Concentration of iron in laterites using in-situ carbonized biomass
Njoroge, Peter Waithaka
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Iron occurs in more than 85 minerals. However, among these, only a few are important ores of the element. For economical extraction of iron, the iron ore must contain over 55% iron. These ores must be concentrated before putting them in a blast furnace. Kenya has widespread documented huge volumes of laterites. However the country spends huge amounts of money in importation of iron and iron products despite having these laterites that are rich in iron. This thesis describes the results of a study undertaken with the aim of finding out whether the level of iron in laterites (murram), can be increased to a level above 55% which can placed in a blast furnace for iron extraction. Samples for this study were obtained from selected murram quarries in, Kamahuha and Juja located in Murang‟a and Kiambu Counties respectively, in the Republic of Kenya. Total elemental analysis was carried out with particular interest on the levels of iron in both the raw and treated samples using Atomic Absorption Spectroscopy (AAS), X-Ray Flourescence Spectroscopy (XFRS) and EthylenediaminetetraaceticAcid (EDTA) Titrations. The mineralogical composition of both the raw and treated materials was determined using a Brucker D2 PhaserDiffractometer. The results of this study show that levels of iron in the raw laterites from Kamahuha ranged between 24-39% while those form Juja ranged between 12-17%. The iron in the raw laterites is present predominantly as the minerals goethite, FeO.OH and haematite, Fe2O3, as shown by presence of peaks at diffraction angles of 2θ = 21.51˚ and 2θ = 54.11˚respectively, which are attributed to these minerals. The concentration of iron in the laterites was done by heating a laterite/charcoal mixture in the temperature range 500-700oC in a ceramic container, under a slow current of air (0.5-0.7cm3/sec) from a compressed air cylinder. On cooling this mixture, the iron-containing mineral was readily picked with a permanent horse-shoe magnet (about 92milliteslas). The experiment was repeated using carbonized saw dust, leaves and dried potato peelings obtained from solid municipal waste in place of charcoal. The optimum ratio of biomass: laterite was found to be 1:20 by mass. After magnetic-separation iron was present predominantly as the mineral, magnetite Fe3O4, and had a broad diffraction peak at 2θ = 36˚.Furthermore, the percentage of iron in the magnet-separated product from both Kamahuha and Juja had increased to 55-62%. These results show that iron in the laterites can be increased to a level that can be used for iron extraction. Biomass from solid municipal waste can be used as a source of carbon monoxide to reduce goethite and hematite to magnetite. The use of biomass from the solid municipal waste also impacts positively on the environment. From the results obtained this process should be scaled up by setting up a pilot plant to concentrate iron laterites and determine the economic viability of the process.
- PHD-Chemistry