Formation of Fe(III)-precipitates

Formation of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water:

Bright field TEM image (left) and SAED pattern of Lepidocrocite formed by the oxidation of Fe2+.

The biogeochemical cycling of nutrients and pollutants is strongly influence by the formation and presence of colloids. In this study we focused on the microscopic analysis of colloids formed due to iron oxidation and hydrolysis in synthetic carbonate-buffered groundwater (pH 7, 2-30 mg/L Fe(II)). We investigated the influence of phosphate (2-20 mg/L P), silicate (2-20 mg/L Si), and Ca (2.5 mM Ca- or 8 mM Na-bicarbonate) on colloid formation. The morphology, chemistry and crystallography of the colloids were characterized using HR-TEM (high resolution transmission electron microscopy), TEM-EDX (energy dispersive x-ray analysis) and SAED (selected area electron diffraction).