Abstract: Disclosed is a process for the purification of an exhaust gas which contains dust and gaseous pollutants, such as SO.sub.2, SO.sub.3, HCl, HF and nitrogen oxides. In the process 70 to 90% of the total amount of sorbent required is introduced as a dry powder into the gas stream and the remaining 10 to 30% of the sorbent is introduced into the gas stream as a solution or suspension after a turbulence has been induced in the gas stream.

Abstract: The sulfur-containing roasting gases of an ore-roasting plant are cooled in a waste-heat boiler, which produces steam, and then are subjected to particle removal in an electrostatic precipitator or cyclone. The gases are then scrubbed with recirculated aqueous sulfur acid and the gas is then passed through an electrostatic precipitator before being supplied to a plant for the contact process production of sulfur acid. According to the invention, the process is improved by condensing water from the gas in an indirect cooler between the scrubber and the final electrostatic precipitator while water or aqueous sulfur acid is sprayed into the gas upstream of the indirect gas cooler to augment the heat transfer from the gas to the cooled wall thereof.