Modification in Properties of Fly Ash through Mechanical and Chemical Activation

This paper is a critical overview on chemical, structural, and morphological changes in fly ash properties with mechanical activation using high energy planetary ball mill and chemical activation by digesting with various mineral acids (HCl, HNO3, H2SO4 and HClO4) at 110ºC. Mechanical activation results in increase in silica percentage, amorphous nature, specific surface area and surface roughness, as evident by analytical measurements using XRF, XRD, FT-IR, BET surface area and SEM techniques. The chemical activation of Fly ash performed by different acids results in increased silica content and surface area due to leaching of several metal ions from silico-aluminate skeleton. The surface silanol groups responsible for generating Brönsted acidity are enhanced as evident by pyridine adsorbed FT-IR. Activation with HClO4 is also evident to generate surface active Lewis acid sites due to formation of Al-OH phases on the surface. The mechano-chemical activation can generate sufficient activity on fly ash surface rendering its potential application in heterogeneous acid catalysis