Particles finer than 10 um often cause problems in flotation. The current under- standing of the nature of the following effects is discussed: slime coatings on particles, carrier flotation, increased froth stability, entrainment of ultrafine gangue, excess reagent consumption, slower rate of flotation, more reactive surfaces._x000D_
The review emphasizes the principles underlying these effects rather than details of progress in practical solutions to the problems they cause. The princi- ples of selective flocculation and floc flotation and the various approaches to achieving selectivity are discussed._x000D_
Hydrodynamic effects on floc growth are reviewed. The evidence suggests that satisfactory performance in the ultrafines fraction will be achieved only by simul- taneously increasing the rate of flotation of the ultrafine valuable mineral and de- creasing the rate of entrainment of ultra- fine gangue.