Collection of atomic mercury by electrostatic precipitators

Abstract

ELECTROSTATIC precipitators are widely used to remove dust particles from gases and the mechanism of this is well understood. One major application is in the cleaning of a sulphur dioxide produced in smelting of metalliferous sulphide ores before its conversion to sulphuric acid and the precipitated material is often found to contain mercury. We have shown that the concentration of mercury is below the saturation level and therefore present as atoms so the accepted mechanism for solid particle collection is not involved in mercury removal. We have investigated the phenomenon in the laboratory using air as the carrier gas at room temperature, and by large scale tests carried out in an 800 tonne d−1 sulphuric acid plant treating the gases formed by roasting zinc sulphide concentrate. In both types of test a discharge wire and earthed collector tube precipitator configuration was used. In the plant tests the roaster gas contained 9% sulphur dioxide and was saturated with water. In both the laboratory and plant tests the gas streams were unsaturated with respect to elemental mercury vapour.