Three types of surface modification methods for barite powder
Barite is a sulfate mineral of orthorhombic (orthorhombic) crystal system, with relatively stable physical and chemical properties, insoluble in water and hydrochloric acid, high density, good filling, non-toxic, non-magnetic, easy to absorb radiation, good Optical performance and other advantages, it is an important inorganic chemical product, widely used in petrochemical, building materials, plastics, coatings, rubber, automobile brake pads and other industries.
At present, the most effective method is to modify the surface of barite, so that the modifier forms an adsorption layer or a monolayer film on the surface of barite, changes its surface characteristics, and improves its dispersion and compatibility with organic matter. Sex, expand its scope of application, and increase the added value of the product.
The surface modification of barite and its application as a filler have been extensively studied, but there are still two issues in the modification of barite that need to be further studied: one is the selection of suitable modification methods and new modification methods. The first is the development of permanent methods to meet the needs of different types of barite and their application objects; the second is the optimization of modifiers and the development of new modifiers to meet the needs of products with higher performance.
At present, the modification methods for barite mainly include surface chemical coating method, mechanochemical method, chemical deposition method and so on.
1. Surface chemical coating method
The surface chemical coating method is a method of uniformly and stably coating the modifier on the particle surface by chemical action, thereby changing the surface characteristics of the particle.
The mechanism of chemical coating modification on the surface of barite: the surface modifier is adsorbed on the surface of barite or reacts with the hydroxyl groups on the surface to form chemical bonds, so as to organically coat the barite, and use steric repulsion or electrostatic interaction Prevent the collision between particles and cause agglomeration, thereby improving the dispersion of barite.
2. Mechanochemical method
The mechanochemical method mainly uses mechanical force to activate the surface of the particle, and promotes the chemical reaction between the particle and the modifier to achieve the coating of the particle surface.
Mechanochemical modification mechanism of barite: it mainly uses ultra-fine pulverization and other strong mechanical force to activate the surface free energy of powder particles purposefully, so as to change the surface structure, structure and performance of powder, and produce lattice distortion And dislocations, enhance its reactivity with the modifier, greatly improve the powder activity and improve the uniformity of particle distribution and enhance the interface between it and the matrix.
The mechanochemical modification process is relatively simple, the production cost is low, and it has been widely used in practical applications. It is mainly suitable for barite with larger particles, but for nano-barite with smaller particles, a single mechanical Mechanochemical modification is not effective. Further improve the uniformity of the action of the powder and the modifier in the modification process and reduce the amount of the modifier, improve the coating effect by combining with other modification methods, introduce new modification equipment to simplify the process, reduce energy consumption, and improve The environmental protection of the modification process, such as: jet mill, honeycomb, will be the development direction of mechanochemical modification.
3. Chemical deposition method
The chemical deposition method is to add a modifier or a precipitant to carry out a precipitation reaction on the surface of the particle, and after washing, filtering, drying, roasting and other steps, a coating film is firmly formed on the surface of the particle, thereby improving the optical, electrical and magnetic properties of the particle. , heat and other properties.
The mechanism of barite chemical deposition method modification: mainly through the chemical reaction to deposit the modifier on the barite surface to form one or more coating layers, this coating treatment can reduce the surface activity of the particles and prevent them Agglomeration improves the dispersion and stability of barite in different media. This method is mainly suitable for the modification of inorganic surface modifiers, but the reaction process is not easy to control to obtain a uniform coating layer. Therefore, it is necessary to further explore the process conditions and the influencing mechanism that affect the deposition uniformity in the chemical deposition process, so as to improve the controllability of the process.
About Ultrafine Powder Classification Technology
Ultrafine powder is not only the basis for preparing structural materials, but also a material with special functions. field is required. With the application of ultra-fine powder in modern industry more and more widely, the position of powder classification technology in powder processing becomes more and more important.
1. The meaning of classification
In the pulverization process, only a part of the powder usually meets the particle size requirements. If the products that have reached the requirements are not separated in time, and then pulverized together with the products that do not meet the particle size requirements, it will cause energy waste and over-crushing of some products. .
