Changes in surface properties of minerals with grinding and regrinding play a key role in mineral flotation performance, being recognised in industry through the development of the IsaMill and Stirred Mill Detritor. This paper describes some initial results in a larger study which attempts to quantify changes in the flotation properties of sulphide minerals with regrinding using different mills. Pyrrhotite has been chosen in the current study due its importance in the recovery of Platinum Group Minerals and in its separation from pentlandite in Sudbury basin nickel ores. This current paper focuses on the results obtained using a Magotteaux Mill® only.

Factors which affected pyrrhotite flotation were particle size, grinding media contamination, and exposure of new mineral surface. Pyrrhotite recovery decreased with size reduction from 90%, achieved before regrinding, to 77%, 64%, 30% and 7% after regrinding with stainless steel medium to d80 values of 60, 40, 20 and 10 μm, respectively. Contact angle measurements, using the Washburn Technique, were applied to quantify surface hydrophobicity as a function of particle size and the BET method was used to obtain the surface area. Increased collector addition only partially restored pyrrhotite recovery. The surface of the pyrrhotite mineral was changed by regrinding in a way that hindered collector adsorption onto the new mineral surface. A further dramatic depression of pyrrhotite recovery when using mild steel regrinding medium demonstrated that there was an additional contribution to pyrrhotite depression from media contamination in this case.