Mineralogy and Geochemistry of A Low Grade Iron Ore Sample from Bellary-Hospet Sector, India and Their Implications on Beneficiation

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 Al 2 O 3 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 Fe 2 O 3 with silica and alumina thus indicating there is no iron silicate phase as well as alumina contribution from iron oxide minerals in the form of solid solution is insignificant. Positive correlation of silica with alumina indicates that the clay is the major contributing mineral for both the silica and alumina phase and presence of gibbsite. The role of gangue minerals and the interrelationship of silica, alumina and iron oxide, with reference to beneficiation are discussed. Jigs and heavy media cyclones for this type of ores can be used but at the cost of poor yield because of complex nature of alumina distribution. As long as alumina and silica mineralization is not too fine and the ore composed of magnetite/hematite with coarse grained quartz, magnetic route is the most effective. 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.