Mineralogical Constraints on Beneficiation of Low-grade Iron Ores: Case Studies from Jharkhand and Goa

Abstract

Due to increasing demand of iron ores in India, much emphasis is given on beneficiating low-grade iron ores with a cut-off of +52% Fe instead of the traditional cut-off grade of +58% Fe. In such an attempt we have characterized bulk low-grade iron ores from two different sectors namely, Gua area in the state of Jharkhand and iron ore mines from southern Goa. An integrated instrumental method of characterization using optical microscope (OM), scanning electron microscope (SEM, +EDAX), and X-ray diffraction (XRD) reveal that while the Goan low-grade ores are mineralogically simple consisting primarily of martite and quartz, the ores from Jharkhand are complex consisting of hematite, goethite, clay, quartz, and gibbsite. The tenor/grade of the Goan ore is much less (~43% Fe) compared to the ore of Jharkhand which contains ~54% Fe. Alumina (Al2O3) which is the main problem in the low-grade ores of Jarkhand or generally in Eastern India is found to occur associated with clay, gibbsite and as adsorption in goethite. Textural evidences indicate that while it may be possible to remove these gangue phases from the inter-granular pore spaces it will be quite difficult to liberate the intra-granular impurities that are bound within hematite and goethite in micron levels. On the contrary, these problems do not occur in the studied Goan ores where the iron-bearing phases are not chemically contaminated and are liberated well by comminution. These mineralogical studies indicate that though the Goan ores are low in Fe content, these can be beneficiated to get a higher grade (+63% Fe) with a high recovery while it will be difficult to improve the Jharkhand ores to similar grade with higher yield.