If sulfur oxides derived from concentrate at a smelter are released into the atmosphere, they have a major negative impact on the surrounding environment. We make efforts to protect the environment through the effective use of sulfur oxides as resources, recovering them in the form of sulfuric acid and gypsum.
Akita Zinc (zinc smelting) sulfuric acid plant
Toyo Smelter and Refinery (copper smelting) sulfuric acid plant
1. Recovery of SO2 Gas
Zinc and copper concentrates, the major raw materials in zinc and copper smelting, contain sulfur, the raw material used for producing sulfuric acid and gypsum.
The heat of SO2 gas emitted by concentrate in flash furnaces and roasters is recovered in waste heat boilers, fine particle zinc and copper are collected and transferred to the gas purification process.
2. SO2 Gas Purification
Moisture in recovered SO2 gas is removed in a Peabody scrubber and impurities are eliminated in an electrostatic precipitator and a B/N tower.
3. Sulfuric Acid Production
Moisture is removed from the purified SO2 gas in a drying tower, which then undergoes heat exchange and oxidation in a converter to form SO3 gas. Next, in an absorption tower, the SO3 gas is reacted with water in sulfuric acid to produce concentrated sulfuric acid. (SO3 absorbed within H2O+H2SO4).
Both smelters use the double contact method to increase yield, contributing to environmental protection and quality assurance.
The sulfuric acid is stored in a tank and then shipped nationwide in tank trucks or chemical tankers.
Absorption tower in de-sulfurization plant
Residual SO2 gas is recovered from an absorption tower and converted into gypsum.
*All photos are of processes at Akita Zinc Co., Ltd.