Theoretical study on the organic acid promoted dissolution mechanism of forsterite mineral

Abstract

Olivine-type minerals are the most probable minerals for vast carbon dioxide sequestration since their abundant and wide distribution around the world. Nevertheless, mineral dissolution rate is the key factor restricting its carbon dioxide sequestration process. In this study, first principles calculation combined with the scanning electron microscope (SEM) were used to investigate different types of organic acids that promoted mineral dissolution mechanism of Mg2SiO4, including the adsorption configuration, adsorption energy, and electronic properties. Thermodynamics calculations on the complexation paths between organic acid molecules and the Mg(OH)2 or Si(OH)4 groups are studied. Results show that cations on the olivine surface prefer bonding with carbonyl O of the carboxyl group after the organic acid molecule was adsorbed onto the surface with charge transferred and orbital hybridization. The H - O bond in the carboxyl group will be broken up, resulting in the mineral surface hydroxylation. A greater number of carboxyl groups will be better for the mineral dissolution with more etch pits appearing. Multiple types of complexes formed by ionized organic acid molecules and Mg2+ coexist with different reaction paths and Gibbs free energy from thermodynamics calculations. The strong interaction between the dissolved cations and carbonyl O of the carboxylate radical was the first time to predicted, which could be useful to find reasonable additives to improve the mineral dissolution kinetics.