High reflectivity superfine barium sulfate, its preparation method and application

Abstract

The application provides high-reflection ultrafine barium sulfate, a preparation method and application thereof, and belongs to the technical field of barium sulfate preparation. The preparation method comprises the following steps: slurry is prepared by mixing barium sulfate coarse powder and water, 1# impurity removal reagent is added into the slurry to adjust the pH value of the slurry; the slurry after preliminary impurity removal is mixed with 2# impurity removal reagent, the impurity removal slurry, water and 1# grinding aid are mixed, the obtained barium sulfate slurry is subjected to twice wet grinding and then subjected to grading treatment, the graded slurry is subjected to liquid-phase wet modification by using a composite modifier, and the modified slurry is sequentially subjected to cooling aging, spray drying treatment and post-treatment. The preparation method combines wet stirring grinding, grinding and wet and dry twice grading processes, and simultaneously realizes liquid-phase impurity removal and modification processes, so that a natural ultrafine barium sulfate with high purity, high whiteness, narrow particle size, low oil absorption and good compatibility is obtained, and the solar light reflection ratio and hemispherical emissivity of heat insulation reflective paint can be improved.

Description

Technical Field

[0001] This invention relates to the field of barium sulfate preparation technology, and in particular to a high-reflectivity ultrafine barium sulfate, its preparation method, and its application. Background Technology

[0002] Statistics show that building energy consumption accounts for over 30% of global total energy consumption, with heating and cooling accounting for a significant portion. Against this backdrop, heat-reflective coatings, a passive energy-saving technology that is directly applied to the surface of building envelopes and fundamentally reduces heat input by reflecting sunlight, have seen tremendous market opportunities due to their economic efficiency, convenience, and high effectiveness.

[0003] The core technology of heat-insulating reflective coatings lies in their optical performance—that is, maximizing the reflection of visible and near-infrared energy from sunlight. Currently, high-performance coatings commonly use rutile titanium dioxide as the main reflective material, but it is expensive and primarily targets the visible light band, with limited reflectivity for near-infrared light, which accounts for 52% of solar energy. Therefore, developing a high-performance functional filler that can synergize with titanium dioxide, compensate for its near-infrared reflectivity shortcomings, and simultaneously reduce formulation costs has become an urgent need for technological upgrading in the coatings industry.

[0004] Barium sulfate, due to its extremely high refractive index (1.64), excellent photochemical stability, and low oil absorption, has been theoretically studied and preliminarily proven to be an ideal candidate. However, ordinary natural barium sulfate products cannot meet the requirements of high-performance heat-insulating coatings due to problems such as unreasonable particle size distribution, low whiteness, and poor compatibility with resins. Precipitated barium sulfate, with its fine particle size and high surface energy, is prone to agglomeration. Agglomerates become light scattering centers, leading to uneven coating gloss, reduced reflectivity, and even affecting the density of the paint film. Furthermore, its batch-to-batch dispersion stability is poor, posing significant defects when added to heat-insulating reflective coatings.

[0005] Therefore, there is an urgent need to develop a high-reflectivity ultrafine barium sulfate that meets the performance requirements of heat-insulating reflective coatings. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-reflectivity ultrafine barium sulfate, its preparation method, and its applications. This invention utilizes ultrafine wet grinding and surface modification to obtain a high-purity, high-whiteness, narrow-particle-size ultrafine barium sulfate, which can meet the performance requirements of heat-insulating reflective coatings for fillers.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-reflectivity ultrafine barium sulfate, comprising the following steps: 1) Prepare a slurry by mixing barium sulfate powder and water. Add No. 1 impurity removal reagent to the slurry to adjust the pH value to 5.5~6.5 to obtain a slurry with preliminary impurity removal. 2) The preliminarily purified slurry is mixed with impurity removal reagent #2 to obtain purified slurry; 3) Mix the impurity-removing slurry, water, and No. 1 grinding aid to obtain barium sulfate slurry; 4) The barium sulfate slurry is subjected to two wet grinding processes followed by classification to obtain a classified slurry; 5) The graded slurry and composite modifier are subjected to liquid-phase wet modification to obtain modified slurry; 6) The modified slurry is sequentially cooled and aged, spray-dried, and post-treated to obtain high-reflectivity ultrafine barium sulfate.

[0008] Preferably, the barium sulfate coarse powder in step 1) is obtained by grinding acid-washed barite ore, wherein the mass content of barium sulfate in the acid-washed barite ore is >95%, and the D50 of the barium sulfate coarse powder is 8~8.4μm and the D97 is 31~33μm. The slurry has a solid content of 40-50%, and the mass of the No. 1 impurity removal reagent is 0.3-0.5% of the mass of barium sulfate crude powder. After adding the No. 1 impurity removal reagent to the slurry, it is stirred at a stirring rate of 200-400 r / min. The No. 1 impurity removal reagent is a mixture of citric acid and oxalic acid, and the mass ratio of citric acid to oxalic acid is 2-4:1.

