Grinding of Class-F fly ash using planetary ball mill: A simulation study to determine the breakage kinetics by direct- and back-calculation method

Abstract

Dry grinding of Class F fly ash (FA) was carried out using the planetary ball mill to obtain mechanically activated nanostructured FA particles. The resulting FA powders were characterized for (i) particle size: dynamic light scattering and sieve analyzer, (ii) specific surface area: BET-analyzer, (iii) structure: X-ray diffractometer, (iv) chemical composition: field emission scanning electron microscope with the electron diffraction spectrum analyzer and x-ray fluorescence analyzer, and (v) aggregation and shape of the particles: Fourier-transformed infra-red spectrometer and scanning electron microscope. A significant enhancement in surface and bulk properties of milled FA was obtained over fresh FA. The breakage parameters (i.e., the specific rate of breakage and primary breakage distribution function) of FA were determined by the direct experimental method using the narrowly-sized fraction of FA over the short grinding period under identical milling environment. A relatively simple back-calculation method was employed to determine above breakage parameters of FA also using time-variant milling data that were obtained after the grinding of distributed-sized FA feed. The parameters obtained from the direct experimental and back-calculation method yielded comparative milling simulation results with the acceptable accuracy. Keywords: Planetary ball mill, Fly ash, Population balance model, Direct- and back-calculation method, Breakage parameters, Parameter optimization