Impact of grinding aids on dry grinding performance, bulk properties and surface energy

In dry fine grinding processes the relevance of particle-particle interactions rises with increasing product fineness. These particle-particle interactions reduce the grinding efficiency and complicate the process control. The adsorption of grinding aid molecules on the product particle surface is a common measure to handle these effects. To ensure an efficient grinding aid application, the impacts of additives on particle and bulk properties, which influence the micro-processes inside the mill, need to be understood. Within this study the effects of several grinding aids on dry fine grinding of limestone in a laboratory vibration mill were investigated. Unlike in many other scientific works, the impacts of grinding aids were analyzed on different levels simultaneously: Grinding success and agglomerate size distributions were evaluated by wet and dry particle size measurements, respectively. Additionally, material coating on the grinding media, powder flowabilities and particle specific surface energies were measured. It was shown that all of the investigated grinding aids influence the grinding efficiency. However, the formation of agglomerates is not necessarily linked to the product fineness. Furthermore, a strong impact of certain grinding aids on the flowability of the product powder was determined. Thereby, the bulk flow behavior also determines the grinding result as it affects the stress mechanism inside the mill. Moreover, a direct relation between surface energy and powder flowability as well as agglomeration behavior could be demonstrated. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.