9328
J. Phys. Chem. C 2010, 114, 9328–9343
1
H, 29Si, and 27Al MAS NMR as a Tool to Characterize Volcanic Tuffs and Assess Their Suitability for Industrial Applications Piero Ciccioli,† Paolo Plescia,‡ and Donatella Capitani*,§ Dipartimento di Scienze della Terra, UniVersita` degli Studi di Perugia, Piazza UniVersita`, 06123, Perugia, Italy, Istituto per lo Studio dei Materiali Nanostrutturati del CNR (ISMN), Area della Ricerca di Roma 1, 00016, Monterotondo Scalo e Via dei Taurini, 19, 00185, Roma, Italy, Laboratorio di Risonanza Magnetica “Annalaura Segre”, Istituto di Metodologie Chimiche, Area della Ricerca di Roma 1, 00016, Monterotondo Scalo (Roma), Italy ReceiVed: October 5, 2009
The type and quality of the information provided by the direct analysis of volcanic tuffs by 1H, 29Si, and 27Al NMR were investigated. At this aim, five tuffs, characterized by different origin, bonding mechanism, and clast composition, were used as test materials. Results consistent with the different nature of the tuff matrix and mineral composition were obtained. While the relative content of Al in the crystal and amorphous phase was determined by 27Al MAS and 3Q MAS NMR, the prevalent glassy or zeolitic nature of the matrix was assessed by 29Si and 1H MAS NMR. Zeolites present at levels as low as 15% w/w were detected by 29Si MAS NMR, and in some tuffs, identification of their framework type was performed together with the determination of the Si/Al ratio and, for the first time, of their configurational entropy. Data obtained were coherent with those provided by X-ray fluorescence (XRF), X-ray powder diffraction (XPRD), thermogravimetric analysis (TGA), differential thermal gravimetry (DTG), cation exchange capacity (CEC) determinations, and scanning electron microscopy, used in both backscattering imaging mode (SEM) and for elemental analysis (SEM-EDS). Results show that, under favorable conditions, solid state NMR techniques can provide a comprehensive view of the chemical and physicochemical behavior of a tuff. A combined use of these techniques is suitable for characterization of tuffs on a routine basis, and can be particularly useful to decide if a material is suitable for industrial applications. I. Introduction The numerous applications recently found for volcanic tuffs1–4 have increased the demand for fast and specific techniques, providing direct information on the components responsible most for their chemical and physicochemical behavior. Volcanic tuffs are rocks composed of a consolidated ash matrix made of particles smaller than 2 mm, containing lithic (xenoliths of sedimentary origin and lava fragments), vitric (pumice fragments and glass shards), and crystal clasts (primary and accessory minerals) at different amounts.5 Large differences in texture and chemical and petrographic compositions are observed among tuffs, because they are formed from pyroclastic flow or plinian and surge and fall deposits, and numerous factors, such as the nature of the primitive magma, the deposition and compaction of the emitted material, and postdepositional processes, concur to define the final product.5,6 In addition to the relative contents of clasts (see Table 1), also the nature of the matrix is different, and a broad distinction is made between welded and lithified tuffs (see Table 1).5,6 The term “welded tuffs” identifies rocks bonded by sintering and compaction of glass in the matrix. Since the welding process occurs when the deposit is still hot and plastic, large vitric scoriae, highly deformed into disk-shaped lenses, called fiamme, are often present in these tuffs, and used for field identification.6 The term “lithified tuffs” applies to rocks * Corresponding author. E-mail:
[email protected]. Phone: (+39).06.90672700. Fax: (+39).06.90672477. † Universita` degli Studi di Perugia. ‡ Istituto per lo Studio dei Materiali Nanostrutturati del CNR (ISMN). § Istituto di Metodologie Chimiche.
whose original ash matrix has undergone such profound chemical alterations, that authigenic minerals, mainly composed of zeolites, act as binding agents for the material.2,4,7–9 Secondary mineralization occurs most in open or closed hydrological systems subjected to mild temperatures (
