Pyrite and Cu-concentrate were roasted in vertically suspended state in an externally heated tube. Tubes of three different lengths of reaction zone were used for three different reaction times. Roasted ores were submitted to chemical analysis and the extent of roasting reactions was determined. In case of pyrite, extent of roasting reactions was not affected much by reactor length and heating temperature (above 500C), but was considerably by ore/air ratio. Micro- scopic and XMA examinations led to the conclus- ion that pyrite particles decomposed to pyrrho- tite and then pyrrhotite was oxidized to give Fe-S-0 melt, magnetite and hematite. The extent of reaction was not uniform in all particles but had a wide distribution from unreacted pyrite to completely oxidized particles._x000D_
Combustion of Cu-concentrate from Kuroko complex sulfide ore ) was unstable under a uniform wall temperature of 450C, but proceed- ed rapidly at temperatures above 500C._x000D_
Sticking of roasted ores to the wall of the reaction tube induced choking of the tube, caused by melting of roasted ores, at tempera- tures above 950C. Enrichment of oxygen exterted less influence on reaction rate than heating temperature of the tube. Particle size of ore had a big effect on reaction rate.