**2. Genesis**

Natural iron oxides occur extensively and are obtained from deposit of various types. Hematite is mainly sourced from iron ore of sedimentary origin inclusive hydrothermal, metamorphic and volcanic deposits. Mafic and ultramafic rocks are linked with magnetite. This is also associated with skarn-type metamorphic deposits. Products of weathering such as limonite, ochre, sienna, umber and goethite exist in gossans. In addition, they are obtained from sulphide minerals and other iron-rich rocks [8].

Deposits precipitated from seawater are used in production of umber. These are located on the seafloor. Sulphide deposits are known to provide ochre and iron oxide coatings via oxidation. Black pigments are provided by magnetite deposits besides red and yellow ochre and iron oxide coatings derived from weathering of magnetite. Hematite deposits outcrop around the margins of the great sedimentary basins worldwide. There are oxide-rich deposits of igneous and metamorphic origin in Sweden. In Africa, good quality iron ores lie near the Mediterranean in Morocco and Algeria. There are extensive deposits in Brazil, India and China. Iron ore deposits are distributed widely in different geological formations [9].

The largest concentrations of ore are found in Precambrian age banded sedimentary iron formations. These formations make up the bulk of the world's iron ore incomes. These ores vary from hard blue massive type to soft, friable or schistose texture. The orebodies generally stand out as ridges with the ore both on the crests and on the flanks. Small patches are enriched by manganese derived from surface solution. The iron content extends from 64 to 68% after beneficiation. The leached out iron could be carried downwards to be precipitated as bodies of ochre and iron oxide coatings within the existing sedimentary rocks. This product is a soft earth mixture of hematite, limonite and goethite from which various red and yellow ochre and iron oxide coatings can be extracted [10].

and biological activities [1]. In addition, they are useful as pigments and catalyst in industries and hemoglobin in blood circulation. Iron oxides that are economically viable in natural and beneficiated forms are considered as second to oil and gas in relation to demand and utility in the global market. They occur as divalent compound, trivalent compound and a combination of both. The interplay and conversion of these components from one form to another are essentially controlled by bacterial species. These bacteria use iron and reduce trivalent iron

Different geological conditions control the spread of iron ore deposits worldwide. They occur in basins of sedimentation, with eroded, deep-seated intrusive and where deep tropical weathering conditions prevail. Magnetite deposits occur in the deeply dissected regions of

Several authors have provided information in the environmental outcome of exploration and exploitation of iron ore. These include pollution of the atmosphere and ecosystem courses of water. Pollution of the atmosphere involves release of poisonous gases such as nitrous oxide, carbon dioxide, carbon monoxide and sulfur dioxide. Pollution of the ecosystem involves release of metal load into courses of water. While there is limited remediation programme on the former, the latter has gained considerable attention, and elaborated ochre is a product of

Natural iron oxides occur extensively and are obtained from deposit of various types. Hematite is mainly sourced from iron ore of sedimentary origin inclusive hydrothermal, metamorphic and volcanic deposits. Mafic and ultramafic rocks are linked with magnetite. This is also associated with skarn-type metamorphic deposits. Products of weathering such as limonite, ochre, sienna, umber and goethite exist in gossans. In addition, they are obtained

Deposits precipitated from seawater are used in production of umber. These are located on the seafloor. Sulphide deposits are known to provide ochre and iron oxide coatings via oxidation. Black pigments are provided by magnetite deposits besides red and yellow ochre and iron oxide coatings derived from weathering of magnetite. Hematite deposits outcrop around the margins of the great sedimentary basins worldwide. There are oxide-rich deposits of igneous and metamorphic origin in Sweden. In Africa, good quality iron ores lie near the Mediterranean in Morocco and Algeria. There are extensive deposits in Brazil, India and

China. Iron ore deposits are distributed widely in different geological formations [9].

The largest concentrations of ore are found in Precambrian age banded sedimentary iron formations. These formations make up the bulk of the world's iron ore incomes. These ores vary from hard blue massive type to soft, friable or schistose texture. The orebodies generally stand out as ridges with the ore both on the crests and on the flanks. Small patches are enriched by manganese derived from surface solution. The iron content extends from 64 to 68% after

oxides to divalent form during metabolism.

24 Iron Ores and Iron Oxide Materials

plutonic intrusions in North America [2, 3].

**2. Genesis**

the aqueous oxidation of iron and oxides of iron [4–7].

from sulphide minerals and other iron-rich rocks [8].

The main product is a dark red hematite variety. Some ore deposits consist of magnetite with occasional hematite; varying amounts of sulphide occur mostly as pyrite and pyrrhotite with minor amount of chalcopyrite. The ore is composed of ferriferous oolites and grains of quartz bounded by a cement of clay minerals or of chlorites and carbonates. The oolites consist of iron hydroxides or limonite, with variable proportions of silica, alumina and phosphorus. The strikes of the orebodies are sometimes in accordance with the iron formation and sometimes discordant. The high-grade ore could be magnetite that is partially oxidized at the outcrops to hematite, with minor quantities of silicate minerals, anthophyllite and chlorite [11].

Deposits of iron may be categorized under the following: magmatic, sedimentary and metamorphic. In some regions of the world, the major sources of high-grade iron ore are derived from magmatic iron and metasomatic hydrothermal iron deposits. These especially the skarn-type iron deposits are mainly associated with intermediate-felsic igneous rocks, with only a minor proportion related to mafic intrusions. The iron redox cycle is a substantial process that exists in most terrestrial environments, which can be conducted by both abiotic and microbial processes. In anoxic, pH-neutral environments, microbial Fe(II) oxidation is driven by either nitrate-reducing bacteria, photoferrotrophic bacteria or neutrophilic microaerophilic bacteria [11, 12].

