Effect of addition of Cu(II), Ni(II) and Co(II) ions on conversion of crystalline goethite to magnetite in NH 3–FeSO 4–H 2O medium

Abstract

Conversion of crystalline goethite to magnetite was carried out in the presence of Cu(II), Ni(II) or Co(II) ions in NH 3–Fe(II)–H 2O 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(Il) ion concentrations. The characterization of the products was carried out using XRD, Mössbauer spectroscopy, TEM and TG-DTA techniques. The XRD patterns of the converted products showed the presence of only magnetite. Mössbauer 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 Mössbauer 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 Mössbauer. 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.