The importance of size reduction processes in the mining mineral processing industry is well understood. Direct costs for energy and grinding media constitute approximately ten percent of the cost of producing finished metals. And the indirect cost of mineral losses due to inadequacies in valuable mineral liberation and suitable sizing for downstream processes can be much greater. Needless to say, a basic measurement of plant grinding efficiency is a necessary tool to run these businesses effectively.

In February of this year, The Global Mining and Standards Group published “The Bond Guideline for Industrial Grinding Circuit Efficiency”. The Bond Sub-Committee, part of the Industrial Comminution Efficiency (ICE) committee, consisted of industry specialists, leading equipment manufacturers, and testing laboratory and plant operating company representatives from around the globe. The proposed Bond Guideline was drafted, reviewed and debated, revised and ultimately finalized and approved by unanimous vote of the ICE group. It can now be found on the GMSG website.

Although widely known as a tool for sizing and selection of crushing and grinding equipment, use of the Bond Work Index Equation as a tool to measure grinding efficiency is less widely known and used. Bond specified the specific energy (W, in kWh/t) that should be needed, that is for circuit design, based on average plant performance of his day, from the test Work Index as:

W = WlTest x ( 10 / SQRT P80 - 10 / SQRT F80)

The plant circuit Operating Work Index can be calculated from operating plant data.

WIo = W / (10 / SQRT P80 - 10 / SQRT F80)

Then by comparing the ratio of the Bond Laboratory Test Work Index to the Operating Work Index, we are measuring the relative efficiency of the particular circuit.

Bond WI Efficiency Ration = Bond Test WI / Circuit Operating WI

Details on the Bond Test laboratory methods, needed plant measurements, and the method of Work Index Ratio Efficiency calculation are provided in the guideline. Still to come are the establishment of standard materials and reference test laboratories, and, beyond Bond’s, an expanded industrial plant data base.

Rob McIvor is a CEEC Advocate, and Chief Metallurgist – Grinding Systems, Metcom Technologies, Inc.