Flocculation of metal-rich colloids in a stream affected by mine drainage

Flocculation of a white substance was observed in the Rio Naracauli (Sardinia, Italy) contaminated by mine tailings drainage. The flocculation occurs when an increase of pH is observed. The flocculated material takes up dissolved metals, especially Zn, from the water, possibly by adsorption onto hydrated silica colloids in an iron-poor, near-neutral environment. Chemical data of flocculated phase(s) show up to 520 g/Kg Zn, 106 g/Kg Si, 6 g/Kg Pb, 1 g/Kg Cd and respectively 215 and 80 mg/Kg Cu and Ni.