Mercury emission and speciation from industrial gold production using roasting process

• Hg emission factors for roasting and cyanidation process are 0.517 × 10− 3 and 1.753 × 10− 3 g/g, respectively.
• The ratio of Hgp:Hg2 +:Hg0 in the roasting flue gas is 11:57:33.
• Hg removal efficiency of GCT, ESP, FF, VT, ESD and AP is 4%, 6%, 12%, 7%, 31% and 96%, respectively.
• The cyanidation procedure takes up 77% of the total Hg emission due to the absence of APCDs.

Gold production has been identified as an important source of anthropogenic mercury emissions. Few measurements have been conducted on the mercury emission in the industrial gold production. In this study, field measurements on mercury concentration and speciation profile in the roasting flue gas were conducted in a two-stage roasting gold smelter, and the corresponding mercury emission factors were obtained using mass balance analysis. The average mercury concentration in the feed gold concentrates was 730.0 μg/kg, and the daily input mercury was 94.9 g in this research. In the roasting procedure, 38.4%, 27.3% and 9.0% of input mercury was removed into the sulfuric acid, contaminated water and arsenic, respectively, while 22.8% of input mercury flowed into the cyanidation-refining procedure within the roasting residue and the dust collected from the gas cooling tower and the electrostatic precipitator. Finally, 2.3% and 5.9% of input mercury was emitted into the atmosphere with the roasting flue gas and the refining flue gas. Mercury concentration in the roasting flue gas was 4.02 μg/m3, where the proportion of Hgp:Hg2 +:Hg0 was 11:57:33. The balance calculation results indicated that the atmospheric mercury emission factor was 2.27 × 10− 3 g mercury/g gold produced for the tested smelter. Both the emission factor and mercury removal efficiencies of air pollution control devices are useful for development of a more accurate emission inventory.