Smelter Gases and Dusts VS Air Quality

When sulphide ores are oxidized during the smelting stage, huge amounts of sulphur dioxide are produced. If the sulphur dioxide goes up the strokestack of a smelter, it can react with the water vapor in the air to form sulphuric acid, the acid in acid rain or snow. It is estimated that about 60% of all sulphur emitted to the atmosphere comes from smelting and other industrial activity. Ores that can be treated by hydrometallurgical methods do not produce air emissions, but process waters may have to be treated before they can be discharged.

Many smelters now trap their sulphur dioxide to make sulphuric acid, which is a useful product in itself. A large smelter can produce thousands of tonnes of sulphuric acid a day. The gases are drawn through a catalytic oxidation process that turns the sulphur dioxide into sulphur trioxide. Dissolved in water, this chemical reacts to form sulphuric acid which can be sold to the general bulk chemical trade or used to make agricultural fertilizers.

Dusts in the smelter exhausts can be recovered by passing them through cyclones and electrostatic precipitators. These units can recover up to 95% of particulate dusts, returning them for processing to recover their metal content.