Infrared Thermography for Iron Ore Grading

Abstract

Day by day there is a scarcity of high-grade iron ores in the world and India is no exception to it along with additional problem of high alumina content. The lower grade ores are being crushed and beneficiated mainly by gravity techniques using water. However, the scarcity of water in the mining areas slowly warrants development of some dry gradation techniques for iron ores so that the inferior ore pieces can be rejected in order to improve the grade of the concentrate. The present gradation of ores by mineral/chemical method is time consuming and cumbersome. We discuss here an Infrared (IR) thermography based non-invasive technique for faster gradation of iron ores, taking into account the variation in thermal absorptivity of the ore constituents. Iron ores from three different mines, with Fe contents ranging from 59 to 67 wt% were selected and crushed to around 10 mm particle size. The crushed iron ores are uniformly heated using a microwave oven, for a time period sufficient to create a difference in infrared emission between the ore particles. The thermal images of the heated ores are captured by IR thermography and the peak temperature of each ore specimen is obtained from the thermal profile. A program is developed for ore gradation based on peak temperature of each ore which corresponds to its iron content. A threshold was selected through chemical verification of ores and accordingly the ores are categorized as high, medium and low grade.