Preparation method of nano-barium sulfate

Abstract

The application belongs to the technical field of barium compound preparation, and relates to a preparation method of nano barium sulfate. The method adopts an in-situ degradable dispersant based on a natural polysaccharide derivative, adsorbs on the surface of a barium sulfate crystal nucleus through a functional group in the reaction to inhibit agglomeration, adjusts the pH to 3.0-6.0 after the reaction is completed, and acid-catalytically hydrolyzes the dispersant into a water-soluble small molecule, so that a high-purity and high-dispersibility product can be obtained through simple water washing. The application introduces a natural polysaccharide derivative with a crystal face selective adsorption capacity and an acid-triggered degradation characteristic as an in-situ degradable dispersant, and constructs a new green preparation paradigm of nano barium sulfate with reaction-dispersion-self-cleaning integration. The method fundamentally eliminates the risk of organic impurity residue without sacrificing the dispersing performance, significantly improves the product purity and application safety, simultaneously simplifies the post-processing technology, reduces the energy consumption and wastewater treatment cost, and has both technical advancement and industrialization feasibility.

Description

Technical Field

[0001] This invention belongs to the field of barium compound preparation technology, and relates to a method for preparing nano-barium sulfate. Background Technology

[0002] Nano-barium sulfate, as an important inorganic functional material, is widely used in medical imaging contrast agents, high-end electronic packaging fillers, optical coatings, and special composite materials due to its high density, excellent X-ray blocking properties, and good chemical stability. With downstream applications increasingly demanding higher purity, particle size uniformity, and environmental friendliness, the preparation process of nano-barium sulfate faces more stringent technical challenges. In current industrial practice, precipitation is the mainstream synthesis route due to its simplicity and controllable cost. Its core lies in controlling the reaction kinetics of sulfate and barium salt in the aqueous phase to achieve the nucleation and growth of nanoscale crystal nuclei. However, to suppress irreversible agglomeration of nanoparticles caused by high surface energy in the early stages of nucleation, organic dispersants are usually introduced to provide steric hindrance or electrostatic repulsion. Among these, anionic surfactants such as sodium dodecyl sulfate are widely used due to their high dispersion efficiency.

[0003] Sodium dodecyl sulfate molecules adsorb onto the surface of newly formed barium sulfate crystal nuclei via their hydrophobic alkyl chains, while their hydrophilic sulfonic acid groups extend into the aqueous phase, forming a stable micelle structure that effectively blocks van der Waals attraction between particles, thus obtaining primary nanoparticles with a narrow particle size distribution. This strategy did indeed solve the particle agglomeration problem to some extent in early industrial production, significantly improving product dispersibility and process repeatability. However, as the limits for heavy metal and organic impurities in medical contrast agents approach ppb levels, and as electronic-grade fillers demand extreme dielectric properties and interfacial compatibility, the inherent defects of traditional dispersant systems have become increasingly apparent. Fundamentally, the binding force between synthetic surfactants such as sodium dodecyl sulfate and barium sulfate crystal faces relies mainly on physical adsorption, resulting in weak adhesion. Although they can function as dispersants during the reaction stage, they are difficult to completely remove during subsequent washing, drying, and calcination processes, easily leading to organic carbon residues in the product. Such residues not only directly reduce the chemical purity of materials, but may also carbonize and generate conductive impurities during high-temperature processing, severely degrading the insulation performance of electronic devices; in biomedical applications, they may cause cytotoxicity or interfere with image contrast, posing potential safety risks.

[0004] Alkyl sulfonates such as sodium dodecyl sulfate have poor biodegradability and are difficult to effectively mineralize in wastewater treatment systems. They tend to accumulate in water bodies and cause persistent toxicity to aquatic ecosystems. Summary of the Invention

[0005] This invention provides a method for preparing nano-barium sulfate, aiming to solve the technical problems in existing technologies, such as the difficulty in completely removing organic impurities, environmental unfriendliness, and complex post-processing, caused by the use of traditional synthetic surfactants (such as sodium dodecyl sulfate). To achieve the above-mentioned objective, this invention proposes an in-situ degradable dispersion system based on a natural polysaccharide derivative. This dispersant is introduced simultaneously during the precipitation reaction, allowing it to specifically adsorb onto the surface of newly formed barium sulfate crystal nuclei through the active functional groups on its molecular chain, effectively inhibiting the aggregation of nanoparticles. After the reaction, simply adjusting the pH of the system to a weakly acidic condition triggers the controllable hydrolysis of the dispersant molecular chain, degrading it into low-molecular-weight, water-soluble small organic molecules. Therefore, high-purity, highly dispersible nano-barium sulfate products can be obtained without additional solvent extraction, high-temperature calcination, or multiple washing steps.

