Biohydrometallurgical processes for heavy metals removal from acid mine drainage

The present experimental work has been carried out in the framework of the agreement of scientific cooperation between the Institute of Environmental Geology and Geoengineering of the CNR, Italy and the Institute of Geotechnics of Slovak Academy of Sciences, Slovakia (years 2007-2009). The main scope was to remediate Acid Mine Drainage (AMD) by application of biohydrometallurgical processes, environmentally friendly, to remove heavy metals such as Zn, Cu, Mn, Cd, Al and Fe. The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from a zinc mine located in Italy and from a cooper - iron ore deposit in Slovakia. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve 95-99% Zn removal. Culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The kinetic of the selective precipitation of Cu and Zn of AMD by SRB has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the about 98-99% elimination of Cu and Zn by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration.