanol. After being dispersed for 3min by an ultrasonic processor with a power of 300W, the sample was injected. The instrument automatically analyzed and reported the median particle size D50 and characteristic values ​​D10 and D90 according to the Mie scattering theory. The particle size span calculation formula is (D90-D10) / D50.

[0075] The microstructure of the sample was observed using a field emission scanning electron microscope. A small amount of sample powder was adhered to a conductive adhesive and sputtered with gold. The sample was then observed and photographed at a magnification of 100,000 times under an accelerating voltage of 15.0 kV and a working distance of 8 mm.

[0076] The cobalt content was determined by chemical titration. 0.15 g of sample was accurately weighed and dissolved in 20 mL of 20% hydrochloric acid. The solution was heated until completely dissolved, cooled, and then ammonia was added to adjust the pH to 8-9. A small amount of ammonium purpurate indicator was added, and the solution was titrated with 0.05 mol / L disodium ethylenediaminetetraacetate standard solution until the solution turned a stable blue-purple color. The mass fraction of cobalt in the sample was calculated based on the volume consumed in the titration.

[0077] Sodium content was determined by atomic absorption spectrometry. 0.5 g of sample was accurately weighed, dissolved in hydrochloric acid, and diluted to 100 mL in a volumetric flask. The absorbance was measured at a wavelength of 589.0 nm using an air-acetylene flame. The mass fraction of sodium in the sample was calculated using a pre-plotted standard curve, and the result was expressed in ppm.

[0078] The tapped density was measured using a tapped density meter. A certain volume of sample sieved through a 120-mesh sieve was taken and vibrated 1000 times in a graduated cylinder under the conditions of an amplitude of 3 mm and a frequency of 250 times / min. The volume after tapping was recorded and its mass was weighed. The tapped density was calculated and the result was expressed in g / cm³. The average value of three tests was taken.

[0079] The cobalt precipitation rate is calculated as the ratio of the total mass of cobalt in the final product to the total mass of cobalt contained in cobalt sulfate heptahydrate in the synthesis process feed, expressed as a percentage.

[0080] Test results:

[0081] Table 1: Test results of each embodiment and comparative example

[0082] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Median particle size D50 (μm) 1.6 1.8 1.4 12.5 4.2 8.7 Particle size span (D90-D10) / D50 0.75 0.82 0.70 1.95 1.30 1.15 Particle morphology (SEM observation) Regular spherical shape, composed of tightly packed primary nanoparticles. Nearly spherical, with a relatively dense structure Regular spherical shape, good dispersion Irregular flocculent aggregates Quasi-spherical shape with obvious soft aggregates Irregular blocky crystals Cobalt content (mass fraction, %) 47.1 46.8 47.3 46.5 46.9 47.0 Sodium content (ppm) 85 120 75 350 180 210 Tap density (g / cm³) 1.45 1.38 1.49 0.82 1.20 1.52 Cobalt precipitation recovery rate (%) 99.7 99.4 99.8 98.5 99.2 99.5

[0083] As can be seen from Table 1, the technical solutions of the present invention represented by Examples 1 to 3 successfully and comprehensively solved the defects of the existing process.

[0084] Under mild conditions without the use of any organic complexing agents, the median particle size D50 of the product in the examples was stably controlled within a fine range of 1.4-1.8 μm, with a particle size distribution spanning 0.70-0.82, and a regular spherical morphology. In stark contrast, the product of Comparative Example 1, without the addition of any modifier, had a coarse D50 of up to 12.5 μm, a span of 1.95, and an irregular flocculent agglomerate morphology. This significant difference directly confirms that the "surface-engineered gadolinium-doped cerium oxide nanoparticles" introduced in this invention, as a novel inorganic modifier, completely replaces the role of organic complexing agents in regulating crystal growth. By providing a large number of uniform heterogeneous nucleation sites in the precipitation system, precise control of small particle size and spherical morphology is achieved at room temperature, thereby avoiding the introduction of organic matter, subsequent complex purification steps, and the corresponding increase in cost.

[0085] The necessity of surface engineering of the modifier was verified by Comparative Example 2: When using unengineered (unphosphorylated) gadolinium-doped cerium oxide nanoparticles, the product D50 was 4.2 μm and soft agglomeration was present, which was significantly worse than the 1.6 μm of Example 1. This indicates that the surface functional layer constructed by sodium pyrophosphate treatment is crucial for improving the dispersibility and nucleation induction efficiency of the modifier.

[0086] The sodium bicarbonate / sodium carbonate dual precipitant system specific to this invention has also proven indispensable: after Comparative Example 3 was modified to use an ammonium salt system, irregular blocky crystals with a D50 of 8.7 μm were still generated even when the same modifier was used. This highlights the unique synergistic effect between the dual sodium salt system and the modifier of this invention, which can optimize precipitation kinetics, while the traditional ammonium salt route is difficult to achieve the same effect.

