Free Access
Issue
Metall. Res. Technol.
Volume 117, Number 4, 2020
Article Number 403
Number of page(s) 10
DOI https://doi.org/10.1051/metal/2020034
Published online 25 June 2020

© EDP Sciences, 2020

1 Introduction

India’s steel vision 2030 calls for 300 million tons of annual steel production, which requires approximately 500 million tons of high-grade iron ores (∼ 60% Fe). India does not have adequate high-grade hematite ores but possesses abundant resources of low-grade iron ores such as banded hematite quartzite/Jasper (BHQ, BHJ). A significant generation of low-grade iron ores that occurred during conventional mining of hematite ore leads to vast deposits of banded iron ores, which are unutilized because of low iron content and lack of beneficiation practice [1,2]. The beneficiation studies of low-grade iron ores are limited to high-intensity magnetic separation and reduction roasting to generate iron-rich concentrate [2,35]. The application of microwave in mineral processing has grown significantly. Some established applications include ore grinding, carbothermic reduction of metal oxides, leaching, and waste management [1,47]. Microwave exposure offers selective and volumetric heating, enhanced leaching kinetics, better liberation, and enhanced magnetic properties [8].

The mineralogical alteration on ilmenite ore during microwave irradiation showed that microwave exposure led to the formation of inter-granular fractures, consequently enriching the concentrate grade and metal recovery [9]. The microwave irradiation on paramagnetic ore led to a change in magnetic properties, and 15 min exposure resulted in a rapid increase in magnetic susceptibility, and prolonged exposure for 40 min resulted in the sintering of powder with localized melting [10]. The microwave irradiation of 2 min at 1900 W on pyrite ore increased the iron recovery to 80% compared to 25% in magnetic concentrate [11]. The microwave heating leads to decomposition of pyrite ore and formation of the ferromagnetic phase, i.e., γ-hematite and pyrrhotite [12]. The microwave processing studies on various minerals suggest that sulfides and oxides are strong receptors of microwave radiations, compared to silicates [13,14].

In our previous study, a mixture of low-grade iron ore (BHJ/BHQ) and carbon has been investigated for the production of iron-rich concentrate for iron/steel making using a microwave. The excellent microwave susceptibility of the carbonaceous material is exploited, and it is reported that the amount of carbon required to obtain comparable results was less than the conventional ironmaking process [15,16]. The key difference lies in the fact that the rate-controlling step during conventional reduction is conduction heat flow from the surface to center, whereas volumetric heating in the microwave enhances the diffusion kinetics and results in faster heating [17,18]. It is shown that the magnetic field, coupled with thermal energy, improved the efficiency of the carbothermic reduction process.

The purpose of this investigation is to evaluate the beneficiation and reduction of two low-grade banded iron ores. The effect of reduction parameters on these ores is investigated and compared with pure hematite powder and a mixture of hematite and quartz. These findings will be of extreme importance for ores with similar iron content. The feasibility of economical reductants such as coking and non-coking coal in microwave-assisted carbothermic reduction is evaluated, and finally, the selectivity of low-grade ores is determined for a large scale application.

2 Materials and methods

Banded iron ore samples used in this study were procured from working mines located in the different regions of India. An analytical grade iron oxide powder and quartz were mixed in adequate proportion to form a synthetic mixture that mimics the ore composition. For investigating the effect of chemical bonding and liberation characteristics of low-grade iron ores, experiments were also conducted on the synthetic mixture. The actual photographs of the hand specimen samples of BHJ and BHQ ore are shown in Figure 1. The ore sample reflects the lamellar structure with different thickness bands of hematite and quartzite.