In addition, after the particles are refined to a certain extent, the phenomenon of crushing and agglomeration will appear, and even the crushing process will deteriorate due to the larger particle agglomeration. For this reason, in the process of ultrafine powder preparation, it is necessary to classify the product. On the one hand, the particle size of the product is controlled to be within the required distribution range; Then crush to improve the crushing efficiency and reduce energy consumption.
With the improvement of the required powder fineness and the increase of output, the difficulty of classification technology is getting higher and higher. The problem of powder classification has become the key to restrict the development of powder technology, and it is one of the most important basic technologies in powder technology. one. Therefore, the research on ultrafine powder classification technology and equipment is very necessary.
2. The principle of classification
Classification in a broad sense is to divide the particles into several different parts by using the different characteristics of particle size, density, color, shape, chemical composition, magnetism, and radioactivity. Classification in a narrow sense is based on the fact that particles of different particle sizes are subjected to centrifugal force, gravity, inertial force, etc. in the medium (usually air and water), resulting in different motion trajectories, so as to realize the classification of particles of different particle sizes.
3. Classification of classifiers
According to the medium used, it can be divided into dry classification (the medium is air) and wet classification (the medium is water or other liquids). The characteristic of dry classification is that air is used as fluid, which is relatively cheap and convenient, but it has two disadvantages. One is that it is easy to cause air pollution, and the other is that the classification accuracy is not high. Wet classification uses liquid as the classification medium, and there are many post-processing problems, that is, the classified powder needs to be dehydrated, dried, dispersed, and waste water treatment, etc., but it has the characteristics of high classification accuracy and no explosive dust.
According to whether it has moving parts, it can be divided into two categories:
(1) Static classifier: There are no moving parts in the classifier, such as gravity classifier, inertia classifier, cyclone separator, spiral airflow classifier and jet classifier, etc. This type of classifier has a simple structure, does not require power, and has low operating costs. The operation and maintenance are more convenient, but the classification accuracy is not high, so it is not suitable for precision classification.
(2) Dynamic classifier: There are moving parts in the classifier, mainly referring to various turbine classifiers. This type of classifier is complex in structure, requires power, and consumes a lot of energy, but it has high classification accuracy and is easy to adjust the particle size of the classifier. As long as the rotation speed of the impeller is adjusted, the cutting particle size of the classifier can be changed, which is suitable for precision classification.
Application of active wollastonite powder
Active wollastonite powder is a white, fine, soft powder. The difference from ordinary wollastonite powder is that a layer of fatty acid soap is adsorbed on the surface of the particle, which makes it have colloidal activation performance, and its relative density is lower than that of ordinary wollastonite (approx. 2.3-2.5), the production process is basically the same as that of ordinary wollastonite powder, except that a surface treatment process is added.
Application range: Wollastonite powder after high temperature activation has a wide application range, and has been widely used in natural rubber, synthetic rubber, epoxy resin, phenolic resin, thermoplastic polyester, thermosetting polyester, polyolefin, polypropylene, polyethylene , polyvinyl chloride, unsaturated resin, leather, nylon, glass steel, ceramics, paint and coatings and other industries. Its body shape can replace harmful substances such as asbestos and glass fiber. It can replace some expensive titanium dioxide, and can replace 30% lithopone in paint. The advantage of activated wollastonite powder itself containing silicon dioxide can replace 50%-80% of white carbon black. Wollastonite has acicular shape and white glass luster and has been applied to various industrial fields. It has the reputation of industrial monosodium glutamate.
Active wollastonite powder is used in the rubber industry: firstly, it can reduce the production cost of the product and increase the bulk density; more importantly, it can improve the comprehensive performance of the product as a functional filler. Such as strengthening and reinforcing products; adjusting the fluidity of rubber and the plasticity of mixing, anti-shrinkage, surface properties, etc., can improve the chemical properties of rubber products, such as reducing permeability, changing interface reflection, water resistance and weather resistance, Fire retardant, oil resistant coloring and opacity. It can also improve the heat resistance and electrical insulation of the product. Increase the heat distortion temperature of the product; reduce the specific heat and increase the thermal conductivity. It can replace white carbon black, and the main properties of its products have been improved to varying degrees; such as hardness, elongation, breaking strength, permanent deformation and volume wear, etc. are superior to white carbon black. It has a very good reinforcing effect. Especially suitable for high wear-resistant products such as rubber shoes and tires.
