Mercury speciation in tailings of the Idrija mercury mine

Five hundred years of mercury (Hg) mining activity in Idrija, Slovenia caus ed widespread Hg contamination. Besides Hg emissions from the ore smelter, tailings have been found to be the major source of river sediment contamina tion. In the present study, solid phase binding forms and the aqueous mobil ity of Hg have been investigated in tailings of the Idrija Hg mine by means of a pyrolysis technique and aqueous Hg speciation. Results show that Hg b inding forms differ with the age of the tailings due to the processing of d ifferent ores with different roasting techniques. In older tailings, the pr edominant Hg species is cinnabar (HgS), due to incomplete roasting, whereas in tailings of the 20th century the amount of cinnabar in the material dec reased due to a higher efficiency of the roasting process and the increasin g use of ores bearing native Hg. ln younger tailings, metallic Hg (Hg-0) so rbed to mineral matrix components such as dolomite and Fe-oxyhydroxides bec ame the predominant Hg binding form in addition to unbound Hg-0 and traces of HgO. Leaching tests show that in younger tailings high amounts of solubl e Hg exist in reactive form. In older tailings most of the soluble Hg occur s bound to soluble complexes. It might be assumed that in the long term, ma trix-bound Hg-0 could be bound to humic acids derived from soils covering t he tailings. This means that, despite the lower total Hg concentrations fou nd in the younger tailings, the long-term risk potential of its mobile matr ix-bound HgO is higher than that of older tailings bearing mostly immobile cinnabar. (C) 1999 Elsevier Science B.V. All rights reserved.