Understanding of the Bond Equation & the terms “work index”

Bassarear and Horts, in their paper on evaluating plant performance , illustrate how work index data can be used to evaluate process performance and modifications. The particularly discussed the semi-autogenous-ball mill grinding circuits at. Cyprus Pima and the use of computer base controls. The simplified grindability test procedure employed for the Pima ore types was developed to give work index as defined by Bond and includes periodic checking with standard Bond Grindability test. Test such as this can be used for specific ores where there is not a wide variation in specific gravity and in breakage patterns.

Relative to its use in computer programs for controlling a grinding circuit or reporting grinding circuit performance, a correct understanding of the Bond Equation and the terms “work index” is required. The Bond Equation measures work done or-to be done. Work index as defined is power. Since there is no factor in the equation that takes into account the classification function, the Bond Equation is not a math model for a closed grinding circuit. 

Being a measure of grindability, work index can be used in math models when a grindability function is called for.

Work indices calculated from operating data, either manually or by computer, with or without comparison to work indices obtained from grindability test, can be used however, do not indicate the cause for the inefficient use of grinding power, nor do they indicate the acceptability of the product produced by the grinding circuit. Supervisory, technical and operating personnel studying the operating data and checking the operation of the plant can determine the cause for any inefficient use of power and the acceptability of the product produced.