Microfluidic study of calcium carbonate dissolution and precipitation in confinement
Creators: name: Xu, Jianping
Publisher: name: The University of Texas at Austin
Year: 2023
Subjects: subject: Calcium carbonate
subject: Dissolution and precipitation in confinement
subject: Microfluidics
subject: Reactive transport
subject: Geosciences
subject: Energy and the environment
subject: Geochemistry
subject: FOS: Earth and related environmental sciences

description: Calcium carbonate is the major carbon sink in the Earth system and its dissolution and precipitation are essential for carbon cycling between the geosphere, hydrosphere, and atmosphere. Given that the Earth is a rocky planet populated with life, often these dissolution and precipitation processes occur not in open waters, but in small confinement of rock and soil pores and cellular spaces in organisms. Examples include Karst dissolution and formation, rock weathering, soil carbonation, biomineralization, geologic carbon storage and petroleum reservoir acidizing. Fundamental understanding and control of dissolution and precipitation in confinement are still challenging due to the high complexity generated from multi-coupling between fluid transport, interfacial interactions, chemical reactions, and mineral phase transition. In this work, we fabricate glass microfluidic chips that house rock micropore-like confinements for the lab-on-a-chip investigations of calcium carbonate dissolution and precipitation. Optical transparency of the chips allows direct visualizations of pore-scale dynamic behaviors with high temporal and spatial resolutions, which is crucial for quantitative characterizations. First, through extensive experiments we discovered a series of novel regimes, patterns and mechanisms of calcium carbonate dissolution and precipitation confined in micrometer geometries. Previously unknown behaviors such as CO₂ bubble breathing during carbonate dissolution, power-law particle size distribution of calcium carbonate precipitates, and the hydrodynamic instability induced by mineral phase transition are observed and quantified. Numerical and theoretical modeling are implemented to interpret the experimental results and demonstrate that small spatial confinement is actively shaping the mineral dissolution and precipitation dynamics. Second, novel experimental methodologies are developed to grow calcium carbonate in a glass microfluidic confinement either as scattered crystal particles or carbonate porous media. Utilizing the in situ grown carbonate porous media, we for the first time realize all the five classical carbonate rock dissolution regimes in a microfluidic chip. Extensive experiments are conducted to examine the effects of porous media heterogeneity and nonaqueous phases of oil and CO₂ on the carbonate dissolution dynamics. Third, high-resolution microfluidic visualizations provide an analytical basis for tracking mineral surfaces and precise measurements of dissolution and precipitation rates. Therefore, the microfluidic approach can be utilized as a screening tool for faster carbonate mineralization, which is important for geologic carbon storage and other decarbonization technologies such as enhanced rock weathering and soil carbonation.