Microbial Fe(III) reduction forms the other component of the Fe cycle, generated by intracellularly by magnetotactic bacteria [12] or outside of the cell wall by dissimilatory iron-reducing bacteria. These combines with the oxidation of organic substrate or hydrogen with the reduction of poorly crystalline, short-range ordered Fe(III) minerals (e.g. ferrihydrite) [13]. This can lead to the development of many different iron mineral phases and compounds including goethite, magnetite, green rust and siderite (Fe2 CO3 ). The mineralogical composition of these products of reduction depends on geochemical parameters, inclusive Fe(III) reduction rate, pH, temperature and the availability of electron shuttle [14, 15].

Based on redox condition, magnetite can donate or accept electron in different metabolic processes involving Fe. In this respect, knowledge of the mineralogical outcomes of biomineralization characteristics can help provide signatures of microbial reactions with fluid, rocks, mineral deposits and subsequent diagenesis. Banded iron formation (BIF) is a chemically produced rock of sedimentary origin. This was precipitated in Precambrian time, comprising intercalated microcrystalline quart, iron oxides and silicates rich in iron. In line with depositional settings, the BIFs fall into Algoma type and superior type [16–18].

The constituents are discontinuous silica- and iron-rich bands with similar mineralogical properties of Fe, chert and carbonate minerals. Arc/back-arc basins or intra-cratonic rift zones host the Algoma type, and the latter is hosted by clastic carbonate rocks linked with shallow marine environments. As the main mineral constituents of BIFs, magnetite has been broadly reported for BIFs' depositional systems, mineralization characteristics and possible microbial involvements. Chemical and sedimentary methods in normal seawater could produce marine Fe-Mn oxides/oxyhydroxides. These are formed by precipitation of micron range particles of these components onto rock substrates at seabed [19–21].

Iron oxide pellets are used as the raw material in shaft furnace smelting. This is due to their uniformity in size, enormous strength and excellent permeability. However, production may be hampered by the rupture and fragmentation of pellets. Strength of pellet is closely connected to the modification of internal structure. In high-temperature reduction process, the strength changes are led mainly by internal stress. Phase alteration of oxides of iron in process of reduction may generate internal stress. To avoid this, magnetite should take the place of hematite crystalline in the pellet oxide roasting process. This will reduce volume expansion

Genesis, Uses and Environment Implications of Iron Oxides and Ores

http://dx.doi.org/10.5772/intechopen.75776

27

Direct-reduced iron (DRI) has been carried out in recent times to provide justifiable metallurgical operations. DRI possesses enormous benefits because it does not depend on cokemaking and sintering. Where coke-making and sintering are fronted at the conventional blast furnace, then ironmaking ends up being a costly process and is consistently causing environmental concerns. The DRI procedure consists of reduction of iron oxide by carbothermic method and converted natural gas. In this process, volatiles are directly liberated during coal devolatilization besides carbon monoxide regeneration from coal char. This process provides application prospect for the high volatile coals, which were ordinarily impractical in the steel industry. Extensive work has been reported on reduction of iron ore and coal-ore mixtures

Optimization of the coal-based DRI process requires understanding of the thermal properties of the coal-ore mixtures and mechanism reactions of reduction, which have still not been well understood. It is therefore necessary to have an insight into fundamental mechanisms for these complex reactions. The Itakpe iron ore is the deposit of the main concern to the Nigerian steel industry. The ore comprises substantial quantity of quartz and silica present itself in parallel layers to each other. About 29–37% Fe is contained in the ore grade, thus averaging 35% Fe. High flue dust losses are the basic characteristics of constituents which provide marked interruption during reduction. In addition, this could lead to attenuated furnace operation. Reducibility and clustering behaviour are significantly influenced by additions of 5% slaked

The consequence of iron ore tailings (IOT) on modification of cement tropical black clay was considered. The naturally occurring soil was worked on using 4% cement and 10% IOT per soil dry weight. Samples of tested soil compressed with British Standard measurement mechanism were exposed to catalog, sieve examination, compaction and shear strength parametric study. The outcome of laboratory study displaying attributes of the improved soil was enhanced when tested with cement-IOT blends. Experimental results expressed attenuation of the satisfactory fraction, attenuation in liquid and plastic limits and enhancement in optimum dry density, with a reduction in optimum content of moisture (OMC) besides attenua-

The role of ochre and oxides of iron in copper and zinc adsorption has been studied by [39–48]. Ochre and oxides of iron present in aqueous metal load are known to be good adsorbents. Heavy metal contaminants especially heavy metal load in the aquatic environment, discharged

during reduction process [31–33].

and its kinetics [34, 35].

lime to Itakpe iron ore pellet [36, 37].

**2.2. Environmental implications**

tion in shear strength rate of the natural soil [38].

The Itakpe iron ore deposit in Nigeria with an estimated reserve of about 200 million ton was discovered in 1977. The areal extent of this deposit spans about 3000 m in length inclusively in several layers of ferruginous quartzite. Tectonically, this deposit is located at the southern flank of the Itakpe-Ajabanoko anticline with host rock and ore layers striking sublatitudinally and slightly bending to the north and dipping southwards with local minor-fold complexes. Itakpe iron ore deposit comprises variable constituents of hematite and magnetite and particle sizes. This deposit with an Fe content of 35% consists of fine ores occurring in thin layers and coarse-grained mixed components. Direct-reduced iron (DRI) is the direct reduction of iron ore to iron n steel making. The DRI constituents of the pellet include: slag containing oxides of calcium, magnesium, alumina, silica. DRI pellets contain 67% Fe and 3% silica. In establishing a steel plant, availability of economically beneficiated iron ore deposit stands out as the main factor. The concentrates required at Ajaokuta and Delta steel plant would be supplied by the Itakpe iron ore deposit [22–25].
