Effects if crystal orientation on the dissolution kinetics of calcite surfaces by an atomic emission spectrscopic and interferometric approach

Abstract

<p>Geologic C02 sequestration has emerged as a technology to reduce greenhouse gas emissions by injecting C02 into subsurface mineral reservoirs consisting predominately of cementing carbonate minerals, e.g. calcite. However, geochemical reactions between subsurface minerals and C02 containing fluids can potentially alter the porosity and permeability of subsurface minerals which can ultimately cause undesirable leakage of C02 from sequestration reservoirs back to the atmosphere. The purpose of the present work was to examine the effects of polished crystal surface orientation and degree of solution under saturation on the dissolution kinetics of calcite as a means of improving our understanding of fundamental reactions that may influence the efficacy of C02 sequestration in geological formations. Surface orientations of interest include ~ 1 cm2 areas of both the (104) crystallographic plane of natural calcite specimens, consisting of flat terraces with few steps, as well as fully kinked surfaces created by sectioning approximately parallel to the (001) plane. Dissolution reactions were carried out by exposing calcite surfaces, polished to an approximate roughness of 50 nm, to experimental solutions with compositions similar to C02 sequestration environments. Atomic Force Microscopy (AFM) imaging provided surface characterization for samples both before and after dissolution reactions, whereas absolute rates of calcite dissolution were ultimately determined from solution analyses using atomic emission spectroscopy. Images of post-reacted surfaces taken with a vertical scanning interferometer (VSI) facilitated a second, independent calculation of calcite dissolution rates for the surfaces of interest. The results from these investigations may lead to the development of relatively simple models for mineral grain shape evolution during dissolution, a process that impacts pore sizes and shapes in subsurface environments.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>