[0009] Preferably, in step 2), the slurry that has undergone preliminary impurity removal is heated to 60-70°C before adding impurity removal reagent #2; the mass of impurity removal reagent #2 is 1.0-1.5% of the mass of barium sulfate crude powder, and impurity removal reagent #2 is a mixture of sodium dithionite and sodium hypophosphite, with a mass ratio of sodium dithionite to sodium hypophosphite of 3-5:1; The mixing is carried out under stirring at a speed of 400-600 r / min for 1-2 hours.

[0010] Preferably, the impurity-removed slurry in step 3) is washed and filtered twice before being mixed with water and No. 1 grinding aid; the solid content of the barium sulfate slurry is 65-75%, and the mass of No. 1 grinding aid is 1-2‰ of the mass of barium sulfate coarse powder; the mixing is carried out under stirring, with a stirring speed of 400-600 r / min and a time of 5-10 min.

[0011] Preferably, the media used in the two wet grinding processes in step 4) are zirconia beads. In the first wet grinding process, the mass ratio of 1.0 mm, 1.5 mm, and 2.0 mm zirconia beads is 2-4:1-2:1, and the media filling rate is 50-60%. In the second wet grinding process, the mass ratio of 0.4 mm, 0.6 mm, and 0.8 mm zirconia beads is 3-5:1-2:1, and the media filling rate is 60-70%.

[0012] Preferably, grinding aid #1 is added during the first wet milling process. The mass of grinding aid #1 is 0.5~1‰ of the mass of barium sulfate coarse powder. Grinding aid #1 is an ammonium polyacrylate dispersant with a molecular weight of 5000~8000. The first wet milling time is 20~30 min. The slurry obtained after the first wet milling process has a D50 of 1.2~1.5 μm, a D97 of 2.5~3.0 μm, and a slurry mass content of particles ≤2 μm >75%. The second wet milling process involves adding grinding aid #2, which has a mass of 3-5‰ of the barium sulfate coarse powder mass. Grinding aid #2 is a high molecular weight polycarboxylate ammonium salt dispersant with a molecular weight of 30,000-40,000. The second wet milling process lasts for 30-40 minutes. The resulting slurry has a D50 of 0.4-0.6 μm, a D97 of 0.9-1.2 μm, and a D100 of 1.4-1.5 μm.

[0013] Preferably, the mass of the composite modifier in step 5) is 6-8‰ of the mass of barium sulfate crude powder, and the composite modifier comprises γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphoryloxy)titanate and stearic acid emulsion, and the mass ratio of γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphoryloxy)titanate and stearic acid emulsion is 3-5:2:2; In the liquid-phase wet modification, the slurry temperature is 70~80℃, the rotation speed is 300~400r / min, and the liquid-phase wet modification time is 20~30min.

[0014] Preferably, the cooling and aging time in step 6) is 10~20 min, cooling to the slurry temperature ≤40℃; the inlet temperature of the spray drying process is 160~190℃, and the outlet temperature is 85~95℃; the post-processing includes grading, cyclone collection, and sieving; the grading includes wet grading and dry air grading.

[0015] The present invention also provides high-reflectivity ultrafine barium sulfate prepared by the preparation method described above.

[0016] The present invention also provides the application of the aforementioned high-reflectivity ultrafine barium sulfate in heat-insulating reflective coatings.

[0017] The beneficial effects of this invention are: 1) The preparation method of high reflectivity ultrafine barium sulfate of the present invention combines wet stirring milling, grinding and wet and dry two-stage classification process, and at the same time, through liquid phase impurity removal and modification process, to prepare a natural ultrafine barium sulfate with high purity (barium sulfate mass content ≥98%), high whiteness (whiteness ≥97%), narrow particle size (D50 is 0.6~0.8μm, D97 is 1.1~1.3μm, D100 is 1.5~1.6μm), low oil absorption (13~14mL / 100g) and good compatibility. It is applied in heat insulation reflective coatings as an optical performance enhancer and structural performance optimizer to improve the solar reflectance of the coating film (≥0.92) and maintain high hemispherical emissivity (≥0.89).

