Effect of sulphate ions on iron precipitation from aqueous solutions

In the present work, the effects of sulphate ions oil the iron precipitation from aqueous solution were investigated. It was shown that sulphate ions delayed the iron precipitation when this ion was added in form of Na2SO4. This effect became less significant in presence of magnesium or calcium. The iron precipitates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). In all experiments iron oxide hydroxide (FeOOH) precipitates were obtained. The sulphate ions were adsorbed oil the surfaces of the iron precipitates. The effect of temperature Oil these precipitates was also studied. At 237 degrees C, the iron oxide hydroxide precipitates obtained front NaCl solution was transformed in crystallized hematite, Fe2O3. At 793 degrees C, the hematite was partially transformed into magnetite (Fe3O4). In presence of sulphate ions, this transformation was not detected. (C) 2008 WILEY-VCH GmbH & Co. KGaA, Weinheim.