The as-received samples of BHJ, BHQ, and quartzite were stage-wise crushed using a jaw and roll crusher followed by grinding in a laboratory ball mill. The ground samples were sieved below 75 μm, ensuring similar particle size distribution for all the samples. The upgradation studies were carried out by exposing the ore sample to high microwave power (900 W) in an attempt to break the bonded structure. Alternatively, conventional and microwave carbothermal reduction route is exploited to reduce the iron-bearing phases and distort the bonded structure. Carbothermal reduction experiments were carried out in a microwave furnace (Enerzi, 800 W, 2.45 GHz) and muffle furnace (Carbolite Gero, CWL1200) using activated charcoal as a reductant. The proximate analysis depicts 88% fixed carbon, 10.1% volatile matter, and 1.1% ash content. The stoichiometric amount of carbon required for the complete reduction of hematite to metallic iron is calculated as ̴ 6% using equation (1) for both ores. The operating range of parameters influencing the reduction experiments was selected based on the preliminary experiments [15]. Reduction time was the least influential factor and was fixed at 60 min for muffle furnace and 10 min for microwave reduction. The reduction parameters investigated are reductant dosage (3–12%) and temperature (600–800 °C). The reduced product was processed using low-intensity magnetic separation (LIMS) at 1800 G. The schematic of the experimental procedure followed is shown in Figure 2. Alternatively, coking and non-coking coal were also investigated as reductants at optimized conditions. The proximate analysis yielded approximately 67,58% fixed carbon, and 32,38% volatile content in coking and non-coking coal, respectively. The reduction process efficiency was evaluated based on saturation magnetization, process yield, and metallic iron content. The metallic iron content was determined using standard chemical analysis, and the structural alterations during the processing were investigated using backscattered electron (BSE) images equipped with EDS analysis. Saturation magnetization was measured using a vibratory sample magnetometer (VSM) to evaluate the magnetic property quantitatively. The yield of the magnetic concentrate is determined using equation (2). (1) (2)

thumbnail Fig. 1

Hand specimen photographs of (a) Hematite; (b) BHQ; (c) BHJ and; (d) Quartz (H-Hematite, Q-Quartzite, J-Jasper).

thumbnail Fig. 2

The experimental procedure followed in the study.

3 Results and discussion

X-ray diffraction (XRD) plot of the representative sample shown in Figure 3a depicts hematite and quartzite as the major constituent phases in both ores with traces of magnetite in BHJ. The chemical composition of the ores shown in Figure 3b is following the XRD findings. The magnetization values for Hematite, BHQ, BHJ, and synthetic mixture are 0.6, 3.38, 5.02, and 0.47 emu/g, respectively indicating a slightly magnetic nature of BHJ compared to other samples. The saturation magnetization of the sample is equal to the cumulative sum of the magnetization of its constituents [19]. Therefore, the trace amount of magnetite, i.e., undetected in the XRD spectra, is determined by the linear additivity of the saturation magnetization of ore and the magnetite fraction in the BHJ and BHQ ore is 2.9% and 1.25% respectively.

thumbnail Fig. 3

Feed sample (a) XRD plot; (b) Chemical composition of Hematite, BHQ, BHJ, and Quartz where k denotes 1000 times (H-Hematite, Q-Quartz, M-Magnetite).

