Conversions between test types

Converting between comminution test types

Different tests are used in different grindability models for substantially the same purposes. Certain grindability tests are compatible with other tests, and an approximate conversion can be established by comparing to a database of testwork.

The determination of which tests are compatible with other tests is largely a function of the particle size of the specimens subjected to testing.^{Doll & Barratt, 2011} Ore properties also play a role because some tests are sensitive to changes in ore density and other tests operate with a biased sample consisting only of competent pieces.

Medium size class

The three tests in the medium size class are:

• Bond rod mill work index (Wi_RM)
• SAG Grindability index (SGI) or SAG Power index (SPI™)
• Drop weight test, both JK and SMC (A×b, DWI, Mia, etc)

Bond rod mill work index versus A×b Only considering rod mill work index tests performed in laboratory mills equipped with wave liners. This is the standard specified by F. Bond and is typical of laboratories in North and South America. Only considers A×b values less than 250 as values greater than that are meaningless.
Bond rod mill Wi versus A×b for copper porphyries A slightly better relationship can be determined if the database is limited to projects of a similar lithology. Limiting to only the Andean copper porphyry projects results in a slightly better correlation.
Non-bond rod mill work index versus A×b Only considering rod mill work index tests performed in laboratory mills equipped with smooth liners gives a different relationship. These work index mills are typical of laboratories in Australia and are not consistent with the specification of F. Bond.
Bond rod mill work index versus SGI & SPI Only considering rod mill work index tests performed in laboratory mills equipped with wave liners. SGI does not contain a density correction, and this relationship is probably only valid for ore density in thr range of 2.50 to 2.80 t/m3 Only considers SGI values less than 250 as values greater than that are meaningless.