Soil remediation - Mercury speciation in soil and vapor phase during thermal treatment

Spectroscopic (XRD, XPS, ICP-MS and AAS) and microscopic (ESEM) techniques have been used in order to study the chemical effects with emphasis on mercury speciation, during thermal treatment of a mercury contaminated soil. In the untreated soil, mercury was found concentrated in spherical particles, which were successively broken down upon thermal treatment. Hg(0) and inorganic mercury compounds (presumably HgO(s) and HgSO(4)(s)) could be detected. No (CH(3))(2)Hg and only traces of CH(3)Hg(+) could be found. The dependence on temperature and heating time indicated that the evaporation of mercury from the soil was partly controlled by diffusion mechanisms. Mercury volatilized in two separate stages during heating; initial elemental vaporization, and subsequent volatilization of the oxide or sulfate phase at higher temperatures (> 230 degrees C). By thermal treatment at 470 degrees C and 20 min, a removal of > 99% of the mercury could be achieved.