Event: AGU Fall Meeting, Washington DC (USA), December 2018
Abstract by Satoshi Izumoto , Johan Alexander Huisman, Egon Zimmermann, Yves Méheust, Francesco Gomez, Joris Heyman, Wu Yuxin, Harry Verecken, Tanguy Le Borgne
Abstract
Induced calcite precipitation is used in a range of in-situ geotechnical applications to modify the mechanical and hydrological properties of soils and fractured rocks. It is also a model process for mixing-induced biogeochemical reactions that occur naturally in a broad range of hydrological systems. Laboratory experiments have shown that spectral induced polarization (SIP) measurements can be used to monitor calcite precipitation. However, the results of the limited number of previous studies investigating the SIP response of calcite precipitation were not fully consistent.
This study aims to investigate how the SIP response of calcite depends on solute composition, since this may explain the differences in SIP response observed in previous studies. For this, a five-phase experiment with SIP measurements on a column filled with sand was performed.
In phase I, calcite precipitation was generated for a period of 12 days by injecting Na2CO3 and CaCl2 solutions through two different ports. This resulted in a well-defined calcite precipitation front, which was associated with an increase in the imaginary conductivity in the kHz frequency range.
In phase II, the injected solutions were stepwise diluted. This resulted in a clear decrease in the imaginary conductivity.
In phase III, the injection of the two solutions was stopped. Nevertheless, calcite precipitation continued and solute concentrations in the mixing zone decreased. As in phase II, this led to a decrease in the imaginary conductivity.
In phase IV, the injection rate of the Na2CO3 solution was reduced to shift the mixing zone away from the calcite precipitation front, which also decreased the imaginary conductivity.
Finally, the column was flushed with a solution in equilibrium with calcite in phase V, which led to a very small SIP signal.
These results imply that the SIP response of calcite is very sensitive to the solution composition near the precipitates, which may explain the previously reported conflicting results. In a next step, the relationship between SIP response, volume of calcite, and solute composition will be quantitatively investigated using SIP measurements on a 2D milifluidic cell with an artificial porous media that allows visualizing the temporal dynamics of calcite precipitation.
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