TY - JOUR
T1 - Laboratory measurements of zeta potential in fractured Lewisian gneiss
T2 - implications for the characterization of flow in fractured crystalline bedrock
AU - Vinogradov, Jan
AU - Hidayat, Miftah
AU - Kumar, Yogendra
AU - Healy, David
AU - Comte, Jean-Christophe
N1 - Funding: This research received no external funding.
Acknowledgments: Miftah Hidayat was supported by the Aberdeen-Curtin PhD studentship. Yogen- dra Kumar was supported by a scholarship from the Government of India. Chandrakant Jadhav from the Department of Physics and John Still from the School of Geoscience, University of Aberdeen are acknowledged for their assistance in processing the XRD and SEM data. David Healy acknowledges funding from UKRI NERC grant NE/N003063/1.
PY - 2021/12/24
Y1 - 2021/12/24
N2 - Despite the broad range of interest and possible applications, the controls on the electric surface charge and the zeta potential of gneiss at conditions relevant to naturally fractured systems remain unreported. There are no published zeta potential measurements conducted in such systems at equilibrium, hence, the effects of composition, concentration and pressure remain unknown. This study reports zeta potential values for the first time measured in a fractured Lewisian gneiss sample saturated with NaCl solutions of various concentrations, artificial seawater and artificial groundwater solutions under equilibrium conditions at confining pressures of 4 MPa and 7 MPa. The constituent minerals of the sample were identified using X-ray diffraction and linked to the concentration and composition dependence of the zeta potential. The results reported in this study demonstrate that the zeta potential remained negative for all tested solutions and concentrations. However, the values of the zeta potential of our Lewisian gneiss sample were found to be unique and dissimilar to pure minerals such as quartz, calcite, mica or feldspar. Moreover, the measured zeta potentials were smaller in magnitude in the experiments with artificial complex solutions compared with those measured with NaCl, thus suggesting that divalent ions (Ca2+, Mg2+ and SO42−) acted as potential determining ions. The zeta potential was also found to be independent of salinity in the NaCl experiments, which is unusual for most reported data. We also investigated the impact of fracture aperture on the electrokinetic response and found that surface electrical conductivity remained negligibly small across the range of the tested confining pressures. Our novel results are an essential first step for interpreting field self-potential (SP) signals and facilitate a way forward for characterization of water flow through fractured basement aquifers.
AB - Despite the broad range of interest and possible applications, the controls on the electric surface charge and the zeta potential of gneiss at conditions relevant to naturally fractured systems remain unreported. There are no published zeta potential measurements conducted in such systems at equilibrium, hence, the effects of composition, concentration and pressure remain unknown. This study reports zeta potential values for the first time measured in a fractured Lewisian gneiss sample saturated with NaCl solutions of various concentrations, artificial seawater and artificial groundwater solutions under equilibrium conditions at confining pressures of 4 MPa and 7 MPa. The constituent minerals of the sample were identified using X-ray diffraction and linked to the concentration and composition dependence of the zeta potential. The results reported in this study demonstrate that the zeta potential remained negative for all tested solutions and concentrations. However, the values of the zeta potential of our Lewisian gneiss sample were found to be unique and dissimilar to pure minerals such as quartz, calcite, mica or feldspar. Moreover, the measured zeta potentials were smaller in magnitude in the experiments with artificial complex solutions compared with those measured with NaCl, thus suggesting that divalent ions (Ca2+, Mg2+ and SO42−) acted as potential determining ions. The zeta potential was also found to be independent of salinity in the NaCl experiments, which is unusual for most reported data. We also investigated the impact of fracture aperture on the electrokinetic response and found that surface electrical conductivity remained negligibly small across the range of the tested confining pressures. Our novel results are an essential first step for interpreting field self-potential (SP) signals and facilitate a way forward for characterization of water flow through fractured basement aquifers.
KW - zeta potential
KW - fractured gneiss
KW - surface electrical conductivity
KW - effect of concentration
KW - composition and mineralogy
KW - impact of fracture aperture and confining pressure
U2 - 10.3390/app12010180
DO - 10.3390/app12010180
M3 - Article
VL - 12
JO - Applied Sciences
JF - Applied Sciences
SN - 2076-3417
IS - 1
M1 - 180
ER -