Conversions between test types

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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 (WiRM)
  • 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.
ExampleDB-WiRMvAxb-comparison.png
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.
Published A×b and WiRM results for Andean porphyries
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.
ExampleDB-Aussie WiRMvAxb-comparison.png
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 the range of 2.50 to 2.80 t/m3

Only considers SGI values less than 250 as greater values are meaningless.
ExampleDB-WiRMvSGI-comparison.png

Extra parameters for Drop Weight Tests (DWT)

A drop weight test is usually interpreted using a plot of the %passing 10% of the original particle size (t10) versus the energy of the weight that impacted the specimen (Ecs). These are plotted at fit to an exponential relationship with fitting parameters "A" (coefficient) and "b" (exponent).

There are several derived parameters that are commonly used in modelling that can be calculated using these A and b values, usually based on the slope of the curve at the origin of the plot. This is commonly referred to as the (A×b) value.

  • DWI = (density, kg/L) × 96.70 × (A×b)-0.992
  • Mia = 392.18 × (A×b)-0.814
  • Mih = 580.6 × (A×b)-1.000
  • Mic = 305.78 × (A×b)-1.005
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