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[OLD] Effect of confining pressure on stability of minerals


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From: Wang Lian

Subject: Effect of confining pressure on stability of minerals

To study pore water chemistry, we use high pressure (30 Mpa) squeezing technique to extract pore water from clay cores. The pH of the squeezed water was found lower than expected. Trying to interpret the observation, we are looking at two things: effect of the pressure on the double layer and on the stability of minerals. The clay we are studying contains few percents of pyrite and calcite, of which the stability/solubility may have impact on pH. We are trying to treat the pressure using thermodynamics but wandering what mechanisms to consider. Craig, in your FAQ list of GWB, the effect of pressure is not a big issue with exceptions such as sulfate minerals. Can you direct me to some relevant literatures about pressure effect? Any other suggestions are welcome as well.


From: Lauren Browning

Subject: Re: Effect of confining pressure on stability of minerals

I know of a situation that may be somewhat analogous to yours. Yang et al used high pressure (e.g. hundreds of MPa) uniaxial compression to squeeze pore waters out of volcanic tuff at Yucca Mt., NV. Bill Murphy and I evaluated the measured pore water compositions, and found some thermodynamic inconsistencies between the measured pH and the reported concentrations of various C-bearing species, among other problems. John Apps also looked at the data, and found additional types of problems. Both groups used correction methods to reinterpret the measured water compositions. I don't know if these reports would be of any use to you or not, but I've copied some of the references below.


Yang, I. C., Rattray, G. W., and Yu, P., 1996. Interpretation of chemical and isotopic data from boreholes in the unsaturated zone at Yucca Mountain, Nevada. U.S. Geological Survey, WRIR 96-4058, Denver, Colorado.


Yang, I. C., Yu, P., Rattray, G. W., Ferarese, J. S., and Ryan, R. N., 1998. Hydrochemical investigations in characterizing the unsaturated zone at Yucca Mountain, Nevada. U. S. Geological Survey, WRIR 98-4132, Denver, Colorado. J. A. Apps LBNL-40376, UC-814, 1997


Browning L., et al. (2000) Thermodynamic Interpretations of Chemical Analyses of Unsaturated Zone Water from Yucca Mountain, Nevada. Nuclear Waste Management Symposium Proceedings. Materials Research Society.

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