New applications for Remediation of Acid Mine Drainage from Italian and Slovak deposits

The main aim of the present experimental work - carried out in the framework of the S&T Cooperation Programme between Italy and Slovakia (years 2004-2007) - was to remediate Acid Mine Drainage (AMD) by the application of new technologies, chip and environmentally friendly, to eliminate the heavy metals content (Zn, Cu, Mn, Al and Fe). The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from the abandoned and flooded deposit of Smolník, located in Slovak Republic and from the zinc mine located in Montevecchio (Italy). Electrowinning tests have been carried out after chemical iron-aluminum precipitation, that permitted a complete Fe-Al removal. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve about 95% Zn removal. The culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The treatment of AMD by SRB is based on the ability of SRB to reduce sulphates to hydrogen sulphide, which binds readily with metals to form sparingly soluble precipitates. The kinetic of the selective precipitation of Cu and Zn has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the 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.