1,720,995 research outputs found
Zeoliti naturali, Zeolititi e loro applicazioni
No full textDopo una approfondita descrizione delle Zeoliti naturali e delle rocce a prevalente contenuto in Zeolite (Zeolititi) e delle loro proprietà chimico-fisiche e tecnologiche, vengono criticamente rivisti e descritti i risultati di laboratorio e a pieno campo ottenuti utilizzando diverse tipi di Zeolititi italiane ed estere nella nutrizione animale, depurazione acque, agricoltura e floricultura.Stampato presso Grafiche Gemma (Borgoricco - PD
In mangiatoia c’è spazio per le zeoliti
No full textDopo una breve descrizione delle Zeoliti e delle rocce a prevalente contenuto in Zeolite (Zeolititi) e delle loro proprietà chimico-fisiche, viene discusso criticamente il loro impiego nella nutrizione animale ed i conseguenti risultati positivi sotto il profilo sanitario
Rietveld structure refinement of NH4-exchanged natural chabazite
No full textIn this work the results of the X-ray Rietveld structure refinement of a natural and the corresponding NH4-exchanged chabazite from Nova Scotia (Canada) are exposed. Experimental data were collected using a laboratory powder diffractometer equipped with copper tube and graphite crystal monochromator. The outcome of this crystal-structure study is useful for (i) understanding the structure modifications induced by the NH4+ exchange: (ii) understanding the physical-chemical and technological properties of NH4-chabazite, a zeolite vastly used for industrial applications, (iii) understanding the mechanism of proton conductivity of the NH4-exchanged zeolites, precursors of catalytically active H+ forms. The position and orientation of the NH4+ ion were initially refined using the rigid body model and later with the aid of soft constraints. The coordination number of the ammonium ion is 9 with two equally possible and mutually exclusive configurations. One coordination environment includes 3 oxygen atoms O3, 3 oxygen atoms O4, and 3 H2O molecules W2a. The other environment includes 3 oxygen atoms O3. 3 oxygen atoms O4, and 3 H2O molecules W3. As already shown for other NH4-zeolites, the N-O distances are larger than the N-H2O distances. The local geometry of the ammonium ion points to a monodentate configuration. A bidentate configuration of the hydrogen bonds for NH4+ is also possible if the long H2(center dot center dot center dot)O3 separation is considered to be at bond distance. For industrial and technological applications, knowledge of the local environment of NH4+ in the cavities of zeolites is important. Weak hydrogen bonds with framework oxygen atoms implies that the ammonium molecule can be easily exchanged or desorbed. This property is attractive for agronomy, horticulture and soil remediation where zeolite can be added to chemical fertilizers to improve the soil's chemical and physical properties for plant growth, to increase fertilizer efficiency and to reduce the leaching of nutrients, to reduce the dissolution rate of a soluble fertilizer via ion exchange or combination of mineral dissolution and ion exchange, and to act as remediation agents in soils
NATURAL ZEOLITES - MINERALOGY AND APPLICATIONS
No full textAfter a brief description of the crystallochemical peculiarities of zeolites, which enable them to be used in many technological fields, the present and potential applications of natural zeolites are reviewed. The possibility of using Italian chabazite and phillipsite to reduce problems connected with nitrogen pollution is considered
Crystal chemistry of diagenetic zeolites in volcanoclastic deposits of Italy
No full textZeolites from the most important volcanoclastic deposits of Italy include: (1) phillipsite and heulandite from the cinerite of the central northern Apennines; (2) chabazite and phillipsite from phonolitic tephritic ignimbrites contg. black pumices; (3) phillipsite from the tufo lionato of Vulcano Laziale; (4) chabazite and phillipsite from the Campanian ignimbrite; (5) phillipsite from the Neapolitan yellow tuff; and (6) chabazite and phillipsite from the pyroclastics of Monte Vulture. Compared with sedimentary phillipsites and chabazites described in the literature, the chabazites and phillipsites studied have lower Si/Al ratios and higher K contents. These chem. peculiarities are correlated with both the K-rich vesuvianitic-leucititic, latitic-phonolitic, and potassic alkali-trachytic chem. of the ash from which they were derived and, very likely, with the character of the hydrol. open system environment in which they formed. The zeolites of the heulandite-clinoptilolite group from the cinerites of the central northern Apennines is classified as a true heulandite on the basis of its chem. compn. and thermal behavior
