APPARENT ACTIVATION ENERGIES OF ACID DISSOLUTION OF CARBONATES BY AN ISOTHERMAL AUTOMANOMETRIC APPARATUS

Abstract

Activation energies of acid dissolution of dolomite and calcite were previously determined by measuring CO2 evolution with respect to time, employing manually read mercury manometers. This approach is limited to slow CO2 evolving reactions. In this study, activation energies of acid dissolution of calcite and dolomite and several samples of agricultural limestone were determined through the use of an isothermal automanometric apparatus. The results indicate that the activation energy of dolomite, a slowly acid-reacting mineral, is in close agreement with that previously reported in the literature. The activation energy of calcite, a rapidly acid-reacting mineral, however, differs considerably from that reported in the literature. The activation energies of the agricultural limestone samples varied widely. Compositional analysis combined with x-ray diffraction and Fourier transform infrared spectra showed that samples with activation energies ranging from approximately 40 to 50 kJ.mol−1 consist mainly of dolomite, while limestone samples with activation energies ranging from approximately 7 to 20 kJ.mol−1 consist mainly of consist mainly of calcite. The study also demonstrated that the isothermal automanometric apparatus can be routinely employed to evaluate limestone acid reactivity.