Visualization of CuFeS2 Particle Ignition and Combustion Under Simulated Flash Smelting Conditions

Flash smelting involves complex reactions between copper sulfide ores, silica sand, impurities, and oxygen gas while dropping. In situ observations of particle oxidation (ignition and combustion) under simulated flash smelting conditions can promote an understanding of this phenomenon. However, previous studies were limited by technical difficulties. In this study, in situ observations, two-color temperature measurements, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and thermodynamic equilibrium calculations were used to characterize the oxidation of CuFeS2 particles under simulated flash smelting conditions. CuFeS2 particles changed in four phases in oxidation within 300 ms. The first process was ignition (approximate to 25 ms) with an average temperature of 2100 degrees C. This was triggered by fine particles (several mu m in diameter) on coarse particles (approximately 50 mu m in diameter) and formed sphere particles consisting of two phases (sulfide and oxysulfide, Phase I) or three phases (sulfide, oxysulfide, and iron oxide, Phase II). The second process was combustion (< 300 ms) with an average temperature of 1900-2000 degrees C. In addition to the spherical particles, particles surrounded by a flame consisting of two phases (oxysulfide crust and oxide core, Phase III) were observed during combustion. The flame may be generated by the continuous sulfur vapor emitted from the oxysulfide crust, which vanishes after the consumption of the sulfur vapor. Finally, oxide particles (Phase IV), similar to those in the thermodynamic equilibrium phase, were formed.