Amorphization of Kaolinite and Media Motion in Grinding by a Double Rotating Cylinders Mill. A Comparison with a Tumbling Ball Mill.

Kaolinite powder was ground under atmospheric condition by a co-axial double rotating cylinders mill (UF mill) and a tumbling mill to investigate the amorphization behavior of kaolinite. Motions of media balls in both mills were also numerically simulated by a PEM. The UF mill lead to amorphous state of kaolinite for a shorter time than the tumbling mill. The ball impact energy in the UF mill was about five times larger than that of the tumbling ball mill. Simulated total kinetic energy of media balls required for 80% amorphization of the sample by the OF mill was considerably lower than that using the tumbling mill. NMR analysis on 27Al in the structure of kaolinite revealed that a pentagonal coordination remains in the amorphous state by the UF mill, while it almost disappears in the sample ground by the tumbling mill for a prolonged time.