**2. Plasma**

It is not unusual to refer plasma as the fourth state of matter as it is an ionized gas comprised of molecules, atoms, ions (in their ground or in various excited states), electrons, and photons. Plasma possesses a unique property known as quasineutrality since plasma is electrically neutral. In contrast to an ordinary gas, plasma encloses free electric charges that are commonly produced from the gas itself by a variety of ionization processes. In a steady-state situation, the rate of ionization in the plasma is balanced by the rate of recombination. Depending upon the energy content of the plasma, the degree of ionization may be so high that virtually no neutral particles are left, i.e., the plasma becomes fully ionized [3, 4].

#### **2.1 Classification**

Since plasma is a broad topic as concerned, all together plasmas are classified into three main categories [5]:

**95**

**Figure 1.**

*Typical plasmas characterized by their energies and densities.*

*Plasma Processing of Iron Ore*

argon-nitrogen plasma, etc.

**2.2 Plasma chemistry**

**Figure 2**.

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

• CTE plasmas (complete thermodynamic equilibrium)

• Non-LTE plasmas (nonlocal thermodynamic equilibrium)

Among the above three types, CTE plasmas are used for thermonuclear fusion experiments. The latter two types are used as laboratory plasmas and also implemented for industrial purposes like MINTEK, South Africa. Again according to density and energy, typical plasmas are categorized as shown in **Figure 1**.

Plasmas generated by electron and photon belong to the nonlocal thermodynamic equilibrium category. LTE plasmas are also called as hot plasmas or thermal plasmas and non-LTE plasmas as cold plasmas or non-thermal plasmas. Based on temperature, plasmas are subcategorized into two groups, i.e., low-temperature plasma and high-

gies less than 10 eV per particle are to be called as low-temperature plasmas. Beyond this limit, it is said to be high-temperature plasma. It is also not unusual for plasma to be called as per its gas name, i.e., oxygen plasma, argon plasma, nitrogen plasma or

Plasma chemistry refers to the thermodynamic characteristics of various plasma

The diatomic molecules require 90 to 200 kcal mole-1 to dissociate between 4000 to 10,000°K, while ionization requires 340 to 600 kcal mole-1 between 10,000 to 30,000°K [5]. The upper practical limit of flame temperature is about

forming gases. Both monoatomic and diatomic gases like argon, helium, neon, nitrogen, oxygen, hydrogen, carbon monoxide, carbon dioxide, air, and a mixture of gases are used as plasma forming gases. The relation between energy and temperature of some commonly used monoatomic and diatomic gases are shown in

°K or in other words, ener-

• LTE plasmas (local thermodynamic equilibrium)

temperature plasma. Plasmas with temperatures below 105

*Iron Ores*

linings.

operations.

**2. Plasma**

**2.1 Classification**

into three main categories [5]:

ii.Gangue content: The excavated ore always includes gangue contents viz. alumina, silica, and magnesia along with alkali, sulfur, and phosphorus. The type and quantity of gangue affect the entire process kinetics in terms of metallic yield and quality. The primary ore needs to be upgraded through various separation techniques, i.e., physical, gravitational, etc. which is

iii.Mineral phases: The mineral phases present in the ore are of interest as the entire extraction process is dependent on the various minerals present in the parent ore. Minerals in the ore are detected as metal oxides, hydroxides, carbonates, and also associated with gangue as silicates, aluminates. The silicates and aluminates phases are not only difficult to reduce but also consume high flux and energy for which ores with high content of such phases are commonly discarded at the mines site itself. The decomposition of hydroxides and carbonates results in higher coke consumption. The presence of alkali not only affects the process but also has a high impact on refractory

iv.Process: With the increased demand for steel across the globe in the scenario of unaffordability of high grade ores, research on the applicability of fines, dust, and other industry by-products has become essential in order to control the depletion of earth minerals. These fines are agglomerated through pelletization, sintering, and briquetting routes, which has various drawbacks in terms of production rate, energy consumption, charging, and environmental impact. Ore and agglomerate must be of suitable for minimal transportation loss, hightemperature sustainability, and low disintegration rate. The porosity, density, and crushing strength of agglomerate must be adequate in order to achieve a higher reduction rate and metallic yield. If such properties are not in the predesigned range, it can cost higher and affect smooth operation by promoting

