Characterization of suspended solids in a stream receiving acid mine effluents,Bersbo, Sweden

Suspended particulate matter was recovered by filtration (0.40 μm) of water from a stream receiving acidic effluents from a mine tailings deposit. This solid phase formed rapidly as pH increased from 3.5 at the release point to 6.5, approximately 2 km downstream. The suspended solid was present in concentrations that ranged from 10–20 mg/l for anoxic conditions (winter) to 30–120 mg/l for oxic conditions (early spring). The solid consisted of FeOOH + Fe(OH)₃(am) and AlOOH + Al(OH)₃(am), as well as silicates. The organic content (of natural origin) was up to 30% (dry wt). Most of the Fe and Al from the leachate was precipitated in the particulate phase, approximately 98% of total metal content in the aqueous phase, as well as ∼50% of Mn, Cu, Zn, Cd and Pb. These elements were predominantly adsorbed on the hydrous oxide precipitate, or to some extent (Mn and Pb) coprecipitated, as indicated from a sequential leaching procedure and powder X-ray diffractometry. All the elements, particularly Cu, were to a significant degree associated with organic matter.