2.5.3. Environmental issues

Avoiding or minimizing pollutants is of large importance in nowadays environmental industrial policies, but also the objective is reducing the ecological footprint of the sintering process. In a second plane, environmental improvements will enhance the profitability of the sintering process from the economical point.

Sintering process is also used in the ironmaking and steelmaking as recycling system as apart from using iron ore fines and additives (such as fluxes and coke breeze), mill scale, collected dusts (and to a much lower extent sludges) from gas cleaning, other recycled by-products of steel manufacture and recycled sinter particles from sinter screening are treated in the sintering machine. Air pollutants are the most significant and are presented here:

Carbon dioxide: primary metal production is responsible for around 5% of the total world anthropogenic greenhouse gas emissions, while the iron and steel industry accounts for around 70% of this 5% [48], around 200 kg CO2/t sinter are generated in European plants [49] mainly as a consequence of fossil fuels combustion and carbonate's decomposition. JFE Steel Corporation developed a hydrogen-based gas fuel injection technology, reducing CO2 emissions by 60,000 tons/year [50]. Yabe and Takamoto proposed a process that used pre-reduced iron ore as sinter raw material (produced by reducing the iron ore to the degree of wüstite with blast furnace gas [51]). Coke breeze consumption is reduced (40,000 tons/year less of coke breeze in integrated plant of 4 Mt/year hot metal production) and 50,000–12,000 tons CO2/year less by using 10% pre-reduced iron ore.

Long et al. observed that with 0.05% urea, it was achieved a decrement of 63.1% in urea emission if compared with sinter without urea [66]. Lechtanska and Wielgosinski proposed

Iron Ore Agglomeration Technologies http://dx.doi.org/10.5772/intechopen.72546 71

Heavy metals: metals and heavy metals emissions are other important problem in the iron ore

PAH (Polycyclic Aromatic Hydrocarbons): are generated by the inhomogeneous and incomplete combustion processes. Several techniques are described in [7] to reduce PAHs emission

Measures to enhance air quality can be divided into three categories [65]: primary measures, based on preventing or minimizing the release of pollutants; secondary measures, consist in basically end-of pipe treatments; tertiary measures, consist in treating polluting wastes and

Sintering is an energy and polluting intensive process in integrated steelworks. Around 9–12% of the energy consumed in an integrated steelwork is consumed in the sintering process, and 75– 80% of this energy is produced by using contaminant solid fuels, such as coke breeze, anthracite, etc. [68]. These fossil fuels generate diverse pollutants, mainly CO2, SOX and NOX, and have made researchers to focus on studying more ecological alternatives as biochar, straw, or charcoal [65]. These new fuels are CO2-neutral, and lead to a significant reduction in SOX and NOX emissions. Other possibility is using blast furnace dust, as it has 24–40% carbon [69], although the amounts that are possible to recycle are limited fundamentally because of the zinc emissions. Secondary measures, as we mentioned, have the objective of reducing pollutant emissions in sinter plants. They have been applied since the last decades of the last century [65], in general combined with other primary measures. In this way, for instance, in an attempt of reducing PCDD/Fs in Servola sinter plant (Italy), they used urea (primary measure) and the WETFINE (Wet electrostatic Precipitator, secondary measure or end of pipe measure), reaching <0.4 ng I-TEQ/Nm<sup>3</sup> when using both systems (around 2 ng I-TEQ/Nm<sup>3</sup> when using only one) [70].

Secondary measures are deeply described in [65], but the main technologies of this group of end of pipe technologies are: WETFINE system, MEROS process, EOS system, AIRFINE

Solar energy when properly concentrated offers a great potential in applications where high temperature is required as for instance metallurgical processes [71]. Even when the possibility of using concentrated solar energy in the sintering process is very limited because of the large volume of material to be treated, it could find a great potential in iron recovery from metallurgical wastes such as slags or other by product. In our basic researches in this field, we used iron oxide (III) mixed with carbon, and a 1.5 kW medium size vertical axis solar furnace at the laboratory PROMES-CNRS (Font Romeu-Odeillo-Via, France). Sun radiation is concentrated in a spot of 12.2 mm in diameter, being controlled the power by means of a venetian blind. 14 samples were prepared by mixing iron oxide (III) (100% Fe2O3, d50 = 6.7 μm) with different

sintering, specially associated with PM10/2.5. See in [65] the sources of heavy metals.

raw materials in a single facility, concentrating there the source of pollutants.

the use of ammonium sulfate as inhibitor of dioxin formation [67].

concentrations from 591.7 mg/t sinter to 0.2 mg/sinter.

system and EFA process.