Roggianite: revised chemical formula and zeolitic properties
No full textThe holotype roggianite from Alpe Rosso (Novara, Italy) has been chemically re-analysed using modern analytical procedure (microprobe, atomic absorption,spectrophotometer, TG analyses) and tested for its zeolitic behaviour. When compared with that given in the original description, the new chemical composition shows an appreciable amount of Be and a different Si/Al ratio. An accurate powder pattern is also given. Since the mineral showed an almost complete rehydration after heating at 750°C and an appreciable ion exchange capacity, it must be considered a zeolite. It is the only zeolite with Be as fundamental constituent and with OH groups in the frameworl like partheite
The crystal chemistry of gmelinites
No full textGmelinite [12251-35-3] specimens were analyzed by electron microprobe and their unit-cell dimensions were detd. by x-ray powder diffractometry. Four samples showed compositional zoning, the others being highly homogeneous. The mineral compn. ranges approx. from Al7Si17O48 to Al8.4Si15.6O48. The major exchangeable cations are Na and Ca. K and Mg are present in small amts., Ba is always absent, and Sr frequently absent. The lattice parameters are strongly correlated with the exchangeable-cation content: a increases and c decreases with increasing divalent-cation content
Chemistry of levynes and epitaxially overgrown erionites
No full textThis paper deals with the chemistry of 12 levyne-erionite intergrowths. The two zeolite species differ for both framework and extraframework cation contents being levyne constantly Si- and K-poorer and Ca-richer than overgrown erionite. The relative increase of K in the parent solution during the crystallization process is considered the main responsible for the growth of erionite instead of levyne. The dominance of Na among extraframework cations in both levyne and overgrown erionite crystals of three samples of sea-shore occurrence is justified with later cation exchange with sea-water.This paper deals with the chemistry of 12 levyne-erionite intergrowths. The two zeolite species differ for both framework and extraframework cation contents being levyne constantly Si-and K-poorer and Ca-richer than overgrown erionite. The relative increase of K in the parent solution during the crystallization process is considered the main responsible for the growth of erionite instead of levyne. The dominance of Na among extraframework cations in both levyne and overgrown erionite crystals of three samples of sea-shore occurrence is justified with later cation exchange with sea-water
Secondary mineral assemblages as indicators of multistage alteration processes in basaltic lava flows: evidence from the Lessini Mountains, Veneto Volcanic Province, Northern Italy
No full textThe secondary mineral assemblages in the Tertiary basalts from the Lessini Mountains are mainly clay minerals and zeolites, and result from multistage alteration processes. In the earliest Stage I, clay and silica minerals precipitate along the inner walls of the vesicles, followed by the deposition of the fine-grained zeolites of the Stage II (erionite, offretite, analcime, natrolite, heulandite and stilbite). The final Stage III is marked by a new generation of large, well-shaped zeolites (phillipstite-harmotomo, gmelinite, chabazite, willhendersonite and yugawaralite), followed by extensive crystallization of calcite. New morphological and chemical data are presented herein in order to reveal the chemical compositions of Lessini zeolite species, which have never been analyzed before. Textural and chemical observations indicate that the chemical elements for Stage I and II alteration minerals derived from the alteration of the basaltic glass and the primary phases in the volcanic host rocks. The final mineral assemblages of the Stage III suggest a variation in the crystallization conditions, probably related to the presence of new, late-stage fluids enriched in Ca and (CO3)2-, leached from the surrounding calcareous rocks
Zeolite content and cation exchange capacity of zeolite-rich rocks
No full textThe zeolite fraction of zeolite-rich rocks of different occurrence was calculated using quantitative phase analysis by combined Rietveld and Reference Intensity Ratio (RIR) methods and cation exchange capacity (CEC) by NH, solution. The cross-check results are in good agreement apart from a clinoptilolite-rich sample whose zeolite content from CEC was significantly underestimated
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