The precipitated barium sulfate appearance was a white amorphous powder having a relative density of 4.50 (15 ° C) and a melting point of 1 580 ° C. Due to its high refractive index (1.63~1.65), it shows a white color and a certain hiding power. It is almost insoluble in water, ethanol and acid and is soluble in hot sulfuric acid. Easily made with mixed crystal of potassium permanganate, calcium carbonate, or metal nitrate. It can be reduced to strontium sulfide with carbon at high temperature.
It is an important basic chemical raw materials, the main purposes: as paints, coatings, inks, plastics, rubber materials or fillers and the battery; printing paper and paperboard copper surface coating agent; textile industry sizing As a clarifying agent in glass products, it can play the role of defoaming and increasing gloss. It can also be used as a protective wall material for radiation protection, and also used in industries such as porcelain, enamel and dyes, as well as raw materials for the manufacture of other strontium salts.
1 Status of industrial production technology of precipitated barium sulfate
1.1 Glauber's salt -sodium sulfate method
Glauber's salt-sodium sulphate method is a traditional method with mature technology and strong applicability. The raw materials are barite and thenardite. The by-product of this method is sodium sulfide. The chemical reaction is as follows:
BaSO4+4C→BaS+4CO (1)
BaS+Na2SO4→BaSO4+Na2S (2)
The specific process is: The barite and coal powder-mixed in a certain proportion, and then into the roaster from the tail, countercurrent contact with hot gas stream at high temperature 1100 ~ 1 500 ℃ reduction reaction, the reaction heat required for the source of pulverized coal or The burning of heavy oil, the preparation of clinker clinker (commonly known as "black ash"), after leaching, sedimentation and clarification, so that the concentration of barium sulfide is 130-160 g / L. At the same time, a certain amount of barium sulfate wastewater (diluted sodium sulfide solution) is placed in the chemical tank, heated to 40 °C with a steam engine, the mixer is started, the thenardite is input into the tank, heating is continued to 90 °C, and the sample is removed by sodium sulfide. Ca, Mg impurity concentration of water lies in the nitrate 1.2 ~ 1.22 g / cm3, and then incubated nitrate water sedimentation standby.
After clarifying the above two solutions, the clarified liquid is placed in a compounding tank in a certain proportion to carry out a metathesis reaction, and the reaction reaches an equivalence point or a slight excess of hydrazine halide as an end point. The prepared barium sulfate and sodium sulfide solution are placed in a filter for solid-liquid separation, and the sodium sulfide solution is introduced into a recovery device for concentration by evaporation. The filter cake was washed with water barium, pickling, barium slurry is discharged into the pool, the pH was adjusted to 2-8 with sulfuric acid or phosphoric acid, after full acidified with frame filter press to remove excess water, and then conveyed through the cake barium The machine is transported to the drying cylinder for drying, and then pulverized to a packaging bin by a Raymond machine, and the finished product of precipitated barium sulfate is packaged.
Sodium sulphide, a by-product of this process, is widely used in the pharmaceutical, paper, tanning, sulphur dyes and other industries, especially the rapid development of new special engineering plastics such as polyphenylene sulfide, which has contributed to the development of the sodium sulphide industry. In the traditional dye industry, due to the closure of foreign production facilities and the continuous expansion of China's sulphur dyes, China has become the world's largest producer and consumer of sodium sulphide, and sulphur dyes have become the main downstream users of sodium sulphide.
Most enterprises in China use this technology, such as Shanxi Southwest Wind Chemical Group, Shaanxi Fuhua Group, Guangxi Lianzhuang Chemical Co., Ltd., etc. Some enterprises use Yuanming powder to replace Glauber's salt and strontium sulfide. This kind of process route is relatively long, the environmental pollution is more prominent, the technology is mature, and the industrial sodium sulfide is also produced by-product. The precipitated barium sulfate produced has a high whiteness. After mechanical grinding, the maximum particle size is about 10 μm, while the average particle size is about 1.2-1.3 μm. The particle size distribution is wide and the size is different, so the light is generated. Diffuse reflection, so that the coating film is dull, the gloss is not high, limiting its use in high-grade paints and coatings, can only meet the general coating quality requirements, in the field of low-end ink, ceramics and other fields.
In addition, since antimony sulfide is unstable in the air, it is easy to form antimony polysulfide, so the precipitated barium sulfate produced has a high impurity content, the barium sulfate mass fraction is about 97%, and the free barium content is high, sometimes due to sulfur ions. High in content and produces hydrogen sulfide taste (smelly egg flavor).
1.2 Sulfide sulfide-sulfuric acid method
The bismuth sulfide-sulfuric acid process is the same as the Glauber's salt-sodium sulphate method except that sulfuric acid is used instead of sodium sulphate. Its by-product is hydrogen sulphide. The chemical reaction process is:
BaS+H2SO4→BaSO4+H2S (3)
The specific process is as follows: the barite and the pulverized coal are mixed in a certain ratio, and the high temperature reaction is carried out at 1100 to 1500 °C to prepare clinker sulphide clinker (commonly known as "black ash"), and after leaching and sedimentation clarification, strontium sulfide is obtained. The mass concentration is 130-160 g/L. Then, about 30% of the sulfuric acid is slowly added to the clarified hydrazine brine, and the reaction is carried out in a sealed compounding tank, and the reaction reaches an equivalence point or a slight excess of hydrazine halide as an end point.
