Cordilleran Section - 108th Annual Meeting (29–31 March 2012)
Paper No. 4-10
Presentation Time: 11:50-12:10


AGUILAR-CARRILLO, Javier1, CLARKE, Cathy E.1, and ROYCHOUDHURY, Alakendra N.2, (1) Earth Sciences, Stellenbosch University, Cnr Ryneveld and Merriman Streets, Stellenbosch, 7602, South Africa,, (2) Stellenbosch, 7602, South Africa

Drying induced pH changes were quantified on the surface of Na+, Ca2+, Mg2+ and Al3+ saturated smectite and kaolinite clays. This was achieved using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy to measure real time changes to a pH indicator, sorbed to the clay surface, during wetting and drying events. Using this technique it was possible to measure how low the pH of the surface drops during dehydration, the critical water content at which acidification of the surface begins and lastly how reversible the pH decrease is. The results show that only Al3+-smectite shows acidification below pH 4.8 with drying. The pH starts to decrease on the Al3+-smectite surface even when significantly hydrated (gravimetric water content ~ 125 mg/m2), and falls to between 1.2 and 1.4 when completely air dry. The drying induced pH decrease is completely reversible on rewetting, suggesting large pH oscillations may occur on smectite surfaces with appreciable exchangeable Al3+. Aluminium saturated kaolinite did not show significant acidification in response to drying (pH > 3.5), however, a 0.1M AlCl3 solution evaporated to a final pH of 2.8. The enhanced acidification observed on an Al-smectite clay compared to a solution containing free Al3+ ions highlights the role of highly charged surfaces in the hydrolysis reaction that occurs within the hydration shell of exchangeable Al3+ ions.

Cordilleran Section - 108th Annual Meeting (29–31 March 2012)
General Information for this Meeting


Session No. 4
Environmental Geochemistry I
Hotel Misión Juriquilla: Goyesco 1
08:30-12:55, Thursday, 29 March 2012

Geological Society of America Abstracts with Programs, Vol. 44, No. 3, p. 8

© Copyright 2012 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.