From synergy to inhibition: Effects of multi component solutions on the crystallization of divalent carbonates in natural and synthetic environments

Abstract

The understanding of the processes governing the mechanisms, kinetics, and pathways of carbonate crystallization is crucial in the context of carbon capture and storage through mineralization. However, uncertainty still exists about the precise nature of how minerals, specifically carbonates, form and how specific factors (e.g., foreign ions, supersaturation and temperature) affect their kinetics and mechanisms of formation. By understanding the mechanisms, kinetics and pathways of carbonate formation and transformation, we gain the foundational knowledge in order to control the crystallisation and stability of carbonates. Prior to this study, the influence of ions on carbonate formation was predominantly limited to single ions. The aim of this thesis is to examine the effects of multi-component solutions on the crystallization of common divalent carbonates, in both synthetic and natural polymineralic systems. Using a combination of in situ crystallisation, microscopic, solid-state and spectroscopic techniques, including UV-Vis spectrophotometry, scanning electron microscopy and powder X-ray diffraction we carried out a comprehensive exploration of the impact of foreign ions on the kinetics and mechanisms governing divalent (Ca, Sr, Ba) carbonates crystallisation, leveraging in situ experiments. Following this, our focus shifted towards the captivating evolution of a complex divalent (Ca, Mg, Fe) carbonate natural cement, which crystallized during an in-situ basalt carbonate mineralization process. These main variables taken into consideration included: i) the ions? ratio and concentration in solution; ii) the saturation state within aqueous solutions; iii) the dehydration of divalent (e.g., Ca2+, Mg2+, Sr2+, Ba2+) ions; iv) variations in the ionic radii of these divalent cations; v) the effects of the differing coordination numbers of these divalent cations among carbonate types. This thesis has demonstrated that the synergistic influence of ions significantly diverges from their individual effects, thereby offering profound insights into the impacts of multi-component solutions on natural and synthetic carbonate crystallisation. By seamlessly integrating homogeneous nucleation experiments, mineral replacement reactions, and meticulous (high-resolution) examinations of naturally carbonated basalts, alongside geochemical modelling, we have achieved a profound mechanistic insight into carbonate formation. This newfound knowledge holds the key to regulating the kinetics and mechanisms of carbonate formation, whether in the context of field-based geological processes or industrial carbon capture and storage (CCS) applications.