Understanding the drawbacks of the currently popular approach to determining the breakage rate parameters for process analysis and mill scale-up design

Abstract

The currently popular approach to a direct determination of the specific breakage rate of particles of a given size in the ball milling operation involves: (i) using material crushed in jaw/roll crushers as the starting feed charge, (ii) batch grinding in four–five steps for a total period of 4–8 min, and (iii) determining the slope of the best-fit straight line of a log-linear ‘first-order disappearance kinetics’ plot. In this paper, using published data on grinding of the mixtures of minerals, and effect of the mill operating variables on grinding kinetics, it has been shown that this approach is not quite suitable for carrying out a meaningful analysis of the grinding operation as the specific breakage rate of particles varies quite significantly during the period of grinding covered in the test work. It has been emphasized that the disappearance kinetics of the crushed particles as a top size should not be of any concern to us for the purpose of design and scale-up. It is the instantaneous specific breakage rate of particles produced in the test ball mill under the operating conditions of interest that needs to be determined.

Keywords:

• Ball milling
• specific breakage rate
• first-order disappearance kinetics
• breakage rate determining factors
• correct approach