Microwave reduction of a nickeliferous laterite ore Michail Samouhos a,⇑ , Maria Taxiarchou a , Ron Hutcheon b,1 , Eamonn Devlin c a School of Mining and Metallurgical Engineering, Laboratory of Metallurgy, National Technical University of Athens, Greece 9, Iroon Polytechniou Street, 157 80 Zografou, Athens, Greece b Microwave Properties North (MPN), 325 Wylie Road, Deep River, Ontario, Canada K0J 1P0 c Demokritos National Center for Scientific Research, Institute of Materials Science, Patriarchou Grigoriou 15310, Ag. Paraskevi, Attica, Greece article info Article history: Received 25 January 2012 Accepted 9 April 2012 Available online 15 May 2012 Keywords: Iron ores Pyrometallurgy Reduction Extractive metallurgy abstract The use of microwave radiation as an alternative energy source in mineral processing and extractive met- allurgy has been studied since the initial work of Worner at the Univ. of Wollongong in 1986. Microwaves deliver heat directly to the interior of a sample, avoiding the usual slow heating mechanisms of thermal and convective heat transfer. Furthermore, the depth to which the microwaves penetrate and the amount of heat deposited at depth is dependant on the complex dielectric constant of the material which means that by careful choice of materials, a microwave heating system can deliver heat to specific chosen mate- rials, while much reducing the heating of others, such as thermal insulation and oven walls, and thus improving efficiency. In the current study, the carbothermic reduction of a hematitic nickeliferous laterite was investigated, both by large-scale microwave oven experiments, and by measuring the complex dielectric constant (real (e 0 ) and imaginary (e 00 ) permittivities) of small samples at 2.45 GHz over the temperature range 5–980 °C, using the cavity perturbation method. The microwave oven heating behavior of the laterite–lignite mixture was explored using a 2.45 GHz ThermWave 1.3, variable power, microwave furnace, fitted with an optical pyrometer and an infrared thermal camera. The carbothermic reduction of laterite (i.e. the reduction of hematite contained in later- ite) was attempted, and the effect of heating time, power, carbon content and sample mass was studied in detail. Using twice the stoichiometric carbon content (i.e. double the amount of carbon required to fully reduce the hematite to metallic iron), about 70% reduction degree was achieved at temperatures some- what above 900 °C. The use of scanning electron microscopy and Mössbauer spectroscopy gave evidence of a lack of microstructural homogeneity in the reduced samples and the presence of phases which are not stable in the same temperature ranges, indicating some thermal inhomogeneity. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Nickeliferous laterite ores currently provide 42% of the corre- sponding contribution of the global nickel supply; this figure is ex- pected to rise to 51% in 2012, exceeding the sulfide ores in the nickel extractive metallurgy industry (Davli et al., 2004). Nickelif- erous laterite ores are created as a result of chemical and mechan- ical weathering of ultramafic rocks (serpentinite, peridotite, dunite) in a humid sub-tropical environment (Aleva, 1994). Gener- ally, during the laterization process primary rocks are gradually en- riched in Fe with the simultaneous decrease of Na, K, Mg, Ca and Si concentrations. The upper bed of the rock, which is directly influ- enced by weathering, can be characterized as laterite. The lower bed comprises the unaltered parent rock, while the intermediate bed, which is partially weathered, is called saprolite. Nickeliferous laterites are classified in three types according to their mineralogical characteristics (Brand et al., 1998):  Type A: Silicate Ni deposits containing 20–40% Ni, consist- ing of a mixture of the phyllosilicate minerals serpentinite, talc and chlorite.  Type B: Silicate Ni deposits containing 1.5–2% Ni, consisting of partially weathered serpentinite and smectite.  Type C: Oxide Ni deposits containing <2% Ni, consisting mainly of Fe oxyhydrates (goethite, hematite) and secondly of serpentinite and chlorite. Greek nickeliferous laterite deposits are rich in iron and are classified as type C. The iron content of the laterite samples inves- tigated in the present study is almost completely incorporated in the hematite phase. Greek nickeliferous laterites are processed 0892-6875/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2012.04.005 ⇑ Corresponding author. Tel.: +30 210 7722051; fax: +30 210 7722168. E-mail address: msamouhos@metal.ntua.gr (M. Samouhos). 1 Tel.: +1 613 584 1029. Minerals Engineering 34 (2012) 19–29 Contents lists available at SciVerse ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng