UNION PROCESS INC. : QL-100 Circulation Attritors are high-production grinding mills with high pumping rates, resulting in a faster grind and a narrower particle size distribution. The circulation system typically includes a separate holding or premix tank that can be 10 times larger than the size of the mill. The entire contents of the holding tank will pass through the grinding chamber approximately eight times an hour. E-maileli@unionprocess.com.UNION PROCESS INC.