ABSTRACT: In this study, a new grinding tool, named “Attritor”, Model 1S, was used to grind and disintegrate an Egyptian kaolin ore. The “Attritor” unit is often referred to generically as a “stirred ball mill”, where the ore and grinding media were agitated by a shaft with arms, rotating at high speed in 8 liter bowel capacity. This causes the media to exert both shearing and impact forces on the ore. Major parameters influencing the grinding process, including shear rate (rotation speed) and time, pulp solid concentration, particle size and particle size distribution of the feeding material were optimized. Results showed an extraordinary fineness, reaching 2.85um and 10um for D50 and D90, respectively. The optimum working conditions of the mill was 30 min milling time, 458rpm rotor speed, and 73% solid (6% ore, and 67% grinding balls by wt.). Keywords: Kaolin ore-Attritor- fine grinding-shear, impact forces-stirred ball milling 1. INTRODUCTION Most of the mills used in the fine grinding of mineral ores are stirred media mills, rather than conventional tumbling ball mills [1]. Although many studies [2-12, 13, 14-19] on the slurry rheology in tumbling ball mills have been published, there is still little understanding on the slurry rheology relevant to ultrafine grinding at high slurry densities [20, 21]. This is because the breakage mechanism of ultrafine comminution in stirred media mills is rather different from that of tumbling ball mills. In the case of tumbling ball milling, the size reduction is mainly dependent on the cataracting and cascading motions of charge balls, leading to striking charge particles nipped against other balls, and rubbing charge particles between balls in the bed on the bottom of cylinder [16, 22]. The impact stress from cataracting and cascading is far larger than shear stress from rubbing [16]. However, the fragment in stirred media mills for ultrafine grinding is mainly subject to shear stress [1]. The predominant comminution mechanisms are dependent on shear, compression and torsion stresses, which are invoked by stirring the particles–grinding media mixture at a very high velocity [23-26]. The effective motion of the mixture is much related to the flow field in the grinding chamber. Therefore, the effect of the slurry flowabilities or slurry rheology in wet ultrafine comminution in stirred media mills becomes of particular importance. It is important to mention that fine particles are particles that have an aerodynamic diameter of 2.5 μm or less (PM2.5), where the fine particles which are smaller than 0.1 μm are referred to as ultrafine particles (PM0.1). In addition, in the case of the requirements of product fineness, cylinder ball mills are suitable for coarse comminution and can efficiently achieve the aim that X80 (the particle size at which 80 wt. % particles pass) is not larger than 75 um [27]; however, the objective of ultrafine grinding in stirred media mills is at least the median size (X50) less than 2 um [28] or 90 wt. % particles below 10 um [1, 20]. Since the product fineness significantly increases with grinding time in wet ultrafine grinding characterized by a very fine product size and a high slurry concentration, the surface properties tend to predominate in the system [29]. This results in changes in the rheological properties in wet ultrafine grinding operations due to the agglomeration and aggregation resulting from the inter-particle forces, such as van der Waals forces [30] and electrostatic forces. In the case of Newtonian fluids, η is constant. For non-Newtonian fluids, η is variable, which means that the shear stress (s) varies with the rate of shear strain (c). As known, most semisolids, such as mineral slurries, which are either found in nature or synthesized in laboratory, exhibit non-Newtonian fluids [30]. The information for characterization of the rheology of non-Newtonian mineral slurries is outlined in Figure 1. It is worthy to mention that “Thixotropy” is concerning materials that are gel-like at rest, but fluid when agitated. They are having high static shear strength at the same time and not lose viscosity under stress. Dilatancy: The property of dilating or expanding, especially by means of an increase in space between the component parts; the phenomenon of some substances whose viscosity increases with shear rate, or with pressure. A pseudoplastic material displays high viscosity at low shear, low viscosity at high shear, and recovers viscosity immediately upon the release of shear [30]. FINE DISINTEGRATION OF EGYPTIAN KAOLIN S. Ibrahim 1 , Ali Q. Selim 2 , and Mohamed K. Abd-El Rahman 1 1 Central Metallurgical Research of Development Institute, P.O. Box :87, Helwan, Cairo, Egypt 2 Geology Department, Faculty of Science, Beni Suif University, Egypt