Visualization
experiments using one-dimensional (1-D) porous media
made of Plexiglas and two-dimensional glass porous networks were conducted
to obtain qualitative and quantitative information concerning the
precipitation and crystal growth of CaCO3 under varying
flow and concentration conditions. Supersaturated solutions were prepared
by mixing sodium bicarbonate and calcium chloride solutions before
the pore networks. Nucleation and crystal growth were assumed to occur
within the porous media. Changes in the initial and final solution
composition were monitored. At low initial supersaturation values
(SRinitial), a few crystals were observed within the flow
channels and crystal growth took place exclusively on the newly formed
crystals. As the SRinitial increased, more crystals were
formed along the flow channels and new crystallites were continuously
formed during the course of the experiments. Nucleation and crystal
growth were not uniform. The crystal growth rates depended on the
initial value of SR and flow path inside the medium. Porosity for
the 2-D networks decreased when the SRinitial was high
or when calcite-cemented sand was used as substrate.
In the present work, the effect of wettability on CaCO 3 precipitation was approached by monitoring crystal formation in microchips of different wettability degree. Solutions of calcium chloride and sodium bicarbonate were mixed in hydrophilic and neutral-wet Y-junction microchips, and the precipitation of CaCO 3 crystallites was monitored. Sequential pictures showed the formation and growth of CaCO 3 crystals as a function of time, and the precipitates were identified by Raman spectroscopy. The obtained results indicated that in hydrophilic microchips, the increase of supersaturation ratio value resulted in higher growth rates and aggregate formation. The neutral-wet microchip surfaces were found to accelerate the precipitation of CaCO 3 compared to hydrophilic surfaces, and in the case of neutral-wet surfaces, crystallites were formed mainly close to the wall surfaces. In hydrophilic microchips, calcite was the main precipitate, while aragonite formation was favored in neutral-wet microchips.
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