[0018] 2) This invention uses a mixture of citric acid / oxalic acid and sodium dithionite / sodium hypophosphite as a purification agent to remove impurities such as polyvalent Fe and Mn from barite, effectively improving the purity of natural barite powder. Low molecular weight ammonium polyacrylate and high molecular weight ammonium polycarboxylate dispersants are used as grinding aids, taking into account both the efficiency of wet grinding and the water resistance of the product itself. The wet classification + dry airflow secondary classification process effectively controls the particle size distribution of ultrafine barium sulfate. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for preparing high-reflectivity ultrafine barium sulfate according to the present invention. Detailed Implementation

[0020] This invention provides a method for preparing high-reflectivity ultrafine barium sulfate, comprising the following steps: 1) Prepare a slurry by mixing barium sulfate powder and water. Add No. 1 impurity removal reagent to the slurry to adjust the pH value to 5.5~6.5 to obtain a slurry with preliminary impurity removal. 2) The preliminarily purified slurry is mixed with impurity removal reagent #2 to obtain purified slurry; 3) Mix the impurity-removing slurry, water, and No. 1 grinding aid to obtain barium sulfate slurry; 4) The barium sulfate slurry is subjected to two wet grinding processes followed by classification to obtain a classified slurry; 5) The graded slurry and composite modifier are subjected to liquid-phase wet modification to obtain modified slurry; 6) The modified slurry is sequentially cooled and aged, spray-dried, and post-treated to obtain high-reflectivity ultrafine barium sulfate.

[0021] In this invention, the barium sulfate coarse powder in step 1) is preferably obtained by grinding acid-washed barite ore. The barium sulfate mass content in the acid-washed barite ore is preferably >95%, more preferably ≥96%, and even more preferably ≥97%. The D50 of the barium sulfate coarse powder is preferably 8~8.4μm, and the D97 is preferably 31~33μm. The solid content of the slurry is preferably 40-50%, more preferably 42-48%, and even more preferably 45-46%; the mass of the No. 1 impurity removal reagent is preferably 0.3-0.5% of the mass of barium sulfate crude powder, more preferably 0.35-0.45%, and even more preferably 0.4%; after adding the No. 1 impurity removal reagent to the slurry, it is stirred at a stirring rate of preferably 200-400 r / min, more preferably 250-350 r / min, and even more preferably 300 r / min; the No. 1 impurity removal reagent is preferably a mixture of citric acid and oxalic acid, and the mass ratio of citric acid to oxalic acid is preferably 2-4:1, more preferably 2.5-3.5:1, and even more preferably 3:1.

[0022] In this invention, in addition to adjusting the pH of the system to make it slightly acidic, citric acid, as the purification reagent #1, can also act as a complexing agent to react with the metal ions (Fe) subsequently reduced. 2+ Mn 2+ This forms a stable, soluble complex, preventing it from redepositing or developing color, thus improving purification efficiency.

[0023] In this invention, the mixing in step 2) is preferably done by heating the pre-treated slurry to 60-70°C and then adding the No. 2 impurity removal reagent; the mass of the No. 2 impurity removal reagent is preferably 1.0-1.5% of the mass of barium sulfate crude powder, more preferably 1.1-1.4%, and even more preferably 1.2-1.3%; the No. 2 impurity removal reagent is preferably a mixture of sodium dithionite and sodium hypophosphite, and the mass ratio of sodium dithionite to sodium hypophosphite is preferably 3-5:1, more preferably 3.5-4.5:1, and even more preferably 4:1; The mixing is preferably carried out under stirring, with the stirring speed preferably being 400~600 r / min, more preferably 450~550 r / min, and even more preferably 500 r / min. The stirring time is preferably 1~2 h, and even more preferably 1.5 h.

[0024] In this invention, sodium dithionite in reagent #2 serves as the main reducing agent to provide an initial rapid reduction reaction, reducing high-valence, water-insoluble impurities such as Fe and Mn in barite powder. Sodium hypophosphite serves as an auxiliary reducing agent to provide long-lasting reducing properties, maintaining the reducing properties of the system in the later stages of the reaction and further promoting the full progress of the reduction reaction.

[0025] In this invention, the impurity-removing slurry in step 3) is washed and filtered twice before being mixed with water and No. 1 grinding aid; the solid content of the barium sulfate slurry is preferably 65-75%, more preferably 67-72%, and even more preferably 70%; the mass of No. 1 grinding aid is preferably 1-2‰ of the mass of barium sulfate coarse powder, and even more preferably 1.5‰; the mixing is preferably carried out under stirring, the stirring speed is preferably 400-600 r / min, more preferably 450-550 r / min, and even more preferably 500 r / min, and the stirring time is preferably 5-10 min, more preferably 6-9 min, and even more preferably 7-8 min.

