Direct method zinc oxide is produced from various zinc-containing minerals or impurities. 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 99.5%.
The raw material of the indirect method zinc oxide 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 to 10 μm 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.