3.1 Microwave exposure

The differential microwave absorption capability of the ore phases causes selective heating, which eases the liberation of iron phases from quartzite. The time-temperature plot of the hematite, BHQ, and BHJ sample at different microwave power levels is shown in Figure 4. It can be seen that both the ores follow a similar trend compared to synthetic materials. At 1.4 kW, the time-temperature slope is initially steeper and further reduces around 600 °C. However, at 0.8 kW, microwave absorption is not sufficient, resulting in limited temperature rise with time. In BHJ, a similar temperature (350 °C) can be attained within 2 min exposure at 1.4 kW compared to 13.5 min at 0.8 kW. The exponential temperature rise at higher power suggested that a minimum volume of microwave density is required to activate the dipolar movement inside the material. It can be observed that the area under the curve in the time-temperature plot was larger in BHQ compared to BHJ ore. Larger area suggests better response of BHQ ore to microwave irradiation compared to BHJ ore. The time-temperature plot of the synthetic mixture at 1.4 kW showed better microwave response compared to ore samples. It suggests that a certain fraction of microwave energy may be absorbed by the ore to break the bond between quartzite and hematite phase leading to lesser thermal energy transformation and, consequently, lower temperature rise. Therefore, it can be concluded that the BHJ ore responded effectively to microwave exposure towards the bond breakage and iron enrichment. With the increase in temperature, the magnetic susceptibility, and microwave absorption of the ore decreased, which resulted in the slope change of the temperature-time plot, as shown in Figure 4. Above 600 °C, the slope decreases from 187 °C/min to 65 °C/min for both BHJ and BHQ ore at 1.4 kW and remains unchanged at 0.8 kW. The saturation magnetization of the irradiated samples does not increase significantly and concentrate yield was considerably low. Carbon is an excellent microwave absorber, and hence activated charcoal was added as a reductant in the ore sample to enhance the microwave absorption and reduce the paramagnetic iron-bearing phase into the ferromagnetic phase.

thumbnail Fig. 4

The time-temperature plot in a microwave furnace at different power levels.

3.2 Microwave carbothermal reduction

Carbothermal reduction experiments were conducted in the microwave furnace at constant power of 0.8 kW. It was observed that the surface temperature reached 1050 °C in 10 min exposure. Therefore, a higher power was not attempted to avoid high energy input. The reduced product obtained after the microwave treatment is shown in Figures 5a5d. It indicates the formation of dispersed and lustrous metallic particles in the product with a particle size of 80–150 microns with ductile characteristics and is inferred as ferrite phase. The formation of eutectic composition in some regions decreased the melting point of iron and led to localized melting [10,15,20]. It is imperative that localized iron melt was formed in BHJ and BHQ ore and not observed in pure iron oxide and synthetic mixture. Figure 5e shows the variation in yield, saturation magnetization, and metallic iron content with charcoal dosage. The formation of ferrite initiated above 6% charcoal and is in close agreement with theoretical carbon requirements determined according to equation (1). The metallic content measured in BHJ and BHQ is approximately 17 and 19.5%, respectively, compared to 7 and 5% in pure hematite and synthetic mixture at 12% charcoal. The temperature attained in both the ores was comparable and reached approximately 1050 °C and 900 °C is attained in pure hematite under similar conditions. The observed trend suggested that the temperature was the sole responsible factor for the formation of the ferrite phase in the ore. The saturation magnetization of the concentrates showed an increment above 6% and followed a similar trend. The saturation magnetization value for BHJ and BHQ at 9% carbon is 25, and 29 emu/g, respectively, whereas for hematite and the synthetic mixture is 18.5 and 13 emu/g. The yield values of BHJ concentrate do not vary significantly, whereas the yield of the BHQ ore was mainly affected by the charcoal dosage. The yield increased from 30% to 65% on adding 12% charcoal. Pure hematite and synthetic mixture also showed an increase in yield values with charcoal dosage.

The BSE image of the reduced product of BHQ and BHJ is shown in Figures 6a and 6b. Both images show the localized formation of ferrite, whereas the fayalite is dispersed all over the matrix and interlocked with the quartz phase. It is also envisaged that wustite concentration in pure hematite is comparatively higher than ore at the same conditions. The adequate presence of silica promotes fayalite formation. Also, the low melting point of fayalite resulted in the formation of a localized melt region, and it may trap the carbon particles, thereby decreasing the reduction efficiency as reduction occurs by trapped solid carbon [20,21]. Figure 6c shows the occurrence of iron phases in the concentrate at varying charcoal dosage. The low charcoal dosage of 3% carbon is inferred to be inadequate for phase reduction, and no traceable phase change occurred except BHJ. Semi-quantitative XRD analysis of the reduced product indicated sequential transformation of hematite to magnetite to fayalite and finally ferrite with increment in charcoal dosage. It was envisaged from phase analysis at low charcoal dosage that presence of silica reduced the activity of wustite and restricted ferrite formation. Although the microwave processing of ores provides significant iron enrichment in these ores, the specific energy consumption during the treatment is quite high (∼ 405 kWh/t). The formation of wustite and other metastable iron phases is undesirable for further utilization of the microwave reduced product. Therefore, conventional reduction in muffle furnace was attempted in pursuit of lower energy consumption with controlled reduction products.

