Milling of particles is important to a large number of industries including the mineral processing, pharmaceutical, fertilizer and energy industries. Often it is desirable to produce particles of a certain size range while minimizing process time and/or energy usage. Production of fines can lead to powder handling problems and inefficient processes. In the pharmaceutical industry, excessive production of fines during milling of the drug crystals can increase risk of dust explosions. In mineral processing, the milling process is extremely energy intensive with large amounts of energy lost to hear or noise. There is a need to better understand milling in order to optimize milling processes and reduce energy usage.

Presented here is the application of the Attainable Region (AR) approach to optimizing the milling process. Previously, the AR approach has been used to optimize complex reactor networks and separation systems. Due to the similarities between reaction networks and the comminution process, the AR lends itself well to determining the optimal control strategy for a milling project. Though the optimization done in this work is for a ball mill and a specific material, the concepts can be applied to any system consisting of breakage and classification.

We have experimentally determined the optimal control strategy for achieving a certain size distribution with the use of the least amount of energy. The control strategy recommends a variation of speed throughout the process - fast speed at first, followed by a slightly slower speed, and then the lowest speed - to achieve the maximum amount of material of a certain size. Benefits of this approach can be realized anywhere milling is found, as a size profile over time can be predicted. Therefore, a design methodology can be constructed without complicated mathematical tools.