Dehydroxylation of Dioctahedral Phyllosilicates

L. Heller-Kallai
1980 Clays and clay minerals  
Abstraet--Mrssbauer spectroscopy of dioctahedral phyllosilicates showed that on dehydroxylation iron which originally occupied M(2) and M(1) sites became, respectively, 5-and 6-coordinated. The 6-coordinated sites are very distorted 9 No migration of cations occurs in the course of heating the specimens for 1-3 hr at 600~176 By using a combination of several physicochemical methods, different successive stages of the dehydroxylation process could be distinguished: (1) migration of protons; (2)
more » ... on of protons; (2) localized dehydroxylation of individual associations without significant change in the overall configuration of the octahedral sheets; and (3) loss of most of the hydroxyl groups with concomitant changes in the cell dimensions. Penetration of Li into the octahedral sheets does not affect the course of the reaction, but reduces the dehydroxylation temperature and the stability of the products. Dehydroxylation was preceded by or associated with the oxidation of any divalent iron present 9 Fe n+ derived from Fe ' 2+ was indistinguishable by MSssbauer spectroscopy from iron initially present in the trivalent form 9 High concentrations of Fe lower the dehydroxylation temperature and reduce the stability of the dehydroxylate to the extent that partial disintegration may precede complete dehydroxylation. 356 Heller-Kallai and Rozenson Clays and Clay Minerals comparing X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) measurements with results obtained by infrared (IR) and MSssbauer spectroscopy. EXPERIMENTAL Materials The identity of the following starting materials was confirmed by XRD and IR examination: : Upton, Wyoming (API Reference clay No. 25); M+o.9o(SiT.69Alo.31) (Al3.orFeoA, Mgo.51) O2o(OH)4 (HeUer-Kallai, 1975) Beidellitic montmorillonite: Scan Raft, Sweden; M+a.16(Sir.46A10.54) (A13.o2Fe3+0.34FeZ+0.06Mg0.ss) Oz0(OH)4 (Bystrom-Brusewitz, 1976) This smectite has a higher tetrahedral charge than is commonly found for montmorillonite and is designated "'beidellitic" to distinguish it from the Wyoming montmorillonite. Nontronite: Grant County, Washington (CMS Source clay repository SWa-1); (Ca, Mg)o.49(SiT.25Alo.78 ) (Alo.ssFeZ+2.75Mgo.33Tio.25) O2o(OH)4 (Rozenson, 1975) Muscovite: Pegmatite deposit, Israel (M 9061, Hebrew University collection);
doi:10.1346/ccmn.1980.0280505 fatcat:szgt2c6wuza3zmb5kkb4uevqsm