The utilization of lean ore and wastes in iron making requires wide research and adopting new advanced technologies for quality production with time-saving

It is not unusual to refer plasma as the fourth state of matter as it is an ionized gas comprised of molecules, atoms, ions (in their ground or in various excited states), electrons, and photons. Plasma possesses a unique property known as quasineutrality since plasma is electrically neutral. In contrast to an ordinary gas, plasma encloses free electric charges that are commonly produced from the gas itself by a variety of ionization processes. In a steady-state situation, the rate of ionization in the plasma is balanced by the rate of recombination. Depending upon the energy content of the plasma, the degree of ionization may be so high that virtually no

Since plasma is a broad topic as concerned, all together plasmas are classified

neutral particles are left, i.e., the plasma becomes fully ionized [3, 4].

fines generation and hinders Boudouard reaction.

critical for high gangue amounts.

**94**


Among the above three types, CTE plasmas are used for thermonuclear fusion experiments. The latter two types are used as laboratory plasmas and also implemented for industrial purposes like MINTEK, South Africa. Again according to density and energy, typical plasmas are categorized as shown in **Figure 1**.

Plasmas generated by electron and photon belong to the nonlocal thermodynamic equilibrium category. LTE plasmas are also called as hot plasmas or thermal plasmas and non-LTE plasmas as cold plasmas or non-thermal plasmas. Based on temperature, plasmas are subcategorized into two groups, i.e., low-temperature plasma and hightemperature plasma. Plasmas with temperatures below 105 °K or in other words, energies less than 10 eV per particle are to be called as low-temperature plasmas. Beyond this limit, it is said to be high-temperature plasma. It is also not unusual for plasma to be called as per its gas name, i.e., oxygen plasma, argon plasma, nitrogen plasma or argon-nitrogen plasma, etc.

## **2.2 Plasma chemistry**

Plasma chemistry refers to the thermodynamic characteristics of various plasma forming gases. Both monoatomic and diatomic gases like argon, helium, neon, nitrogen, oxygen, hydrogen, carbon monoxide, carbon dioxide, air, and a mixture of gases are used as plasma forming gases. The relation between energy and temperature of some commonly used monoatomic and diatomic gases are shown in **Figure 2**.

The diatomic molecules require 90 to 200 kcal mole-1 to dissociate between 4000 to 10,000°K, while ionization requires 340 to 600 kcal mole-1 between 10,000 to 30,000°K [5]. The upper practical limit of flame temperature is about

**Figure 1.** *Typical plasmas characterized by their energies and densities.*

#### **Figure 2.** *Temperature and energy relationship of various plasma gases.*

3500°K, where molecules begin to dissociate, while the lower limit of plasma temperatures is about 10,000°K. As most laboratory plasmas are heated electrically, their temperatures will lie in the bottom end of the ionization curve, i.e., above 10,000°K for diatomic gases. For any process operating below 1000°K, an air-fuel flame (~2000°K) or an oxygen-fuel flame (~3000°K) will have a high percentage of energy available for the process. However, for the reaction occurring at 2500°K, only one-sixth of energy contained in an oxygen flame will be available, and rest must be either wasted or recovered in the expensive heat exchangers. On the other hand, a plasma flame composed of atomic nitrogen at 10,000°K would have more than 90% of its energy available above 2500°K. This high energy efficiency may more than offset the economic advantage that combustion energy over electrical energy; certainly, this advantage will increase as electrical energy becomes cheaper while fossil energy gets more expensive. Although by utilizing plasma high temperature can be achieved with the liberation of huge heat energy in a chemical reaction, plasma gases are generally not used as reactants in the reaction.
