Mechanical Operations
Rittinger's crushing law states that

For a given machine and feed, crushing efficiency is dependent on the size of the feed & product
Work required to form a particle of any size is proportional to the square of the surface to volume ratio of the product
Work required to form a particle of a particular size is proportional to the square root of the surface to volume ratio of the product
Work required in crushing is proportional to the new surface created

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Mechanical Operations
Work index is defined as the

Gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen
Energy needed to crush one tonne of feed to 200 microns
Energy needed to crush one ton of feed to 100 microns
Energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product passes a 200 mesh screen

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