The Bond work index – so crucial to comminution planning

Fred Bond is being inducted into the International Mining Technology Hall of Fame in the comminution category for 2015. The word Bond is synonymous with grinding circuit design, e.g. Bond Grindability and Bond Work Index.  Fred Bond’s work on circuit design occurred from the late 1930s to the mid 1960s and it changed the method of design completely. In the pre-Bond era the prediction of the power required per tonne to grind material to a known product size was based on experience and judgment, in the post Bond era the method of prediction had become engineering practice which was based on measurement and calculation. Bond’s work defined the relationship between ore hardness, tonnage processed, size reduction achieved and power required. It set the standard for circuit design in the 1950s and it is widely used today, although modifications have been made to handle the large increases which have occurred in mill sizes, feed sizes and feed rates.

Bond worked for Allis Chalmers from 1930 and he knew the limitations of design techniques which were current at the time. During the late 1930s and the 1940s he studied the relationship between energy and size reduction and in 1952 he proposed a “Third” theory of comminution to define this relationship. Rittinger and Kick had proposed the first two. To apply it he defined “Work Index” (W_i) for an ore as the specific energy (kWh/tonne) required to reduce the ore from infinite grain size to 100 µm and he showed that for any ore the Work Index can be calculated from plant data and determined in a laboratory test.

The Bond Work Index approach is the standard method of selecting ball mills to grind from about 3 mm to 25 µm provided that correction factors are used if necessary. The power prediction is fairly accurate for devices that produce a product with a size distribution parallel to that of the feed. It does not work well for devices such as the AG/SAG mill and high pressure grinding rolls where the product size distribution is not parallel to that of the feed.

Don’t forget to put your nominations in (to for the 2016 inductions. There are 12 categories:

  1. Exploration
  2. Underground development
  3. Underground Production
  4. Surface mining
  5. Comminution
  6. Concentration
  7. Mining software
  8. Safety
  9. Bulk handling
  10. Metallurgy
  11. Environmental management and stewardship
  12. Outstanding innovator


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