Sample preparation and aging effects on the dissolution rate and surface composition of diopside

Abstract

This study shows that the initial dissolution rate of ground diopside powders depends on sample preparation history, in general agreement with the findings of previous studies. However, our attempts to reproduce our own dissolution rate experiments were unsuccessful. Instead, we have found that the initial dissolution rate of all diopside powders used in this study decrease with the time elapsed since the sample was ground. This aging effect, measured from samples stored in air and at room temperature, was followed over a period of several months. These results suggest that diopside surfaces created by grinding gradually relax toward a less-reactive state under these conditions. In addition, aging also affects the surface composition (measured using X-ray photoelectron spectroscopy) of the pretreated ground diopside powders. Surface reaction controlled dissolution of silicate minerals is a complicated function of variables both internal and external to the dissolving crystal. The internal variables ( e.g. dislocations, structural distortion, microcracks, surface composition, etc.) are affected by mechanical or chemical pretreatments. Various mechanisms by which pretreatments and aging may affect these variables and thereby affect initial dissolution rates and surface composition are discussed.