Thermodynamic Considerations in Reduction of Nickeliferrous Laterite by Methane
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ethane as a reducing agent has been studied for the reduction of iron oxide,[1] chromium oxide, cobalt oxide, and zinc oxide.[2] However, there is no reporting as yet on its use in the reduction of nickel Laterite. The present study has been undertaken to study the thermodynamic feasibility of using methane as a reductant for nickel Laterite adopting the free-energy minimization method. The studies of the equilibria for the different possible reactions require knowledge of the several solid phases that are present in the ore body. Mineralogy of the ore has thus been investigated prior to the theoretical model calculations. For the present investigation, Sukinda Laterite ore (Orissa, India) has been selected. The ore sample has been characterized using X-ray diffraction (XRD) and a scanning electron microscope (SEM) with an attached energy-dispersive spectrometer (EDS). Analysis of the XRD pattern, as presented in Figure 1, has revealed the presence of phases such as goethite, haematite, quartz, and chromite. No characteristic peak of either elemental nickel or its simple compounds could be traced in the diffractogram. The ore sample has been chemically analyzed for the major constituents of interest such as Ni, Cr, Mn, and Fe with the help of atomic absorption spectroscopy
(AAS). The bulk EDS analysis of the ore body also confirmed the presence of both chromium and nickel almost in equal amounts. The obtained concentrations of the major constituents are represented in Table I, which shows that the data obtained through EDS and AAS studies are found to agree within reasonable limits. The chemical analysis and the identified phases of the ore body form the basis of the theoretical assessment in judging the thermodynamic possibility of reducing nickeliferrous Laterite by methane. The model calculations based on free-energy minimization have been performed with the help of Thermochemical software and the FactSage database.[3] In the FactSage database, goethite is not considered as a constituent, and accordingly, this has been approximated in terms of haematite and ferric hydroxide. Stoichiometrically, 2 moles of goethite have been approximated for the present calculation as equivalent amounts of Fe(OH)3 and Fe2O3, as shown subsequently: 2ðFeOOHÞ 0:667 FeðOHÞ3 ; 0:667Fe2 O3
The model calculation is based on 1 ton of nickeliferrous Laterite on a dry basis. For model calculations, the approximate analysis of the ore body has been assumed to be 50 wt pct Fe, 1 wt pct Ni, 1 wt pct Cr, and remainder silica, which is very close to the chemical composition of the ore in Table I. On this basis, the phases of Laterite, as evidenced from XRD results, are the following: (1) 50 wt pct Fe corresponds to 476.2 kg Fe2O3, 318.5 kg Fe(OH)3; (2) 1 wt pct Ni corresponds to 12.76 kg NiO = 170 mole NiO; (3) 1 wt pct Cr corresponds to 14.6 kg Cr2O3 = 96 mole Cr2O3; and (4) by difference, SiO2 corresponds to 177.94 kg = 2962 mole SiO2. However, nickeliferrous Laterite is found to contain 26 wt pct moisture in the run of mine ore body.[4] Accordi
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