[0026] In this invention, the media used in the two wet grinding processes in step 4) are preferably zirconia beads. In the first wet grinding process, the mass ratio of 1.0 mm, 1.5 mm, and 2.0 mm zirconia beads is preferably 2-4:1-2:1, more preferably 2.5-3.5:1.2-1.8:1, and even more preferably 3:1.5:1; the media filling rate is preferably 50-60%, more preferably 52-58%, and even more preferably 55-56%. In the second wet grinding process, the mass ratio of 0.4 mm, 0.6 mm, and 0.8 mm zirconia beads is preferably 3-5:1-2:1, more preferably 3.5-4.5:1.2-1.8:1, and even more preferably 4:1.5:1; the media filling rate is preferably 60-70%, more preferably 62-68%, and even more preferably 65-66%.

[0027] In this invention, a No. 1 grinding aid is added during the first wet grinding process. The preferred mass of the No. 1 grinding aid is 0.5-1‰ of the mass of the barium sulfate coarse powder, more preferably 0.6-0.9‰, and even more preferably 0.7-0.8‰. The No. 1 grinding aid is preferably an ammonium polyacrylate dispersant, with a molecular weight of 5000-8000, more preferably 6000-7000, and even more preferably 6500. The preferred time for the first wet grinding process is 20-30 min, more preferably 22-28 min, and even more preferably 25-26 min. The D50 of the slurry obtained after the first wet grinding process is preferably 1.2-1.5 μm, the D97 is preferably 2.5-3.0 μm, and the mass content of the slurry with a particle size ≤2 μm is >75%. The second wet milling process involves adding grinding aid #2. The preferred mass of grinding aid #2 is 3-5‰ of the mass of barium sulfate coarse powder, more preferably 3.5-4.5‰, and even more preferably 4‰. Grinding aid #2 is preferably a high molecular weight polycarboxylate ammonium salt dispersant, with a molecular weight preferably 30,000-40,000, more preferably 32,000-38,000, and even more preferably 35,000-36,000. The preferred time for the second wet milling process is 30-40 min, more preferably 32-38 min, and even more preferably 35-36 min. The D50 of the graded slurry is preferably 0.4-0.6 μm, D97 is preferably 0.9-1.2 μm, and D100 is preferably 1.4-1.5 μm.

[0028] In this invention, grinding aid #1 is a low molecular weight dispersant with a fast diffusion rate in the slurry, which can quickly reach the surface of newly broken particles and adsorb, thus preventing "crack healing" and agglomeration of newly formed fine powder and improving the initial crushing efficiency. At the same time, the ammonium salt dispersant has excellent water resistance and will not affect the water resistance of the coating film when applied to heat-insulating and reflective coatings. Grinding aid #2 has a regular comb-like molecular structure, and the average degree of polymerization of PEO side chains is preferably n=60~90, more preferably n=70~80. It utilizes strong steric repulsion to overcome the strong van der Waals forces between submicron / nano particles and prevent their agglomeration.

[0029] In this invention, the mass of the composite modifier in step 5) is preferably 6-8‰ of the mass of barium sulfate crude powder, more preferably 6.5-7.5‰, and even more preferably 7‰; the composite modifier preferably comprises γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphate)titanate and stearic acid emulsion, and the mass ratio of γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphate)titanate and stearic acid emulsion is preferably 3-5:2:2, more preferably 3.5-4.5:2:2, and even more preferably 4:2:2; In the liquid-phase wet modification, the temperature of the slurry is preferably 70~80℃, more preferably 72~78℃, and even more preferably 75~76℃; the rotation speed is preferably 300~400r / min, more preferably 320~380r / min, and even more preferably 350r / min; and the liquid-phase wet modification time is preferably 20~30min, more preferably 22~28min, and even more preferably 25~26min.

[0030] In this invention, the composite modifier is added in the following order: first, stearic acid emulsion and isopropyltris(dioctylpyrophosphate)titanate are added, and after reacting for 10 minutes, γ-aminopropyltriethoxysilane is added. The carboxyl ions of the stearic acid emulsion are adsorbed onto the barium sulfate surface via ionic or hydrogen bonds, with the long-chain alkyl groups facing outwards, immediately imparting hydrophobicity and creating steric hindrance, thus initially reducing the cohesive force and oil absorption between particles. Isopropyltris(dioctylpyrophosphate)titanate acts as a "molecular lubricant" and "crosslinking agent," reacting with the barium sulfate surface... The hydroxyl groups on the surface react with the γ-aminopropyltriethoxysilane, while its long-chain organic groups can effectively isolate and shield filler particles, reducing the oil absorption of the product. The siloxane end of γ-aminopropyltriethoxysilane reacts with the hydroxyl groups on the barium sulfate surface that are not completely covered, while the active functional groups (such as amino groups) on the other end extend to the outside, forming strong chemical bonds or strong polar interactions with the coating resin matrix. This solves the problem of weak interfaces that may exist in pure physical coating, reduces oil absorption while improving filling rate and compatibility, and is conducive to forming a denser coating with better reflective properties.

