Dissolution of well and poorly crystallized kaolinites; Al speciation and effects of surface characteristics

Abstract

This study compared surface characteristics and dissolution behavior of well-crystallized (KGa-1b) and poorly crystallized (KGa-2) kaolinite standards. Atomic force microscopy (AFM) revealed that particles of KGa-1b generally have nicely hexagonal micromorphology and crystallographically controlled microtopographic features. Particles of KGa-2 are also hexagonal, but their micromorphology tends to be more rounded. Basal-plane surfaces tend to be more irregular with fewer clearly crystallographically controlled features. KGa-1b particles tend to be larger in diameter and thicker than KGa-2 particles. Micromorphologic measurements showed that both KGa-1b and KGa-2 have modal edge- to total surface-area ratios of approximately 0.1 (mean ~ 0.2), although these measurements did not include the potentially large contribution of basal-plane step edges (additional 20% or more).