Solubility and changes of mercury binding forms in contaminated soils after immobilization treatment

Mobility at different pH and binding forms of mercury (Hg) have been investigated in three Hg-contaminated soils after immobilization treatment with alkali-polysulfide (APS) and trimercapto-s-triazine trisodium salt solution (TMT). Changes of solid-phase Hg binding forms after immobilization were determined by Hg pyrolysis. Hg concentrations in the water extra cts of a II samples in creased after treatments due to the formation of soluble mercury sulfides (APS treatment), and the mobilization of humic acid bound Hg at the high pH of the reagents. In contrast, Hg concentrations decreased sharply at low pH due to decomposition of soluble mercury sulfides and precipitation of humic acid-bound Hg, inorganic Hg compounds such as Hg-0 or HgCl2 are effectively transformed to mercury sulfides by APS treatment, whereas TMT could transform HgCl2 but not Hg-0. Both reagents were found to affect humic acid bound Hg byway of increasing Hg desorption temperatures, although APS was found not to desorb Hg completely from humic acids and TMT-HS complexes are actually incorporated into humic acids.