Oxidation mechanism of pyrite concentrates (PCs) under typical circulating fluidized bed (CFB) roasting conditions and design principles of PCs’ CFB roaster

The circulating fluidized bed (CFB) roasting process is a promising way to utilize pyrite concentrates (PCs) which are byproducts in nonferrous metal production processes. The oxidation mechanism of PCs was investigated under typical CFB roasting conditions with the temperature of 850 °C and oxygen concentration of 1–21% on a drop tube furnace. The oxidation reaction pathway and products of PCs are strongly coupled with particle morphology evolution, which affects the oxygen diffusion from the particle surface to the core. A reaction path model of PC oxidation coupled with particle morphology evolution under CFB roasting conditions was proposed. The initial relatively slow oxidation of the porous particle structure followed by the relatively fast oxidation for complete oxidation was demonstrated to be the ideal reaction path for the CFB roasting operation of PCs. The critical issue for PCs roasting in the CFB reactor is to inhibit the particle temperature rise in the dense phase region to avoid the formation of compact solid spheres. The flow and reaction behaviors of PC particles in CFB reactor naturally follow the ideal reaction path and make the CFB roasting technology feasible. Finally, the design principles of PCs CFB roasting process were suggested.