Mass balance of mercury in a pilot scale mercury recovery plant using thermal roasting technology

A pilot scale mercury recovery plant was developed to treat Hg waste by thermal treatment. The capacity of the system was 60 kg/batch and consisted of four units carrying out thermal treatment, dust separation, condensation, and flue gas treatment. The mass balances of Hg from five different wastes in three categories were calculated from Hg recovery data. From the following selected five wastes, Hg-added product, Hg-contaminated soil, byproduct of fluorescent lamp treatment process, and waste sludge from non-ferrous metal industrial process, we recovered 97.5%, 83.61%, 93.07%, 70.25%, and 29.36% of elemental mercury, respectively. Dust interfered during the condensation process, as volatilized Hg vapor was condensed with dust. Hg concentrations in leaching extract of treatment residues from the Hg-added product, Hg-contaminated soil, and the byproduct of fluorescent lamp treatment process were 0.003 mg-Hg/L, 0.0045 mg-Hg/L, and 0.002 mg-Hg/L, respectively, which are below the Korean classification standard of hazardous waste for mercury (0.005 mg-Hg/L). Hg concentration in flue gas was lower than 15 mu g-Hg/m(3) after passing through the activated carbon trap. Byproducts of the pilot scale system, such as activated carbon and dust can be further treated and converted to Hg free waste.