MOBILITY OF ZN, PB, AND CD FROM SEDIMENTS CONTAMINATED WITH MINING WASTES

Availability of metals Zn, Pb and Cd from stream sediments contaminated with mining wastes was investigated via laboratory experiments. Sediments with varying degree of contamination were sampled from three streams nearby the location of former chat piles in Aurora, Missouri, and sequential extraction by the method of Tessier was applied. The metal content in each chemical phase was plotted downstream each stream. The chemical fraction in which each metal was stored, e.g. exchangeable, carbonate, Fe-oxide, organic and residual, was related to the mineral species present and pH and Eh conditions. Concentration patterns showed Pb had the lowest mobility and Cd the highest. Pb was preferentially stored in residual and carbonate fractions which, besides explaining its low mobility, imply that a significant amount would be release from sediments at acidic pH values. Zn preferentially and readily adsorbs to the Fe-oxides fraction, precluding its associated metal Cd to do so and therefore releasing Cd to the water column, where Cd binds largely to organic matter. The results can be used to estimate the amount of metal that would be released from contaminated sediments under varying environmental conditions.