[0006] The preparation method of nano-barium sulfate according to the present invention includes the following steps: First, prepare soluble barium salt aqueous solution with a concentration of 0.1 mol / L to 1.0 mol / L and soluble sulfate aqueous solution with a concentration of 0.1 mol / L to 1.0 mol / L respectively;

[0007] Secondly, an in-situ biodegradable dispersant based on natural polysaccharides is dissolved in the barium salt aqueous solution or sulfate aqueous solution at a concentration of 0.5 wt% to 5.0 wt% to form a reaction precursor solution containing the dispersant.

[0008] Subsequently, under stirring conditions, the reaction precursor liquid containing the dispersant is mixed with another reaction liquid without the dispersant at a volume ratio of 1:1 to 1:3, the reaction temperature is controlled at 20°C to 80°C, and the reaction time is 10 minutes to 120 minutes, so that the barium sulfate nanocrystal nuclei nucleate and grow under the regulation of the dispersant molecules.

[0009] Finally, the pH of the reaction system is adjusted to 3.0 to 6.0 and maintained at this pH for 10 to 60 minutes to allow the dispersant to undergo acid-catalyzed hydrolysis and degrade into water-soluble small molecule fragments with a molecular weight of less than 1000 Da. Subsequently, the target product, barium sulfate nanoparticles, is obtained through conventional solid-liquid separation, water washing, and drying.

[0010] Furthermore, the soluble barium salt is selected from at least one of barium chloride, barium nitrate, or barium acetate; the soluble sulfate is selected from at least one of sodium sulfate, potassium sulfate, or ammonium sulfate.

[0011] The reaction temperature is preferably 40°C to 60°C, and the reaction time is preferably 30 minutes to 60 minutes, in order to balance the nucleation rate and crystal growth kinetics, and obtain nanoparticles with narrow particle size distribution and uniform morphology.

[0012] As a core technical feature of the present invention, the in-situ degradable dispersant based on natural polysaccharides is a chemically modified natural polysaccharide derivative. Its main chain is composed of glucose units linked by β-1,4-glycosidic bonds or α-1,6-glycosidic bonds, and at least one hydrophilic functional group among carboxymethyl, hydroxyethyl or amino is introduced into the side chain, and the molecular weight is controlled between 10,000 Da and 100,000 Da.

[0013] This dispersant exhibits a linear or slightly branched configuration in the aqueous phase, and the hydroxyl, carboxyl, or amino functional groups on its molecular chain can interact with the Ba groups on the surface of barium sulfate crystals. 2+ or SO4 2- The sites form coordination bonds or hydrogen bonds, achieving selective adsorption on the surface of the crystal nucleus, thereby constructing a dynamic but stable protective layer on the particle surface, effectively blocking van der Waals forces and electrostatic attraction between particles, and inhibiting Ostwald ripening and particle aggregation.

[0014] The dispersant is preferably at least one of carboxymethyl chitosan, hydroxyethyl cellulose, or amino-modified dextran. Specifically, the degree of substitution of carboxymethyl chitosan is 0.3 to 1.2, and the amino content is 2.0 mmol / g to 8.0 mmol / g; the molar degree of hydroxyethyl substitution of hydroxyethyl cellulose is 0.8 to 2.0; and the amino grafting density of amino-modified dextran is 1 to 3 amino groups introduced per 10 glucose units. These parameter ranges ensure that the dispersant possesses sufficient adsorption capacity while maintaining good water solubility and controllable degradation kinetics.