thumbnail Fig. 5

Photographs of the reduced product at 800 W, 10 min, and 12% charcoal (a) Hematite; (b) BHQ; (c) BHJ; (d) Synthetic mixture and; (e) effect of charcoal dosage on saturation magnetization, temperature, yield, and metallic iron of concentrate at 800 W, 10 min.

thumbnail Fig. 6

BSE image, EDS (%) of reduced product at 900 W, 10 min, and 12% charcoal (a) BHQ (1–2: Ferrite; 3,4–7: Fayalite; and 5–6: Cristobalite); (b) BHJ (2: Ferrite; 6–7: Ferrosilicon; 1–5: Fayalite; 4: Cristobalite; 3: Cementite) and; (c) Qualitative analysis of the microwave reduced products where Q-Quartz, H-Hematite, M-Magnetite, Fay-Fayalite, W-Wustite, Fe-Ferrite, C-Cristobalite.

3.3 Carbothermal reduction in a muffle furnace

It was observed that a high carbon dosage leads to the formation of a wustite phase, which eventually interacts with quartz impurity at high temperatures to form fayalite. Therefore, the reduction was carried out at low dosages, i.e., 3–6% charcoal for a fixed duration of 60 min in a conventional muffle furnace. Figure 7 shows the variation in saturation magnetization and yield with temperature. At low charcoal and temperature, magnetization does not increase significantly but considerable increment was observed at higher temperature. The concentrate yield increased with temperature due to magnetite formation at high-temperature. On increasing the carbon dosage, pure hematite and synthetic mixture showed linear increase in magnetic property with temperature. The BSE images shown in Figures 8a and 8b envisaged that the phases formed were dispersed and interlocked over the entire matrix suggesting poor liberation or strong locking between Fe–Si bond in both the ores. The elemental analysis suggested wustite formation with minimal fayalite occurrence. The low fayalite content can be due to insufficient temperature. The qualitative phase analysis of concentrate shown in Figure 8c suggested that wustite formation depends on temperature and was independent of charcoal dosage. The quartz content in the concentrate at higher temperatures is reduced, coupled with increased wustite content. As observed in microwave reduction, wustite interacts with quartz to form fayalite and leads to the loss of iron values. The metallic iron content in the reduced product was less than 1%, indicating a lean reduction in muffle furnace compared to microwave.

thumbnail Fig. 7

Effect of temperature on saturation magnetization and yield at (a) 3% charcoal and; (b) 6% charcoal for constant time (60 min).

thumbnail Fig. 8

BSE image, EDS and atomic (%) of reduced product at 700 °C, 60 min with 6% charcoal (a) BHQ (1–2: Wustite; 3: Silicon oxide; 4: silicon oxide surrounded by iron phase; (b) BHJ (1–3: Wustite; 2–4: Silicon oxide) and; (c) Qualitative XRD analysis of reduced magnetic concentrate in a muffle furnace.

