Hydrolysis of Fe^III solution to hydrous iron oxides

Abstract

A range of hydrous iron oxides was prepared from ferric nitrate solutions by varying the rate and manner of hydrolysis. The properties of the resultant products were determined by using various techniques including size fractionation with Amicon Diafilters, rate and extent of dissolution in acid ammonium oxalate solution, X-ray diffraction and Mossbauer spectroscopy. The variation in properties is interpreted in terms of the conditions under which the various materials had been formed. The products of spontaneous hydrolysis at low pH and low FeIII concentration had properties distinctly different from those samples in which hydrolysis was induced rapidly by addition of alkali. The low-pH products were far more resistant to dissolution in acid ammonium oxalate and were relatively well ordered as determined by X-ray diffraction and Mossbauer spectroscopy at 77 K. The crystallographic and magnetic ordering of the rapidly formed phase is normally very limited, but these properties were increased significantly if formation occurred in the presence of low-pH polymeric material which may act as a template for freshly precipitating oxides.