Active wollastonite is used in some products of paints and coatings: it replaces part of lithopone and titanium dioxide to improve the fluidity of coatings. The particle shape of wollastonite is a good suspending agent for coatings. Enhancer for clean paints with high loading due to low oil absorption. The consumption of adhesive substances is reduced, so the cost of coatings is greatly reduced. The alkaline nature of wollastonite is very suitable for polyvinyl acetate coatings, so that the coloring can be evenly dispersed. It can connect pigments suitable for acidic media, and can also be made into bright colored coatings. The surface has uniform distribution and good spraying performance. As a filler; it can improve the corrosion resistance of the fresh coating. It is suitable for water-based coatings such as polyvinyl formal, and can also be used for low-grade paints, intermediate coatings, road marking coatings; sound-proof coatings; fire-resistant coatings, asphalt coatings can replace asbestos. Wollastonite powder can be used as a reinforcing agent in self-cleaning paint. It can be used in white alkyd enamel to replace part of titanium dioxide; wollastonite powder after silane surface treatment can be used in iron red epoxy ester primer and iron red alkyd primer to replace all talcum powder, precipitated barium sulfate and smelted zinc oxide .
Application of Superfine Pulverization Technology in Food Industry
Ultrafine pulverization technology is to use mechanical or fluid power methods to crush materials, and the particle size reaches micron level, so that the structure and surface area of materials are changed. The plant cell wall can be broken by the ultrafine pulverization technology, so that the effective substances in the cells can be released quickly. Ultrafine pulverization can be divided into dry pulverization and wet pulverization. According to different pulverization principles, dry pulverization includes airflow type, high-frequency vibration type, rotating ball (rod) grinding type, hammering type and self-grinding type. ; There are colloid mill and homogenizer for wet pulverization.
Application of Superfine Pulverization Technology in Food Industry
1. Soft drink processing
At present, the soft drinks that have been developed by using the airflow micro-grinding technology include powdered tea, bean solid drinks and calcium-enriched drinks formulated with ultrafine bone powder. Tea culture has a long history in China. If tea leaves are made into powdered tea (with a particle size of less than 5 μm) at room temperature and in a dry state, the human body’s absorption rate of its nutrients can be improved. Adding tea powder to other foods can also develop new tea products.
2. Fruit and vegetable processing
Vegetables are ground into micro-paste powder at low temperature, which not only preserves nutrients, but also makes the fiber taste better due to the micronization. Such as loquat leaf powder, sweet potato leaf powder, mulberry leaf powder, ginkgo leaf powder, bean protein powder, jasmine flower powder, rose pollen, licorice powder, dehydrated vegetable powder, chili powder, etc. In addition, ultrafine grinding can also be used in the preparation of pumpkin powder, garlic powder, celery powder, etc.
3. Grain and oil processing
Adding ultra-finely pulverized wheat bran powder, soybean micropowder, etc. to flour can be made into high-fiber or high-protein flour; soybeans are processed into soybean milk powder after ultrafine pulverization, which can remove fishy smell; mung beans, red beans and other beans It can also be made into high-quality bean paste, soybean milk and other products after ultrafine grinding. Rice, wheat and other grains are processed into ultra-micron powder due to the fine particle size and the activation of surface state starch. The food made by filling or mixing it has excellent processing performance, and is easy to ripen, with good flavor and taste.
4. Aquatic product processing
Spirulina, kelp, pearl, turtle, shark cartilage and other superfine powders have unique advantages. Yang Jun ultrafinely pulverized the turtle shell to less than 10 μm. Animal experiments showed that the animals had enhanced calcium absorption and enhanced immune regulation ability.
5. Functional food processing
6. Seasoning processing
Superfine pulverization can finely crush traditional seasonings (mainly spices) into fine ultrafine particles with uniform particle size and good dispersibility. As the particle size decreases, its fluidity, solubility and absorption rate all increase, and the huge porosity makes the aroma contained in the cavity last for a long time, so the aroma and taste of the superfine powder condiment are very strong, pure, and delicious. It is also better, suitable for the production of instant and convenience food. Sun Junshe and others superfinely pulverized seasoning, stewed meat king, thirteen spices, and cumin to 10-25 μm, which improved the color, aroma, taste and processing characteristics of food.
