Crushing Circuits and Staging for Rock and Minerals

It requires more energy to keep breaking rocks down to a smaller size. Processing plants may use different strategies to achieve comminution largely depending on the ore types. The most common strategies include use of single-stage crushing followed by autogenous (AG) or semi- autogenous grinding mills (SAG), and multiple-stage crushing followed by ball mills and/or rod mills.

The first type (AG or SAG) is used for ores of medium to low competency (or hardness) where only low levels of impact energy are required to cause the rocks to fracture, and part of the feed includes some reasonably competent material, which can act as autogenous grinding media. In these types of circuits, the grinding area is generally where nearly all the power is consumed, as this is where the majority of the comminution process is taking place. Feed to SAG or AG mills is usually from a primary crushed product normally either a jaw or gyratory crusher. The performance of AG or SAG circuits can be enhanced with pebble crushing (to fracture the harder rocks building up within the mill), and/or the addition of a secondary crusher to reduce the feed size to the mill.

The second strategy (employing multiple-staged crushing) is more suited for competent ores which demonstrate a resistance to SAG milling, or ores where there is no competent material at all to act as autogenous grinding media.