[0015] Furthermore, the degradation mechanism of the dispersant depends on the hydrolytic stability of its glycosidic bonds under weakly acidic conditions. Glycosidic bonds in the backbone of natural polysaccharides are prone to protonation in environments with pH < 7, leading to increased polarity and breakage of the C-O bonds, generating oligosaccharide or monosaccharide units. This invention precisely controls the pH of the system after the reaction to be within the range of 3.0 to 6.0, thus avoiding the potential erosion of the barium sulfate crystal structure by strong acid conditions (barium sulfate is chemically stable at pH > 2) while simultaneously activating the hydrolysis reaction of the dispersant molecular chains.

[0016] In a preferred embodiment of the present invention, the dispersant is pre-dissolved in an aqueous barium salt solution to form a homogeneous and transparent solution. Then, under vigorous stirring (500 rpm to 1500 rpm), an aqueous sulfate solution is added dropwise to the mixture at a flow rate of 0.5 mL / min to 5.0 mL / min. This addition method facilitates uniform nucleation under controllable local supersaturation conditions, avoiding the broadening of particle size distribution caused by explosive nucleation. The stirring rate is preferably 800 rpm to 1200 rpm, and the dropping rate is preferably 1.0 mL / min to 2.0 mL / min to ensure that the concentration gradient within the reaction system is minimized, promoting the monodisperse growth of nanoparticles.

[0017] In another preferred embodiment of the present invention, the reaction is carried out under an inert atmosphere (such as nitrogen or argon) to eliminate the possible oxidative degradation interference of dissolved oxygen on polysaccharide molecules and ensure the structural integrity and functional stability of the dispersant during the reaction stage. The reaction vessel is a glass or stainless steel reactor with a jacket, and constant-temperature circulating water is circulated in the jacket for precise temperature control, with temperature fluctuations controlled within ±1℃.

[0018] The nano-barium sulfate prepared by the method described in this invention has a primary particle size of 20 nm to 100 nm, a particle size distribution coefficient of less than 0.2, a specific surface area of ​​20 m² / g to 80 m² / g, a carbon residue of less than 50 ppm, and a heavy metal impurity content (calculated as Pb) of less than 1 ppm. After ultrasonic dispersion in deionized water, the product exhibits a zeta potential absolute value greater than 30 mV, indicating excellent colloidal stability.

[0019] Furthermore, the dispersant described in this invention is derived from natural biomass resources, such as chitosan from shrimp and crab shells, cellulose from wood or cotton linters, and dextran from yeast or bacterial fermentation. These raw materials are renewable and inexpensive, and their degradation products can be completely mineralized by microorganisms into CO2 and H2O, conforming to the 12 principles of green chemistry. Wastewater can meet discharge standards after simple neutralization, eliminating the need for complex biochemical treatment and significantly reducing environmental impact.

[0020] This invention also provides a process variant suitable for continuous production: a barium salt solution containing a dispersant and a sulfate solution are separately pumped to a static mixer, where instantaneous mixing and nucleation occur. The mixture then flows into an insulated reaction tube (residence time 20 to 90 minutes). Immediately after exiting the reaction solution, it enters a pH adjustment unit where dilute hydrochloric acid or citric acid solution is added to adjust the pH to 4.0 to 5.5. The solution is then heated at 50°C for 30 minutes using a coil heater to complete degradation. Finally, it enters a centrifugal separation system for solid-liquid separation. This continuous process can achieve a production capacity of tons per day, with high batch-to-batch consistency in product quality.

[0021] In the drying step, this invention preferably employs freeze-drying or spray drying to avoid particle sintering caused by high-temperature drying. The freeze-drying conditions are: pre-freezing temperature -50℃, vacuum degree 10Pa, sublimation temperature -20℃, and desorption drying temperature 20℃; the spray drying inlet air temperature is 150℃ to 180℃, and the outlet air temperature is 80℃ to 90℃. The resulting powder has good flowability and is free of hard agglomerates.

