Introduction:
A constant level of oxidation in magnetite ores is also of importance for process stability. A distinct concentric oxidation front between the oxidized outer shell and the non-oxidized core is found in magnetite ores oxidized at temperatures above 1000° C. The time needed for 80% oxidation of magnetite ores at 900°C was 8 minutes with 21% O2 in the oxidizing gas. Thermo gravimetric study was to find out the oxidation of magnetite starting from room temperature to 1000° C because the instrument is not capable of having temperature above 1000°C .The oxidation studies were started at 250° C because at this temperature the oxidation rate is not influenced by sintering. The rate of oxidation of magnetite is influenced by sinter formation surrounding the magnetite ore. This sinter is Fe2O3 and it decreases further oxidation so the rate is not as fast as it is found at temperature above 700° C where the rate is fast and the slope is steep as in found in the curve. The oxidation would be complete at 1100° C to 1200° C at the same rate.
Experimental:
1. Instrument used: Perkin Elmer STA 6000.
2. Heating Rate: 10° C increase/ min.
3. Temperature Range: 35° C to 1000°C.
4. Sample Pan: Ceramic crucible used without lid.
5. Purge Gas: Oxygen.
CURVE FOR SARM 12 (CRM OF MAGNETITE)
Fig1 shows the DSC-TGA profile for the Oxidation of Standard Magnetite when heated at the rate of 10° C/min. The weight% curve indicates weight loss and gain at different temperature. The weight losses and gains are seemed to be as follows:
35° C- 250° C: Weight loss due to moisture.
250° C-625° C: weight gain due to oxidation of Fe3O4 to Fe2O3 at slower rate.
625° C-711° C: Weight loss due to partial decomposition of Fe2O3 to Fe3O4 as Fe3O4 is stable at higher temperature.
711° C-1000° C: Steep rise due to Oxidation of Fe3O4 to Fe2O3.
Composition study from increase in weight up to 1000⁰C shows that Fe3O4 is 66% but it contain 83% Fe3O4 as the temperature attainable 1000° C not 1100° C.
Chemical Reaction:
4FeO. Fe2O3 + O2 = 6 Fe2O3 ∆H = -119 KJ/mole.
Chemical Composition of SARM 12:
obtained by classical method.
CURVE FOR UNKNOWN MAGNETITE SAMPLE-1
Fig2 shows the DSC-TGA profile for the Oxidation of unknown Magnetite sample when heated at the rate of 10° C/min. The weight% curve indicates weight loss and gain at different temperature. The weight losses and gains are seemed to be as follows:
35° C- 250° C: Weight loss due to moisture.
250° C-600° C: weight gain due to oxidation of Fe3O4 to Fe2O3 at slower rate.
600° C-690° C: Weight loss due to partial decomposition of Fe2O3 to Fe3O4 as Fe3O4 is stable at higher temperature.
690° C-995° C: Steep rise due to Oxidation of Fe3O4 to Fe2O3.
CURVE FOR UNKNOWN MAGNETITE SAMPLE-2
CURVE FOR UNKNOWN MAGNETITE SAMPLE-3
Chemical Composition of three unknown magnetite sample:
obtained by classical method.
From the thermo grams it is found that the first one is probably magnetite ore having symmetry with the standard but second and third samples are not probably magnetite ore but contain other iron ore as goethite and spathic iron ore.
Conclusion:
The study of the thermogravimetric analysis provides an idea whether the ore is magnetite or not, although the FeO contain more or less same for samples. So the study is useful for grading an iron ore as per magnetite but not the basis of FeO content.