2.5.4. Solar energy in the ironmaking and steelmaking

NOX: NOX emissions can be reduced by using low nitrogen content combustibles as 90% vol.% of NOX comes from the fuel [52]. Using additives to inhibit the NOX generation: hydrocarbons (1% sugar addition) reduced NOX emissions from 533.8 g/t sinter to 283.3 g/t sinter [53]; or increasing Ca-Fe pellets in sintering bed [54]. End of pipe technologies could be other option but the huge volume of gas to be treated makes this option expensive. Flue gas recirculation lead to a significant reduction of pollutants emissions: 35–45% dust, 20–45% NOX, 60–70% dioxins, 25–30% SO2 and 40–50% CO reduction [55].

SOX: sulfur is present as sulfide and sulfate (FeS2, CuS, BaSO4, MgSO4, etc.) in iron ore fines and as elemental sulfur and organic sulfur in solid combustibles, which is oxidized and enters sinter flue gas as SO2, but low SO2 content in flue gas (400–1500 mg/Nm<sup>3</sup> , [56]) is responsible of low desulphurization efficiency of desulphurization processes. Li et al. studied the behavior of SO2 in different zones of sintering bed for flue gas circulation sintering, and observed that moisture condensation zone and sinter mix zone are characterized by a strong SO2 absorption ability, mainly by reaction of SO2 with CaO [56].

Particulate matter (PM10/2.5): the sintering process is the main contributor to PM emissions in an integrated steel factory [57, 58], around 45% of the total emissions. Due to the temperatures reached during the sintering process, components with noticeable vapor pressure like alkalis and heavy metal chlorides are volatilized and then re-condensed in the off-gas system resulting in a high fraction of PM10/2.5 in the dust emission of sinter plants [59]. End of pipe measures include electrostatic precipitators high-quality filter bags, etc. [7, 59]. Gan et al. observed that from over-wetted layer to the burning through point is the main area of PM10 emitting [57]. Ji et al. observed that increasing moisture content and extending granulation time the emission concentration of PM10/2.5 is reduced, while increasing coke breeze rate increases the emission concentration of PM10/2.5 the same as adding recycled materials [58].

Dioxins: sintering has been recognized as an important source of organic micro-pollutants such as PCDDs and PCDFs [7, 60–63]. The mechanism of PCDD and PCDF formation in sinter plants is complex and associated to a de novo synthesis process [64]. The range of PCDD/F emissions in the EU-25 in 2004 is from 0.15 to 14.64 μg I-TEQ/t sinter expressed on an annual average basis [7], with most plants in the range 0.2 to 6.0 μg I-TEQ/t sinter [7]. The best option in the problem of dioxins is minimizing their formation instead of end of pipe treatments as is the most effective method. Several primary measures are considered in [65], we want to emphasize the addition of urea in the raw mix to inhibit the dioxin formation. In this way, Long et al. observed that with 0.05% urea, it was achieved a decrement of 63.1% in urea emission if compared with sinter without urea [66]. Lechtanska and Wielgosinski proposed the use of ammonium sulfate as inhibitor of dioxin formation [67].

Heavy metals: metals and heavy metals emissions are other important problem in the iron ore sintering, specially associated with PM10/2.5. See in [65] the sources of heavy metals.

PAH (Polycyclic Aromatic Hydrocarbons): are generated by the inhomogeneous and incomplete combustion processes. Several techniques are described in [7] to reduce PAHs emission concentrations from 591.7 mg/t sinter to 0.2 mg/sinter.

Measures to enhance air quality can be divided into three categories [65]: primary measures, based on preventing or minimizing the release of pollutants; secondary measures, consist in basically end-of pipe treatments; tertiary measures, consist in treating polluting wastes and raw materials in a single facility, concentrating there the source of pollutants.

Sintering is an energy and polluting intensive process in integrated steelworks. Around 9–12% of the energy consumed in an integrated steelwork is consumed in the sintering process, and 75– 80% of this energy is produced by using contaminant solid fuels, such as coke breeze, anthracite, etc. [68]. These fossil fuels generate diverse pollutants, mainly CO2, SOX and NOX, and have made researchers to focus on studying more ecological alternatives as biochar, straw, or charcoal [65]. These new fuels are CO2-neutral, and lead to a significant reduction in SOX and NOX emissions. Other possibility is using blast furnace dust, as it has 24–40% carbon [69], although the amounts that are possible to recycle are limited fundamentally because of the zinc emissions.