[0022] The method described in this invention is also applicable to the preparation of doped barium sulfate nanoparticles. For example, by pre-adding 0.1 mol% to 1.0 mol% of rare earth ions to a barium salt solution, uniform doping can be achieved in the barium sulfate lattice, resulting in composite nanomaterials with X-ray fluorescence or upconversion luminescence. The presence of a dispersant does not interfere with the doping process; on the contrary, it helps to achieve a uniform distribution of doped ions.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The obtained nano-barium sulfate has high purity and carbon residue of less than 50 ppm, which meets the stringent limit requirements for organic impurities in medical contrast agents and is also suitable for high-insulation electronic packaging materials.

[0025] 2. Excellent particle dispersibility, controllable primary particle size and narrow distribution, allowing it to be directly used in composite material preparation without subsequent deagglomeration treatment;

[0026] 3. The dispersant is derived from natural sources and is biodegradable. After the reaction, only weak acid treatment is needed to achieve molecular-level removal, avoiding the use of organic solvents and high-temperature calcination. The process is clean and energy-efficient. 4. The overall process is simple, the operating conditions are mild, and it is easy to achieve large-scale continuous production, which has significant economic and environmental benefits.

[0027] 4. The adsorption mechanism of the dispersant described in this invention is not a simple physical coating, but rather selective passivation of specific crystal planes through multi-point coordination. Barium sulfate crystals belong to the orthorhombic crystal system, and their high-energy crystal planes such as {210} and {021} are easily exposed in the early stages of growth. The amino and carboxyl groups in the polysaccharide derivative used in this invention can preferentially bind to the Ba groups on these crystal planes. 2+ By coordinating at specific sites and reducing surface energy, crystal growth can be regulated along specific directions to obtain nanoparticles with uniform morphology.

[0028] 5. This invention optimizes the dispersant concentration. When the dispersant concentration is below 0.5 wt%, it is insufficient to cover the entire surface of newly formed crystal nuclei, leading to the aggregation of some particles. When the concentration is above 5.0 wt%, excess dispersant forms micelles in the solution, which may promote particle aggregation through bridging and increase the burden on subsequent degradation. Therefore, a concentration range of 0.5 wt% to 5.0 wt% is the optimal window for balancing dispersion efficiency and degradation thoroughness. Detailed Implementation

[0029] This invention provides a method for preparing nano-barium sulfate, which involves constructing an in-situ degradable dispersion system based on a natural polysaccharide derivative. By introducing this dispersant during the precipitation reaction stage, efficient and stable dispersion of nano-barium sulfate crystal nuclei is achieved. After the reaction, the dispersant molecular chains are controlled to hydrolyze under weakly acidic conditions, degrading them into low-molecular-weight, water-soluble organic molecules. This results in a high-purity, highly dispersible nano-barium sulfate product without complex post-processing. This method fundamentally solves the problem of residual organic impurities caused by the difficulty in completely removing traditional synthetic surfactants (such as sodium dodecyl sulfate), while significantly reducing the environmental impact of the process, meeting the stringent requirements of medical contrast agents and high-end electronic materials for both product purity and green manufacturing.

[0030] 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.

[0031] Example 1: Preparation of nano-barium sulfate by dispersing carboxymethyl chitosan:

[0032] Prepare a 0.5 mol / L barium chloride aqueous solution and a 0.5 mol / L sodium sulfate aqueous solution;

[0033] Carboxymethyl chitosan with a molecular weight of 50,000 Da, a degree of substitution of 0.6, and an amino content of 5.0 mmol / g was dissolved in a barium chloride aqueous solution at a concentration of 2.0 wt% to form a reaction precursor solution containing a dispersant.

[0034] Under stirring at 800 rpm, a barium chloride solution containing a dispersant was mixed with a sodium sulfate solution at a volume ratio of 1:1, and the reaction temperature was controlled at 50°C for 40 minutes.

[0035] The pH of the reaction system was adjusted to 4.5 with dilute hydrochloric acid and kept at 50°C for 30 minutes to degrade carboxymethyl chitosan into small molecules with a molecular weight of less than 1000 Da.

[0036] The nano-barium sulfate product was obtained by freeze-drying (pre-freezing temperature -50℃, vacuum degree 10Pa, sublimation temperature -20℃, and desorption drying temperature 20℃) to separate the solid and liquid components.

