A Method of Calculating Autogenous/ Semi-Autogenous Grinding Mill Specific Energies Using a Combination of Bond Work Indices and Julius Kruttschnitt Parameters, then Applying Efficiency Factors

2012 AusIMM Mill Operators conference


Since the days of mandatory high cost pilot plant testing in 6 ft × 2 ft SAG mills autogenous grinding/semi-autogenous grinding (AG/SAG), mill specific energy is now calculated by various empirical formulae and pilot testing carried out in small laboratory mills. Barratt (1989) described a method using Bond Indices than adding a single factor of 1.25 to arrive at the AG/SAG specific energy. In 1991 the Canadians developed the SAG Power Index (SPI), test using 2 kg of material in a 300 mm diameter mill. This test has been further developed by Starkey, Hindstrom and Orser(2006). This test now includes a Bond Ball mill work index test.

The Macpherson test is still being offered by some testing facilities. This dry test requires at least 180 kg of material. Morrell (2004) formulated an AG/SAG specific energy generator based on a drop weight index Value (DWi). This DWi value is related to the Ab parameter and the material specific gravity. Morrell reconfigured the Bond’s Third Theory formula to cause extra power requirements to be inputed. This technique incorporates the material specific gravity (SG). The AG/SAG specific energy values produced using this method are susceptible to higher values of crushing and rod mill work indices.

This paper offered describes a more simple method to generate AG/SAG specific energies. This programme incorporates Bond work indices, the JKMRC parameter Ab measuring impact breakage and the parameter to measuring the abrasion rate, then employs a series of efficiency values nominated for each transition size (AG/SAG T80). These efficiency values have been compiled over the years from actual operating plants and documented reports.

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