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The main application and preparation of bismuth

wallpapers News 2021-05-14

Bismuth is the element symbol Bi, atomic number 83, atomic weight 208.98, peripheral electrical configuration 6S26P3, located in the sixth cycle ⅤA group, covalent radius 152pm, ionic radius Bi3+120pm, Bi5+74pm, first ionization energy 703.3kJ/mol, electronegativity 1.9. Silvery white or reddish metallic crystal, melting point 271.4℃, boiling point 1560±5℃, mono-atomic molecules and diatomic molecules in the vapor molecules in equilibrium state. The main oxidation number is -3, +1, +3, +5. The quality is crisp and hard, and the volume expands when solidified, with an expansion rate of 3.3%. The density of 9.747 g/cm3. Stable at room temperature in dry air, can be oxidized in moist air. Red heat combustion is blue flame, the formation of yellow oxide Bi2O3. It does not react with water at normal temperature. It can be slowly oxidized by steam when it is red hot. Bismuth powder can spontaneously ignite in chlorine gas and combine with bromine, iodine, sulfur and selenium to form trivalent compounds when heated. Insoluble in dilute hydrochloric acid and dilute sulfuric acid, soluble in nitric acid and concentrated sulfuric acid to form trivalent bismuth salt. Bismuth was discovered in 1753 by Ingiphor Rooftwall. There are two forms in nature: free state and combined state. The main minerals are bismuthite, bismuth China and so on. Abundance in the crust is 2.0×10-5%. It is mainly used for making low melting point alloy (melting point above 45℃ and below 100℃), used as automatic fire extinguishing device, fuse and solder in fire fighting and electrical industry. Also used for making movable type alloy, medicine and so on. Bismuth trioxide is prepared by calcining bismuthite and then is copolymerized with carbon to obtain bismuth.
Application of bismuth powder
The main uses of bismuth are as follows :(1) as a component of low melt alloys used in fireproof equipment, metal contacts, and heat conduction medium. (2) for the preparation of drugs for the treatment of stomach diseases and syphilis. (3) for electrical equipment (thermoelectric alloys and permanent magnets). (4) as a catalyst, especially in the preparation of acrylonitrile. (5) high temperature ceramics and pigments.
The preparation of bismuth powder
1. FeCl3 leaching - iron powder replacement method
The method can be divided into three main steps: leaching of ferric chloride, hydrochloric acid, iron powder replacement and smelting of bismuth sponge.
1) Leaching of FeCl3 + Hydrochloric Acid. Bi2S3 in bismuth sulphide ore was leached with mixed solution of ferric chloride and hydrochloric acid. Soluble bismuth trichloride was formed by dissolving Bi2S3 in the ore with FeCl3.
At the same time, a small amount of natural bismuth mixed in the ore is also dissolved: Bi+ 3FeCl3BICL3 +3FeCl2, while the bismuth oxide in the ore is dissolved by hydrochloric acid: Bi2O3+ 6HCl2BICL3 +3H2O. The addition of hydrochloric acid to the leach helps to prevent the hydrolysis of BICL3 to an insoluble BIOCL precipitate.
2) iron powder replacement. The bismuth in the ore is transferred into the solution after leaching, and the sponge bismuth can be replaced by adding iron powder:
Bicl3 2 + 3 + 3 fe2bi fecl2.
3) Refining of spongy bismuth. The replaced sponge bismuth needs to be heated and melted into bismuth ingot, but serious oxidation reaction will occur in direct melting, so it is melted in the molten sodium hydroxide (melting point 318.4℃, density 2.13g/cm3) in industry, which can prevent the oxidation of bismuth, and the molten liquid bismuth (melting point 27L ℃, The isothermal liquid density is 10.064g/cm3) is also easy to aggregate, and the bismuth oxides and some impurities in the bismuth can also be absorbed by NaOH. The liquid bismuth in the lower layer is formed into a certain size bismuth ingot by flow casting, which still contains some impurities. It belongs to coarse bismuth and must be refined further. The leaching rate of bismuth is high (94% ~ 94.5%) and the environmental pollution is small. The disadvantage is that the material consumption is high. Each ton of bismuth sponge consumes 1.5 ~ 1.8t of hydrochloric acid, 0.4 ~ 0.5t of chlorine gas and 0.5 ~ 0.6t of iron powder. Due to the use of iron powder replacement and chlorine regeneration technology, the accumulation of iron and chloride ions in the solution can not be ignored, the discharge of waste liquid is large, the concentration of ions in the leach solution is higher, the solution viscosity is larger, the filtration and washing of slag is more difficult.

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