The effect of experimental variables on the mechanism of the oxidation of pyrite: Part 1. Oxidation of particles less than 45 μm in size

Abstract

The oxidation of pyrite of particle size less than 45 μm has been studied by simultaneous thermogravimetry- differential thermal analysis (TG- DTA) at a heating rate of 2.5 ° C min −1 in an air atmosphere. Sample masses of approximately 1.8 mg were contained in platinum crucibles. Partially oxidised samples were isolated and the phase composition determined by quantitative X-ray diffraction (XRD). Micrographs of these samples were obtained by scanning electron microscopy (SEM). Four effects were observed in the DTA record. At temperatures of 395–420 ° C there were several sharp exotherms. XRD analysis showed the presence of 90% pyrite and 6% hematite in samples heated to 428° C. Beyond this there was a broad exotherm, with a shoulder on the high temperature side, in the temperature range 420–490 ° C. By 470 ° C, 47% hematite was detected with 36% pyrite remaining. By 505 ° C 65% hematite was present with 10% pyrite unreacted. Beyond this temperature there was a weak endotherm which was complete by 610 °C. Only hematite was detected in a sample heated to 696 ° C. The corresponding TG curves showed two major weight losses, the first in the temperature range 440–480 ° C and the second between 550–605 ° C. The SEM results indicated that reacted particles had little general porosity. Increasing the heating rate progressively from 2.5 to 40 °C min −1 caused a significant change in the TG-DTA curve, with a decrease in the intensity of the major exothermic peak, and the appearance of a new peak between 530–550 ° C. The second weight loss decreased relative to the first weight loss. Changing the atmosphere from air to oxygen and heating at 40 °C min −1 produced a further significant change in the TG-DTA record. Only one intense exotherm and one rapid weight loss were observed between 475–500 ° C. The particles, when examined by SEM, had a very high porosity. The differences in appearance of the TG-DTA records have been attributed to changes in the reaction mechanism which occur as a result of variation in the experimental conditions.