BIOLEACHING OF METALS FROM SOILS OR SEDIMENTS

Bioleaching can be one of few techniques applicable for the removal of toxic metals from polluted soils or sediments. Its principle is a mic robial production of sulphuric acid and leaching of metals with it. Th e use of bioleaching can benefit from the use of low-cost substrates a nd from a possible coupling to other processes of microbial sulphur cy cle, like sulphate reduction to treat spent bioleaching liquor, or par tial sulphide oxidation to recycle sulphur. For the evaluation of biol eaching, the existence of different leaching strategies is considered, i.e. intensive or extensive extraction. The intensive extraction uses high concentrations of acid at short extraction times, whereas low ac id additions and long treatment times are used in extensive processes. On a reference study with wetland sediment receiving mine drainage we demonstrated that the bioleaching is a typical extensive process. The bioleaching experiments involved the use of the different sulphur sub strates, i.e. orthorhombic sulphur flower and microbially produced, re cycled sulphur from partial sulphide oxidation process. The latter typ e of sulphur substrate performed considerably better. (C) 1998 IAWQ. P ublished by Elsevier Science Ltd.