7. Fresh bone meal (mud) processing of livestock and poultry products
Green meat powder food is now gradually becoming a hot spot in the market. Various livestock and poultry fresh bones are not only rich in protein and phospholipids, but also high in calcium, iron and vitamins and other nutrients. If the fresh bone is multi-stage pulverized into ultrafine bone paste or dehydrated into bone meal by airflow ultrafine pulverization technology, more than 95% of nutrients can be maintained and the absorption rate can be improved.
8. Ice cream processing of cold food products
Ultrafine powder can be used as stabilizer, filler, flavor fixative, nutritional binder and antifreeze agent of ice cream. Health-care cold drinks can be developed by using ultra-fine raw materials that are both used for medicine and food.
Advantages of fluidized bed jet mill
Since the advent of jet milling and grading equipment in the 1930s, the types have been continuously updated and the structure has been continuously improved. Bed (on-spray) jet mill, etc.
The fluidized bed jet mill is a new model that was put into use in the late 1970s and early 1980s. It has the characteristics of low energy consumption, light wear, low pollution, low noise, fine particle size and uniform distribution, etc. It is used in synthetic resin, phenolic Production of resins, PVC, pigments and dyes, powder coatings, couplers, pharmaceuticals, cosmetics, advanced ceramics, magnetic powders, abrasives, metal powders, food, spices, stearic acid, fats, waxes, mineral powders, pesticides and wettable powders been widely used in.
The fluidized bed jet mill superimposes the unidirectional jet flow and the reverse counter jet flow, and the unidirectional jet flow enters the grinding chamber through the nozzle. , a concentric reverse jet flow field is formed in the crushing area, and the crushed materials are fluidized under the action of pressure difference. Fluidization refers to the expansion of the particle bed at the critical fluidization velocity in the flow field, and the solid particles in the bed have the flow characteristics of the fluid.
The crushed materials in the crushing area are accelerated in the high-speed counter-jet flow field, and violent impact, collision, friction and shear are generated at the intersection of the jets from each nozzle, resulting in the crushing of the materials. The pulverized materials form an upward airflow around the intersection point, and the materials are brought to the upper horizontal turbine sorter for automatic classification. The powder particles that meet the requirements are selected by the sorter and then collected by the cyclone. Coarse particles slide back to the grinding chamber along the wall and continue grinding until they are separated. Therefore, the powder with good dispersibility and narrow particle size distribution can be obtained through the pulverization and classification treatment of the fluidized bed jet mill.
(1) Change the line and surface impact crushing of the traditional jet mill to the three-dimensional impact crushing of the space, and make full use of the high-speed airflow generated by the jet impact in the flow of materials in the crushing chamber, so that the crushing area is similar to a fluidized state Excellent gas-solid crushing and graded circulation flow effect, which improves the efficiency of impact crushing and the comprehensive utilization of energy. Compared with other traditional methods, the energy consumption is reduced by 30-40% on average;
(2) Since the impact crushing area and the gas-solid flow belt are placed in the middle space of the crushing chamber, the impact and abrasion of the materials driven by the high-speed airflow on the wall of the crushing chamber are avoided, and the most serious wear problem in jet impact crushing is improved, and greatly reduced. the potential for the material to be contaminated;
(3) Protective gases such as high-purity nitrogen or argon are used as the working medium to prevent oxidation, and the closed-loop operation has low gas consumption and reduces costs;
(4) There is no dust flying during the complete closed-loop operation, no pollution to the environment, and no harm to the human body;
(5) After jet milling, the activity of the powder increases. The energy of the high-speed jet flow in the jet mill crushing and classification process can not only cause the particles to be impacted and crushed, but also change the internal structure of the particles, especially the surface state, to a certain extent. The energy of the gas flow removes atoms or ions from the particle lattice, causing a mechanical loss of the crystalline structure. In this way, while the powder material is ultrafinely pulverized, the surface energy or internal energy of the particles increases, and the activity of the particles increases. The increase in the activity of the particles is not only beneficial to the chemical reaction, but also beneficial to the adsorption and coating of the particles.
(6) The particle size of the product is fine, the output is large, and it is suitable for large-scale production; the particle size classification accuracy is high, so the particle size distribution of the product is narrow, and the particle size of the product is also easy to adjust.
