Characterization of Mercury in a Riverwash Soil

Abstract

AbstractThe extent of cinnabar (α‐HgS) degradation in a riverwash soil polluted by Hg mining waste was evaluated by determination of persistent α‐HgS and Hg liberated from the mineral. The soil was sequentially extracted to determine soluble, exchangeable, manganese‐oxide‐associated, and free iron‐oxide‐associated Hg. DTPA, 0.5N NaHCO3, and 0.5N and 1.0N HCl were used to determine available, weakly organic‐bound, and strongly adsorbed Hg, respectively. Particle size and density separations using tetrabromoethane and Clerici's solution were employed to determine Hg in < 1.8, 1.8–2.9, > 2.9, < 4.0, and > 4.0 g cm−3 fractions of clay, silt, and sand separates. A thermal fractionation of the soil was used to measure Hg loss at temperatures from 25 to 450°C.Only traces of Hg were recovered by the chemical extractants, implying that very little existed in an adsorbed or easily soluble state. More than 90% of the Hg was recovered in the > 4.0 g cm−3 fraction. This, along with thermal fractionation and x‐ray diffraction data, indicated that this Hg remained primarily in the α‐HgS form. Loss of Hg in the tetrabromoethane separations and at low temperatures during the thermal fractionation suggested that Hg in both the colloidal and lighter fractions was organically bound.