Early Reaction Determination in Two Hydroxide-Kaolinite Systems by Electron Microscopy and Diffraction

Abstract

Abstract Results of the study of the kaolinite-sodium hydroxide interaction showed extensive dissolution of the kaolinite structure at particle edges, with some production of “silicate relicts” as a secondary effect. The method of specimen preparation for electron micro-scopy precluded electron-diffraction study of soluble reaction products. The study of the kaolinite-calcium hydroxide interaction revealed a similar attack on particle edges and formation of “silicate relics” and, in addition, formation of an insoluble reaction product that was tentatively identified by electron diffraction as prehnite, Ca2Al2Si3O10(OH)2. Both studies showed an ephemeral phase that, by selected area elec- tron diffraction, appeared to be a layer lattice silicate in (001) orientation. In the calcium hydroxide-treated kaolinite, formation of the reaction product was followed from nucleation along particle edges, after 24 hr, to growth of particles about 0.5 to 1 μ in size after 15 days. The combination of electron microscopy of surface replicas to detect changes in morphology with selected area electron diffraction of parallel pseudoreplicas for identification shows promise as a tool for study of the early stages in mineral- chemical interaction.