Secondary measures, as we mentioned, have the objective of reducing pollutant emissions in sinter plants. They have been applied since the last decades of the last century [65], in general combined with other primary measures. In this way, for instance, in an attempt of reducing PCDD/Fs in Servola sinter plant (Italy), they used urea (primary measure) and the WETFINE (Wet electrostatic Precipitator, secondary measure or end of pipe measure), reaching <0.4 ng I-TEQ/Nm<sup>3</sup> when using both systems (around 2 ng I-TEQ/Nm<sup>3</sup> when using only one) [70].

Secondary measures are deeply described in [65], but the main technologies of this group of end of pipe technologies are: WETFINE system, MEROS process, EOS system, AIRFINE system and EFA process.

## 2.5.4. Solar energy in the ironmaking and steelmaking

Carbon dioxide: primary metal production is responsible for around 5% of the total world anthropogenic greenhouse gas emissions, while the iron and steel industry accounts for around 70% of this 5% [48], around 200 kg CO2/t sinter are generated in European plants [49] mainly as a consequence of fossil fuels combustion and carbonate's decomposition. JFE Steel Corporation developed a hydrogen-based gas fuel injection technology, reducing CO2 emissions by 60,000 tons/year [50]. Yabe and Takamoto proposed a process that used pre-reduced iron ore as sinter raw material (produced by reducing the iron ore to the degree of wüstite with blast furnace gas [51]). Coke breeze consumption is reduced (40,000 tons/year less of coke breeze in integrated plant of 4 Mt/year hot metal production) and 50,000–12,000 tons CO2/year

NOX: NOX emissions can be reduced by using low nitrogen content combustibles as 90% vol.% of NOX comes from the fuel [52]. Using additives to inhibit the NOX generation: hydrocarbons (1% sugar addition) reduced NOX emissions from 533.8 g/t sinter to 283.3 g/t sinter [53]; or increasing Ca-Fe pellets in sintering bed [54]. End of pipe technologies could be other option but the huge volume of gas to be treated makes this option expensive. Flue gas recirculation lead to a significant reduction of pollutants emissions: 35–45% dust, 20–45% NOX, 60–70%

SOX: sulfur is present as sulfide and sulfate (FeS2, CuS, BaSO4, MgSO4, etc.) in iron ore fines and as elemental sulfur and organic sulfur in solid combustibles, which is oxidized and enters

low desulphurization efficiency of desulphurization processes. Li et al. studied the behavior of SO2 in different zones of sintering bed for flue gas circulation sintering, and observed that moisture condensation zone and sinter mix zone are characterized by a strong SO2 absorption

Particulate matter (PM10/2.5): the sintering process is the main contributor to PM emissions in an integrated steel factory [57, 58], around 45% of the total emissions. Due to the temperatures reached during the sintering process, components with noticeable vapor pressure like alkalis and heavy metal chlorides are volatilized and then re-condensed in the off-gas system resulting in a high fraction of PM10/2.5 in the dust emission of sinter plants [59]. End of pipe measures include electrostatic precipitators high-quality filter bags, etc. [7, 59]. Gan et al. observed that from over-wetted layer to the burning through point is the main area of PM10 emitting [57]. Ji et al. observed that increasing moisture content and extending granulation time the emission concentration of PM10/2.5 is reduced, while increasing coke breeze rate increases the emission concentration of PM10/2.5 the same as adding recycled materials [58]. Dioxins: sintering has been recognized as an important source of organic micro-pollutants such as PCDDs and PCDFs [7, 60–63]. The mechanism of PCDD and PCDF formation in sinter plants is complex and associated to a de novo synthesis process [64]. The range of PCDD/F emissions in the EU-25 in 2004 is from 0.15 to 14.64 μg I-TEQ/t sinter expressed on an annual average basis [7], with most plants in the range 0.2 to 6.0 μg I-TEQ/t sinter [7]. The best option in the problem of dioxins is minimizing their formation instead of end of pipe treatments as is the most effective method. Several primary measures are considered in [65], we want to emphasize the addition of urea in the raw mix to inhibit the dioxin formation. In this way,

, [56]) is responsible of

less by using 10% pre-reduced iron ore.

70 Iron Ores and Iron Oxide Materials

dioxins, 25–30% SO2 and 40–50% CO reduction [55].

ability, mainly by reaction of SO2 with CaO [56].

sinter flue gas as SO2, but low SO2 content in flue gas (400–1500 mg/Nm<sup>3</sup>

Solar energy when properly concentrated offers a great potential in applications where high temperature is required as for instance metallurgical processes [71]. Even when the possibility of using concentrated solar energy in the sintering process is very limited because of the large volume of material to be treated, it could find a great potential in iron recovery from metallurgical wastes such as slags or other by product. In our basic researches in this field, we used iron oxide (III) mixed with carbon, and a 1.5 kW medium size vertical axis solar furnace at the laboratory PROMES-CNRS (Font Romeu-Odeillo-Via, France). Sun radiation is concentrated in a spot of 12.2 mm in diameter, being controlled the power by means of a venetian blind. 14 samples were prepared by mixing iron oxide (III) (100% Fe2O3, d50 = 6.7 μm) with different carbon (100% C, d50 = 10.2 μm) excesses (10, 25 and 40%) over the stoichiometric. Samples of 0.8–2.5 g were loaded into crucibles of 75 mm length, 12 mm width and 8 mm depth, with three thermocouples placed at the bottom of the crucible. This crucible is then placed below the solar beam and displaced at a controlled speed of 0.25–0.76 mm/s.

