Thermal decomposition characteristics of mercury compounds in industrial sludge with high sulfur content

Sludge generated from metal smelting processes may contain a large amount of mercury with high sulfur content. A sludge roasting technology could be used to recover mercury from such sludge. Thermo-gravimetric analysis was employed to investigate the thermal decomposition properties of mercury and mass in the sludge. At elevated temperatures ranged from 200 to 650 °C at interval of 25 °C, total mass losses of sludge and mercury decomposition from the sludge containing over 2000 ppm of mercury were experimentally investigated. At temperatures of 200–325 °C, the decomposition rate of mercury from the sludge was very low and then the decomposition was taken place very rapidly from 350 to 575 °C. As the discrete mercury decomposition data at elevated temperatures were smoothened by least square method, the kinetic parameters of mercury decomposition reaction were determined for two different temperature zones. The decomposition of mercury could be correlated with thermal mass degradation of the sludge experimented. By comparing derivative thermo-gravimetric results for mercury in the sludge with high sulfur content and pure mercury compound species, HgS and Hg₂SO₄ were found to be the dominant form of mercury in the sludge due to high content of sulfur.