Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng Optimization of microwave carbothermal reduction for processing of banded hematite jasper ore Veeranjaneyulu Rayapudi, Shrey Agrawal, Nikhil Dhawan ⁎ Department of Metallurgical & Materials Engineering, Indian Institute of Technology, IIT-Roorkee, Uttarakhand 247667, India ARTICLE INFO Keywords: Iron ore Microwave Carbothermal reduction Magnetic separation Ferrite ABSTRACT This study investigates the microwave carbothermal reduction of low grade banded hematite jasper iron ore ∼37% Fe. Due to complex association of the iron phase and impurities, the conventional beneficiation was found futile. The susceptibility of iron phases to microwave exposure assists in the liberation of iron values from impurities. The thermodynamic calculations revealed the selective reduction of iron ore phases in the Fe-O-C-Si- Al system. The preliminary experiments revealed that during a few minutes of microwave exposure, a tem- perature of ∼400 °C and ∼1100 °C was achieved for feed and charcoal mixture respectively. Besides iron en- richment in the concentrate, the ferrite balls were also observed in statistical design experiments. It was found that a small fraction of microwave irradiated BHJ ore-charcoal mixture was rapidly melted to produce ferrite balls. The presence of a sufficient amount of bonded silica content in the BHJ ore leads to an easy formation of the fayalite phase. The iron grade falls at prolonged exposure due to the interaction of iron phases with the quartzite as revealed by the XRD analysis. The optimal condition 720 W power, 9% charcoal and 8 min based on statistical design yielded a magnetic concentrate having ∼61.6%Fe, ∼73.4% recovery at a yield of 44% and has a potential to be used for pellet making industry. Similarly, the experimental condition 900 W power, 12% charcoal and 8 min yielded a magnetic concentrate with ∼49.1%Fe, ∼89.3% recovery at a yield of 59.7% along with ferrite balls with a saturation magnetization of ∼153 emu/g. 1. Introduction As per Indian Steel Policy, 300 million tons of steel are required to meet vision 2030 whichr equire approximately 550 million tons of high-grade iron ores. India does not have enough high-grade hematite ores but posses abundant resources of low-grade iron ores such as banded hematite quartzite/jasper (BHQ, BHJ) and banded magnetite quartzite (BMQ). Indian hematite deposits belong to the Precambrian iron ore series and the ore occurs as banded, laminated, friable and also in powder form. During conventional mining of hematite ores, there is a significant generation of low grade banded iron ores such as BHQ, BHJ, and BMQ which ends up in unused stockpile at the mine sites due to a lack of suitable beneficiation technology (IBM, 2017; Rath et al., 2014). The iron bands in these ores are of hematite, magnetite and the silica bands are either quartz or reddish jasper and the thickness of the bands also varies from 0.5 to 1.5 cm. The formation of these banded ores is either through replacement of silica by iron or by leaching of silica under suitable conditions or from the precipitation of iron from the Earth's ancient oceans (IBM, 2017). Also, these ores possess quite dif- ferent characteristics in terms of beneficiation primarily because of negligible alumina content and excessive quartz content which makes them quite hard as compared to conventional hematite ores. The complex association of silica-iron phase i.e., soft-hard lamellae struc- ture, and fine liberation size (< 100 μm) prohibits the direct use of these low-grade iron ores in the steel production cycle. The iron content in these ores varies from 30 to 45% and the rest being siliceous im- purities and is mainly found in the states of Karnataka, Orissa, Chat- tisgarh, and Rajasthan, India. The investigations on the beneficiation of banded iron ores (BHQ, BHJ, and BMQ) are limited and mainly involve processing techniques such as flotation, high-intensity magnetic se- paration, jigging and reduction roasting (Rath et al., 2014; Das et al., 2010; Makhija et al., 2013). At present some of the iron ore companies in India are evaluating these ores of setting up beneficiation plants to recover the iron value. The carbothermal reduction involves roasting of the ore in a reducing environment at 500–700 °C resulting in a partial reduction of hematite to magnetite followed by application of low-in- tensity magnetic separation (LIMS) to produce iron-rich magnetic pro- duct and tailings. The process suffers due to an associated energy penalty with roasting but offers advantages as magnetic separation is simpler and more selective than other separation techniques (e.g., https://doi.org/10.1016/j.mineng.2019.05.004 Received 22 October 2018; Received in revised form 19 February 2019; Accepted 11 May 2019 ⁎ Corresponding author. E-mail address: ndhawan.fmt@iir.ac.in (N. Dhawan). Minerals Engineering 138 (2019) 204–214 0892-6875/ © 2019 Elsevier Ltd. All rights reserved. T