Knowing that the formation of magnetite is easily achieved by using concentrated solar energy, it is possible to think in recovering iron from wastes of the metallurgical industry containing

Iron Ore Agglomeration Technologies http://dx.doi.org/10.5772/intechopen.72546 73

This process was developed by the Nippon Kokan Keihin company (nowadays JFE Steel Corporation) with the objective of using fine iron-rich ores in their plants. The process is based on using pelletizing discs to obtain green pellets that are then coated with coke breeze before their disposal over the sinter strand. A commercial plant with an annual capacity of 6 million tons is working using HPS process at Fukuyama (belonging to JFE Steel Corporation) [18].

In 2001, Iron and Steel Institute of Japan began a research project on porous meso-mosaic texture sinter with the purpose of incorporating Australian goethite/limonite ores (characterized by a high proportion of ultrafine particles, up to 30% <150 μm) [16]. In this way, the purpose was to use important amounts of fine ores by controlling the void structure of the sinter bed structure (achieving a good sinter bed permeability and sinter yield). Consequence of the project is the MEBIOS process [73], which organizes dense granulated pellets in a conventional sinter mixture, allowing for obtaining well-developed voids and few pores that define a ventilation route, where the aging bed is based on Marra Mamba ore (fine ore and coarsely granulated material) while the induction bed is based on pisolitic limonite ore blended with coke and CaO [16]. In this way, dense large pellets support sinter bed and avoid sinter shrinkage, allowing the appearance of ventilation routes that improve permeability [18]. This process has another version known RF-MEBIOS (Return Fine-Mosaic Embedding Iron Ore Sintering). It was applied on Number 3 sinter plant in the NSSMC Kashima Steel Works, and then it was installed on three commercial sintering machines (Kashima, Wakayama, and

Sinter and pellets are loaded in the blast furnace together, but this causes several problems associated to two aspects: spherical shape of pellets (responsible of the tendency to flow toward the center of the furnace, causing unstable operation); and, higher bulk density of pellets, making them to sink into the coke layer during the burden descent [74]. Jiang et al. developed the Composite Agglomeration Process with the purpose of solving the problems caused by the spheroidal shape of pellets and the increase in the supply of fine grained ores [74]. The process consists in: part of fine grained iron ore is transformed into 8–16 mm green pellets, while the rest and the coarse fine ores are mixed with fluxes, fuels and return fines, and then granulated (primary mixture); green pellets and primary mixture are blended (secondary mixture) and then fed to the sintering machine; the mixture is transformed into the composite

iron as oxide, as for instance slags.

2.5.5.1. HPS process: hybrid pelletized sinter

2.5.5. Other alternative processes to sintering and pelletizing

2.5.5.2. MEBIOS: mosaic embedding iron ore sintering

Kokura) belonging to Sumitomo Metal Industries Ltc [18].

2.5.5.3. CAP: composite agglomeration process

Samples were analyzed by x-ray diffraction and SEM–EDX. It was observed that the main phases were Fe2O3, Fe3O4 and in some cases FeO. This indicates that a transformation took place during the experiments, carbon was mainly burnt during the process, so it was not used as reductant agent [71], and for that reason, the appearance of Fe3O4 and FeO takes place because of thermal decomposition of the iron oxide. It is possible to see in Figure 1 the influence of displacement speed and power in the formation of magnetite.

From SEM–EDX, it is clearly observed that the disperse constituent is magnetite (white), while the matrix constituent is a phase formed by silica and alumina (both coming from the crucible [72]), iron and oxygen (see Figure 2). There are, for that reason, both diffusion and melting phenomenon during the process.

Figure 1. Magnetite formation as a function of power (a) and displacement speed (b).

Figure 2. Micrographs obtained with an electronic microscope (E34 P2 (a) and E25 P2 (b)).

Knowing that the formation of magnetite is easily achieved by using concentrated solar energy, it is possible to think in recovering iron from wastes of the metallurgical industry containing iron as oxide, as for instance slags.
