Chapter 20 - Sulfur Dioxide Capture in Sulfuric Acid and Other Products

Abstract

About half the global production of primary nickel is extracted from sulfide minerals. Sulfur dioxide can be harmful to fauna and flora. This chapter describes the following: offgases from nickel extraction; production of sulfuric acid from these gases; and other sulfur dioxide-based by-products. Nickel sulfide roasting and flash smelting produce continuous steams of offgas that contain 10–12% SO2 after dilution with air. These gases are ideal for making sulfuric acid. Sulfur dioxide must be first oxidized to sulfur trioxide, which then reacts with water. The exact compositions of commercial catalysts for the oxidation of sulfur dioxide are proprietary. Sulfuric acid is made from sulfur trioxide by reacting exit gas from the catalytic oxidation with the water in 98.5% sulfuric acid. The double-contact acid-making plant is the most common flowsheet used for capture of sulfur dioxide. A double-contact sulfuric acid plant has the following three acid product streams: weakened acid from dehydration and two strengthened acid streams from the two acid-making towers. An alternative method to the production of sulfuric acid for the capture of sulfur dioxide is the production of liquid sulfur dioxide. The leaching of nickel laterites requires about 0.3 tonnes of sulfuric acid per tonne of concentrate. Sulfur dioxide gas is produced by all nickel sulfide smelters. It is often made into sulfuric acid, which is a useful industrial chemical. Scrubbing also produces useful by-products, such as gypsum and sodium bisulfite.