3.4 Carbothermal reduction using coal

The use of activated charcoal is expensive as reductant; therefore, reduction experiments were conducted at optimal conditions using indigenous coking and non-coking coal. The coal dosages were added according to the carbon content and equivalent carbon dosage of 3–12% is maintained in the mixture. In a microwave furnace, it was observed that the maximum temperature attained was significantly low, i.e., 200 °C and 220 °C using coking and non-coking coal, respectively. On prolonged exposure up to 20 min, the temperature of the mixture reached 370 °C. As expected, no phase transformation occurred in the underlying conditions, with a lower yield of magnetic concentrate compared to charcoal with a saturation magnetization of ∼ 9–11 emu/g. The dielectric loss (tan δ) of coal is consistently low in the temperature range of 25–550 °C and depends upon the mineralogical constituent of coal. It indicates lower dielectric absorption resulting in lean heating. It is reported that the dielectric absorption depends on the temperature, and dielectric loss value of coal increases abruptly at 600 °C or above for coal [22]. Preheating of the coal-ore mixture in the microwave using susceptor for temperature rise in a suitable range of higher dielectric absorption could be the scope for future study. On the contrary, reduction in muffle furnace using coking, non-coking coal showed better reduction kinetics compared to charcoal in both ores. The yield of concentrate obtained in the reduction of hematite using coal was 98–99%, indicating a complete reduction of hematite into magnetite. The saturation magnetization was 64–68 emu/g in coking and non-coking coal compared to 18 emu/g in charcoal. It was also observed that the reduction of BHJ, BHQ, and synthetic mixture with coal led to the formation of the wustite and fayalite phase. On the comparison between coking and non-coking coal, the quality of the reduced product was found similar, suggesting minimal interference of coal impurity during reduction. Therefore, there is a potential of recovering iron values from low grade banded iron ores using non-coking coal as a reductant. Table 1 shows the performance parameters evaluated for the different feed using coking and non-coking coal at best conditions obtained under muffle furnace reduction experiments discussed in the previous section, i.e., 700 °C, 60 min, and 6% C equivalent.

Table 1

Effect of coal on the enrichment of iron values.

3.5 Process selection

Figure 9 shows the magnetization-yield plot of reduction experiments with charcoal on ores and pure hematite and synthetic mixture. The clustered datum points at low magnetization correspond to muffle furnace reduction, whereas dispersed points at high magnetization and yield value signify microwave reduction. Based on the iron recovery and purity, BHJ ore showed a better response compared to BHQ. The synthetic mixture of similar elemental composition showed comparable quantitative values for iron enrichment. Pure iron oxide showed excellent microwave response indicating the potential of microwave treatment for recovery of iron values from ores also. The performance characteristics of the mixture were better than BHQ but inferior to BHJ ore. The chemical bonding between the impurities and iron phases in the ore played a vital role during the carbothermal treatment both in the microwave and muffle furnace as strongly bonded particles allow unrestricted flow of conductive heat, and electromagnetic heating generated the intergranular cracks. Table 2 compares the muffle furnace and microwave reduction based on various process responses. The energy consumption in microwave treatment is high compared to muffle furnace; however, the product quality in terms of iron enrichment is significantly improved, and reduction time is decreased by 85%. The formation of metallic iron in the microwave reduction indicated enhanced reduction kinetics.

thumbnail Fig. 9

Yield (%) vs. saturation magnetization (emu/g).

Table 2

Comparison of process responses in both microwave and muffle furnace reduction.

3.6 Energy calculations

For determining the economic feasibility of microwave and conventional reduction process, the theoretical energy consumed during the entire process is calculated in kWh/ton of ore. Certain assumptions were made during energy calculations and include: the microwave efficiency is 35%, and the microwave power was constant during the experiment. It is assumed that the number of waves absorbed by the material and the energy consumed for 10 min at 900 W power equal to the energy of the total microwaves absorbed by the material during the entire duration. The sample placed in the crucible was assumed as a hemispherical, whereas in conventional reduction, it is assumed that during the experiment, the temperature was constant at a set time value. The calculated total energy consumed during conventional muffle furnace reduction at 800 °C for 60 min is 223.7 kWh/ton for BHJ, and 218.8 kWh/ton for BHQ.

3.6.1 Microwave

Microwave dimensions,

Length, l = 0.4 m; Breadth, b = 0.26 m; Height, h = 0.16 m,

Energy input, Ein = p × t = 0.15 kWh,

Actual energy, Eact = η × Ein = 0.0525 kWh.

