**2.1. Uses**

A mixture of ferrous or ferric oxides constitutes iron oxides provided for pigments. These may contain impurities of manganese oxides, clay and silica. Oxides of iron remain one of the pigments of natural origin inclusive titanium dioxide. They are highly valued because they possess non-toxic, inert, opaque and weather-resistant properties. Oxides of iron constitute the main component of products in the pharmaceutical industry, paint industry, plastic industry, ink industry and cosmetic industry. Oxides containing mica provides anticorrosion properties. Natural pigments which qualify for these applications are limited in occurrence. Thus, synthetic iron oxides obtainable from iron compounds have better uniformity, purity of color, consistency and strength [26, 27].

The physical characteristics of these oxides are more valuable than chemical composition. The suitability of a material for pigment application is dependent on grindability, color uniformity and strength of tinting. Besides these properties, chemical purity is also important for its application in the pharmaceutical and cosmetic industries. Calcination of pyrite and siderite provides iron oxides which meet characteristics for these applications. Other beneficiation processes for commercial production of pigments include decomposition of iron compounds by thermal method, oxidative precipitation of iron salts and reductive process on organic compounds [28, 29].

Synthetic pigments override natural pigments due to their proximity to the place of use and meeting required specifications. The use of magnetite in dense medium separation is based on its physical properties: specific gravity and magnetism. Thus, magnetite could be recovered and used again. Magnetite provides separation of high-density minerals and washing of coal. The banded ores contain thin bands of hematite and magnetite alternating with bands of quartz schists, jasper and iron silicates with occasional bands of siderite. In more metamorphosed varieties, hornblende, olivine and garnet are present. Sulfur and phosphorus are low. Concentration is achieved by roasting to reduce the hematite to magnetite, crushing and magnetic separation followed by sintering and briquetting [29, 30].

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 during reduction process [31–33].

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 and its kinetics [34, 35].

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

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