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 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 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 ].
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.
This can lead to the development of many different iron mineral phases and compounds including goethite, magnetite, green rust and siderite Fe 2 CO 3. 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 , 17 , 18 ]. The constituents are discontinuous silica- and iron-rich bands with similar mineralogical properties of Fe, chert and carbonate minerals. These are formed by precipitation of micron range particles of these components onto rock substrates at seabed [ 19 , 20 , 21 ].
The Itakpe iron ore deposit in Nigeria with an estimated reserve of about million ton was discovered in The areal extent of this deposit spans about 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 sub-latitudinally 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. 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. 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 , 23 , 24 , 25 ]. 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 , 32 , 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 coke-making 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. 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. The consequence of iron ore tailings IOT on modification of cement tropical black clay was considered.
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 ].
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 ].
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 ]. Characteristics of Parys Mountain ochre, United Kingdom [ 46 , 47 ]. Some mineral systems including ochre and oxides of iron coatings confirmed neither promotive nor non-promotive adsorption of heavy metal load throughout the series of concentration of particle investigated.
Adsorption of heavy metal load by ochre and iron oxide coatings revealed a complex attitude throughout the period of aging investigated. Performance of adsorption was dependent on availability of different sites of reaction [ 45 ]. Adsorption of heavy metal load was examined by means of single and mixed mineral systems containing ochre and iron oxide coatings within sulfidic-anoxic environment in the characteristics of wastewater obtained from abandoned mine pits at Parys Mountain in the United Kingdom.
Bodies of water are the receivers of these contaminants. In these bodies of water, human activities including fishing exist. Effort was made to bring down the levels of heavy metal load intake in the bodies of water by means of ochre and iron oxide coatings. These were verified with the mine liquid waste for adsorption characteristics at different pH, concentration of solid and reaction time. In addition, levels of saturation of hydroxyl chemically bonded components were modeled.
Reactions by batch techniques at ambient temperature provided ochre and iron oxide coatings adsorbed more heavy metal load Figure 1. In addition, heavy metal load adsorbed on oxides of iron displayed increases in adsorption with increase in pH [ 46 , 47 ].
Graphical summary for ochre interaction with copper and zinc ions. These provided similar reduction of metal characteristics at the crossover pH. Differences in heavy metal load reduction may be aligned to linkages between adsorbate and water molecules attached to adsorbent and direct attachment of adsorbate to adsorbent. Non-promotive effect of, i.
This feature may be aligned to enhanced aggregation of the ochre and iron oxide coatings of particle sizes. Features of aging progress as reaction time was increased. This may be aligned to the availability of thiol and hydroxyl components and chemical sites of responses.
There is no link to stable introduction of hydroxyl group to species of copper and zinc that could meaningfully account to the reduction of these metals [ 48 ]. Litter by heavy metals of copper and zinc provided by acid mine drainage and liquid waste treatment are the leading sources of blotted water chemistry.
Metal plating, mining and painting cause release of heavy metals of copper and zinc. These metals become a serious health problem. This is because they are dogged and have harmful effect on the environment.
Heavy metals of copper and zinc are required in small quantity element that is essential for nutrition [ 46 , 47 ]. However, when available in overdose, it may be noxious. This could pose adverse danger in groundwater and surface resources as they build-up in living organisms [ 45 ].
It is widely known that surplus of heavy metals of copper and zinc provides depression, lethargy and neurological disorder signs such as nervous confiscations and increased dehydration. Therefore, reduction of these metals from water courses is needed. Anthropogenic activities release metal load into bodies of water. These metal loads damage the ecosystem and are toxic to humans and other forms of life.
Chemical solution and appropriate sorbents determine the availability of dissolved metal species [ 44 ]. Reduction of copper and zinc ions from solutions of aquatic nature is governed by the makeup of the solution. These include the outcome of hydrogen ion concentration and the number of solid particles in the wastewater. The amount of dissolved metal in solution is measured by pH. Another effect of pH includes hydrolysis characterization and surface charge.
Lower pH attenuates hydrolysis and enhances metal build-up in the solution. Adsorption of heavy metals of copper and zinc is controlled by anion nature and the external layer of the adsorbent [ 43 ]. Adsorption related to solute water molecule attachment attenuates as particle concentration increases. Adsorption related to solute direct attachment to adsorbent does not significantly increase in some cases as adsorbent quantity increases.
When adsorption is enhanced as particle concentration increases, then promotive particle concentration effect is reported. The reasons for the promotive adsorption effect by concentration of solid particle remains are uncertain. Ionic species available in solution are influenced by the forces at work at the mineral-solution interface. Micaceous iron oxide imparts unique properties to paints and coatings because the flaky particles align in such a way as to resist penetration by moisture and gases.
These coatings can prevent corrosion and rusting of metals and also resist blistering, cracking and peeling. Deposits of iron oxide pigment occur in many countries, but have been significantly developed in only a few. Countries known for production of iron oxide pigments historically include Cyprus, France, Iran, Italy and Spain. Countries with recent significant production include India, Spain and Honduras. Iron oxide pigments are also created through steelmaking.
When steel is treated with hydrochloric acid to remove surface oxides, the acid is regenerated to be recycled and iron oxide is produced. Regenerated iron oxides are used in a variety of filters, inductors and transformers in electronic home appliances and industrial equipment, as well as in flexible magnets, generators, loudspeakers and electric car motors. New developments in the synthetic iron oxide pigment industry in recent years include granular forms of iron oxides and new versions of nano-sized materials, which are being used in computer disk drives and high-performance loud speakers, and in biology and medicine, including nuclear magnetic resonance imaging.
Visit minerals. Total world production of iron oxide pigments natural: 13 percent and synthetic: 87 percent in was approximately 1. Natural iron oxide pigments have been used in art for tens of thousands of years, since humans created the 32,year-old cave paintings at Lascaux, France. Iron oxide pigments are used as colorants for ceramic glazes, glass, paper, plastic, rubber and textiles as well as in cosmetics and magnetic ink and toner.
Micaceous iron oxide coatings have been used for heavy duty applications in harsh environments, including industrial tanks, refineries, chemical plants, drilling rigs and bridges, and even on the Eiffel Tower. All rights reserved.
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