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Attrition of particulate solids

﻿ Attrition occurs during the transport and storage of particles and leads to loss of material through dust formation and to environmental pollution. Standard tests are all specifically designed to cater for particular needs and are often indicators of relative hardness than of attrition rates. Since little progress has been made into understanding the mechanisms of attrition, the purpose here is to study one of the basic processes that determines the rate of grinding. The aim is thus to establish a fundamental framework within which past work and future developments can be assessed. An annular attrition cell was designed, constructed and commissioned to permit one of the mechanisms of attrition, namely that in failure zones of deforming solids, to be considered in isolation. Sample weights of 100 gm were more than sufficient and the results were found to be reproducible, systematic and generally independent of sample size. Several close-sized material in the size range 250-2000 µm of various shapes were studied including different grades of sodium chloride, sodium carbonate and molecular sieve beads. The mode of attrition, bodily fracture or surface grinding, was easily verified by microscopic examination of attrited product. Results followed Gwyn's empirical law W = K p t m where W denotes the weight fraction attrited, t time and K p , m are characterising parameters. The reliable data permitted the development of simple kinetic models. One supposes first order loss of coarse material, another that attrition rate is dependent on radius reduction. It may be argued that the former applies to a fracturing mechanism, the latter to a surface grinding process. The first order approach has to be modified to allow for the initial high rate of attrition; the second model may be reduced to the Gwyn form. The attrition cell is useful in characterising materials; it should, in future, permit assessment of equipment performance.