Zeta potential in sandpacks: Effect of temperature, electrolyte pH, ionic strength and divalent cations

Abstract

Rocks in many subsurface settings are at elevated temperature and are saturated with brines of high ionic strength (high salinity) containing divalent ions. Yet most laboratory measurements of zeta potential in earth materials are obtained at room temperature using simple monovalent electrolytes at low ionic strength. Consequently, the zeta potential at conditions relevant to many subsurface settings is not known. We report experimental measurements of the temperature dependence of the zeta potential in well characterised, natural quartz sandpacks over the temperature range 23-120°C saturated with electrolytes containing divalent ions at a range of concentrations relevant to natural systems. We find that the key control on zeta potential in these unbuffered experiments is pH, which varies in response to temperature and electrolyte composition. The zeta potential is negative irrespective of sample or electrolyte, but its magnitude is strongly correlated to pH, which varies both with temperature and the concentration of divalent ions. The pH decreases with increasing temperature at low ionic strength, but is independent of temperature at high ionic strength. The pH is also typically lower in the presence of divalent ions, irrespective of the total ionic strength. The zeta potential increases in magnitude with increasing pH. Different relationships between zeta potential, temperature and concentration of divalent ions could be obtained in buffered experiments where the pH is fixed at a given value. Zeta potential in sandpacks: effect of temperature, electrolyte pH, ionic strength and divalent cations.

Zeta potential of porous rocks in contact with mixtures of monovalent and divalent electrolytes

“…; Vinogradov et al . ). Additionally, the experimental results show that the SPC and the zeta potential also depend on the mineral composition of rocks at the same mixtures of electrolytes.…”

“…The variation of pH is explained by the CO 2 uptake from the air or the variation of electrolyte composition, electrolyte concentration, temperature and the mineral composition of rocks as reported in the recent work Vinogradov et al . (). A high input impedance multimeter (Keithley model 2700) and a high‐precision differential pressure transducer (Endress and Hauser Deltabar S PMD75) are used to measure electrical potential differences and pressure differences, respectively.…”

“…() studied the surface charge of calcite particles dispersed in aqueous solutions as a function of pH, ion concentration and type of ions (Na + , Ca 2 + , Cl − , SO 4 2 − ) by measurements of the electrophoretic mobility. Recently, Vinogradov, Jackson and Chamerois () have studied the influence of temperature, electrolyte pH, ionic strength and divalent cations on the zeta potential in sandpacks. They found that the key control on zeta potential is pH which changes with temperature, electrolyte composition and the concentration of divalent ions.…”

Surface Potential/Charge Sensing Techniques and Applications

“…Zeta potential is the electric potential of the slipping plane in the electric double layer with the moving of liquid or solid particles, and is related to the surface charge [98,99]. It is an important parameter describing the behavior of the solid-liquid interface charge, it is affected by solid material properties and liquid phases [100,101], and it represents the key physicochemical surface properties in various fields from electrochemistry to pharmaceuticals [99,102,103]. The zeta potential measurement of a solid wall in solution depends on the streaming potential or electroosmotic mobility measurement technique [104].…”

Wetting Behavior of Tight Rocks: From Core Scale to Pore Scale

“…Several studies have investigated the effect of temperature on zeta potential of intact natural sandstones (Vinogradov & Jackson, 2015), intact natural carbonates (Al Mahrouqi et al, 2016), intact granite (Tosha et al, 2003), pure Ottawa and Fontainebleau sands (Vinogradov et al, 2018), and pure minerals including quartz, calcite, and kaolinite (Rodríguez & Araujo, 2006). Rodríguez and Araujo (2006) observed that zeta potentials of quartz, calcite, and kaolinite increase in magnitude by increasing the temperature at low salinity (0.01 M NaCl concentration).…”