Origin and Position of Exchange Sites in Kaolinite: An ESR Study

Murray B. McBride*
Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada
* Present address: Department of Agronomy, Cornell University, Ithaca, NY 14853, USA.

Abstract: Electron spin resonance (ESR) spectroscopy is used to investigate the nature of exchange sites on kaolinite. ESR spectra of exchangeable Cu2+ and Mn2+ on kaolinite indicate that divalent exchange ions are about 11–12Å apart on kaolinite surfaces and that planar Cu (H2O)42+ ions are oriented parallel to the surfaces. Solution-like spectra for exchangeable Cu2+ and Mn2+ are observed at high relative humidities, suggesting a high degree of mobility of exchange cations on kaolinite surfaces. The evidence seems to eliminate edge sites as being active in cation exchange at least in the acidic range of pH. Similar conclusions are derived from ESR studies of Cu2+ -saturated talc and pyrophyllite. It is proposed that most exchange sites arise from ionic substitutions or mineral impurities in phyllosilicates.

Clays and Clay Minerals; April 1976 v. 24; no. 2; p. 88-92; DOI: 10.1346/CCMN.1976.0240207
© 1976, The Clay Minerals Society
Clay Minerals Society (www.clays.org)