Two-wavelength pyrometry study of the combustion of sulfide minerals: Part III. The influence of oxygen concentration on pyrite combustion

Abstract

The strong influence of oxygen concentration on the combustion of pyrite at a furnace temperature of 1130 K has been investigated by pyrometer measurements of the temperature of individual particles and by morphological examination of the reaction products. Three distinct types of behavior were identified depending on the oxygen concentration. With oxygen levels between 10 and 40 pct, the maximum temperature of the pyrite particles increased linearly from about 2000 to over 3000 K while heating rates also climbed. The characteristics of the combustion pulses from the pyrometer revealed that cenosphere inflation occurred at the maximum particle temperature and that the freezing of a magnetite shell is subsequent to, not associated with, sudden expansion of the particles. For oxygen concentrations between 40 and 80 pct, the maximum particle temperature was independent of oxygen concentration, remaining constant at 3000 to 3400 K; however, heating rates were some-what variable. The combustion pulse characteristics again suggested that particles inflate into cenospheres but there was an increased tendency for them to rupture. At oxygen concentrations of 80 pct and greater, higher heating rates were measured but the maximum particle temperatures were limited to 3200 to 3500 K. The combustion pulse characteristics in oxygen suggested that the termination of reactions is consistent with material ejection or particle disintegration as opposed to cenosphere inflation. The results generally were consistent with the reaction rate being governed by oxygen transport in the gas phase, although at higher oxygen concentrations evaporation of the iron species and other physical phenomena limited the particle temperature.