1. Wet Process
Wet process is the main method for producing zinc sulfate. The process includes zinc ore roasting, leaching, purification, neutralization, crystallization, centrifugation, and drying. The specific steps are as follows:
(1) Zinc Ore Roasting: Zinc ore is mixed with coal powder and roasted in a rotary kiln to produce zinc calcinate.
(2) Leaching: Zinc calcinate is mixed with water and sulfuric acid and leached to produce a mixed solution of zinc sulfate and ferric sulfate.
(3) Purification: Iron filings or pyrite are added to the mixed solution as reducing agents to reduce the iron ions to ferric hydroxide precipitate, which is then removed by filtration.
(4) Neutralization: Lime milk or sodium hydroxide is added to the purified solution to adjust the pH to 4.0-4.5, causing the zinc ions in the solution to precipitate as zinc sulfate.
(5) Crystallization: The precipitated zinc sulfate crystals are centrifuged to obtain zinc sulfate crystals.
(6) Drying: The zinc sulfate crystals are dried to obtain the finished zinc sulfate product.
The wet process is mature, easy to operate, and has low production costs, but it generates a large amount of waste residue that needs to be properly disposed of.
2. Pyrometallurgical Production
The pyrometallurgical production of zinc sulfate mainly uses zinc slag or hot-dip galvanized slag as raw materials, and produces zinc sulfate through acid leaching, purification, and crystallization steps. The specific steps are as follows:
(1) Acid Leaching: The zinc slag or hot-dip galvanized slag is mixed with dilute sulfuric acid and then acid leached to generate a mixed solution of zinc sulfate and ferric sulfate.
(2) Purification: An oxidant (such as hydrogen peroxide) is added to the mixed solution to oxidize the iron ions to ferric hydroxide precipitate, which is then removed by filtration.
(3) Crystallization: The purified solution is evaporated and concentrated to precipitate zinc sulfate crystals.
(4) Centrifugation and Drying: The precipitated zinc sulfate crystals are centrifuged and dried to obtain the finished zinc sulfate product.
The pyrometallurgical production process is simple, but the source of raw materials is limited, resulting in higher production costs.
