PARTITIONING OF HEAVY-METALS IN PODZOL SOILS CONTAMINATED BY MINE DRAINAGE WATERS, DALARNA, SWEDEN

The discharge of acidic mine drainage waters onto a hillslope in Dalar na, central Sweden, has lead to the contamination of the podzol soils with Cu, Fe, Ni, Pb, Zn and sulfate. Samples from contaminated and ref erence soils have been collected for chemical and mineralogical analys es. Jarosite is identified by x-ray diffraction analysis as a precipit ate in the upper horizons (A, E, B) of the contaminated soils, where t he soil acidity (pH(KCl) similar to 2.6) promotes jarosite stability. The sequential chemical extraction of soil samples indicates that, in the reference A horizon, Cu, Pb, Ni and Zn are bound primarily to cati on exchange sites and organic matter. In the A horizon of the contamin ated soils closest to the rock dump, metal partitioning is dominated b y the Fe oxide fractions, despite the high organic matter content; Pb is almost completely bound to crystalline Fe oxides, possibly adsorbed to Fe oxides or occuring in a jarosite solid solution. In the referen ce B and C horizons, Cu, Ni and Zn are primarily adsorbed/coprecipitat ed in the Fe oxide fractions, while Pb remains with a large fraction b ound to organic matter. In the Fe-rich B horizon of the contaminated s oils, the partitioning of the metals in cation exchange sites and to o rganic matter has greatly increased relative to the reference soils, r esulting from the mobilization of organo-metal complexes down the prof ile.