Experience gained with the remediation of contaminated sites over the last 10 to 15 years has strongly increased the insight into the problem and how it can be tackled. A large number of remediation techniques, most of which focus on clean-up, are now available, and some of them are intensively applied in practice. However, the experiences gained with them show that they are not capable of solving all problems. Furthermore, each case of soil pollution is different and the way to manage it requires, within the limits set by policy and the finances available, a careful weighing of all relevant factors. Increased knowledge about the problem has resulted in potential new techniques, such as extensive in-situ treatment, the use of special treatment walls, phytoremediation and intrinsic natural degradation.

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Bioleaching can be one of few techniques applicable for the removal of toxic metals from polluted soils or sediments. Its principle is a microbial production of sulphuric acid and leaching of metals with it. The use of bioleaching can benefit from the use of low-cost substrates and from a possible coupling to other processes of microbial sulphur cycle, like sulphate reduction to treat spent bioleaching liquor, or partial sulphide oxidation to recycle sulphur. For the evaluation of bioleaching, 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 acid 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 substrates, i.e. orthorhombic sulphur flower and microbially produced, recycled sulphur from partial sulphide oxidation process. The latter type of sulphur substrate performed considerably better.