Energy generated is the energy carried by the total number of microwaves generated during the entire duration of exposure. Therefore,

Eact = n × h × v

N – Number of microwaves,

H – Planck’s constant, i.e., 6.64 × 10−34,

ʋ-frequency, i.e., 2.45 GHz.

Number of waves generated during 10 min exposure time,

n = 1.165 × 1029 no. of waves.

Microwaves generated is proportional to the surface area of the chamber,

Surface area of microwave, a = 2 (lb + bh + hl) = 0.736 m2

The radius of the hemispherical sample is determined by back calculating the volume of the sample used by measuring the density of ore,

Radius of sample = 1.50 cm,

Area of sample = 0.00142 m2,

Waves absorbed by the sample,

Energy consumed during microwave reduction for 25 g sample at 900 W, Eabs, is the energy of the microwaves absorbed by the sample,

Eabs = 101.25 × 10−6 kWh

Energy consumed per tonne = 405.02 kWh/ton for 10 min

3.6.2 Muffle furnace

Assumptions,

Mass of sample, m = 500 g

Specific heat of ore, Cp = 0.836 kJ/kg-K

Initial Temperature, Ti = 303 K

Final Temperature, Tf = 1073 K

Heat absorbed by ore, Q1 = mSoreΔT = 363.67 kJ

Loss of ignition ore = 1.42%

Loss of ignition for 1 tonne of ore = 14.2 kg

Energy consumed by water,

, (Assuming, from 25 °C to 100 °C)

Energy consumed during vaporization,

Energy consumed by sample (iron ore), (Assuming, Cp of ore, = 0.213 kcal),

Total energy consumed,

Similarly, the energy consumed for muffle furnace reduction of BHQ ore is determined and calculated as 218.85 kWh/ton of ore.

4 Conclusions

The low-grade iron ores (BHJ and BHQ) constitute approximately 50% hematite phase. The absence of alumina impurity in these ores is advantageous for application in blast furnace after the beneficiation process. It is inferred that the significant iron enrichment can only be achieved through structural alteration of the ore, and therefore magnetic separation was found futile in recovering iron values. It is envisaged experimentally that the intimate bonding between the impurities and iron-bearing phase leads to poor liberation characteristics of ore compared to a synthetic mixture having a similar composition. The excellent microwave absorption capability of the iron-bearing phase resulted in the rapid heat generation and high temperature in short exposure time. The chemical bonding between the iron phase and quartz impurity is expected to break due to strong absorption of microwaves, and BHJ ore responded better compared to BHQ ore. The carbothermal reduction in muffle furnace and microwave led to significant enrichment of saturation magnetization and process yield. The characteristic magnetic property of iron-bearing phases increased significantly for BHQ and BHJ ore in the microwave from 7–42 emu/g and 9–36 emu/g, respectively, and 7–26 emu/g and 7–38 emu/g respectively in a muffle furnace. The reduction kinetics was quite fast, and ferrite particles were formed due to localized melting in the microwave reduction. The carbothermal reduction using charcoal responded efficiently in the microwave, however incorporating coal as a reductant in the microwave has very low reduction efficiency. Conduction heating assisted by susceptor coupled with a microwave can enhance the performance characteristics of coal in carbothermal microwave reduction and can be the scope of future work. On economic parameters, microwave-assisted reduction consumed approximately 400 kWh/ton of electrical energy compared to 220 kWh/ton in a muffle furnace. However, the residence time for the reduction was reduced by 85% in the microwave due to faster heating. It is concluded that the BHJ was found suitable for extracting the iron values compared to BHQ ore. For reduction using industrial-grade coal, muffle furnace showed significant iron values enrichment compared to microwave for BHJ ore.

Acknowledgments

The authors gratefully acknowledge the funding agency Science Engineering Research Board, New Delhi for providing early-career research funds via ECR-000874/2016.