The barium sulfate prepared by the reaction is heated and desulfurized, and then the barium sulfate is discharged into the slurry tank, and the pH is adjusted to 6-8 with a base. After thorough stirring, the excess water is removed by a plate and frame filter press, and then the cake is passed through. The conveyor is transported to the drying cylinder for drying, and then pulverized to a packaging bin by a Raymond machine, and the finished product of precipitated barium sulfate is obtained after packaging. The hydrogen sulfide produced by the reaction is dried and purified for further processing.
Only a few manufacturers in China use this process, such as Hunan Hengnan Chemical Plant. The process is flexible and can be restored to the Glauber's salt-sodium sulphate method at any time with high applicability. The produced precipitated barium sulfate has higher whiteness, whiteness of building materials above 97, strong dispersibility and good stability between batches, and is mainly used for low-grade fillers in powder coatings and plastics. Due to the use of sulfuric acid, the production cost is high and the profit margin is small. However, due to the release of hydrogen sulphide in the production process, such manufacturers make full use of hydrogen sulphide to process products with higher added value as a profit-adding point.
Using hydrogen sulfide as a raw material, many sulfides can be synthesized. For example, the agrochemical herbicide ethyl thiocarbamate is derived from ethanethiol, and ethanethiol is synthesized from ethanol and hydrogen sulfide; The octylthiocarbamate salt produced from octyl mercaptan is a selective and low toxicity insecticide. Methionine in the feed industry is a feeding additive that strengthens feed nutrition and compensates for amino acid balance. It is produced from methyl mercaptan. The use of lime milk to absorb hydrogen sulfide and synthesize it with calcium cyanamide solution to produce thiourea, which is a multifunctional chemical, from the synthesis of pharmaceutical products (fine chemical intermediates) to the textile, dye and paper industries, from plastics and Resin chemistry to metal processing, hydrometallurgy, thiourea has a wide range of uses in these markets. Of course, the Claus process can be used to produce sulfur. The process is mainly achieved by incomplete combustion of hydrogen sulfide. This technology is very mature and has devices at home and abroad, and the recovery rate can reach more than 96%.
1.3 Barium carbonate-sulfuric acid method
The strontium carbonate-sulfuric acid process differs from the former two. Most manufacturers cannot adopt the method of high-temperature roasting barite reduction due to environmental restrictions. They can only be processed by natural high-quality toxic heavy stones or purchased industrial strontium carbonate. Take the precipitated barium sulfate, the chemical reaction formula is as follows:
BaCO3+H2SO4→BaSO4+H2O+CO2 (4)
Specific process: The industrial strontium carbonate is first beaten with water, and the solid mass fraction is controlled to be about 40%. Then, under constant stirring, it is slowly added to a certain amount of 30% sulfuric acid solution, and it is necessary to stir while stirring. Observe to prevent the occurrence of tanking. After the addition was completed, stirring was continued for 30 min to fully react the cesium carbonate, and then filtered, washed, pulverized, spray dried, and packaged into a product. Because a large amount of carbon dioxide gas bubbles in the course of the reaction, a liquid solid two phase reaction gathered in a large specific surface area of the surface of the bubbles, the solid barium sulfate fine particles formed, the particle size distribution is relatively narrow, and to accelerate the progress of the reaction .
Manufacturers using this method in China include: Foshan Anyi Nano Materials Co., Ltd., Hunan Hexin Materials Co., Ltd., Guangzhou Qingyuan Laike New Materials Co., Ltd., etc. The precipitated barium sulfate produced by this process has high whiteness, whiteness of building materials above 98, less impurities, low free strontium content, no hydrogen sulfide taste, easy dispersion, narrow particle size distribution, high specific surface area, and high gloss coating. membrane. Although the production cost is high, the quality of the products produced by this method is high, and the market is highly positioned, and its profits are considerable.
The carbon dioxide produced by this process is sold as a commodity after being dried, purified, and liquefied. In the chemical industry, it is used as raw material for production of barium carbonate, calcium carbonate, etc., or directly used to synthesize organic compounds such as ethylene carbonate; in the beverage industry, it is mainly used as an additive for carbonated beverages, giving special taste to beverages, improving storage performance, and giving The drinker brings a cool and refreshing feeling; in the tobacco industry, the carbon dioxide puffed cigarette silk can reduce the content of tar and nicotine in the tobacco, increase the grade of the cigarette, and save 5% to 6% of the tobacco.
In addition, in the production of industrial precipitated barium sulfate, in addition to the above three methods, there is also a method of recovering from salt sludge. Chlor-alkali industry
In the brine purification process, some manufacturers will initially treat the brine with barium chloride to produce a large amount of salt mud, the main components of which are barium sulfate and calcium carbonate. Therefore, there are many small factories in China that recover precipitated barium sulfate from salt mud. Its product quality is low, impurities are large, particle size is uncontrollable, batch is unstable, whiteness is low (generally below 94), and yellowing is easy. However, in recent years, as China has increased its environmental protection efforts, chlor-alkali enterprises have begun to pay attention to the recovery of barium sulfate in salt mud, and strive to improve the quality of salt sludge recovery and precipitation of barium sulfate.
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