The enhancement of ilmenite magnetic susceptibility by roasting is well known, and it is used routinely in the magnetic separation of mineral sands, yet surprisingly little appears to be known in detail about the development of this magnetisation as roast temperatures increase. An examination of the changes in both magnetic susceptibility and magnetic rotatability within the roast temperature range 350–650°C reveals some interesting low-temperature magnetisation changes. The results suggest the presence at low roast temperatures of very small magnetised regions that behave as though they are superparamagnetic, and suggest that the growth of these regions plays a significant part in the development of roast-induced magnetisation. The results also show that the bulk magnetic development above 500°C is a resultant of several temperature-dependent competing processes.
