Using of Selective Sequential Precipitation for Treatment of Acid Mine Drainage

The main aim was to demonstrate the technical feasibility of the remediation processes by electrowinning and selective sequential precipitation, for toxic metals removal from acid mine drainage coming from a lead and zinc mine located in Tùnel Kingsmill outlet of the Rio Yaulì (district of Yauli - Perù). The study consists in a preliminary work: the experimental tests have been conducted by the 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 has been achieved: in particular, by Zn and Mn electrodeposition, it was possible to achieve about 95-97% Zn and Mn removal (as MnO2), with a relatively low energetic consumption. The principle of the heavy metals selective sequential precipitation is the combined application of sodium hydroxide solution and hydrogen sulfide produced by sulfate-reducing bacteria. For the hydrogen sulfide production the sulphate-reducing bacteria of genus Desulfovibrio was used. The pre-treatment of the synthetic solution by the H2O2 addition improved the selectivity of the process, except Fe and As. The selective sequential precipitation process reaches the selective precipitation of chosen metals with 97-99% efficiency - Fe, As, Al and Mn in the form of metal hydroxides, Cu and Zn as metal sulfides.