[0031] In this invention, the cooling and aging time in step 6) is preferably 10-20 min, more preferably 12-18 min, and even more preferably 15 min, cooling to a slurry temperature ≤40℃; the inlet temperature of the spray drying process is preferably 160-190℃, more preferably 170-180℃, and even more preferably 175℃, and the outlet temperature is preferably 85-95℃, more preferably 88-92℃, and even more preferably 90℃; the post-processing preferably includes grading, cyclone collection, and sieving; the grading preferably includes wet grading and dry air grading.

[0032] In this invention, classification is performed in an air classifier system. The air classifier system classifies the slurry using a horizontal spiral centrifugal classifier to first avoid large particles that may exist in the wet grinding stage, thereby reducing the particle size distribution of the slurry. After the slurry is dried, a 6-head inclined air classifier is used for secondary classification at a frequency of 63Hz to further classify the finished dry powder, ultimately obtaining an ultrafine barium sulfate with a narrow particle size distribution.

[0033] The present invention also provides high-reflectivity ultrafine barium sulfate prepared by the preparation method described above.

[0034] The present invention also provides the application of the aforementioned high-reflectivity ultrafine barium sulfate in heat-insulating reflective coatings.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] In this example, the stearic acid emulsion is Evonik TEGO® Phobe 1405.

[0037] Example 1

[0038] Using acid-washed barite ore with a barium sulfate content of 96% as raw material, after washing, drying, and crushing by jaw crusher and hammer crusher, barite particles with a diameter of 10~50mm are obtained. Barium sulfate coarse powder with D50 of 8.21μm and D97 of 32.17μm is obtained by grinding with Raymond mill. The coarse barium sulfate powder was added to reactor #1, and water was added to prepare a slurry with a solid content of 40%. Then, 0.3% of the barium sulfate powder mass of reagent #1 (citric acid and oxalic acid in a 2:1 mass ratio) was added to the reactor, and the stirring speed was 200 rpm to obtain a slurry with a pH of 6.3. The slurry in the reactor was heated to 60°C, and 1.0% of the barium sulfate powder mass of reagent #2 (sodium dithionite and sodium hypophosphite in a 3:1 mass ratio) was added. The stirring speed was 400 rpm for 1 hour. After two washes with deionized water and filtration, the purified slurry was mixed with water to prepare a slurry with a solid content of 65%. Dispersogen® 1840 dispersant, accounting for 1‰ of the barium sulfate powder mass, was added, and the stirring speed was 400 rpm for 5 minutes to obtain the barium sulfate slurry.

[0039] The barium sulfate slurry was pumped into a 3600L vertical stirred mill (No. 1) for the first wet grinding. The grinding media was zirconia beads with a mass ratio of 1.0mm, 1.5mm, and 2.0mm particles of 2:1:1 and a media filling rate of 50%. Dispersogen® 1840 dispersant, accounting for 0.5‰ of the mass fraction of the coarse barium sulfate powder, was added to the top of the stirred mill. The grinding time was 20 minutes. After the first wet grinding, the slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 1.46μm, the D97 was 2.87μm, and the mass content of slurry particles with a diameter ≤2μm was 76.21%. The slurry after the first wet grinding was pumped into a 3600L vertical stirred mill (No. 2) for a second wet grinding. The grinding media was zirconia beads with a mass ratio of 0.4mm, 0.6mm, and 0.8mm particles of 3:1:1 and a media filling rate of 60%. Dispersogen® 2782 dispersant, accounting for 3‰ of the mass fraction of barium sulfate coarse powder, was added to the top of the stirred mill. The grinding time was 30 minutes. After the second wet grinding, the slurry was classified by a horizontal spiral centrifugal classifier. The classified slurry was tested by a Malvern 3000-E laser particle size analyzer and found to have a D50 of 0.58μm, a D97 of 1.16μm, and a D100 of 1.47μm. The classified slurry was then placed in a storage tank.

[0040] The graded slurry was pumped into reactor #2, where a composite modifier (γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphoryloxy)titanate, and stearic acid emulsion in a mass ratio of 3:2:2) was added at a slurry temperature of 70°C and a stirring speed of 300 r / min for 20 min. Liquid-phase wet modification was then performed (isopropyltris(dioctylpyrophosphoryloxy)titanate and stearic acid emulsion were added first and reacted for 10 min before adding...). The γ-aminopropyltriethoxysilane reaction lasted for 10 minutes. The modified slurry was then pumped into a storage tank for cooling and aging for 10 minutes. The slurry temperature was measured at 38.5℃. After aging, the slurry was pumped into a spray drying system for drying. The inlet temperature was 160℃ and the outlet temperature was 85℃. The dried powder was collected by a bag filter and then entered a transfer silo. The material was then conveyed by airflow into an air classifier system for classification. After being collected by a cyclone, the material entered the finished product silo, where it was sieved, tested, and packaged.