References

  1. IBM, Indian Minerals Yearbook, (Part-III: Mineral Reviews) 56th edition: IRON ORE, (2017) [Google Scholar]
  2. V. Rayapudi, S. Agrawal, N. Dhawan, Optimization of microwave carbothermal reduction for processing of banded hematite jasper ore, Miner. Eng. 132, 202–210 (2019a) [CrossRef] [Google Scholar]
  3. K. Ishizaki, K. Nagata, Microwave induced solid–solid reactions between Fe3O4 and carbon black powders, ISIJ Int. 48(9), 1159–1164 (2008) [CrossRef] [Google Scholar]
  4. J. Yu, Y. Han, Y. Li, P. Gao, Beneficiation of an iron ore fines by magnetization roasting and magnetic separation, Int. J. Miner. Process. 168, 102–108 (2017) [Google Scholar]
  5. J.W. Walkiewicz, A.E. Clar, S.L. McGill, Microwave-assisted grinding, IEEE Trans. Ind. Appl. 27(2), 239–243 (1991) [Google Scholar]
  6. P. Hartlieb, M. Toifl, F. Kuchar, R. Meisels, T. Antretter, Thermo-physical properties of selected hard rocks and their relation to microwave-assisted comminution, Miner. Eng. 91, 34–41 (2016) [CrossRef] [Google Scholar]
  7. C.A. Pickles, Microwaves in extractive metallurgy: Part 2-A review of applications, Miner. Eng. 22(13), 1112–1118 (2009) [CrossRef] [Google Scholar]
  8. N. Standish, W. Huang, Microwave application in carbothermic reduction of iron ores, ISIJ Int. 31(3), 241–245 (1991) [CrossRef] [Google Scholar]
  9. S.W. Kingman, G.M. Corfield, N.A. Rowson, Effect of microwave radiation upon the mineralogy and magnetic processing of a massive Norwegian ilmenite ore, Magn. Electric. 131–148 (1999) [CrossRef] [Google Scholar]
  10. I. Znamenackova, M. Lovas, Modification of magnetic properties of siderite ore by microwave energy, Sep. Purif. Technol. 43, 169–174 (2005) [Google Scholar]
  11. K.E. Waters, N.A. Rowson, R.W. Greenwood, A.J. Williams, Characterising the effect of microwave radiation on the magnetic properties of pyrite, Sep. Purif. Technol. 46, 9–17 (2007) [Google Scholar]
  12. T. Uslu, U. Ataly, A.I. Arol, Effect of microwave heating on magnetic separation of pyrite, Colloid Surf. A: Physicochem. Eng. Aspects 225, 161–167 (2003) [CrossRef] [Google Scholar]
  13. C. Sahyoun, S.W. Kingman, N.A. Rowson, The effect of heat treatment on chalcopyrite, Phys. Sep. Sci. Eng. 12, 23–30 (2003) [CrossRef] [Google Scholar]
  14. S.W. Kingman, N.A. Roason, The effect of microwave radiation on the magnetic properties of minerals, J. Micro. Electromagn. Energy 35, 144–150 (2000) [Google Scholar]
  15. V. Rayapudi, S. Agrawal, N. Dhawan, Evaluation of carbothermal reduction for processing of banded hematite jasper ore, Powder Technol. (2019b). DOI: 10.1016/j.powtec.2019.09.094 [PubMed] [Google Scholar]
  16. V. Rayapudi, N. Dhawan, Investigation of microwave reduction of low-grade banded iron ores, Miner. Process. Extract. Metall. (2019c). DOI: 10.1080/25726641.2019.1668662 [Google Scholar]
  17. M. Hayashi, K. Takeda, K. Kashimura, T. Watanabe, K. Nagata, Carbothermic reduction of hematite powders by microwave heating, ISIJ Int. 53(7), 1125–1130 (2013) [CrossRef] [Google Scholar]
  18. A. Amini, K. Ohno, T. Maeda, Effect of the ratio of magnetite particle size to microwave penetration depth on reduction reaction behaviour by H2, Sci. Rep. 8, 15023 (2019). DOI: 10.1038/s41598-018-33460-5 [Google Scholar]
  19. M. Ahmadzadeh, C. Romero, J. McCloy, Magnetic analysis of commercial hematite, magnetite, and their mixtures, AIP Adv. 8, 1–6 (2018) [Google Scholar]
  20. S. Mishra, G.G. Roy, Effect of amount of carbon on the reduction efficiency of iron ore-coal composite pellets in multi-layer bed rotary hearth furnace (RHF), Metall. Mater. Trans. 47(4), 2347–2356 (2016) [CrossRef] [Google Scholar]
  21. S. Mishra, G.G. Roy, Effect of CaO on the reduction behaviour of iron ore-coal composite pellets in multi-layer bed rotary hearth furnace, Ironmak. Steelmak. 45(5), 426–433 (2018). DOI: 10.1080/03019233.2016.1278515 [CrossRef] [Google Scholar]
  22. O. Williams, A. Ure, L. Stevens, E. Binner, C. Dodds, S. Kingman, B. Das, P.S. Dash, E. Lester, Formation of metallurgical coke within minutes through coal densification and microwave energy, Energy& Fuels 33(7), 6817–6828 (2019) [CrossRef] [Google Scholar]

