Microwave Processing of Low-Grade Banded Iron Ore with Different Reductants
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Microwave Processing of Low-Grade Banded Iron Ore with Different Reductants Shrey Agrawal 1 & Shaila Mir 1 & Nikhil Dhawan 1 Received: 29 March 2020 / Accepted: 9 September 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract The current study investigates the effect of microwave processing on low-grade banded iron ore using charcoal, coking coal, and non-coking coal. Charcoal showed better microwave heating response at low temperatures, and the coals exhibit better heating response at higher temperatures. Low carbon dosage ~ 12% is sufficient to generate concentrate with 61.8% iron grade and ~6% for 94.8% iron recovery comprising of magnetite phase suitable for iron-making applications. The process separation efficiency of ~ 95% is achieved at 6% carbon dosage and decreases with an increase in carbon due to formation of the fayalite phase. The metallization degree showed a strong dependency on reductant dosage and achieved a maximum value of 22.7% at 18% charcoal. The comparison of ore with pure iron oxide and the synthetic mixture of iron oxide indicated that the underlying bonding due to banded structure enhances the Joule heating during microwave irradiation and thereby aids in attaining higher temperature and better separation. Keywords Low-grade iron ore . Microwave reduction . Coal . Ferrite . Magnetite . Fayalite
1 Introduction The continuous increase in steel consumption and the simultaneous depletion of high-grade iron ores are the prime concerns for iron and steel industries. Iron ore industries will have to rely on alternative low-grade iron ores shortly to meet their demands, and processing of such ores requires significant upgradation [1]. Around 380 kg of carbon consumption per ton of pig iron is reported in which 60% is used for iron oxide reduction [2]. Also, during conventional reduction, the conductive heat transfer and gaseous diffusion in agglomerate is the rate-determining step for iron oxide reduction [3]. Microwave processing of ore offers selective, volumetric, and enhanced heating rates due to the combined effect of the thermal and magnetic field, and non-thermal effects aid in improving the reaction kinetics [4–7]. The internal heating of particles during microwave irradiation exempts the consumption of coal for heat generation and may significantly help in mitigating the emission concerns. The comparative
* Nikhil Dhawan [email protected] 1
Extractive Metallurgy Laboratory, Department of Metallurgical and Materials Engineering, Indian Institute of Technology, IIT-Roorkee, Roorkee, Uttarakhand 247667, India
studies on the carbothermic microwave reduction between magnetite and hematite ore suggest similar heating behavior and reduction kinetics [8]. The microwave heating studies of pure magnetite indicate that the sample heats readily with an average heating rate of 1000 °C/min compared with significantly low 165 °C/min in hematite; however, the instantaneous heating rate in hematite increased abruptly above 400 °C which is due to significant variation in t
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