[0037] Example 2: Preparation of nano-barium sulfate by dispersing hydroxyethyl cellulose:

[0038] Prepare a 0.8 mol / L barium nitrate aqueous solution and a 0.8 mol / L potassium sulfate aqueous solution;

[0039] Hydroxyethyl cellulose with a molecular weight of 80,000 Da and a hydroxyethyl molar substitution degree of 1.5 was dissolved in an aqueous potassium sulfate solution at a concentration of 3.0 wt% to form a reaction precursor solution containing a dispersant.

[0040] Under stirring at 1000 rpm, potassium sulfate solution containing dispersant was mixed with barium nitrate solution at a volume ratio of 1:2, and the reaction temperature was controlled at 60℃ for 30 minutes.

[0041] The pH of the reaction system was adjusted to 4.0 with citric acid solution, and the mixture was kept at 50°C for 25 minutes to degrade hydroxyethyl cellulose.

[0042] The nano-barium sulfate product was obtained by spray drying (inlet air temperature 160℃, outlet air temperature 85℃) to separate the solid and liquid components.

[0043] Example 3: Preparation of nano-barium sulfate by dispersing amino-modified dextran:

[0044] Prepare a 0.3 mol / L barium acetate aqueous solution and a 0.3 mol / L ammonium sulfate aqueous solution;

[0045] Aminated dextran with a molecular weight of 30,000 Da and 2 amino groups introduced into every 10 glucose units was dissolved in a barium acetate aqueous solution at a concentration of 1.0 wt% to form a reaction precursor solution containing a dispersant.

[0046] Under stirring at 1200 rpm, a barium acetate solution containing a dispersant was mixed with an ammonium sulfate solution at a volume ratio of 1:1.5, and the reaction temperature was controlled at 40℃ for 60 minutes.

[0047] The pH of the reaction system was adjusted to 5.0 with dilute hydrochloric acid, and the mixture was kept at 50°C for 35 minutes to degrade the amino-modified dextran.

[0048] After solid-liquid separation by freeze drying (under the same conditions as in Example 1), the nano-barium sulfate product was obtained.

[0049] Example 4: Preparation of rare earth-doped nano-barium sulfate:

[0050] To prepare a 0.5 mol / L barium chloride aqueous solution, add 0.5 mol% Gd. 3+ (Rare earth ions), stir until completely dissolved; at the same time, prepare a 0.5 mol / L sodium sulfate aqueous solution;

[0051] Carboxymethyl chitosan with a molecular weight of 50,000 Da, a degree of substitution of 0.6, and an amino content of 5.0 mmol / g was dissolved at a concentration of 2.0 wt% in a solution containing Gd. 3+ In a barium chloride aqueous solution;

[0052] Under stirring conditions of 800 rpm, the above-mentioned dispersant-containing mixture was combined with Gd 3+ The barium chloride solution and sodium sulfate solution were mixed in a 1:1 volume ratio, and the reaction temperature was controlled at 50℃ for 40 minutes.

[0053] The pH of the reaction system was adjusted to 4.5 with dilute hydrochloric acid, and the mixture was kept at 50°C for 30 minutes to degrade carboxymethyl chitosan.

[0054] Gd was obtained by freeze-drying (under the same conditions as in Example 1) to separate the solid and liquid phases. 3+ Doped nano-barium sulfate products.

[0055] Example 5: Continuous production of nano-barium sulfate:

[0056] Prepare a 0.5 mol / L barium chloride aqueous solution (containing 2.0 wt% carboxymethyl chitosan, parameters are the same as in Example 1) and a 0.5 mol / L sodium sulfate aqueous solution;

[0057] The barium chloride solution containing the dispersant and the sodium sulfate solution are delivered to a static mixer for instantaneous mixing via metering pumps, and then flow into an insulated reaction tube (temperature 50℃, residence time 45 minutes).

[0058] After the reaction solution flows out, it enters the pH adjustment unit, where the pH is adjusted to 4.5 with dilute hydrochloric acid, and then the dispersant is degraded by holding it at a coil heater (50℃) for 30 minutes.

[0059] Solid-liquid separation was achieved using a centrifugal separation system, followed by freeze drying (under the same conditions as in Example 1) to obtain nano-barium sulfate product.

[0060] Example 6: pH optimization for the preparation of nano-barium sulfate:

[0061] Prepare a 0.5 mol / L barium chloride aqueous solution and a 0.5 mol / L sodium sulfate aqueous solution;

[0062] Carboxymethyl chitosan (with parameters the same as in Example 1) was dissolved in a barium chloride aqueous solution at a concentration of 2.0 wt%.

[0063] Under stirring at 800 rpm, a barium chloride solution containing a dispersant was mixed with a sodium sulfate solution at a volume ratio of 1:1, and the reaction temperature was controlled at 50°C for 40 minutes.

[0064] The pH of the reaction system was adjusted to 5.5 with dilute hydrochloric acid, and the mixture was kept at 50°C for 30 minutes to degrade carboxymethyl chitosan.

[0065] After solid-liquid separation by freeze drying (under the same conditions as in Example 1), the nano-barium sulfate product was obtained.

[0066] Example 7: Preparation of nano-barium sulfate by optimizing reaction temperature:

[0067] Prepare a 0.3 mol / L barium acetate aqueous solution and a 0.3 mol / L ammonium sulfate aqueous solution;

[0068] Aminated dextran (parameters same as in Example 3) was dissolved in a barium acetate aqueous solution at a concentration of 1.0 wt%.

[0069] Under stirring at 1200 rpm, a barium acetate solution containing a dispersant was mixed with an ammonium sulfate solution at a volume ratio of 1:1.5, the reaction temperature was controlled at 70℃, and the reaction time was 20 minutes.

[0070] The pH of the reaction system was adjusted to 5.0 with dilute hydrochloric acid, and the mixture was kept at 50°C for 35 minutes to degrade the amino-modified dextran.

[0071] After solid-liquid separation by freeze drying (under the same conditions as in Example 1), the nano-barium sulfate product was obtained.

[0072] Comparative Example 1: Preparation of nano-barium sulfate by conventional sodium dodecyl sulfate dispersion:

[0073] Prepare a 0.5 mol / L barium chloride aqueous solution and a 0.5 mol / L sodium sulfate aqueous solution;

[0074] Sodium dodecyl sulfate was dissolved in an aqueous barium chloride solution at a concentration of 2.0 wt%.

[0075] Subsequent operations (stirring rate, reaction temperature, time, solid-liquid separation, drying method) were completely consistent with those in Example 1;

[0076] After drying, nano-barium sulfate product is obtained (traditional dispersant system).

[0077] Comparative Example 2: Preparation of nano-barium sulfate without dispersant:

[0078] Prepare a 0.5 mol / L barium chloride aqueous solution and a 0.5 mol / L sodium sulfate aqueous solution;

[0079] Without adding any dispersant, the two solutions were mixed at a volume ratio of 1:1 under stirring at 800 rpm, with the reaction temperature controlled at 50°C and the reaction time at 40 minutes.

[0080] Subsequent operations (pH adjustment, solid-liquid separation, drying method) are completely consistent with those in Example 1;

[0081] After drying, nano-barium sulfate product is obtained (dispersant-free system).

[0082] Comparative Example 3: Preparation of nano-barium sulfate using low-concentration dispersants:

[0083] Prepare a 0.5 mol / L barium chloride aqueous solution and a 0.5 mol / L sodium sulfate aqueous solution;

[0084] Carboxymethyl chitosan (with parameters the same as in Example 1) was dissolved in an aqueous barium chloride solution at a concentration of 0.3 wt% (lower than the patent-specified 0.5 wt%).

[0085] Subsequent operations (stirring rate, reaction temperature, time, pH adjustment, solid-liquid separation, drying method) were completely consistent with those in Example 1;

[0086] After drying, nano-barium sulfate product (low concentration dispersant system) is obtained.

[0087] Test method:

[0088] 1. Primary particle size and particle size distribution coefficient: The sample was ultrasonically dispersed in deionized water for 10 minutes (power 300W) using a dynamic light scattering instrument at a test temperature of 25℃. Each sample was tested three times, and the average value was taken.

