eRocks

1. Introduction
Rock breakage behaviour has been studied since the 1920s and has been used to quantify the working limits of rock. The energy required for breakage has also been used as a means of quantifying rock comminution characteristics. A great number of different laboratory and in-situ tests have been developed since the 1920s.

The needs of an extractive metallurgist differ from a civil engineer in that they require information related to ease of breakage and any subsequent liberation of any desirable components of a rock matrix.

1.1 Comminution
Comminution processes are linked closely to liberation and involve the size reduction needed to produce a suitable product for further concentration processes. Comminution methods are described by a variety of different terms, essentially dependent upon the size of their products. The major categories in the comminution process are blasting, crushing and grinding.

1.1.1 Cost
The costs involved in comminution are high as the processes are very energy intensive compared to other stages of mineral beneficiation. It has been estimated that the cost of comminution can range from 40% to 70% of the total mineral process operation costs [Walkiewicz et al 1991, Wills 1992] and that, at best, comminution is only 1% efficient with the majority of energy input being lost in the form of heat.

Comminution processes are very physically demanding on equipment and the cost of regular maintenance is high with the need for new mill liners and grinding media. Mill maintenance requires plant down time, which is also a costly factor.

1.1.2 Sliming
Sliming occurs as a result over overgrinding, an effect that leads to the production of untreatable fines which can subsequently be lost to the tailings. The presence of slimes within a process circuit can also have a detrimental effect on additional downstream processes. The removal of fine material from a process adds cost and it is therefore desirable to keep slimes to a minimum.

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