[0087] Regarding the issues of impurities and recovery rate, the sodium impurity content of the product in the example was only 75-120 ppm, far lower than the 350 ppm of Comparative Example 1, demonstrating the excellent washing efficiency of the process and the absence of organic impurity residue. Meanwhile, the cobalt precipitation recovery rate of the example was as high as 99.4-99.8%, which was better than the 98.5% of Comparative Example 1, showing that the two-step precipitation pH control method can achieve near-complete recovery of metal ions while ensuring fine particle size.

[0088] In summary, the test data fully demonstrates that this invention, through the innovative combination of inorganic modifiers and a specific precipitation process, simultaneously overcomes multiple technical bottlenecks of traditional methods in terms of particle size control, process complexity, product purity, and metal recovery rate under simplified and mild conditions.

[0089] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A process for synthesizing small-particle-size basic cobalt carbonate, characterized in that, Includes the following steps: S1, by weight, add 800-1200 parts of deionized water to the reactor and heat to 28-32℃; add 0.5-1.5 parts of surface-engineered gadolinium-doped cerium oxide nanoparticles and stir at 28-32℃ to obtain a suspension; S2, add 220-240 parts of cobalt sulfate aqueous solution and 95-110 parts of sodium bicarbonate aqueous solution to the suspension, adjust the pH to 7.7-7.9, and stir continuously to obtain a mixture; S3, add 10-25 parts of sodium carbonate aqueous solution to the mixture, adjust the pH to 8.1-8.3, and age at 28-32℃ to obtain slurry; S4. The slurry is centrifuged to obtain a filter cake. The filter cake is washed with deionized water at 60-70℃ to obtain a clean filter cake. The clean filter cake is dried at 110-130℃ and finally pulverized by airflow and sieved.

2. The small-particle-size basic cobalt carbonate synthesis process according to claim 1, characterized in that, In step S1, the stirring time at 28-32℃ is 40-60 minutes.

3. The small-particle-size basic cobalt carbonate synthesis process according to claim 1, characterized in that, In step S2, the stirring time is 2-4 hours.

4. The small-particle-size basic cobalt carbonate synthesis process according to claim 1, characterized in that, In step S3, the aging time at 28-32℃ is 1.5-2 hours.

5. The small-particle-size basic cobalt carbonate synthesis process according to claim 1, characterized in that, In step S4, the washed filter cake is dried at 110-130℃ for 24-48 hours.

6. The small-particle-size basic cobalt carbonate synthesis process according to any one of claims 1-5, characterized in that, The preparation steps of the surface-engineered gadolinium-doped cerium oxide nanoparticles include: A1, by weight, mix an aqueous solution containing 75-85 parts of cerium nitrate hexahydrate and an aqueous solution containing 8-12 parts of gadolinium nitrate hexahydrate, and stir to obtain a mixed salt solution; under nitrogen protection and stirring, add the mixed salt solution and 15-25 parts of ammonia solution to deionized water at 58-62℃, adjust the pH to 9.9-10.1, and obtain a slurry; transfer the slurry to a high-pressure reactor and hydrothermally react at 178-182℃ to obtain a reaction mixture; after cooling the reaction mixture, centrifuge to collect the precipitate, wash the precipitate with deionized water, and obtain a gadolinium-doped cerium-based hydrated oxide wet filter cake; A2, disperse the gadolinium-doped cerium-based hydrated oxide wet filter cake in an aqueous solution containing 5-15 parts of sodium pyrophosphate, stir at 78-82℃ to obtain a mixture; centrifuge the mixture to collect the solid product, wash the solid product with anhydrous ethanol to obtain the washed solid product; A3. The washed solid product is placed in a tube furnace and heated to 495-505℃ under a hydrogen / argon reducing atmosphere and held thereto to obtain the calcined solid product. A4. The calcined solid product is ground, dispersed in an ammonia-ammonium chloride buffer solution with a pH of 7.8-8.2, ultrasonically treated, and spray-dried.

7. The small-particle-size basic cobalt carbonate synthesis process according to claim 6, characterized in that, In step A1, the hydrothermal reaction at 178-182℃ takes 36-40 hours.

8. The small-particle-size basic cobalt carbonate synthesis process according to claim 6, characterized in that, In step A2, the stirring time at 78-82℃ is 12-14 hours.

9. The small-particle-size basic cobalt carbonate synthesis process according to claim 6, characterized in that, In step A3, the temperature is raised to 495-505℃ and held for 2-4 hours.

10. The small-particle-size basic cobalt carbonate synthesis process according to claim 6, characterized in that, In step A4, the ultrasonic treatment time is 1-2 hours.