Nucleation and Growth of Calcium Carbonate and Sulfate Minerals from Solutions Close to Equilibrium

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The nucleation and growth of calcium carbonate and sulfate minerals are essential to understanding many energy and environmental processes, such as the long-term stability of geological carbon sequestration, past environmental conditions, the incorporation of radioactive and toxic metals, and the scaling of the desalination process. In this thesis, I investigated the nucleation and growth of calcium carbonate and sulfate minerals from solutions close to equilibrium which is the common condition in many natural and engineered systems. The macroscopic growth rates were measured using a quartz crystal microbalance with dissipation (QCM-D) under close to equilibrium conditions. The results showed well agreement with those reported microscopic growth rates measured by atomic force microscopy (AFM) and other macroscopic measurement techniques. Moreover, it is concluded that the discrepancies of growth rates among different studies resulted from the measured step densities. The discrepancies among measured step densities were likely to be created by different pretreatment process. The heterogeneous nucleation of (Cax,Mg1-x)CO3 particles at various organic-water interfaces under close to equilibrium conditions was investigated using in situ grazing incidence small angle X-ray scattering (GISAXS). The results indicated that different organics regulated the sizes, phases, and Mg contents of heterogeneous (Cax,Mg1-x)CO3 compared with homogeneous precipitates in bulk solution. The calcium sulfate minerals scaling under close to equilibrium conditions on GO modified polyamide membrane surface were investigated in a laboratory-scale cross flow RO setup. The results indicated that gypsum precipitation was inhibited on GO modified membrane due to more negatively charged and hydrophilic surface. However, due to the higher density of carboxyl group forming complexes with Ca, the flux recovery was hindered on GO modified membrane after water flushing process.

Mineral, Nucleation, Growth
Portions of this document appear in: Cao, Bo, Andrew G. Stack, Carl I. Steefel, Donald J. DePaolo, Laura N. Lammers, and Yandi Hu. "Investigating calcite growth rates using a quartz crystal microbalance with dissipation (QCM-D)." Geochimica et Cosmochimica Acta 222 (2018): 269-283. And in: Cao, Bo, Ali Ansari, Xinyi Yi, Debora F. Rodrigues, and Yandi Hu. "Gypsum scale formation on graphene oxide modified reverse osmosis membrane." Journal of membrane science 552 (2018): 132-143.