Uses of Iron Oxides and Ores

Iron oxides are chemical complexes which occur naturally, comprising iron and oxygen. Here, together, 16 types of iron oxides and oxyhydroxides have been identified. These two components of oxides are widely spread naturally. They are vital to humans and useful in most geological and biological activities.

Introduction

The genesis, uses and environmental implications of iron oxides and ores remain a topic of interest to academics, industrial players and environmentalist. Oxides of iron are chemical compounds widely spread naturally, comprising iron and oxygen. Here, two components of oxides are widely spread naturally. They are relevant to humans and useful in most geological 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 oxides to divalent form during metabolism.

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 plutonic intrusions in North America [2, 3].

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].

 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].

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, 32, 33].

Environmental implications

The role of ochre and oxides of iron in copper and zinc adsorption has been studied by [39, 40, 41, 42, 43, 44, 45, 46, 47, 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 by acid mine drainage and treatment plant liquids, constitute the principal derivatives of tarnished water channels. Limited reports of heavy metal removal exist. However, the utilization of oxides and oxyhydroxides inoculated with sulphide of zinc within sulfidic-anoxic setting is a new dimension of research [39, 40]. This report centred on investigating heavy metal load removal onto ochre and iron oxide coatings from virtual wastewater related to effluents. At ambient temperature, batch mode techniques involved inoculating sulphide containing heavy metal into mineral system of ochre and iron oxide coatings [41].

pH of solution, quantity of metal at the onset of reaction, concentration of adsorbent and reaction time were variables investigated (Table 1). There was a strong understanding that goethite-ochre and iron oxide coatings exhibited a linear increase in the adsorption of heavy metal load as solution pH was increased. In addition, quantity of adsorption increased with increase metal concentration [41, 42, 43, 44]

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