Concentration of Iron in Laterites from different Localities of Tunyai Division in Tharaka Nithi County in Kenya using Magnetic Separation
Mutembei, Peterson Kugeria
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Iron is the single element used in industries in larger quantities than all the other metallic elements combined. This is because of the very wide applications of the metal in manufacture of machinery, vehicles, utensils, trains and train rails, ships and bars used in re-enforced concrete. Whereas the element occurs in more than 80 minerals, only a small number is important as a source of iron. However, even these must be concentrated to make them suitable for putting in a blast furnace. In Kenya, laterites commonly called murram, are currently being used mainly for surfacing roads. This study set out to show that laterites can be converted to high quality iron ore which should make Kenya self-reliant in as far as supply of metallic iron is concerned. The area of study was chosen because some of the iron in this area is known to be present as the mineral ilmenite. It was, therefore, of interest to find out whether the heat treatment that converts hematite to magnetite is adequate to decompose ilmenite. The samples of this study were obtained from Tunyai Division, in Tharaka Nithi County, in the Republic of Kenya. During sampling, three sampling sites from each location were selected within a distance of about a km apart. Within a given sampling site, three holes which were at least ten metres apart were dug. The surface materials of up to 30 cm deep were discarded since they contained a lot of organic matter. Three Samples from this depth were obtained, mixed and about one kg of the sample-mixture packed in plastic bags labeled level A awaiting analysis. For each hole, samples were also picked from a depth of one metre, mixed and labeled, B. Laterite samples were concentrated by heating charcoal/laterite mixtures in the ratios of 1:10 by mass in a slow current of air and in the temperature range of 500-700oC. Elemental analysis was carried out on both the raw laterites and the heat treated samples with particular interest on the level of iron using Atomic Absorption Spectroscopy (AAS) and EDTA Titrations for comparison purposes. The minerals present were determined using a Bruker D8 Advance Diffractometer. The results of elemental analysis showed that, raw laterites contain 28-31% iron depending on source. On the other hand, after the heat treatment, the level of iron in the heat-treated sample had increased to 55-64%. Iron ore with this level of concentration is usually what is normally put in a blast furnace. The X-ray diffraction data confirmed that, iron in the raw laterites was present predominantly as the minerals goethite and hematite since these are known to have diffraction peaks at angles 2θ= 21.51˚ and 2θ= 54.11˚, respectively. In this study, whereas these peaks were observed in the raw laterites, they were absent in the heat-treated magnet-separated samples and instead, a strong peak was observed at angle 2θ= 36˚. This peak is attributed to magnetite. This observation confirms that, when the laterite-charcoal mixture is heated in the temperature range 500-700oC in a current of air, both goethite and hematite are converted to the mineral magnetite. The iron present in laterites can, therefore, be readily concentrated using magnetic separation. Furthermore, any ilmenite present in laterites is not affected by this heat treatment.