Abstract
The gradual depletion of high-grade iron ores has necessitated the exploitation of low/off grade iron ore reserves of India. The role of geochemical and mineralogical characterization is paramount to arrive at the process flow sheet development for such complex ores. Detailed studies were conducted on iron ores of Bellary-Hospet sector using microscope, XRD, TG, and EPMA techniques. The results indicate that hematite is the major iron oxide mineral with minor amounts of goethite, magnetite, martite and limonite with quartz and clay as major gangue. There is no evidence of the presence of any iron silicate and iron carbonate minerals. Trace amounts of pyrite were observed under the microscope and is the only iron sulphide phase. Microscopic studies also indicated that most of the quartz grains are present as inclusions within the hematite and magnetite grains. XRD studies revealed hematite as the major mineral with subordinate amounts of goethite, quartz and kaolinite confirming to the microscopic findings. Qualitative mapping and quantitative EPMA studies on these ores indicated the presence of gibbsite as the only alumina bearing phase and apatite as phosphorous bearing mineral. Traces of alumina, present as solid solution in the iron oxide minerals, has also contributed Al2O3 to the ores. Electron microscopic studies revealed that gibbsite grains are in the size range of 10 to 50 microns and are intimately and intricately associated with the iron oxide phases. Major elemental analyses of 47 representative iron ore samples of various types were analyzed to deduce the source of silica and alumina’s contributing phases in the ore and their interrelationships. The geochemistry data revealed negative correlation of Fe2O3 with silica and alumina thus indicating there is no iron silicate phase as well as alumina contribution from iron
Highlights
India is having vast reserves of iron ore, lack of consistency with respect to Al2O3/SiO2 ratio makes these ores unsuitable to use directly in the metallurgical industries without prior beneficiation
Since the quartz grains are too fine and their distribution is very complex for the Bellary-Hospet sector ores, flotation in general and column flotation in particular seems to be more effective
Mineralogical studies by microscope indicated that hematite is the major iron oxide mineral with minor amounts of goethite, magnetite, martite and limonite with quartz and clay as major gangue
Summary
India is having vast reserves of iron ore, lack of consistency with respect to Al2O3/SiO2 ratio makes these ores unsuitable to use directly in the metallurgical industries without prior beneficiation. The Indian iron ores, in general, contain adverse alumina content and require beneficiation to reduce the same in the ore for feeding to the blast furnace. Simple techniques like crushing, scrubbing and washing of iron ores are being adopted to reduce alumina but these techniques have their own inherent limitations and they are not effective to reduce alumina below particular limits This process limitation along with the demand by the steel plants for low alumina iron ores encouraged researchers to characterize the ores in general and different modes of associations of alumina in particular. Soft ore (worst as compared to other types since they contain high alumina and low iron) shows varying characteristics and is lumpy in nature These physical characteristics had great impact on the grinding and further processing as they contain varying amounts of silica and alumina, which is considered to be harmful in the blast furnace. Study of the hand picked iron ore samples indicated that the ores can be grouped into three ore types
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