INVESTIGATION OF THE GRIND LIMIT IN STIRRED-MEDIA MILLING

While it has often been suggested that there are limits to the extent to which particle size can be reduced by comminution, experimental evi dence for the existence of such ''grind limits'' is scarce and general ly inconclusive. An experimental study of long-lime grinding of crysta lline quartz in a stirred-media mill has been carried out with the spe cific aim of identifying the limit of grinding. Product size distribut ions have been characterized using a combination of laser diffraction/ scattering, centrifugal sedimentation, dynamic light scattering and BE T surface area measurement. Qualitative examination of the ground prod ucts by transmission electron microscopy has also been performed. The results of the investigation are consistent with a grind limit in the region of 40 to 50 nm for this system. In terms of breakage parameters , it appears that there is a decrease in breakage rates at sizes small er than about 0.5 mu m and that primary breakage distributions become progressively narrower at submicron sizes.