[0041] Example 2

[0042] Using acid-washed barite ore with a barium sulfate content of 96% as raw material, after washing, drying, and crushing by jaw crusher and hammer crusher, barite particles with a diameter of 10~50mm are obtained. Barium sulfate coarse powder with D50 of 8.17μm and D97 of 31.93μm is obtained by grinding with Raymond mill. The coarse barium sulfate powder was added to reactor #1, and water was added to prepare a slurry with a solid content of 45%. Then, 0.4% of the barium sulfate powder mass of reagent #1 (citric acid and oxalic acid in a 3:1 mass ratio) was added to the reactor, and the stirring speed was 300 rpm to obtain a slurry with a pH of 6.0. The slurry in the reactor was heated to 65°C, and 1.3% of the barium sulfate powder mass of reagent #2 (sodium dithionite and sodium hypophosphite in a 4:1 mass ratio) was added. The stirring speed was 500 rpm for 1.5 h. After two washes with deionized water and filtration, the purified slurry was mixed with water to prepare a slurry with a solid content of 70%. Dispersogen® 1840 dispersant, at a mass fraction of 1.5‰ of the barium sulfate powder mass, was added, and the stirring speed was 500 rpm for 7 min to obtain the barium sulfate slurry.

[0043] The barium sulfate slurry was pumped into a 3600L vertical stirred mill (No. 1) for the first wet grinding. The grinding media was zirconia beads with a mass ratio of 1.0mm, 1.5mm, and 2.0mm particles of 3:1:1 and a media filling rate of 55%. Dispersogen® 1840 dispersant, accounting for 0.7‰ of the mass fraction of the coarse barium sulfate powder, was added to the top of the stirred mill. The grinding time was 25 minutes. After the first wet grinding, the slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 1.32μm, the D97 was 2.73μm, and the mass content of slurry with a particle size ≤2μm was 79.55%. The slurry after the first wet grinding was pumped into a 3600L vertical stirred mill (No. 2) for a second wet grinding. The grinding media was zirconia beads with a mass ratio of 0.4mm, 0.6mm, and 0.8mm particles of 4:1:1 and a media filling rate of 65%. Dispersogen® 2782 dispersant, accounting for 4‰ of the mass fraction of barium sulfate coarse powder, was added to the top of the stirred mill. The grinding time was 35 minutes. After the second wet grinding, the slurry was classified by a horizontal spiral centrifugal classifier. The classified slurry was tested by a Malvern 3000-E laser particle size analyzer and found to have a D50 of 0.52μm, a D97 of 1.07μm, and a D100 of 1.44μm. The classified slurry was then placed in a storage tank.

[0044] The graded slurry was pumped into reactor #2, where a composite modifier (γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphoryloxy)titanate, and stearic acid emulsion in a mass ratio of 2:1:1) was added at a slurry temperature of 75°C and a stirring speed of 350 r / min for 25 min. Liquid-phase wet modification was then performed (isopropyltris(dioctylpyrophosphoryloxy)titanate and stearic acid emulsion were added first and reacted for 10 min before adding...). The γ-aminopropyltriethoxysilane reaction was carried out for 15 minutes. The modified slurry was then pumped into a storage tank for cooling and aging for 15 minutes. The slurry temperature was measured at 36.2℃. After aging, the slurry was pumped into a spray drying system for drying. The inlet temperature was 180℃ and the outlet temperature was 91℃. The dried powder was collected by a bag filter and then entered a transfer silo. The material was then conveyed by air to an air classifier system for classification. After being collected by a cyclone, the material entered the finished product silo, where it was sieved, tested, and packaged.

[0045] Example 3

[0046] Using acid-washed barite ore with a barium sulfate content of 96% as raw material, after washing, drying, and crushing by jaw crusher and hammer crusher, barite particles with a diameter of 10~50mm are obtained. Barium sulfate coarse powder with D50 of 8.12μm and D97 of 31.22μm is obtained by grinding with Raymond mill. The coarse barium sulfate powder was added to reactor #1, and water was added to prepare a slurry with a solid content of 50%. Then, 0.5% of the barium sulfate powder mass of reagent #1 (citric acid and oxalic acid in a 4:1 mass ratio) was added to the reactor, and the stirring speed was 400 r / min to obtain a slurry with a pH of 5.7. The slurry in the reactor was heated to 70℃, and 1.5% of the barium sulfate powder mass of reagent #2 (sodium dithionite and sodium hypophosphite in a 5:1 mass ratio) was added. The stirring speed was 600 r / min for 2.0 h. After two washings with deionized water and filtration, the purified slurry was mixed with water to prepare a slurry with a solid content of 75%. Dispersogen® 1840 dispersant, accounting for 2‰ of the barium sulfate powder mass, was added, and the stirring speed was 600 r / min for 10 min to obtain the barium sulfate slurry.