Dry fine grinding technology applied in the field of agricultural chemistry
Production Process
The reason why pesticide manufacturers develop specific components and dosage forms is to make the active ingredients effective in reducing the factors that are unfavorable to crop growth (such as pests, weeds or fungi... ). Therefore, plant protection agents can be said to be essentially a mixture of different ingredients. These ingredients can basically be summarized into three categories:
active ingredient in the formulation.
Fillers for diluting active substances, such as clay, talc, kaolin or silica.
Auxiliaries and additives to improve formulation quality (e.g. stabilizers, wetting agents, protective agents, defoamers, etc.)
In the pesticide production process, the first step is feeding and mixing; the second step is grinding. Through different types of grinding equipment as shown below, the mixed material particles are ground and dispersed to the target fineness to meet the application requirements. After grinding, it goes through a sieving process to prevent possible oversized particles. Finally, the additives or fillers that do not need to be ground are added, and the dispersive mixing is carried out again.
Reasons why pesticide particles are required to be ultrafine particles and narrow particle size distribution:
The finer the active ingredient particles, the more potent the action, which means that a smaller amount can be used to achieve the same medicinal effect. Here are the safety, environmental and economical factors:
Reduce toxic effects on persons in the spray area.
Reduce pollution to the environment.
Reduce pesticide production costs and increase profits by reducing the amount of the most costly active ingredient used in the formulation.
Narrow particle size distribution facilitates the simplification of pesticide application steps:
The powder is dispersed in water before application on crops. The finer the particles, the more stable the suspension and no settling occurs during handling.
In the process of pesticide spraying, it effectively reduces the problem of large particles clogging the nozzle of the spraying system.
Mechanical impact mills can be used for fine grinding of soft to medium hard materials. Typical fineness ranges for the median particle size are 20 to 500 μm. The peripheral speed is 25 to 150 m/s. NETZSCH can also provide another model with counter-rotating method and a speed of up to 250 m/s. The air flow depends on the rotor type, thus ensuring temperature-stabilized grinding. The rotor is mounted horizontally and the shaft seal is of the non-contact labyrinth type due to the high shaft speed.
Mechanical mill CSM with grading function
This type of grading mill offers the possibility of simultaneously achieving both grinding and grading functions in one system. CSM classifier is a combination of fine impact classifier and guide wheel classifier. Driven by two independent motors, one for the grinding disc and the other for the classifying wheel, the CSM can precisely adjust the classifying wheel speed to obtain a wide range of final product fineness from d97=9μm to 200μm. By utilizing the geometric shape of the impeller of the classifier and the gap air seal between the classifier wheel and the top cover of the machine, the precise control of the upper limit of the particle size of the grinding material is ensured, thereby achieving fine classification.
The Fluidized bed jet mill is suitable for ultra-fine grinding of materials of various hardness (soft to extremely hard). In the grinding area, the particles are driven by the high-speed airflow to collide and grind each other, without additional grinding parts, and the dynamic classifier controls the maximum particle size. The air velocity at the outlet of the nozzle in the grinding chamber can reach 500 to 600 m/s. Because of the high grinding energy and impact velocity that can be generated in the fluidized bed, it is possible to achieve a D50 fineness of 1 to 5 μm.
Due to this structural feature, the jet mill has a very attractive feature: there is no temperature rise in the grinding chamber during the grinding process. The reason is that the heat generated when the particles collide with each other is offset by the cooling phenomenon of the expanded compressed gas, so that the temperature in the grinding chamber remains constant, and the active substance molecules will not be destroyed.
As a machinery manufacturer, ALPA has been devoting itself to designing grinding equipment and systems, and the machines have many designs that are convenient for customer maintenance. The design of the top cover with the grading wheel assembly can be fully opened, the rotating cavity shape and the properly selected maintenance door make it very easy for users to access the internal components. It is constructed of stainless steel, finely polished, and has a drain valve at the bottom of the grinder so it can be cleaned with water for easy cleaning.
Natural Zeolite Modification Technology and Its Application in Wastewater Treatment
Among many water treatment technologies, adsorption method has become an ideal wastewater treatment technology due to its advantages of simple operation, low energy consumption, good removal effect and high selectivity. The development of low-cost and high-efficiency adsorbents is the core of adsorption methods. Compared with other synthetic high-efficiency adsorbents, low-cost natural adsorbents have higher economic benefits and environmental protection value.
