XVI ReuniÃ³n CientÃfica de la Sociedad EspaÃ±ola de Arcillas - Libro ...

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Lerf A et al. / Comunicaciones SEA 2001 – Baeza (Jaén) [3], according to whose arguments we refrain from the assignment of these sites to the cis (M2) sites and the trans (M1) sites, respectively . An alternative interpretation is based on the assumption that the different iron sites are due to the particular distribution of two- and three-valent metal ions and vacancies around the Fe 2+ [4-6]. No serious effort appears to have been made so far to establish a relationship between the different Fe 2+ components in the Mössbauer spectra and the metal ion distribution in the octahedral layers of the trioctahedral micas. Figure 1. ME spectrum of the Na form of the vermiculite from Santa Olalla We have tried also to influence the Fe 2+ /Fe 3+ ratio by redox reactions of the vermiculite from Santa Olalla with H 2 O 2 , Na 2 S 2 O 4 , N 2 H + 5 and phenylendiamine (PDA). The Fe 2+ content of the starting material (loaded with sodium ions in the interlayer gap, instead of the Mg-ions naturally present) is in the order of 10 %. The Fe 2+ can be oxidized completely with H 2 O 2 , while the reduction of Fe 3+ is much more difficult. Applying the recipes used in previous studies of the redox reactions of vermiculites [7-10], we do not get any substantial changes in the Fe 2+ /Fe 3+ ratio with respect to the starting material. Major changes are achieved only if the concentration of the reagents is increased (H 2 O 2 ), the reaction times
Lerf A et al. / Comunicaciones SEA 2001 – Baeza (Jaén) extended (H 2 O 2 , dithionite) and/or the reaction solutions changed several times (dithionite). We ascribe such differences in behaviour to the particle size used in our experiment and conclude that these reagents react mainly at the outer surface of the crystals. Figure 2. ME spectrum of the Na-vermiculite of Santa Olalla measured after treatment with 0.1M aqueous PDA solution adjusted to pH = 6.5 To check this hypothesis, the vermiculite has also been treated with reagents which can be inserted in the interlayer space by ion exchange. As reagents of this kind we chose hydrazine, which has also been used previously [11-13], and PDA, which shows a color reaction due to the formation of radical ions during oxidation. Carrying out the reduction with the latter reagents in solutions with pH 6-7 leads to an immediate reduction and color reaction indicating that the intercalation of the reducing agents shortens the reaction time dramatically (a typical ME spectrum of a reduced sample is shown in figure 2). However, to get the maximum possible degree of reduction, the reaction conditions have to be optimized and we are not certain that we already have found the optimum conditions. The extent of reduction is influenced by the reaction times and by a repeated change of the reaction solutions (PDA). In addition there is some evidence that the degree of
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XVI Reunión Científica de la Soci
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Comité de Honor Presidente Excmo.
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4 09:30-10:45 Sesión Oral de Cerá
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Page 15 and 16: 14 Nombramiento como Socio de Honor
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Page 19 and 20: COMUNICACIONES DE LAS SESIONES CIEN
Page 21 and 22: Mineralogía de arcillas de leptoso
Page 23 and 24: I. CRISTALOQUÍMICA
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Page 67 and 68: Ruiz Cruz MD et al. / Comunicacione
Page 69 and 70: Ruiz Cruz MD et al. / Comunicacione
Page 71 and 72: Sánchez CJ et al. / Comunicaciones
Page 75 and 76: II. GEOLOGÍA Y GÉNESIS
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Page 97 and 98: Abrantes I et al. / Comunicaciones
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Jiménez Millán J et al. / Comunic
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Comunicaciones SEA 2001 - Baeza (Ja
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Machado A et al. / Comunicaciones S
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Martín M et al. / Comunicaciones S
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Martins V et al. / Comunicaciones S
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III. MINERALOGÍA DEL SUELO
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García-González MT / Comunicacion
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Bellinfante N et al. / Comunicacion
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Bellinfante N et al. / Comunicacion
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Pascual Cosp J et al. / Comunicacio
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Pascual Cosp J et al. / Comunicacio
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Delgado R et al. / Comunicaciones S
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Galhano AC et al. / Comunicaciones
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Marín Sanleandro P et al. / Comuni
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Martín-García JM et al. / Comunic
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Rubio B, Gil-Sotres F / Comunicacio
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IV. CERÁMICA ANTIGUA Y PATRIMONIO
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Cultrone G et al. / Comunicaciones
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Cultrone G et al. / Comunicaciones
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Flores V et al. / Comunicaciones SE
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García Ramos G et al. / Comunicaci
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Siguenza Carballo MB et al. / Comun
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Silva J et al. / Comunicaciones SEA
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Aranda P et al. / Comunicaciones SE
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Artigas R et al. / Comunicaciones S
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Blanco I et al. / Comunicaciones SE
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Celis R et al. / Comunicaciones SEA
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Cerdeño del Castillo FJ et al. / C
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Coroado J et al. / Comunicaciones S
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Coroado J et al. / Comunicaciones S
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Corpas Iglesias FA et al. / Comunic
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Corpas Iglesias FA et al. / Comunic
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Ferraz E et al. / Comunicaciones SE
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Ferraz E et al. / Comunicaciones SE
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Jamoussi F et al. / Comunicaciones
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Jamoussi F et al. / Comunicaciones
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Letaïef S et al. / Comunicaciones
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Liso Rubio MJ et al. / Comunicacion
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Llavona MA et al. / Comunicaciones
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Llavona MA et al. / Comunicaciones
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Martínez LM et al. / Comunicacione
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Mayayo MJ et al. / Comunicaciones S
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Morillo E et al. / Comunicaciones S
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Rigol-Sánchez JP et al. / Comunica
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Rigol-Sánchez JP et al. / Comunica
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Rodríguez Rubio P et al. / Comunic
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Rodríguez Rubio P et al. / Comunic
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Salvador R et al. / Comunicaciones
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Vázquez M et al. / Comunicaciones
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Vázquez M et al. / Comunicaciones
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Vázquez M, Jiménez Millán J / Co
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Vázquez M, Jiménez Millán J / Co
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Velasco Vélez J et al. / Comunicac
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