[0047] The barium sulfate slurry was pumped into a 3600L vertical stirred mill (No. 1) for the first wet grinding. The grinding media was zirconia beads with a particle size ratio of 1.0mm, 1.5mm, and 2.0mm of 4:2:1 and a media filling rate of 60%. Dispersogen® 1840 dispersant, accounting for 1‰ of the mass fraction of the coarse barium sulfate powder, was added to the top of the stirred mill. The grinding time was 30 minutes. After the first wet grinding, the slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 1.24μm, the D97 was 2.59μm, and the mass content of slurry with a particle size ≤2μm was 85.21%. The slurry after the first wet grinding was pumped into a 3600L vertical stirred mill (No. 2) for a second wet grinding. The grinding media was zirconia beads with a mass ratio of 0.4mm, 0.6mm, and 0.8mm particles of 5:2:1 and a media filling rate of 70%. Dispersogen® 2782 dispersant, accounting for 5‰ of the mass fraction of barium sulfate coarse powder, was added to the top of the stirred mill. The grinding time was 40 minutes. After the second wet grinding, the slurry was classified by a horizontal spiral centrifugal classifier. The classified slurry was tested by a Malvern 3000-E laser particle size analyzer and found to have a D50 of 0.43μm, a D97 of 0.95μm, and a D100 of 1.42μm. The classified slurry was then placed in a storage tank.

[0048] The graded slurry was pumped into reactor #2, where a composite modifier (γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphoryloxy)titanate, and stearic acid emulsion in a mass ratio of 5:2:2) was added at a slurry temperature of 8‰ and a stirring speed of 400 r / min. Liquid-phase wet modification was then performed for 30 min (isopropyltris(dioctylpyrophosphoryloxy)titanate and stearic acid emulsion were added first and reacted for 10 min before adding...) The γ-aminopropyltriethoxysilane reaction lasted for 20 minutes. The modified slurry was then pumped into a storage tank for cooling and aging for 20 minutes. The slurry temperature was measured at 34.2℃. After aging, the slurry was pumped into a spray drying system for drying. The inlet temperature was 190℃ and the outlet temperature was 95℃. The dried powder was collected by a bag filter and then entered a transfer silo. The material was then conveyed by airflow into an air classifier system for classification. After being collected by a cyclone, the material entered the finished product silo, where it was sieved, tested, and packaged.

[0049] The high reflectivity ultrafine barium sulfate, conventional ultrafine barium sulfate (G-097C, Qingdao Yili Special Steel), and precipitated barium sulfate (CB-700, Yunfu Hongzhi) prepared in Examples 1-3 were tested according to GB / T 37041-2018 for relevant indicators. The test results are shown in Table 1.

[0050] Table 1. Detection results of different barium sulfate products

[0051] The high-reflectivity ultrafine barium sulfate, conventional ultrafine barium sulfate, and precipitated barium sulfate prepared in Examples 1-3 were used to make heat-insulating and reflective coatings. The formulations of the heat-insulating and reflective coatings are shown in Table 2, and the values ​​in Table 2 are the mass fractions of each component.

[0052] Table 2 Formulation of heat-insulating and reflective coatings

[0053] The test results of the heat-insulating reflective coatings prepared from high-reflectivity ultrafine barium sulfate, conventional ultrafine barium sulfate, and precipitated barium sulfate in Examples 1-3 are shown in Table 3.

[0054] Table 3 Test results of heat-insulating and reflective coatings

[0055] As shown in Table 3, the high reflectivity ultrafine barium sulfate products of Examples 1-3 of this invention, when applied to heat-insulating reflective coatings, exhibit a higher solar reflectance (above 0.92) and hemispherical emissivity (above 0.89) compared to traditional ultrafine barium sulfate and precipitated barium sulfate. Their brightness is significantly better than ordinary ultrafine barium sulfate, with higher contrast and gloss. Furthermore, the temperature difference in infrared lamp temperature rise tests is significantly lower than that of traditional ultrafine barium sulfate and precipitated barium sulfate, demonstrating significant performance advantages.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-reflectivity ultrafine barium sulfate, characterized in that, It includes the following steps: 1) Prepare a slurry by mixing barium sulfate coarse powder with water. Add No. 1 impurity removal reagent to the slurry to adjust the pH value of the slurry to 5.5~6.5 to obtain a slurry with preliminary impurity removal. 2) The preliminarily purified slurry is mixed with impurity removal reagent #2 to obtain purified slurry; 3) Mix the impurity-removing slurry, water, and No. 1 grinding aid to obtain barium sulfate slurry; 4) The barium sulfate slurry is subjected to two wet grinding processes followed by classification to obtain a classified slurry; 5) The graded slurry and composite modifier are subjected to liquid-phase wet modification to obtain modified slurry; 6) The modified slurry is sequentially cooled and aged, spray-dried, and post-treated to obtain high-reflectivity ultrafine barium sulfate.

