2. Pelletizing process and raw materials

The iron ore is mined mostly from open pit deposits through mining operations and the raw product, "run of mine," is subjected to mineral processing. Thus, the material is exposed to a series of operations of fragmentation, separation by size, concentration, dewatering, etc., aiming to adequate the chemical, physical, and metallurgical characteristics to meet the demands of ironmaking processes. The particle size distribution of iron ore is a very important requirement to be characterized after its mineral processing.

Materials containing a very fine particle size distribution are not adequate to be used directly in the reduction reactors, requiring to be agglomerated by different processes such as sintering or pelletizing.

The main used reduction reactors are the blast furnace (BF) and direct reduction reactors (DR). In the blast furnace, iron is reduced and melted and the most common product is liquid iron called hot metal. In direct reduction, iron remains in solid state and the product is the so-called direct reduced iron (DRI).

Generically, the iron ore products for ironmaking can be classified as shown in Table 1.

Pellets are balls formed by rolling moist concentrates and fines iron ores of different mineralogical and chemical composition, with the addition of additives and binder, in a horizontal drum or in an inclined disc [1, 4].


Table 1. Iron ore products classification for ironmaking [3].

Pellets produced to be used in ironmaking processes must have characteristics that meet the list of quality specifications regarding physical, chemical, and metallurgical properties. Almost all of those properties are standardized as shown in Table 2.

To avoid such effects, binders are added to the material to be pelletized, aiming to:

• prevent the collapse of pellets during the initial stages of heating, when a large volume of

Iron Ore Pelletizing Process: An Overview http://dx.doi.org/10.5772/intechopen.73164 45

Evenly distributed moisture and binder in the feeding process is decisive to improve the characteristics of pellets, especially to avoid the formation of undesirable agglomerates before

Bentonite is an effective, widely used binder in the iron ore pelletizing process. Its low price is

However, bentonite incorporates silica and alumina, which are undesirable contaminants to pellets. Additionally, it is a natural material with variable composition depending on its origin. Obtaining a suitable binding effect requires a relatively large amount of material, around 0.5%

Figure 2 shows a flowchart of a typical pelletizing plant, highlighting the additive preparation, mixing and pelletizing feed preparation, the balling step, in this case using a disc pelletizer,

Figure 2. Typical pellet plant using disc pelletizer as balling technology. Source: Elaborated by the authors from Metso [9]

• increase the strength of pellets before heating (green strength);

the pellet formation.

and the induration step.

and Vale [10].

an important factor for its extensive use.

gas generated by water vaporization tends to crack the pellets.

by weight, which makes handling more difficult and increases logistics costs.

Aiming to achieve those specifications, binders and additives are used in the pelletizing process. Additives such as limestone, dolomite, and hydrated lime are used to modify the chemical composition of the pellets, most often for correction of the basicity.1 Certain substances such as hydrated lime serve as both additive and binder. Fines of anthracite or coke are also added during the pelletizing process for reducing the consumption of fuel required for internally heating the ball [7].

Pellets are obtained by adding an appropriate amount of water to the iron ore concentrate; this is a fundamental factor in the formation and growth of pellets, which creates a surface tension that holds the mineral grains cohesive, thus allowing their handling [6, 8].

This cohesive tension of fine particles due to water is called neutral tension. Neutral tension, however, is not sufficient to keep cohesive grains as dense as iron minerals. Furthermore, when the pellet is heated, the vaporization of water occurs and the pellets tend to disintegrate.


Source: elaborated by the author with data from Campos et al. [5] and Moraes [6].

Table 2. Quality specification of iron ore pellets.

1 Basicity in this context is the ratio between the weight percent of CaO and SiO2. To avoid such effects, binders are added to the material to be pelletized, aiming to:

• increase the strength of pellets before heating (green strength);

Pellets produced to be used in ironmaking processes must have characteristics that meet the list of quality specifications regarding physical, chemical, and metallurgical properties. Almost

Aiming to achieve those specifications, binders and additives are used in the pelletizing process. Additives such as limestone, dolomite, and hydrated lime are used to modify the chemical composition of the pellets, most often for correction of the basicity.1 Certain substances such as hydrated lime serve as both additive and binder. Fines of anthracite or coke are also added during the pelletizing process for reducing the consumption of fuel required for

Pellets are obtained by adding an appropriate amount of water to the iron ore concentrate; this is a fundamental factor in the formation and growth of pellets, which creates a surface tension

This cohesive tension of fine particles due to water is called neutral tension. Neutral tension, however, is not sufficient to keep cohesive grains as dense as iron minerals. Furthermore, when the pellet is heated, the vaporization of water occurs and the pellets tend to disintegrate.

that holds the mineral grains cohesive, thus allowing their handling [6, 8].

Physical ISO 4701 Determination of size distribution by sieving

ISO 4700 Determination of the crushing strength

JIS M 8711 Determination of shatter strength

ISO 3271 Determination of the tumble and abrasion index

dynamic method

ISO 11256 Determination of the clustering index

Porosity

ISO 13930 Determination of low-temperature reduction-disintegration index by

ISO 11257 Determination of the low-temperature reduction-disintegration index and degree of metallization

Determination of crashed resistance by the number of drop falls

Determination of reduction under load/Determination of the reducibility by the final degree of reduction index/Determination of the lowtemperature reduction-disintegration index and degree of metallization

all of those properties are standardized as shown in Table 2.

Norm Description

Chemical Chemical property of the pellets

Source: elaborated by the author with data from Campos et al. [5] and Moraes [6].

Basicity in this context is the ratio between the weight percent of CaO and SiO2.

Metallurgical ISO 4698 Determination of the free-swelling index

Internal procedures (pelletizing companies)

ISO 7992 / ISO 7215 / ISO

Internal procedures (pelletizing companies)

Table 2. Quality specification of iron ore pellets.

11257

internally heating the ball [7].

44 Iron Ores and Iron Oxide Materials

Type of specification

1

• prevent the collapse of pellets during the initial stages of heating, when a large volume of gas generated by water vaporization tends to crack the pellets.

Evenly distributed moisture and binder in the feeding process is decisive to improve the characteristics of pellets, especially to avoid the formation of undesirable agglomerates before the pellet formation.

Bentonite is an effective, widely used binder in the iron ore pelletizing process. Its low price is an important factor for its extensive use.

However, bentonite incorporates silica and alumina, which are undesirable contaminants to pellets. Additionally, it is a natural material with variable composition depending on its origin. Obtaining a suitable binding effect requires a relatively large amount of material, around 0.5% by weight, which makes handling more difficult and increases logistics costs.

Figure 2 shows a flowchart of a typical pelletizing plant, highlighting the additive preparation, mixing and pelletizing feed preparation, the balling step, in this case using a disc pelletizer, and the induration step.

Figure 2. Typical pellet plant using disc pelletizer as balling technology. Source: Elaborated by the authors from Metso [9] and Vale [10].
