Zinc oxide mainly has three major categories: indirect method, direct method and wet chemical method:
The raw material of the indirect method is a metal zinc ingot or zinc slag obtained by smelting. Zinc is converted into zinc vapor in a graphite crucible at a high temperature of 1000 ° C, and then oxidized by the blasted air to form zinc oxide, and zinc oxide particles are collected after cooling the tube. The indirect method was promoted in 1844 by the French scientist LeClaire and is therefore also known as the French law. The indirect method for producing zinc oxide has a simple process technology and the cost is greatly affected by the raw materials. The zinc oxide particles produced by the indirect method have a diameter of about 0.1-10 microns and a purity of between 99.5% and 99.7%. Indirect method is the most important method for producing zinc oxide based on total production. Zinc oxide produced by indirect method can be used in rubber, varistor, paint and other industries. The heavy metal content of zinc ingot or zinc slag directly affects the heavy metal impurity content of the product, and the product with low heavy metal content can also be used in livestock feed, medicine, medical care and other industries.
The direct method uses various zinc-containing minerals or impurities as raw materials. When zinc oxide is reacted with coke, it is reduced to metal zinc by steam, and then oxidized to zinc oxide by oxygen in the air to remove most of the impurities. The zinc oxide particles obtained by the direct method are coarse, and the purity of the product is between 75% and 95%, and is generally used in the rubber and ceramic industries with lower requirements.
Wet chemical methods can be roughly divided into two categories: acid method and ammonia method. The two are respectively reacted with a raw material using an acid or a base, and then a zinc carbonate or zinc hydroxide precipitate is prepared. After filtration, washing, drying and calcination at 800 ° C, a high-purity light zinc oxide having a particle diameter of 1-100 nm is finally obtained. The acid process typically involves reacting a zinc-containing feedstock with sulfuric acid to provide a non-pure zinc sulfate solution containing heavy metal ions. Then, after oxidation and impurity removal, reduction and impurity removal, and multiple precipitation, a large amount of iron, manganese, copper, lead, cadmium, arsenic and the like are removed to obtain a pure zinc sulfate solution. This solution was neutralized with a soda ash to give a solid basic zinc carbonate. The basic zinc carbonate is washed, dried and calcined to obtain a light zinc oxide. The quality of the products produced by the acid process is high. The ammonia method usually uses ammonia water and ammonium bicarbonate to react with a zinc-containing raw material to obtain a zinc-ammonium complex, and then removes impurities to obtain a qualified zinc-ammonium complex solution, and then converts the zinc-ammonium complex into a basic form by steaming ammonia. Zinc carbonate. Finally, it is dried and calcined to obtain light zinc oxide. The cost of ammonia is relatively low.