2. The preparation method according to claim 1, characterized in that, Step 1) The barium sulfate coarse powder is obtained by grinding acid-washed barite ore. The mass content of barium sulfate in the acid-washed barite ore is >95%, and the D50 of the barium sulfate coarse powder is 8~8.4μm and the D97 is 31~33μm. The slurry has a solid content of 40-50%, and the mass of the No. 1 impurity removal reagent is 0.3-0.5% of the mass of barium sulfate crude powder. After adding the No. 1 impurity removal reagent to the slurry, it is stirred at a stirring rate of 200-400 r / min. The No. 1 impurity removal reagent is a mixture of citric acid and oxalic acid, and the mass ratio of citric acid to oxalic acid is 2-4:

1.

3. The preparation method according to claim 1 or 2, characterized in that, Step 2) The slurry that has undergone preliminary impurity removal is heated to 60~70℃ and then impurity removal reagent #2 is added; the mass of impurity removal reagent #2 is 1.0~1.5% of the mass of barium sulfate crude powder, and impurity removal reagent #2 is a mixture of sodium dithionite and sodium hypophosphite, with a mass ratio of sodium dithionite to sodium hypophosphite of 3~5:1; The mixing is carried out under stirring at a speed of 400-600 r / min for 1-2 hours.

4. The preparation method according to claim 3, characterized in that, Step 3) The impurity-removed slurry is washed and filtered twice before being mixed with water and No. 1 grinding aid; the solid content of the barium sulfate slurry is 65-75%, and the mass of No. 1 grinding aid is 1-2‰ of the mass of barium sulfate coarse powder; The mixing is carried out under stirring at a speed of 400-600 r / min for 5-10 min.

5. The preparation method according to claim 4, characterized in that, Step 4) The media used in the two wet grinding processes are zirconia beads. In the first wet grinding process, the mass ratio of 1.0 mm, 1.5 mm, and 2.0 mm zirconia beads is 2~4:1~2:1; the media filling rate is 50~60%. In the second wet grinding process, the mass ratio of 0.4 mm, 0.6 mm, and 0.8 mm zirconia beads is 3~5:1~2:1; the media filling rate is 60~70%.

6. The preparation method according to claim 5, characterized in that, The first wet milling process involves adding grinding aid #1, which is 0.5-1‰ of the mass of the barium sulfate coarse powder. Grinding aid #1 is an ammonium polyacrylate dispersant with a molecular weight of 5000-8000. The first wet milling process lasts for 20-30 minutes. The slurry obtained after the first wet milling process has a D50 of 1.2-1.5 μm, a D97 of 2.5-3.0 μm, and a slurry mass content of particles ≤2 μm >75%. The second wet milling process involves adding grinding aid #2, which has a mass of 3-5‰ of the barium sulfate coarse powder mass. Grinding aid #2 is a high molecular weight polycarboxylate ammonium salt dispersant with a molecular weight of 30,000-40,000. The second wet milling process lasts for 30-40 minutes. The resulting slurry has a D50 of 0.4-0.6 μm, a D97 of 0.9-1.2 μm, and a D100 of 1.4-1.5 μm.

7. The preparation method according to claim 5 or 6, characterized in that, Step 5) The mass of the composite modifier is 6-8‰ of the mass of barium sulfate crude powder. The composite modifier contains γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphate)titanate and stearic acid emulsion. The mass ratio of γ-aminopropyltriethoxysilane, isopropyltris(dioctylpyrophosphate)titanate and stearic acid emulsion is 3-5:2:

2. In the liquid-phase wet modification, the slurry temperature is 70~80℃, the rotation speed is 300~400r / min, and the liquid-phase wet modification time is 20~30min.

8. The preparation method according to claim 7, characterized in that, Step 6) The cooling and aging time is 10~20 min, cooling to the slurry temperature ≤40℃; the inlet temperature of the spray drying treatment is 160~190℃, and the outlet temperature is 85~95℃; the post-treatment includes grading, cyclone collection, and sieving; grading includes wet grading and dry air grading.

9. High-reflectivity ultrafine barium sulfate prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the high-reflectivity ultrafine barium sulfate as described in claim 9 in heat-insulating reflective coatings.

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