The smectitic minerals in a bentonite deposit from Melo (Uruguay)

摘要: A nearly monomineralic 1.5 m thick bentonite bed sampled in Melo (Uruguay) appears to be a pure high-charge montmorillonite: [Si 3.94 Al 0.06 ](Al 1.40 Fe 3+ 0.11 Ti 0.02 Mg 0.49 Mn 0.01 )O 10 (OH) 2 Na K 0.08 Ca 0.18 . However, contrasting swelling behaviours have been demonstrated by fitting the experimental X-ray diffraction patterns which were recorded on oriented preparations of same sample different saturation states. According expandability layers Ca-, K- and K-Ca-saturated (i.e. saturated first with + subsequently 2+ ) states, three 'layer types' defined. Low-, intermediate-, are fully, partly, not expandable, respectively, after K-saturation. Collapse is reversible subsequent Ca-saturation, probably because tetrahedral substitutions. These layer types segregated two distinct randomly interstratified mixed-layer phases. Total surface area cation exchange capacity shown depend interlayer composition.