**4. Plasma processing of iron-bearing minerals**

The present study demonstrates the plasma processing of three iron-bearing minerals viz. blue dust, siliceous type iron ore, and manganiferous iron ore.

#### **4.1 Plasma processing of blue dust**

Blue dust is the purest form of iron oxide mineral (hematite) abundantly available in many states of India. For the present study, blue dust of Koira origin, Odisha, India, was collected, which is in fine form (150 μ). The chemical analysis of blue dust is given in **Table 2**. The ore is mainly composed of Fe2O3, and XRD analysis also confirmed the presence of single mineral hematite.

Plasma smelting operations were carried out for mixtures of blue dust and coke in argon and nitrogen ionizing atmosphere [14]. The coke percentage in charge mixture (500 gm) was varied from 5–20%. The plasma gas flow rate was maintained at 2.5 LPM.

The highest recovery rate exceeding 86% was achieved for using nitrogen as plasma forming gas. The recovery rates in argon plasma are comparatively less than those of nitrogen plasma. It is because of the diatomicity of N2 gas, which liberates higher energy flux than the monoatomic gas Ar. The loss of Fe in the process involves loss accounted for in charging and splashing of metal droplets due to the high velocity of the plasma jet in the course of smelting. The loss of metal splashing is further minimized by adjustment of power input and controlling gas flow rate. The recovery rate attains 95% maximum in closed furnace type arrangements.

As the gangue in blue dust is low, the metallization (Fe) occurs in the absence of complex slag phases. Blue dust with different carbon percentages (i.e., 5, 10, 12, 15, and 20) smelted by using nitrogen plasma shows the change of ferrite, ferritecementite to fully pearlite structure, which can be attributed to the Hull-Mehl model of pearlitic transformation [15]. The silica in blue dust in the high reducing atmosphere reduces into SiO, observed in smelting tests as fumes. The smelting duration for the conversion of Fe2O3 into Fe was 17 minutes, which is several hours in BF iron making. Moreover, blast furnace limits the direct charging of blue dust to avoid lowering the porosity of charge burden, which increases process cost and affects smooth operation.

To use blue dust in BF, agglomeration and heat treatment are required. Although stiff vacuum extrusion briquetting avoids heat treatment, binder requirement is still essential. The cement and bentonite binder adds cost and also requires unnecessary slag generation and separation from the purest Fe2O3 ore.

The direct smelting of blue dust in thermal plasma has several advantages over conventional processes in terms of cost-saving operation, purity level in hot metal, and high production rate. The production cost will be much less for industrial large scale furnace and by using cheap gases such as methane, coke oven gas, etc.

#### **4.2 Plasma processing of siliceous type iron ore**

For this study, partially reduced briquettes made from iron minerals were collected from an industry in the vicinity of Rourkela, Odisha, India. Briquettes upon solid state reduction at 1250°C are partially melted which hinders further reduction at higher temperatures. The industrial trial of such briquettes in mini BF suggested its infeasible use for iron making due to high FeO loss in slag. The chemical composition of the briquette sample is given in **Table 3**.

The amount of silica and alumina in the briquette is about 16% in cumulative. XRD analysis detected wustite (FeO), fayalite (Fe2SiO4), and hercynite (FeAl2O4) as major phases in the briquette sample. The presence of such phases suggests the high affinity of FeO towards silica and alumina for which low melting fayalite forms, melts early and hinders CO gas passage to the core. Partial melting of briquette also affects the furnace operation and increases flux addition, and hence increases the process cost.

**101**

**Table 3.**

**Table 2.**

*Chemical composition of briquette.*

*Plasma Processing of Iron Ore*

*Chemical composition of blue dust.*

*DOI: http://dx.doi.org/10.5772/intechopen.94050*

Here, an attempt was made for the utilization of these briquettes for the value addition with maximized extraction [16]. Since plasma processing does not restrict the slag chemistry, briquettes were smelted with and without flux (CaO). Initial trials with flux addition targeting melilite slag (CaO-MgO-Al2O3-SiO2) improved Fe recovery in metal. For the CaO/SiO2 ratio in the range of 0.9–1.0, metallic yield exceeds 88%. The flow characteristics of such slag allow a better reduction in the

**Constituents In Wt. %** FeT 72.2 SiO2 8.6 Al2O3 7.2 MgO 0.63 CaO 1.4 TiO2 0.4 Others 9.57

**Constituents In Wt. %** Fe2O3 96.87 SiO2 0.45 Al2O3 0.21 MgO Trace LOI 1.48

Another approach was aimed at the direct smelting of briquettes without adjustment of slag chemistry. Since the briquettes are composed of fayalite, additional coke was provided for the reduction of silicon along with iron. These briquettes were smelted for a longer period than previous slag practice. The metallic recovery was appreciably higher, i.e., exceeds 94% by using nitrogen as plasma forming gas. Phase and microstructure evolution confirms the formation of the iron silicide (Fe3Si) phase in the alloy along with Fe. These ferrosilicon alloys can be used for

This study suggests that the utilization of silicate-based iron minerals are more suitable for ferrosilicon production rather than iron making. Although the energy consumption is a little higher for FeSi production from these briquettes, flux consumption and melting of excess slag can be eliminated. Moreover, the product

Manganiferous iron ore is the type of lean manganese ore containing a maximum

about 10–15% of Mn. These are of less importance in ferromanganese production; however, reduction roasting and magnetic separation improve Mn/Fe ratio. The primary objective of such a process is to reduce Fe2O3 into Fe3O4, which easily

slag layer where unreduced Fe-oxides are more promptly metalized.

deoxidation purposes, which is of greater value than metallic Fe.

(FeSi) cost puts importance on its feasible production.

**4.3 Plasma processing of manganiferous iron ore**

### *Plasma Processing of Iron Ore DOI: http://dx.doi.org/10.5772/intechopen.94050*


#### **Table 2.**

*Iron Ores*

tained at 2.5 LPM.

affects smooth operation.

**4.1 Plasma processing of blue dust**

Blue dust is the purest form of iron oxide mineral (hematite) abundantly available in many states of India. For the present study, blue dust of Koira origin, Odisha, India, was collected, which is in fine form (150 μ). The chemical analysis of blue dust is given in **Table 2**. The ore is mainly composed of Fe2O3, and XRD

Plasma smelting operations were carried out for mixtures of blue dust and coke in argon and nitrogen ionizing atmosphere [14]. The coke percentage in charge mixture (500 gm) was varied from 5–20%. The plasma gas flow rate was main-

The highest recovery rate exceeding 86% was achieved for using nitrogen as plasma forming gas. The recovery rates in argon plasma are comparatively less than those of nitrogen plasma. It is because of the diatomicity of N2 gas, which liberates higher energy flux than the monoatomic gas Ar. The loss of Fe in the process involves loss accounted for in charging and splashing of metal droplets due to the high velocity of the plasma jet in the course of smelting. The loss of metal splashing is further minimized by adjustment of power input and controlling gas flow rate. The recovery

As the gangue in blue dust is low, the metallization (Fe) occurs in the absence of complex slag phases. Blue dust with different carbon percentages (i.e., 5, 10, 12, 15, and 20) smelted by using nitrogen plasma shows the change of ferrite, ferritecementite to fully pearlite structure, which can be attributed to the Hull-Mehl model of pearlitic transformation [15]. The silica in blue dust in the high reducing atmosphere reduces into SiO, observed in smelting tests as fumes. The smelting duration for the conversion of Fe2O3 into Fe was 17 minutes, which is several hours in BF iron making. Moreover, blast furnace limits the direct charging of blue dust to avoid lowering the porosity of charge burden, which increases process cost and

To use blue dust in BF, agglomeration and heat treatment are required. Although stiff vacuum extrusion briquetting avoids heat treatment, binder requirement is still essential. The cement and bentonite binder adds cost and also requires unnecessary slag generation and separation from the purest Fe2O3 ore. The direct smelting of blue dust in thermal plasma has several advantages over conventional processes in terms of cost-saving operation, purity level in hot metal, and high production rate. The production cost will be much less for industrial large

scale furnace and by using cheap gases such as methane, coke oven gas, etc.

chemical composition of the briquette sample is given in **Table 3**.

