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The scope of the paper was to demonstrate the technical feasibility of the remediation processes by electrowinning and selective sequential precipitation, for toxic metals removal from acid mine drainage. By electrochemical experiments, high metals removal has been achieved: in particular, by Zn and Mn electrodeposition, it was possible to achieve about 93-99% 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 selective sequential precipitation process reaches the selective precipitation of chosen metals with 99% efficiency – Fe, As, Al and Mn in the form of metal hydroxides, Cu and Zn as metal sulfides.

Multidisciplinary research carried out on primary gold ores in the evolving Cretaceous island arc terranes of the Dominican Republic has shown the existence of three groups of deposits and occurrences. The first comprises the Lower Cretaceous ores, including the giant Pueblo Viejo deposit and several uneconomic showings with traces of Au-Ag in the El Valle area west of Miches; comparison of the acid-sulphate hydrothermal system of Pueblo Viejo with the disseminated, one-stage system of the El Valle region accounts for the fundamental differences in gold tonnages and grades between the two districts. The Upper Cretaceous barite-polymetallic (Cu-Zn)-Au-Ag epithermal ores in the northwest Dominican Republic and Haiti form the second group; Cu-Mo anomalies in oxidation zones are consistent with the observed presence of Cu-Mo porphyries at depth. The third group is formed by Upper Cretaceous-Tertiary metasediment-hosted, metamorphic quartz-sulphide, granitic vein swarms of the Miches area. These rocks are the probable source for the Miches lateritic/alluvial gold, which has been reworked during erosion and lateritization. Leaching tests have demonstrated the viability of routes other than cyanidation for gossanous golden-riched samples from El Valle and Restauración (northwest Dominican Republic). The results of a thiocyanate leach test appear to be the most promising on comparison with those obtained from tests with thiourea and ammoniacal thiosulphate. [ABSTRACT FROM AUTHOR]

In the present paper, a study on laboratory scale to perform a treatment for valuable metals recovery from electronic and galvanic industrial wastes, is reported. The characterisation of the waste, performed by XRD, SEM, EDX and chemical analysis, showed a high metals content in the sludge, such as Cu, Ni, Mn, Pb, Sn, W. A leaching process, coupled by electrowinning, is then proposed in order to reduce the volume of the waste material and to recover selectively valuable metals, such as Cu and Ni. During the leaching step, carried out by using H2SO4, several factors were investigated (acid concentration, temperature and time of treatment). The leached liquor has been successfully treated with an electrowinning process, to recover copper and nickel. The copper and nickel depositions, were performed in acid and alkaline conditions, respectively. The Faraday yield was of about 95%. The energy consumption was 2.13 and 4.43 kWh per kg of copper and nickel recovered, respectively. At the end of the process, about 94–99% of the initial content of Cu and Ni was recovered at the cathode. The experimental results obtained, showed the technical feasibility of the process. [Copyright &y& Elsevier]