2.3. Extrusion

the iron content, but also the agglomeration processes to achieve a homogeneous material's

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].

Five iron ore agglomeration technologies can be defined: briquetting, nodulization, extrusion, pelletization and sintering. Sintering and pelletization are the most important agglomeration technologies, in this way, in the EU-27, 14 countries operate 34 iron ore sinter plants with 63 iron ore sinter strands, producing in the first decade of the twenty-first century 130 million tons of sinter annually, on its behalf, 6 pelletization plants produce 27 million tons of pellet annually [7]. Here we are going to describe all these agglomeration technologies, with special

Briquetting is the simplest agglomeration process. Fine grained iron ore is pressed into two pockets with the addition of water or some other binder agent (molasses, starch, or tar pitch) to form briquettes [8]. A traditional application is the agglomeration of coal [8], other example is

Nodulization is a process like sintering as it does not need a binder agent. The iron ore concentrate is mixed with carbon, and fed into a rotary kiln, where the material is tumbled at

the agglomeration of ultrafine oxidized dust produced in the ferroalloys industry [9].

dedication to pelletizing and sintering as they are the most used worldwide.

size that could ensure a suitable operation in the furnace.

62 Iron Ores and Iron Oxide Materials

2. Iron ore agglomeration technologies

2.1. Briquetting

2.2. Nodulization

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