Bio-hydrozincite: a promising tool for water bioremediation

Biominerals play an active role in controlling metal dispersion in polluted water and soil systems. At the Ingurtosu Pb¿Zn mine (SW Sardinia), heavy metal concentration in waters of the Naracauli stream, the main stream of the area, is abated by the seasonal bioprecipitation of hydrozincite. Hydrozincite could be used in a controlled process to attenuate metal pollution in mining waters. Information on environmental conditions that promote the biomineralization process is fundamental for the development of remediation strategies. According to field observations, correlated with speciation and equilibrium calculations, the optimum condition for hydrozincite precipitation occurs in late spring of rainy years, when the hydraulic regime in the stream reaches stationary conditions, and Saturation Index values with respect to hydrozincite and pH reach the highest values, in agreement with the higher stability of the hydrozincite solid phase in contact with slightly alkaline waters. Obtained results suggest that the bioprecipitation of hydrozincite could be applied to attenuate metal pollution in mining environments where no problems of water acidi¿cation exist.