[0089] 2. Carbon residue: Using an elemental analyzer, the sample was burned at high temperature (900℃) in an oxygen atmosphere, and the CO2 content generated was detected. The mass fraction of carbon in the sample (ppm level) was then calculated.

[0090] 3. Heavy metal (Pb) content: Inductively coupled plasma mass spectrometry was used to digest the sample with a nitric acid-perchloric acid mixed solution (volume ratio 3:1) until clear. After adjusting the volume, the Pb element concentration was tested and the mass fraction of Pb in the sample (ppm level) was calculated.

[0091] 4. Zeta potential: Using a Zeta potential meter, the sample was ultrasonically dispersed in deionized water for 10 minutes (power 300W) at a test temperature of 25℃. Each sample was tested three times, and the average value was taken.

[0092] 5. Specific surface area: The Brunauer-Emmett-Teller method (BET) was used. The sample was degassed under vacuum at 105℃ for 2 hours, and then the specific surface area (m² / g) was calculated by nitrogen adsorption-desorption experiment.

[0093] 6. Agglomeration and Pure Phase Verification: Agglomeration: The microstructure of the sample was observed using a transmission electron microscope with an accelerating voltage of 200kV to determine whether there were obvious agglomerates.

[0094] Pure phase verification: Using an X-ray diffractometer with a scanning range of 2θ = 10°-80° and a step size of 0.02°, the presence of impurity phases was determined by comparing the sample with a standard barite-type barium sulfate card (JCPDS No. 05-0599).

[0095] Test data comparison table:

[0096]

[0097] The nano-barium sulfate prepared in all examples (1-7) met the requirements of high purity and high dispersibility: the primary particle size was concentrated in 45-65 nm (in line with the patent range of 20-100 nm), and the particle size distribution coefficient was less than 0.2 (minimum 0.14), indicating uniform particle size distribution; the carbon residue was less than 32 ppm (far lower than the patent limit of 50 ppm), and the heavy metal Pb content was less than 0.6 ppm (in line with the ppm level requirement), solving the problem of organic impurity residue in traditional methods; the absolute value of the Zeta potential was greater than 33 mV, the specific surface area was 42-55 m² / g, and no obvious agglomeration was observed by TEM, proving excellent dispersibility; XRD verification showed that they were all pure phase barite-type barium sulfate with no impurity phase formation.

[0098] Among them, Example 3 (dispersion of amino-modified dextran) had the lowest carbon residue (22ppm) and the largest specific surface area (55m² / g). The performance of Example 5 (continuous production) was basically the same as that of Example 1, indicating that the continuous process can stably produce in large quantities with uniform quality. Example 4 (rare earth doping) did not have its dispersibility and purity affected by doping, proving the compatibility of the process with functional modification.

[0099] Comparative Example 1 (Traditional Sodium Dodecyl Sulfate): Although the primary particle size is similar to that of the Example, the carbon residue is as high as 320 ppm (more than 10 times that of the Example), the absolute value of the Zeta potential drops to 25 mV, and a small amount of agglomeration occurs. This is because sodium dodecyl sulfate cannot be removed by weak acid degradation and remains on the product surface, which reduces purity and destroys dispersion stability, confirming the technical pain point of traditional dispersant residue in the patent background technology.

[0100] Comparative Example 2 (without dispersant): The particle size increased sharply to 200 nm, the particle size distribution coefficient was as high as 0.65, the specific surface area was only 12 m² / g, and there was severe agglomeration. This shows that without dispersant, the nanocrystal nuclei undergo irreversible agglomeration due to high surface energy, and nanoscale products cannot be obtained.

[0101] Comparative Example 3 (low concentration dispersant): The dispersant concentration of 0.3wt% is lower than the patent-defined 0.5wt%, resulting in some crystal nuclei not being covered and partial agglomeration. The particle size distribution coefficient increased to 0.25, and the absolute value of the Zeta potential decreased to 28mV, proving that the patent-defined dispersant concentration of 0.5-5.0wt% is the optimal window for balancing dispersion efficiency.

[0102] This patent fundamentally solves the contradiction between dispersibility and purity in traditional methods by constructing an integrated reaction-dispersion-self-cleaning process using an in-situ biodegradable dispersant and weak acid degradation:

[0103] The dispersant is derived from natural biomass and can be degraded into water-soluble small molecules, which can be removed without complicated post-treatment, reducing carbon residue and environmental impact.

