Large-scale experiments for microbiological evaluation of measures for safeguarding sulfidic mine waste.

In the framework of a German-Romanian scientific cooperation, experiments were performed to evaluate feasible and cheap techniques for the safe storage of mine waste to prevent acid rock drainage (ARD). A large four-chamber percolator (4CP) was installed in a waste heap at Ilba Mine, Romania, to test the effect of biocides and alkaline layers on the bacteria causing acid rock drainage (ARD). The 4CP consisted of four chambers each containing 65 m3 of sulfidic waste material. The 4CP enabled the transfer of laboratory results to a technical scale. The detergent sodiumdodecylsulfate (SDS) was proved to be active against the leaching bacteria. Organotrophic micro-organisms were not effected by the SDS application. The alkaline layers caused an increase of pH, however, a decrease of cell numbers was measured only in adjacent ore layers, but not in the whole ore body. A rapid evaluation of the effects of these countermeasures on ARD formation became possible by microcalorimetric activity measurements for bioleaching.