Migration of Cations in Copper(II)-Exchanged Montmorillonite and Laponite upon Heating

C. Mosser1, L. J. Michot2, F. Villieras2 and M. Romeo3
1 Centre de Géochimie de la Surface, UPR 6251 du CNRS, 1, rue Blessig 67084 Strasbourg Cedex, France
2 Laboratoire “Environment et Minéralurgie”, INPL-ENSG et URA 235 du CNRS, B.P. 40, 54501 Vandoeuvre Cedex, France
3 Institut de Physique et Chimie des Matériaux, UMR 46 du CNRS, 23, rue du Loess, 67037 Strasbourg Cedex, France

Abstract: Two clay minerals, a dioctahedral, Na-montmorillonite from Wyoming and a trioctahedral, synthetic Na-laponite, were exchanged by cupric (Cu(II)) ions and subsequently heated at 100 °C intervals up to 500 °C. The resulting materials were analyzed by chemical analysis, X-ray diffraction (XRD), cation exchange capacity (CEC) measurements, combined thermogravimetric and differential thermal analysis (TGA-DTA), infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). Montmorillonite exhibits a well-known Hoffmann-Klemen effect in that, when heated, cupric (Cu) ions migrate into the lacunae of the octahedral sheet, where they compensate the negative charge deficit of the clay layer. In the case of laponite, CEC measurements and spectroscopic measurements reveal that Cu ions migrate into the octahedral sheet where they replace Li and Mg ions. After heating at 200 °C approximately half the interlayer Cu ions are exchanged. The exchange appears to be 1 Cu for 1 Li, resulting in a slight decrease of the negative charge of the layer. After heating at 300 °C, the remaining Cu ions are exchanged by either 1 Mg or 2 Li, which does not result in any further charge reduction. At 400 °C some of the extracted Mg remigrates into the structure and exchanges some Li (1 Mg for 2 Li). The final product at 400 or 500 °C is then a Li-laponite with Cu(II) in the octahedral sheet.

Key Words: CEC Measurements • Cu-Laponite • Cu-Montmorillonite • EPR • Hofmann-Klemen Effect • IR • XPS

Clays and Clay Minerals; December 1997 v. 45; no. 6; p. 789-802; DOI: 10.1346/CCMN.1997.0450603
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)