Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by De Pablo, L. Articles by Monsalvo, R. Search for Related Content GeoRef GeoRef Citation

THE STATE OF HYDRATION OF Ca-EXCHANGED MONTMORILLONITE AT A DEPTH OF 2–2.7 KILOMETERS

Liberto De Pablo^1,, M. Lourdes Chavez² and Raúl Monsalvo³

¹ Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México, D.F., México
² Facultad de Química, Universidad Nacional Autónoma de México, 04510 México, D.F., México
³ Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México, D.F., México

E-mail address: liberto{at}servidor.unam.mx

Monte Carlo simulations in NP_zzT and µVT ensembles of the hydration of Ca-saturated Wyoming-type montmorillonite show that one-layer Ca-exchanged montmorillonite hydrate with a d₀₀₁ of 12.11 Å is stable at 353 K, 300 bar, and –7.21 kcal/mol potential. Two- and three-layer hydrates do not appear stable. At 353 K and 625 bar, the one-layer hydrate is nearly stable. In the interlayer space, molecules of H₂O are clustered on the interlayer midplane, alternatively oriented with their protons toward the siloxane surfaces on both sides and on the midplane. The Ca²⁺ cations are solvated, in outer-sphere coordination, and located 2.77 Å from the H₂O molecules. In sedimentary basins under normal geotherms, one-layer Ca-exchanged montmorillonite is the single hydrate stable at 2 km depth. In overcompacted sediments at 2.7 km depth, the hydrate could be unstable.

Keywords: Ca-exchanged montmorillonite, relation with depth, simulated clay, stability relations.