For this study, partially reduced briquettes made from iron minerals were collected from an industry in the vicinity of Rourkela, Odisha, India. Briquettes upon solid state reduction at 1250°C are partially melted which hinders further reduction at higher temperatures. The industrial trial of such briquettes in mini BF suggested its infeasible use for iron making due to high FeO loss in slag. The

The amount of silica and alumina in the briquette is about 16% in cumulative. XRD analysis detected wustite (FeO), fayalite (Fe2SiO4), and hercynite (FeAl2O4) as major phases in the briquette sample. The presence of such phases suggests the high affinity of FeO towards silica and alumina for which low melting fayalite forms, melts early and hinders CO gas passage to the core. Partial melting of briquette also affects the furnace operation and increases flux addition, and hence increases the

**4.2 Plasma processing of siliceous type iron ore**

analysis also confirmed the presence of single mineral hematite.

rate attains 95% maximum in closed furnace type arrangements.

**100**

process cost.

*Chemical composition of blue dust.*


#### **Table 3.**

*Chemical composition of briquette.*

Here, an attempt was made for the utilization of these briquettes for the value addition with maximized extraction [16]. Since plasma processing does not restrict the slag chemistry, briquettes were smelted with and without flux (CaO). Initial trials with flux addition targeting melilite slag (CaO-MgO-Al2O3-SiO2) improved Fe recovery in metal. For the CaO/SiO2 ratio in the range of 0.9–1.0, metallic yield exceeds 88%. The flow characteristics of such slag allow a better reduction in the slag layer where unreduced Fe-oxides are more promptly metalized.

Another approach was aimed at the direct smelting of briquettes without adjustment of slag chemistry. Since the briquettes are composed of fayalite, additional coke was provided for the reduction of silicon along with iron. These briquettes were smelted for a longer period than previous slag practice. The metallic recovery was appreciably higher, i.e., exceeds 94% by using nitrogen as plasma forming gas.

Phase and microstructure evolution confirms the formation of the iron silicide (Fe3Si) phase in the alloy along with Fe. These ferrosilicon alloys can be used for deoxidation purposes, which is of greater value than metallic Fe.

This study suggests that the utilization of silicate-based iron minerals are more suitable for ferrosilicon production rather than iron making. Although the energy consumption is a little higher for FeSi production from these briquettes, flux consumption and melting of excess slag can be eliminated. Moreover, the product (FeSi) cost puts importance on its feasible production.

#### **4.3 Plasma processing of manganiferous iron ore**

Manganiferous iron ore is the type of lean manganese ore containing a maximum about 10–15% of Mn. These are of less importance in ferromanganese production; however, reduction roasting and magnetic separation improve Mn/Fe ratio. The primary objective of such a process is to reduce Fe2O3 into Fe3O4, which easily

separates as magnetic particles. However, the feasibility of the upgrading process becomes questionable when both iron and manganese oxides are in associated form, i.e., bixbyite (Fe, Mn)O3 mineral.

As an alternative, these ores are subjected to smelting for obtaining FeMn alloy with low Mn content. It is a cost-saving operation, and smelting operations can be carried out even in BF. The complexity arises for such ores with high gangue amount, which affects the extraction kinetics by forming silicates, aluminates, and/or complex mixtures phases.

In the present study, lean manganese ore was collected from Joda valley, Odisha, India. The ore is in fine form and is being discarded as waste at the mines site itself. The initial assessment of the ore through wet chemical analysis indicated that the ore contains about 17% of alumina and 9% of silica. The Mn content in the fines is about 12%, which falls into the manganiferous category. The reduction studies of such briquettes evidenced the formation of hercynite, galaxite, fayalite-manganon, and spessartine phases at different temperatures. These phases lower the reducibility of the ore and also deteriorate the physical and mechanical properties of the agglomerate.

