New technologies for heavy metals removal from Acid Mine Drainage of Smolník Deposits

The present experimental work has been carried out in the framework of the S&T Cooperation Programme between Italy and Slovakia (years 2004-2007). The main aim was to demonstrate the technical feasibility of the remediation processes by electrowinning and bioprecipitation, for toxic metals removal (Zn, Cu, Mn, Al and Fe) from acid mine drainage (AMD) coming from the abandoned and flooded deposit of Smolník, located in Slovak Republic. The study consists in a preliminary work: the experimental tests have been conducted by synthetic solutions. 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 99% Zn removal, with an energetic consumption of 25 kWh/kg. 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.