Abstract
Knowledge of crystal nucleation and growth is paramount in understanding the geometry evolution of porous medium during reactive transport processes in geo-environmental studies. To predict transport properties precisely, it is necessary to delineate both the amount and location of nucleation and precipitation events in the spatiotemporal domain. This study investigates the precipitation of calcium carbonate crystals on a heterogeneous sandstone substrate as a function of chemical supersaturation, temperature, and time. The main objective was to evaluate solid formation under different boundary conditions when the solid–liquid interface plays a key role. New observations were made on the effect of primary and secondary substrates and the role of preferential precipitation locations on the rock surfaces. The results indicate that supersaturation and temperature determine the amount, distribution pattern, and growth rate of crystals. Substrate characteristics governed the nucleation, growth location, and evolution probability across time and space. Moreover, substrate surface properties introduced preferential sites that were occupied and covered with solids first. Our results highlight the complex dynamics induced by substrate surface properties on the spatial and temporal solute distribution, transport, and deposition. We accentuate the great potentials of the probabilistic nucleation model to describe mineral formation in a porous medium during reactive transport.
Highlights
During solute transport and flow of a reactive fluid within a porous medium, crystal nucleation and growth may change the pore geometry and transport properties of the porous medium.[1−4] Solid precipitation and accumulation change the available surface area for nucleation and growth, which leads to alterations in the reactivity of the system, reaction rates, and overall progress.[4−7] Predicting potential events and the evolution of transport properties of a porous medium is paramount in many natural and engineered systems dealing with reactive transport processes coupled with thermo−hydro−mechanical effects
Based on classical nucleation theory (CNT), crystal nucleation and growth kinetics of an aqueous solution are governed by supersaturation, temperature, interfacial free energy between the nucleating mineral and substrate, and solution composition
Motivated by the importance of crystallization and growth kinetics in a variety of multiphase and multiscale processes occurring in geo-environmental processes and systems, this paper extends the understanding of factors controlling crystal nucleation and growth rates, the impact of ambient and aqueous phase properties, and the substrate characteristics
Summary
During solute transport and flow of a reactive fluid within a porous medium, crystal nucleation and growth may change the pore geometry and transport properties of the porous medium.[1−4] Solid precipitation and accumulation change the available surface area for nucleation and growth, which leads to alterations in the reactivity of the system, reaction rates, and overall progress.[4−7] Predicting potential events and the evolution of transport properties of a porous medium is paramount in many natural and engineered systems dealing with reactive transport processes coupled with thermo−hydro−mechanical effects. Solute transport, chemical reactions, and fluid−solid interactions may vary markedly over different time- and length-scales in such systems and processes.[1,8−10] Prediction of such complex natural or engineered perturbations is far from trivial in geo-environments It requires an updated understanding of crystal nucleation and growth, governing factors, and interactions at solid−liquid surfaces and interfaces. The surface mineral synthesis experiments were performed with a threefold purpose: (a) to provide new insights into probabilistic crystal nucleation and growth, (b) to delineate how primary and secondary substrates govern solid accumulation, and (c) to describe heterogeneous nucleation as a function of aqueous-phase supersaturation, temperature, and evolution time. To explore the effect of solute concentration, temperature, and experimental elapsed time on the surface coverage area and the number of precipitated crystals, we carried out calcium carbonate synthesis experiments on the surface of heterogeneous quartz-rich sandstone with a solution stoichiometry of close to 1 (CCa/CCO3 ≈ 1)
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