Here an attempt was made to utilize these fines directly in thermal plasma, avoiding any agglomeration. Smelting of such ores by using other technologies results in poor Mn recovery (≈30%) and high FeO loss into slag; flux addition was essential.

The smelting of ore with flux addition targeting melilite and mayenite slags in ionizing atmosphere improved Mn recovery and was 80% maximum. Although plasma arc provides high energy flux, the slag chemistry also governed the process kinetics. By adjusting slag chemistry to a too basic slag lowered the activity of silica and alumna; however, the formation of high melting silicate compounds such as dicalcium silicate and tricalcium silicate increases the viscosity of the slag. The flowability of such slag hinders carbon contact with metal oxides and hence lowers the reducibility.

In the current scenario, ferromanganese production follows rich slag and discard slag practices. The rich slag retained in primary smelting (low fluxing) is further smelted in another step to produce silicomanganese or ferro-silicomanganese. In discard slag practices, the slag retained in primary smelting, which contains less than 15–30% MnO, is discarded.

The present study refers to the discard slag practice followed by plasma smelting with the highly basic slagging operation. As the ore contains high alumina, primary smelting similar to rich slag practice will result in slag with alumina bearing compounds, which will be difficult to reduce in the secondary smelting for obtaining silicomanganese. Moreover, the cost of smelting these high melting compounds will increase reductant, energy consumption, and also lower the furnace refractory life cycle.

The extraction of metals from these types of complex ores in single-stage smelting operation should be chosen in such a way that the slag can be used in secondary products such as cement.

### **5. Hydrogen plasma**

In iron making, coke is used as a heat source and reductant. The application of plasma in iron making lowers COX emission for being used as plasma as a heat source. The reducibility of metal oxides by solid carbon or CO gas is lower than that of H2. The use of methane as plasma forming gas is beneficial over argon or nitrogen from a cost perspective. However, ecofriendly gas emission in iron making is only

**103**

**Author details**

Sumant Kumar Samal1

and Bhagiratha Mishra2

\*, Manoja Kumar Mohanty1

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 National Institute of Technology, Rourkela, India

production costs by avoiding decarburization.

\*Address all correspondence to: sumantnitr@gmail.com

2 Suraj Products Limited, Rourkela, India

provided the original work is properly cited.

, Subash Chandra Mishra1

*Plasma Processing of Iron Ore*

production [17, 18].

the cost of the process.

**6. Conclusion**

*DOI: http://dx.doi.org/10.5772/intechopen.94050*

possible through hydrogen plasma processing; the exit gas is water vapor, which reduces environmental pollution and will be much beneficial in impurity-free metal

At present, research projects are being carried out for hydrogen reduction of iron ore in a pilot-scale, such as HYBRIT [19]. The primary installation of such reactors costs high; continuous improvements are essential. The primary beneficiation of iron ores will improve the purity of iron ore, which in turn will reduce

The importance of plasma in iron making is discussed considering different types of ore minerals and its various aspects of processing. The freedom in size, composition, and smelting conditions required for complex ore minerals fits into the processing of iron ore in thermal plasma. The use of coke as a heat source in conventional iron making processes can be eliminated with the application of thermal plasma. The recovery rate and purity level in hot metal extracted from complex mines waste is noticeable higher by using thermal plasma. The future eco-friendly hydrogen plasma processing is of interest. Moreover, the use of hydrogen plasma can result in carbon-free metal/alloys, which can lower

### *Plasma Processing of Iron Ore DOI: http://dx.doi.org/10.5772/intechopen.94050*

possible through hydrogen plasma processing; the exit gas is water vapor, which reduces environmental pollution and will be much beneficial in impurity-free metal production [17, 18].

At present, research projects are being carried out for hydrogen reduction of iron ore in a pilot-scale, such as HYBRIT [19]. The primary installation of such reactors costs high; continuous improvements are essential. The primary beneficiation of iron ores will improve the purity of iron ore, which in turn will reduce the cost of the process.