Cite this article as: Shrey Agrawal, Veeranjaneyulu Rayapudi, Nikhil Dhawan, Comparative study of low-grade banded iron ores for iron recovery, Metall. Res. Technol. 117, 403 (2020)

All Tables

Table 1

Effect of coal on the enrichment of iron values.

Table 2

Comparison of process responses in both microwave and muffle furnace reduction.

All Figures

thumbnail Fig. 1

Hand specimen photographs of (a) Hematite; (b) BHQ; (c) BHJ and; (d) Quartz (H-Hematite, Q-Quartzite, J-Jasper).

In the text
thumbnail Fig. 2

The experimental procedure followed in the study.

In the text
thumbnail Fig. 3

Feed sample (a) XRD plot; (b) Chemical composition of Hematite, BHQ, BHJ, and Quartz where k denotes 1000 times (H-Hematite, Q-Quartz, M-Magnetite).

In the text
thumbnail Fig. 4

The time-temperature plot in a microwave furnace at different power levels.

In the text
thumbnail Fig. 5

Photographs of the reduced product at 800 W, 10 min, and 12% charcoal (a) Hematite; (b) BHQ; (c) BHJ; (d) Synthetic mixture and; (e) effect of charcoal dosage on saturation magnetization, temperature, yield, and metallic iron of concentrate at 800 W, 10 min.

In the text
thumbnail Fig. 6

BSE image, EDS (%) of reduced product at 900 W, 10 min, and 12% charcoal (a) BHQ (1–2: Ferrite; 3,4–7: Fayalite; and 5–6: Cristobalite); (b) BHJ (2: Ferrite; 6–7: Ferrosilicon; 1–5: Fayalite; 4: Cristobalite; 3: Cementite) and; (c) Qualitative analysis of the microwave reduced products where Q-Quartz, H-Hematite, M-Magnetite, Fay-Fayalite, W-Wustite, Fe-Ferrite, C-Cristobalite.

In the text
thumbnail Fig. 7

Effect of temperature on saturation magnetization and yield at (a) 3% charcoal and; (b) 6% charcoal for constant time (60 min).

In the text
thumbnail Fig. 8

BSE image, EDS and atomic (%) of reduced product at 700 °C, 60 min with 6% charcoal (a) BHQ (1–2: Wustite; 3: Silicon oxide; 4: silicon oxide surrounded by iron phase; (b) BHJ (1–3: Wustite; 2–4: Silicon oxide) and; (c) Qualitative XRD analysis of reduced magnetic concentrate in a muffle furnace.

In the text
thumbnail Fig. 9

Yield (%) vs. saturation magnetization (emu/g).

In the text

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