Heavy metal coprecipitation with hydrozincite [Zn-5(CO3)(2)(OH)(6)] from mine waters caused by photosynthetic microorganisms

An iron-poor stream of nearly neutral pH polluted by mine tailings has been investigated for a natural phenomenon responsible for the polishing of hea vy metals in mine wastewaters, A white mineralized mat, which was determine d to be hydrozincite [Zn-5(CO3)(2)(OH)(6)] by X-ray diffraction analysis, w as observed in the stream sediments mainly in spring. The precipitate shows a total organic matter residue of 10% dry weight and contains high concent rations of Pb, Cd, Ni, Cu, and other metals. Scanning electron microscopy a nalysis suggests that hydrozincite is mainly of biological origin, Dormant photosynthetic microorganisms have been retrieved from 1-year-old dry hydro zincite. The autofluorescent microorganisms were imaged by a scanning confo cal laser microscope, A photosynthetic filamentous bacterium, classified as Scytonema sp. strain INC-1, was found associated with microalga Chlorella sp, strain SA1, This microbial community is responsible for the natural pol ishing of heavy metals in the water stream by coprecipitation with hydrozin cite.