The abundant pores and channels in natural zeolites and the negative charge on the surface make them have good adsorption capacity for cations and little adsorption capacity for anions. This greatly limits the application of natural zeolites in the removal of anionic pollutants in water. For this reason, many studies have been carried out on the modification of natural zeolites in order to increase the affinity for anions. Surface modification is an effective way to increase the affinity of natural zeolites for anionic pollutants.
Different modification methods will have different effects on the physical and chemical properties of zeolite, such as changing the internal pore structure and size of zeolite, as well as hydrophilic and hydrophobic and surface functional groups. The main purpose of physical modification is to remove some impurities on the surface of zeolite and increase the specific surface area. The purpose of chemical modification is: (1) to remove impurities and dredge pore channels to facilitate the entry and transfer process of target substances, (2) to introduce new functional groups to change the surface properties of zeolite, such as hydrophobicity, thereby providing Novel binding sites for target pollutants.
Composite modification can achieve the purpose of synergistic modification by combining multiple modification methods. In order to better balance the preparation cost and removal effect, it is a better choice to improve the adsorption capacity of natural zeolite to anionic pollutants in water by means of compound modification.
There are still many challenges in the practical wastewater treatment of zeolites. For example, the pore size of natural zeolites usually belongs to the category of micropores, which are smaller than the radius of anions, which will hinder their migration and diffusion inside the zeolite, which is not conducive to the adsorption process. Moreover, the components in the actual wastewater are complex and changeable, and zeolites are easily affected by coexisting ions and pH values, resulting in poor adsorption effects and even structural damage. In addition, the saturated zeolite may be transformed into a new pollution source if it is not properly disposed of.
(1) The surface modification method will affect the physical and chemical properties of natural zeolite. Composite modification is an effective way to improve the anion adsorption performance of natural zeolite. For example, by introducing mesoporous materials to expand the pore size of zeolite and improve the diffusion efficiency of anions in the internal structure of zeolite. By introducing functional groups with affinity for target pollutants, the adsorption sites of zeolites can be enriched and the adsorption selectivity can be improved.
(2) Combining natural zeolite with other water treatment processes or materials can effectively improve its application potential in actual wastewater treatment. The pollution components in actual wastewater are complex and changeable, and the combined use of multiple materials/processes has become the mainstream way to improve the effect of actual wastewater treatment. Materials or combined processes containing natural/modified zeolites have been widely used in the treatment of wastewater, domestic sewage, rivers and lakes, etc. Natural zeolites and their modified forms have good application prospects in practical wastewater treatment.
(3) The modification and regeneration process of zeolite may involve toxic solvents, causing great harm to the environment and human health. A safe, pollution-free preparation and regeneration scheme should be sought, or a stable encapsulation method developed as a practical solution for final and safe disposal of zeolites.
What are the methods and common equipment for powder classification?
In terms of powder preparation, classification is of great significance, and it is one of the main deep processing technologies of powder in the field of inorganic non-metallic materials. Based on the particle size requirements of modern industry for fine powders, classification technology has shown more and more important status. It is not difficult to manufacture micron-sized powders, but how to reduce energy consumption and produce powders with very fine particle size and narrow particle size distribution is a challenge encountered in recent years.
The key of grading technology lies in grading equipment and grading process. In order to meet the high-precision classification, it is required to optimize the combination of various classifications. Therefore, it is particularly important to understand and master the main types and structural principles of grading equipment for the optimization of the grading process. In this field, it mainly involves fine particle classification, which is classified according to the nature of the medium. There are two types of fine classification: dry classification (the medium is air) and wet classification (the medium is water or other liquids).
The fluid medium of dry classification is generally gas, which can be divided into gravity classification, inertial force classification and centrifugal force classification according to the force. Next, I will introduce the grading principle, application scope and characteristics of representative grading equipment in dry grading.
Gravity Classification & Inertial Force Classification
The principle of gravity classification is to classify particles of different sizes in the gravitational field with different final settlement velocities. In a suitable gas medium, under a certain temperature, for a particle with a certain density, the final sedimentation velocity is only related to the particle diameter. In this way, classification according to particle size can be realized according to the difference in the end velocity of particle sedimentation. According to the direction of air flow, it can be divided into horizontal flow type, vertical flow type and zigzag flow type.
