The adsorption capacity for vapor-phase elemental mercury (Hg0) of residual carbon separated from fly ash was studied in an attempt for the control of elemental mercury emissions from combustion processes. At low mercury concentrations (< 200 microg/m3), unburned carbon had higher adsorption capacity than commercial activated carbon. The adsorbality of unburned carbon was also found to be source dependent. Isotherms of FS carbon (separated from fly ash of a power plant of Shishi in Fujian Province) were similar to those classified as type II. Isotherms of XJ carbon (separated from fly ash of a power plant of Jingcheng in Shanxi Province) were more like those classified as type II. Due to the relatively low production costs, these residual carbons would likely be considerably more cost-effective for the full-scale removal of mercury from combustion flue gases than other technology.