Abstract: A process is described for the recovery, in metallic form, of mercury present in roasting gases, containing SO.sub.2, so that the purified gas has less than 0.1 mg/m3 of this element. Essentially, the system consists of a conventional device for the cooling and scrubbing of the gas; two irrigated towers with an acid solution of Hg(SCN).sub.4.sup.2- free SCN.sup.- and active carbon; two wet electrostatic precipitators, one in front of the first tower and another between them and a reactor for scrubbing the emulsion (soot) obtained from the condensation, with ammonium. All mercury-bearing tailings are recycled to the roasting oven at appropriate intervals, until under certain conditions the hot gases attain a mercury content of more than 40 mg/m3.

Abstract: The present invention relates to a process for purifying metallurgical gases containing sulphuric anhydride by extracting mercury, using the sulphurous anhydride which accompanies the metallurgical gases as an oxidizing agent for the mercury, an additional contribution of sulphurous anhydride being made when the latter is deficient, and employing in addition an acid to facilitate the oxidization of the mercury and a soluble thiocyanate in order to complete the oxidation of the mercury.