Inertial force classification is the operation of dispersing and suspending solid particle groups in the airflow and changing the direction of movement of the airflow sharply, using the difference in inertial force between light and heavy particles to classify the particle group. Its representative devices include curved inertial classifier, elbow jet inertial classifier and K-type classifier.
Centrifugal force classification
Principle: Because the force on the fine particles in the gravitational field is too small, it is difficult to classify the fine particles, so the centrifugal force field is used instead of the gravitational field to achieve the purpose of strengthening the classification. The gas flows through the rotor, and the fine particles flow together with the gas flow due to the drag force of the gas flow. When entering the interior of the rotor, the particles are subjected to outward centrifugal force. When the air drag force is greater than the centrifugal force, the particles pass through the rotor together with the air and become fine products; otherwise, the particles cannot pass through the rotor and become coarse products.
Scope of application: It is suitable for fine classification of micron-sized products in dry process. It can classify spherical, flake and irregular particles, and can also classify particles of different densities. The particle size of the graded product can reach D97: 3-150 microns, the product particle size can be adjusted steplessly, and the variety replacement is extremely convenient.
Classification efficiency: 60% to 90%. The classification efficiency is related to the properties of the material and the content of particles that meet the particle size. If the material has good fluidity and the content of particles that meet the particle size requirements is high, the efficiency will be high, and vice versa.
Equipment features: It has the advantages of stepless adjustable product size, high classification efficiency, and accurate cutting point.
Application industry: Widely used in chemical industry, minerals (especially suitable for the classification of non-mineral products such as calcium carbonate, kaolin, quartz, talc, mica), metallurgy, abrasives, ceramics, refractory materials, medicine, pesticides, food, health care products, new materials, etc. industry.
Titanium dioxide inorganic and organic coating modification technology
Rutile titanium dioxide is a semiconductor with a bandgap width of about 3.0eV. It has strong photocatalytic activity without surface modification, so that it can produce highly active oxygen free radicals under the radiation of solar ultraviolet rays. , this oxygen free radical can exert a strong oxidation ability, which will damage the medium around titanium dioxide and affect the service life of the product. Therefore, surface modification is an extremely important task in the production and processing of titanium dioxide.
Surface modification is the use of modifying additives to react with the surface of titanium dioxide, thereby changing the surface characteristics and improving the performance of the product. At present, the surface modification of titanium dioxide is roughly divided into two methods: inorganic coating and organic coating.
1. Titanium dioxide inorganic coating
Inorganic coating is to coat the surface of titanium dioxide particles with a single-layer or multi-layer inorganic thin film by means of sedimentation reaction, forming a barrier between the particles and the medium, so as to improve the performance of titanium dioxide. Inorganic surface modification of titanium dioxide is generally carried out by aluminum coating, silicon coating, zirconium coating and multiple mixed coating methods.
For silicon coating, the film formed under neutral and slightly acidic conditions is relatively "fluffy", while the film formed under alkaline conditions is relatively dense, generally through the hydrolysis of sodium silicate to generate silicon The micelles are then fixed on the surface of titanium dioxide through Ti-O-Si bonds, and at the same time, the formation of Si-O-Si bonds can also be used to ensure that the film is continuous and uniform.
For aluminum coating, the Ti-O-Al bond is formed through the reaction of OH-Al and the -OH group on the surface of titanium dioxide. The increase in the number of clusters facilitates the coating. At the same time, under high pH conditions, the directional growth rate of OH-Al occupies a dominant position relative to the sedimentation rate when the temperature is raised, and the film morphology changes from uniform and continuous sheet-like layers to relatively loose flocs.
Inorganic coating is specifically divided into two methods: dry coating and wet coating according to different processing methods.
(1) Titanium dioxide dry coating
In dry coating, metal halides are generally attached to the surface of titanium dioxide by air spraying, and after roasting and oxidation, hot steam is introduced to promote its hydrolysis to form a thin film coating on the particle surface.
(2) Titanium dioxide wet coating
Wet coating is mainly carried out in water medium, which is also subdivided into three types: boiling method, neutralization method and carbonization method.
