An iron ore usually consists of hematite and other impurities like Alumina silicates. LOI for iron ores essentially corresponds to the combined water content from goethite / limonite and impurities such as Kaolinite etc, and to the CO2 content of carbonate phases. A study has been taken to find out the loss at different stages on heating from room temperature to 950oC in an inert atmosphere .The relationship between different losses at different temperature gave an idea about the presence of limonite, goethite, Kaolinite and Calcite also. So a broad idea about the basic nature of the ore was found out which is extremely useful for ore verification.
Three different iron ore sample with difference in iron percentage content were analyzed with help of TGA. An FTIR study was also taken to find out the presence of Fe-O-H bond. The main reactions occurring during heating of iron ores are:
• 100-150oC: Free water (moisture) removal
• 250-400oC: Release of combined water from hydroxyl iron minerals
• 400-600oC: Release of combined water from hydrated silico-aluminates
• 600-850oC: Loss of CO2 due to decomposition of calcite, magnesite, siderite
Besides these under oxidizing atmosphere, parasitic reactions can also occur (e.g. magnetite oxidizes to hematite).
A) Chemical Analysis of the Samples:
B) TGA & FTIR Analysis:
From TGA, presence of the iron Ore in difference phases specially limonite and goethite were studied and it was found that with decreasing concentration of iron in iron ore, concentration of goethite and limonite increases which is also evidenced from FTIR spectrum as shown below:
C) Comparison between TGA loss and wet analysis results:
Decomposition of goethite and limonite takes place at the same temperature zone. Scan accurate estimation of goethite and limonite are not possible. Limonite usually forms from the hydration of hematite and magnetite and all this study requires further confirmation by determination of C & H from CHN analyzer.