Abstract:
Conversion of crystalline goethite to magnetite was carried out in the presence of Cu(II), Ni(II) or Co(II) ions in NH3-Fe(II)-H2O medium. The conditions used were: temperature 403 K, ammonia 25 g l(-1), time 2 h, ferrous iron concentration 45 g l(-1) and metal ion concentration 200 mg l(-1). The reacted products were chemically analyzed for ferrous iron, total iron, Cu(II), Ni(II) and Co(II) ion concentrations. The characterization of the products was carried out using XRD, Mossbauer spectroscopy, TEM and TG-DTA techniques. The XRD patterns of the converted products showed the presence of only magnetite. Mossbauer spectra showed presence of ferric iron (not associated with magnetite) in case of addition of cobalt ions during conversion and its TEM showed some well-crystallized magnetite particles with agglomerated clusters. No phase other than magnetite was obtained by Mossbauer analysis of converted product obtained by the addition of Ni(II) or Cu(II). The TEM of converted product obtained by the addition of Ni(II) showed some fine needle-shaped particles of goethite in the dominantly present cubical magnetite particles. The percentage of unreacted goethite was in very low amount so as to escape detection both in XRD as well as Mossbauer. The low iron content of the products obtained in presence of Cu(II) and Ni(II) has been explained on the basis of adsorbed water, retaining of ammonium sulphate and some adsorbed anions but the exact composition of the compound/compounds could not be ascertained. (C) 2003 Elsevier Science B.V. All rights reserved.