2. Titanium dioxide organic coating
The development history of organic coating is shorter than that of inorganic coating, but it develops very rapidly due to the characteristics of small dosage (usually only 0.1% to 1% of the weight of the pigment) and large effect. There are three main methods of organic coating in the laboratory, namely high-speed dispersion wet method, vibration dispersion method and gas powder machine pulverization method. In the daily experiment process, we mainly adopt the high-speed dispersion wet method for processing.
Generally, in the process of organic coating, a part of the organic treatment agent is connected to the surface of the titanium dioxide by physical adsorption, and the other part reacts with the hydroxyl groups on the surface of the particles and then closely combines with the surface of the titanium dioxide. Dispersants, coupling agents, surfactants, etc. are used.
3. Composite coating with titanium dioxide
Since inorganic coating and organic coating have their own emphasis. Generally speaking, the main purpose of inorganic coating is to reduce the photocatalytic activity of titanium dioxide, improve its weather resistance, thereby increasing the service life of the product, while the main purpose of organic coating is to improve the dispersion ability of the product in various media and dispersion stability.
The two methods cannot replace each other, so in practical application operations, the operation mode of first inorganic coating and then organic modification is mostly used to modify the surface of titanium dioxide particles to achieve the purpose, that is, to use silicon, Soluble inorganic sources such as aluminum and zirconium (such as silicon dioxide, aluminum oxide, etc.) complete one or even multiple layers of inorganic coatings under their respective appropriate temperature and pH conditions to enhance their weather resistance. Then select a suitable bridging structure to connect fatty acid or aromatic acid groups with strong hydrophilicity to enhance its water dispersibility and dispersion stability.
Grinding of refractory raw materials
Crushing is an essential process in the refractory industry. The raw materials delivered to the factory range from powder to about 350mm, most of which are blocks over 25mm. The crushing process and raw material selection in the factory are the key to the production of high-quality products, which have a direct impact on the properties of the product. In addition, from the point of view of cost accounting, the power consumed by crushing and crushing equipment accounts for a large proportion. In order to save energy and reduce costs, attention must be paid to the crushed process.
The essence of the crushing process is related to the following factors, that is, overcoming the surface tension of the material's surface particles and overcoming the Coulomb attraction between the material's internal particles. Starting from the basic concept of the silicate physical and chemical dispersion system, it is not difficult to see that the particles of the crushed material are still very large when they are first crushed, so the surface and surface energy of the particles are small. , It is difficult to crush the material below 1μm (micron), the smaller the particle, the higher the surface energy, so when finely crushing, more energy will be consumed to overcome the surface energy. In addition, during fine grinding, due to the accelerated thermal movement of particles, the collision probability of particles increases, and coalescence and coagulation may also occur. Therefore, the crushing process must be organized correctly, and the crushing method and equipment should be selected according to the degree of dispersion of the final product.
The purpose of crushing:
(1) Crushing is an important operation link in the beneficiation process. When separating and enriching particles of the same component from raw ore aggregated by two or more different minerals, the raw ore should be crushed first in order to distinguish by type.
(2) In order to promote the interaction between the various phases, or evenly disperse the solid particles into the liquid, for example, prepare mud.
(3) Prepare various particle sizes according to process requirements. Increase the lattice defects and specific surface of the material, accelerate the physical and chemical reactions, and promote sintering.
The crushing methods can be roughly divided into the following four types: extrusion, impact, grinding and splitting. The function of various crushing machines is a combination of the above methods.
Crushing is divided into dry crushing and wet crushing. Wet crushing is mostly used in the production of ceramics or special refractory materials. Compared with dry crushing, it has the following advantages:
(1) The crushing ratio is large, and the particle size of the crushed material is small;
(2) The crushing efficiency is high, and the phenomenon of "powder wall" during dry crushing is not easy to occur (but when the particle size of the crushed product is less than 0.01mm, powder aggregation will also occur);
(3) The friction loss of equipment and grinding body is small;
(4) Good dust prevention, which is conducive to civilized production and process automation.
In addition, there are low-temperature crushing, dry crushing, and self-generating crushing based on the impact and friction of crushed materials, which are classified according to the crushing medium.
When crushing raw materials, the volume density and strength index of the material are of great significance to the selection of crushing equipment and the analysis of crushing efficiency.