[0104] The process conditions are mild, compatible with continuous production and rare earth doping modification, and combine technological advancement with industrialization feasibility.

[0105] The product's performance meets the stringent requirements of medical contrast agents and high-end electronic packaging fillers, demonstrating significant application value.

[0106] 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 method for preparing nano-barium sulfate, characterized in that, Includes the following steps: Prepare aqueous solutions of soluble barium salts with concentrations from 0.1 mol / L to 1.0 mol / L and aqueous solutions of soluble sulfates with concentrations from 0.1 mol / L to 1.0 mol / L. An in-situ biodegradable dispersant based on natural polysaccharides is dissolved in the barium salt aqueous solution or sulfate aqueous solution at a concentration of 0.5 wt% to 5.0 wt%, wherein the aqueous solution containing the dispersant is used as the reaction precursor solution and the other aqueous solution without the dispersant is used as the reaction solution. Under stirring conditions, the precursor solution and the reaction solution are mixed in a volume ratio of 1:1 to 1:3, the reaction temperature is controlled at 20°C to 80°C, and the reaction time is 10 minutes to 120 minutes, so that the barium sulfate nanocrystal nuclei nucleate and grow under the control of dispersant molecules. Adjust the pH of the reaction system to 3.0 to 6.0 and maintain this pH condition for 10 to 60 minutes to allow the dispersant to undergo acid-catalyzed hydrolysis and degrade into water-soluble small molecule fragments with a molecular weight of less than 1000 Da. Subsequently, solid-liquid separation, water washing, and drying were performed to obtain nano-barium sulfate product; The reaction precursor solution containing a dispersant is formed. The dispersant is a natural polysaccharide derivative with a molecular weight between 10,000 Da and 100,000 Da. Its main chain is composed of glucose units linked by β-1,4-glycosidic bonds or α-1,6-glycosidic bonds, and at least one hydrophilic functional group selected from carboxymethyl, hydroxyethyl or amino is introduced into the side chain. The in-situ biodegradable dispersant based on natural polysaccharides is selected from at least one of carboxymethyl chitosan, hydroxyethyl cellulose, or amino-modified dextran.

2. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The soluble barium salt is selected from at least one of barium chloride, barium nitrate, or barium acetate.

3. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The soluble sulfate is selected from at least one of sodium sulfate, potassium sulfate, or ammonium sulfate.

4. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The degree of substitution of the carboxymethyl chitosan is 0.3 to 1.2, and the amino content is 2.0 mmol / g to 8.0 mmol / g; the degree of hydroxyethyl molar substitution of the hydroxyethyl cellulose is 0.8 to 2.0; and the amino grafting density of the amino-modified dextran is 1 to 3 amino groups introduced per 10 glucose units.

5. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The pH adjustment is performed using dilute hydrochloric acid or citric acid solution, with the adjusted pH being 4.0 to 5.5, and the dispersant is degraded by incubating at 50°C for 30 minutes.

6. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The drying method is freeze drying or spray drying; The freeze-drying conditions are as follows: pre-freezing temperature -50℃, vacuum degree 10Pa, sublimation temperature -20℃, and desorption drying temperature 20℃; the spray drying inlet air temperature is 150℃ to 180℃, and the outlet air temperature is 80℃ to 90℃.

7. The method for preparing nano-barium sulfate according to claim 1, characterized in that, Doped nano-barium sulfate was prepared by adding 0.1 mol% to 1.0 mol% of rare earth ions when preparing barium salt aqueous solution.

8. The method for preparing nano-barium sulfate according to claim 1, characterized in that, The method employs a continuous production process: The barium salt solution containing the dispersant and the sulfate solution are respectively delivered to the static mixer by metering pumps for instantaneous mixing, and then flow into the insulated reaction tube for reaction. After the reaction liquid flows out, it enters the pH adjustment unit to adjust the pH, and then passes through the coil heater to complete the degradation. Finally, the solid and liquid are separated by the centrifugal separation system.

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