The effect of micronization on kaolinites and their sorption behaviour

The effect of micronization on the crystalline structure of kaolinite clay mineral and the role of this mechanically modified kaolinite structure on the adsorption/ion-exchange properties of toxic heavy metals are discussed. Two methods of micronization (ball milling and oscillatory milling) were used for the purpose. Micronization using a ball mill was found to be a slow process where dry grinding proved to have some effect compared to wet grinding. But grinding in an oscillatory mill could produce almost complete destruction of the clay structure (amorphization) within one hour of grinding time. The ground samples were characterized using XRD, IR spectrometry, TGA, DTA, SEM, surface area and pore volume measurements and particle size analysis. Adsorption kinetics for Cd and Cu show a slight improvement during the initial stages of grinding (i.e., from 4.24 – 4.68 meq/100 g for Cd and 2.79 to 3.45 meq/100 g for Cu at a grinding time of 10 min) brought in by the delamination after which the rate of adsorption decreases (1.024 meq/100 g and 1.09 meq/100 g for Cd and Cu respectively). For lead ions, there is an increased sorption and also it was observed that it takes a longer period for attaining equilibrium compared to cadmium and copper.