1. Introduction

Iron and steel are widely used in modern societies despite the appearance of new materials. In this way, there is a growing tendency in the production of steel as according to the historical data, around 200 Mt were produced in 1950, 595 Mt in 1970, 760 Mt in 1990, 848 Mt in 2000 and 1630 Mt in 2016 [1, 2]. There is an irregular distribution of steel production worldwide as most of the steel is produced in Asia (more than 50%, mainly in China), followed by Europe (205 Mt in 2013), Russia, and USA. In the same line, Asia was the place where the steel production grew more in the last 40 years (from 121 Mt in 1970 to 1123 Mt in 2013), while in Europe the production remains stable in around 200 Mt, and in North America (USA and Canada) decreased from 131 Mt in 1970 to 102 Mt in 2013 [1, 2]. This growing tendency has led to the depletion of high-quality iron ore resources, and the use of concentration processes to increase

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the iron content, but also the agglomeration processes to achieve a homogeneous material's size that could ensure a suitable operation in the furnace.

high temperature to form nodules [8]. Reached temperature is enough to soften the ore but not to fuse it. Problems of the nodules are the considerable differences in composition and density (they are too dense), and the lack of a well-developed porosity (permeability) which is of great importance for the operation in the blast furnace. This process, as briquetting, is mainly used

Iron Ore Agglomeration Technologies http://dx.doi.org/10.5772/intechopen.72546 63

Extrusion is a process widely used in the ceramic industry, but it has begun to be used in the ironmaking and steelmaking industry in the agglomeration of powders generated in the factories as Basic Oxygen Furnace and Electric Arc Furnace powders. A certain level of moisture is required, as well as a binder agent, for instance bentonite or Portland cement. The

Pelletization is an agglomeration process of iron ore concentrates with a granulometry lower than 150 μm and low concentration of impurities [10, 11]. This iron ore is mixed with water, bentonite (or other organic binders less expensive and contaminant [12]), and lime and treated in a furnace at temperatures of around 1200�C, with the purpose of obtaining a product of 10– 20 mm in diameter with suitable physical, chemical, and mechanical properties to be fed into the blast furnace or to the production of DRI (Direct Reduction Iron) [10]. Sintering raw mixes with a high proportion of fines (<150 μm) deteriorates the operation of the Dwight-Lloyd sinter machine, and for that reason pelletizing is the best method for treating this kind of material. The formation of liquid phases, which agglomerate the iron ore, in pellets is achieved by an external source of energy (fuel, natural gas or pulverized coal), as opposed to sintering, where

Chemically, pellets are characterized by (approximately): 94% Fe2O3, 3.3% SiO2, 1.0% CaO, 0.20% MnO, 0.50% MgO and 1.0% Al2O3, and as we mentioned previously, a granulometry of 10–20 mm [2]. According to this question, it is possible to say that pellets are characterized by [10]: great uniformity regarding the size (10–20 mm in diameter); high mechanical strength; almost inert behavior facing to water as a consequence of the low CaO content that makes possible storing and transporting pellets outside; good reducibility; and, high iron content.

As in the case of the sintering, mixing is an important step to obtain homogenous pellets. This mixing is easy when the materials to be mixed have the same particle size and physical properties, however, binder additions (around 1%) are necessaries and they are less dense than the ore. For that reason, segregation between particles must be considered when mixing the

Bentonite clay is the most common binder agent in iron ore pelletization as we mentioned previously, and is added at levels of 0.5–1.5% by weight [8]. There are others, that can be classified into two categories: organics (do not add impurities to the pellet and can be added in amounts of 1/10 of the equivalent in bentonite, although sometimes do not provide sufficient strength to the indurated pellets), and inorganics (usually result in strong pellets, which is good for shipping and handlings, but have the problem of impurities) [8]. Examples of

mixture is sent to the extrusion machine to obtain the agglomerated product [8].

liquid phases are consequence of the combustion of coke breeze [2].

materials in the production of pellets.

for the recycling of iron ore wastes in steel plants.

2.3. Extrusion

2.4. Pelletization

Until the 1950s of the last century, oxidized iron ores with a granulometry within 10 and 120 mm were loaded into the blast furnace (lower sizes led to permeability problems in the furnace bed) [3]. However, nowadays, 70% of the blast furnace ferrous bed belongs to sinter [4], and is for that reason the main agglomeration process. As we said previously, the depletion of the high-quality iron sources has caused the utilization of concentration operations after size reduction processes, having as objective enriching the ore by eliminating the gangue, but causing a fine granulometry that makes necessary the utilization of agglomeration processes, such as nodulizing, briquetting, extrusion, pelletizing, and sintering. Concentration processes can be classified into four categories according to the properties of the materials to separate them from the gangue [5]: classification, based on particle size; gravimetric concentration, based on density and/or volume differences; flotation, based on superficial properties; and, magnetic or electrostatic separation, based on magnetic susceptibility or electric conductivity. The obtained product is rich in iron but with a fine granulometry, making necessary the utilization of the previously mentioned agglomeration processes. However, increasing the particle size is not the single aspect that makes necessary the utilization of agglomeration processes. Nowadays, the existence of a global iron ore market with ores with different precedence and quality is responsible of that the raw material that reaches the iron and steelmaking factories has neither the same chemical composition nor the same granulometry. This question could affect blast furnace behavior, when a stable and homogenous operation is pursued with the objective of achieving economic efficiency, consistency in the pig iron and minimal coke consumption [6].
