Zinc sulfate heptahydrate is also called zinc vitriol and alum vitriol. Its relative molecular mass is 287.56. Its appearance is white particles or powder. It belongs to the orthorhombic crystal system and its relative density is 1.97. It gradually weathers in dry air. The main production methods include sulfuric acid method and smithsonite method.
The sulfuric acid method is used to produce zinc sulfate heptahydrate, which uses sulfuric acid to dissolve various materials containing zinc or zinc oxide, such as by-products of zinc powder production, defective zinc oxide, residual materials from the metal processing industry and non-ferrous metallurgical industry, and zinc slag and zinc mines, etc.
Zinc-containing materials are crushed by a ball mill and dissolved with 18% to 25% sulfuric acid. Dissolution is carried out in a reaction kettle lined with acid-resistant material, such as lead, and equipped with a stirrer. The reaction formula is as follows:
Zn+H2SO4→ZnSO4+H2↑ZnO+H2SO4→ZnSO4+H2O
The reaction is exothermic and the temperature rises above 80°C. If the material contains a large amount of metallic zinc, a large amount of hydrogen will be produced. Therefore, the reactor must be equipped with a strong exhaust device. In order to accelerate the reaction rate in the later stage of the reaction, excess zinc-containing materials can be added. The pH value at the end of the reaction is controlled at around 5.1, and the slurry is clarified and filtered. The zinc content in the filter residue should be less than 5%. In addition to zinc sulfate, the filtrate also contains sulfate corresponding to the metal impurities in the raw materials. Removing impurities can be done in two steps. First, copper, nickel, etc. are removed, and then iron is removed. The filtrate is heated to 80°C in the displacer, zinc powder is added, and the mixture is stirred vigorously for 4 to 6 hours. Since zinc has a lower reduction potential than copper, nickel, and cadmium, these metals can be displaced from the solution. The reaction formula is as follows:
Zn+CuSO4→ZnSO4+CuZn+NiSO4→ZnSO4+NiZn+CdSO4→ZnSO4+Cd
The replaced solution is filtered by pressure to remove fine muddy metal slag. The filtrate is sent to an oxidation dish, heated to 80°C, and sodium hypochlorite, potassium permanganate, manganese dioxide, etc. are added to oxidize it into high-valent iron. After oxidation, an appropriate amount of lime is added. milk to precipitate the high-valent iron hydroxide and then filter it out. When using bleaching powder, boil the solution after precipitation to destroy the remaining bleaching powder. When using potassium permanganate, zinc oxide can be added to adjust the pH value of the solution to 5.1 due to the precipitation of free acid. The filtrate is concentrated by evaporation, cooled to below 25°C, and zinc sulfate heptahydrate ZnSO4·7H2O crystals precipitate, which can be dehydrated and dried.
Post time: Oct-30-2024
