Fluidized Bed Roasting of Zinc Sulfide Concentrate: Role of Particle Size

Industrial roasting of zinc sulfides into its oxide/calcines is customarily practiced in fluidized bed reactor. High extent of conversion is desired to facilitate acid-leaching of the zinc calcine. Industrially, degree of such roasting is quantified in terms of the sulfide-sulfur index describing extent of sulfides being unreacted. This is governed by multiple roasting process parameters (viz., concentrate feed rate, air flow, moisture etc.) and essentially particle residence time of the feed concentrate inside roaster. In the present study, an attempt has been made to estimate the roasting process from analysis of calcines obtained from different sites of roaster, especially with regards to the role of particle size. Towards this, industrial sample characterization, minerology and plant data monitoring has been done. Results of such, indicated the calcine size ranges where extent of roasting is minimal. Furthermore, possibilities of precious metal recoveries from calcines after being withdrawn from specific roaster locations has also been outlined that effectively lacked in past investigations. Finally, owing to the complexity of such high temperature process, need for improving process monitoring techniques for superior process stabilization has also been recommended.