Introduction

Crushing is the first mechanical stage in the process of comminution in which the main objective is the liberation of the valuable minerals from the gangue.

It is generally a dry operation and is usually performed in two or three stages. Lumps of run-of-mine ore can be as large as 1.5 m across and these are reduced in the primary crushing stage to 10 20 cm in heavy-duty machines.

In most operations, the primary crushing schedule is the same as the mining schedule. When primary crushing is performed underground, this operation is normally a responsibility of the mining department; when primary crushing is on the surface, it is customary for the mining department to deliver the ore to the crusher and for the mineral processing department to crush and handle the ore from this point through the successive oreprocessing unit operations. Primary crushers are commonly designed to operate 75% of the available time, mainly because of interruptions caused by insufficient crusher feed and by mechanical delays in the crusher (Lewis et al., 1976).

Secondary crushing includes all operations for reclaiming the primary crusher product from ore storage to the disposal of the final crusher product, which is usually between 0.5 and 2 cm in diameter. The primary crusher product from most metalliferous ores can be crushed and screened satisfactorily, and the secondary plant generally consists of one or two size-reduction stages with appropriate crushers and screens. If, however, the ore tends to be slippery and tough, the tertiary crushing stage...