If the particles of grinding products are too coarse, the dissociation is not sufficient, the selected high quality mineral grade and recovery are too low. If the particles are too fine, the dissociation is enough, but it will generate more minuteness particles, that is over crushing. Over crushing is not only harmful for the separation process, lowers the high quality mineral grade and recovery, but also increases the consumption in crushing process and separation process caused by the unnecessary crushing, so as to enhance the mineral separation costs. Therefore, the suitable grinding fineness is the necessary factor to realize the separation of useful minerals and gangue minerals. The workers should pay attention to the crushing process and the machinery selection, strictly conduct the operation, controlling the grinding fineness in the specified optimal scope.