Preparation and characterization of Cu(II), Ni(II) or Co(II) ion-doped goethite samples and their conversion to magnetite in NH3–FeSO4–H2O medium

Crystalline goethite samples doped with Cu(II), Ni(II) and Co(II) ions were prepared by a coprecipitation method using ferric nitrate, sodium hydroxide and metal ion salt solutions. These samples were characterized by XRD and were also chemically analyzed. The XRD patterns of Cu(II), Ni(II) or Co(II) ion-doped goethite matched with that of pure goethite but showed slight shift in their d-values. These samples were treated in ammoniacal medium in the presence of ferrous sulphate under the following conditions [Hydrometallurgy (2002) in press]: temperature=403 K; ammonia=25 g L−1; time=2 h; and ferrous iron concentration=45 g L−1. The converted products were analyzed both for ferrous and total iron. The characterization was carried out using instrumental techniques such as TEM, TG-DTA and Mössbauer Spectroscopy. Though the XRD patterns of the converted products showed presence of only magnetite, the Mössbauer spectra and TEM showed unreacted goethite in the converted product of Cu ion-doped goethite. Pure magnetite was confirmed by chemical and instrumental analysis for the product obtained from Ni-doped goethite. A nonmagnetic ferrous iron fraction along with magnetite was confirmed from the Mössbauer spectra in the product obtained from Co ion-doped goethite. These results are compared with the products obtained in another study [Int. J. Miner. Process (2002) submitted for publication] related to the addition of Cu(II), Ni(II) or Co(II) ions during treatment of pure crystalline goethite in NH3–FeSO4–H2O system.