Search Results (4)

A mineralogical mapping (terrain analysis) based on micro-mounts has been performed in the Archipelago of the Canary Islands, Spain. The rare elements Be, F, Li, Nb, Ta, Zr, Hf, and rare earth elements (REE) were investigated on the largest island of the Canary Islands Archipelago, Tenerife, Spain. This study forms a contribution to the metallogenetic evolution of the offshore area of the NW African Rare Mineral Province. The finds made at Tenerife were correlated by means of minero-stratigraphy with the adjacent islands La Gomera, Gran Canaria and Fuerteventura, where typical critical element host rocks, e.g., carbonatites, are exposed. At Tenerife, these hidden rock types are only indicated by a wealth of 128 compositional first-order marker minerals hosting Be, F, Zr, Nb, Ta, Zr, Hf, Li, Cs, Sn, W, Ti and REE plus Y and another 106 structural second-order marker minerals describing the geodynamic and morpho-structural evolution of Tenerife (Mn, Fe, Pb, U, Th, As, Sb, V, S, B, Cu, Zn, Mo, Au). Based upon the quantitative micro-mineralogical mapping of lithoclasts and mineralogical xenoliths (foid-bearing monzodiorite/gabbro, (nepheline) syenite, phonolite trachyte) in volcanic and volcaniclastic rocks, hidden intrusive/subvolcanic bodies can be delineated that are associated with contact-metasomatic, zeolitic and argillic alteration zones, as well as potential ore zones. Two potential types of deposits are determined. These are pegmatite-syenites with minor carbonatites bound to a series of agpaitic intrusive rocks that are genetically interlocked with rift zones and associated with a hotspot along a passive continental margin. Towards the east, the carbonatite/alkali magmatite ratio reverses at Fuerteventura in favor of carbonatites, while at Gran Canaria and La Gomera, shallow hypogene/supergene mineral associations interpreted as a marginal facies to Tenerife occur and a new REE discovery in APS minerals has been made. There are seven mineralizing processes different from each other and representative of a peculiar metallogenic process (given in brackets): Protostage 1 (rifting), stages 2a to 2d (differentiation of syenite–pegmatite), stages 3 to 4b (contact-metasomatic/hydrothermal mineralization), stages 5a to 5b (hydrothermal remobilization and zeolitization), stage 6 (shallow hypogene-supergene transition and kaolinization), and stage 7 (auto-hydrothermal-topomineralic mineralization). The prerequisites to successfully take this holistic approach in economic geology are a low maturity of the landscapes in the target area, a Cenozoic age of endogenous and exogenous processes amenable to sedimentological, geomorphological, volcano-tectonic and quantitative mineralogical investigations. The volcanic island’s mineralogical mapping is not primarily designed as a proper pre-well-site study on the Isle of Tenerife, but considered a reference study area for minero-stratigraphic inter-island correlation (land–land) and land–sea when investigating the seabed and seamounts around volcanic archipelagos along the passive margin, as exemplified by the NW African Craton and its metallogenic province. This unconventional exploration technique should also be tested for hotspot- and rift-related volcanic islands elsewhere on the globe for mineral commodities different from the ones under study. Full article

The present work reports the synthesis of efficient Ti–Au/zeolite Y photocatalysts by different processing of aluminosilicate gel and studies the effect of titania content on the structural, morphological, textural, and optical properties of the materials. The best characteristics of zeolite Y were obtained by aging the synthesis gel in static conditions and mixing the precursors under magnetic stirring. Titania (5, 10, 20%) and gold (1%) species were incorporated in zeolite Y support by the post-synthesis method. The samples were characterized by X-ray diffraction, N₂-physisorption, SEM, Raman, UV–Vis and photoluminescence spectroscopy, XPS, H₂-TPR, and CO₂-TPD. The photocatalyst with the lowest TiO₂ loading shows only metallic Au on the outermost surface layer, while a higher content favors the formation of additional species such as: cluster type Au, Au¹⁺, and Au³⁺. A high TiO₂ content contributes to increasing the lifetime of photogenerated charge careers, and the adsorption capacity of the pollutant. Therefore, an increase in the photocatalytic performances (evaluated in degradation of amoxicillin in water under UV and visible light) was evidenced with the titania content. The effect is more significant in visible light due to the surface plasmon resonance (SPR) effect of gold interacting with the supported titania. Full article

New photocatalysts were obtained by immobilization of titanium and gold species on zeolite Y, hierarchical zeolite Y, MCM-48 and KIT-6 supports with microporous, hierarchical and mesoporous cubic structure. The obtained samples were characterized by X-ray diffraction (XRD), N₂-physisorption, scanning and transmission electron microscopy (SEM/TEM), diffuse reflectance UV–Vis spectroscopy (DRUV-Vis), X-ray photoelectron spectroscopy (XPS), Raman and photoluminescence spectroscopy. The photocatalytic properties were evaluated in degradation of amoxicillin (AMX) from water, under UV (254 nm) and visible light (532 nm) irradiation. The higher degradation efficiency and best apparent rate constant were obtained under UV irradiation for Au-TiO₂-KIT-6, while in the visible condition for the Au-TiO₂-MCM-48 sample containing anatase, rutile and the greatest percent of Au metallic clusters were found (evidenced by XPS). Although significant values of amoxicillin degradation were obtained, total mineralization was not achieved. These results were explained by different reaction mechanisms, in which Au species act as e⁻ trap in UV and e⁻ generator in visible light. Full article

Au was deposited on ultrastable Y (USY) zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH₄-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, NH₄-forms of mordenite, and ZSM-5. Treatment of the Au-loaded USY zeolite in a H₂ atmosphere, afforded Au⁰ nanoparticles. These particles were thermally stable even at 973 K, where their mean particle diameter was 3.7 nm. In contrast, highly aggregated Au particles were observed after thermal treatment at temperatures lower than 523 K, followed by storage in air for a month. The resulting particle sizes were in good correlation with the IR band intensity of the adsorbed CO and the catalytic activity of Au in the aerobic oxidation of benzyl alcohol. The Au nanoparticles showed highest activity when the Au/USY zeolite was thermally treated at 673–973 K. A negligible deactivation was observed after repeating the reaction at least 12 times. In the case of Au/TiO₂ catalyst prepared by the deposition-precipitation method, the highest activity was observed at 573 K, which was lower than the temperature used for the Au/USY zeolites. This study demonstrated the potential use of the NH₄-form of USY zeolites for supporting Au. Full article