Papers on Chemistry and Physics of Minerals and Rocks Volcanology
Streaming potential measurements: 1. Properties of the electrical double layer from crushed rock samples
Article first published online: 20 SEP 2012
Copyright 1999 by the American Geophysical Union.
Journal of Geophysical Research: Solid Earth (1978–2012)
Volume 104, Issue B8, pages 17857–17877, 10 August 1999
How to Cite
1999), Streaming potential measurements: 1. Properties of the electrical double layer from crushed rock samples, J. Geophys. Res., 104(B8), 17857–17877, doi:10.1029/1999JB900156., , and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 20 APR 1999
- Manuscript Received: 3 APR 1998
The ξ potential has been inferred from streaming potential measurements with crushed rock samples as a function of pH and electrolyte concentration for various salts. The value obtained for crushed Fontainebleau sandstone at pH = 5.7 and a KCl solution with a resistivity of 400 Ω m is −40±5 mV, where the error is dominated by sample to sample variations. The sensitivity of the ξ potential to the electrolyte resistivity for KCl is given experimentally by ρf0.23±0.014 where ρf is the electrolyte resistivity. The point of zero charge (pzc) is observed for pH = 2.5±0.1, and the ξ potential is positive for pH < pzc and negative for pH > pzc. For pH > 5 the variations of the ξ potential with pH can be approximated by ξ(pH)/ξ(5.7) = 1 + (0.068±0.004)(pH-5.7) for ρf = 100 Ω m. The ξ potential has been observed to be sensitive to the valence of the ions and is approximately reduced by the charge of the cation, unless specific adsorption takes place like in the case of Al3+. The experimental results are well accounted for by a three-layer numerical model of the electrical double layer, and the parameters of this model can be evaluated from the experimental data. The sensitivity of the ξ potential to the rock minerals has also been studied. The ξ potential obtained for granitic rocks is comparable to that obtained for Fontainebleau sandstone but can be reduced by a factor of 2–4 for sandstones containing significant fractions of carbonates or clay. To take into account the effect of the chemical composition of the electrolyte, a chemical efficiency is defined as the ratio of the ξ potential to the ξ potential measured for KCl. This chemical efficiency is measured to be ∼80% for typical groundwater but can be as low as 40% for a water with a high dissolved carbonate content. The set of empirical laws derived from our measurements can be used to assess the magnitude of the streaming potentials expected in natural geophysical systems.