1,720,993 research outputs found
Formation of Supramolecular Clusters at the Interface of Zeolite X Following the Adsorption of Rare-Earth Cations and Their Impact on the Macroscopic Properties of the Zeolite
No full textThe adsorption behavior of neodymium (Nd3+) and yttrium (Y3+) cations on synthetic FAU zeolite X in its sodium form (NaX) has been investigated by means of macroscopic (adsorption isotherm determination and thermal analysis) and microscopic measurements (including solid-state NMR spectroscopy and X-ray powder diffraction). The multidisciplinary study reveals some unexpected features. Firstly, adsorption constants of cations are not correlated to their ionic radii or hydration enthalpy. The adsorption constant of Y3+ on NaX was indeed about twice that of Nd3+, which is the opposite of what could be expected based on the size of the cations. In addition, adsorption was accompanied by partial dealumination of the zeolite framework. The extent of dealumination changed depending on the exchanged cations, with the extent being more significant on the Nd-exchanged zeolite than on the Y-exchanged one. The most interesting finding of this study, however, is the presence of supramolecular clusters composed of water, Nd3+, residual sodium ions, and extra-framework aluminum at the interface of Nd-exchanged zeolite. The hypothesis that these host-guest complexes are responsible of the significantly different behavior exhibited by NaX towards the adsorption/desorption of Nd3+ and Y3+ has been formulated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Antarctic snow: metals bound to high molecular weight dissolved organic matter
No full textIn this paper we studied some heavy metals (Cu, Zn, Cd, Pb, As, U) probably associated to high molecular weight organic compounds present in the Antarctic snow. Snow-pit samples were collected and analysed for high molecular weight fraction and heavy metals bound to them by means of ultrafiltration treatment. High molecular weight dissolved organic matter (HMW-DOM) recovered by ultrafiltration showed a dissolved organic carbon concentration (HMW-DOC) of about 18–83% of the total dissolved organic carbon measured in Antarctic snow. The characterisation of HMW-DOM fraction evidenced an ageing of organic compounds going from surface layers to the deepest ones with a shift from aliphatic compounds and proteins/amino sugars to more high unsaturated character and less nitrogen content. The heavy metals associated to HMW-DOM fraction follows the order: Zn > Cu > Pb >> Cd ∼ As ∼ U. The percentage fraction of metals bound to HMW-DOM respect to total metal content follows the order: Cu >> Pb > Zn, Cd in agreement with humic substance binding ability (Irwing-William series). Going down to depth of trench, all metals except arsenic, showed a high concentration peak corresponding to 2.0–2.5 m layer. This result was attributed to particular structural characteristic of organic matter able to form different type of complexes (1:1, 1:2, 1:n) with metals. © 2017 Elsevier Lt
Materiali per progettare. Guida all'informazione tecnica e normativa sui prodotti edilizi.
No full textEXPERIMENTAL EVALUATION OF INTRAORAL SCANNERS IN EDENTULOUS MANDIBLES
Full text linkAim: the main difficulties for intraoral scanners (IOS) are found in
the edentulous mandibles. The reduced bucco-lingual surface, the
limited height of the bone crest and the mobility of the soft tissues
generate criticalities for the acquisition of the digital impression.
The purpose of this study is to evaluate the comparison between
digital and analog impressions in these particular conditions.
Methods: two scans were obtained for the 11 subjects. The first
intraoral scan was carried out with intraoral scan (Omnicam
DentsplySirona) and the second was acquired by digitizing a plaster
model, obtained from an impression taken with an analogue
method, the best choice in these cases. All scans were converted
to standard tessellation language (STL). The STL files obtained for
each patient were superimposed by means of the GEOMAGIC
Control X software, to evaluate the comparison.
The average distance values obtained through the Geomagic
3D software constitute our primary outcome measure. 1 sample
t-test was used to prove the hypothesis that the average
distances of the points obtained between the two files are relevant
(α = .05).
Results: concerning the scans ability to reproduce the analog
impression the intraoral scans carried out with a intraoral scan
generated files with single measurements in terms of minimal
distance between objects far from scans obtained with analogue
methods (t =-7.29, P < .001).
Conclusion: regarding the results obtained, it was possible to
conclude that the STL files deriving from digital impressions
are significantly different from those deriving from analog impressions,
highlighting a difference between the two methods
La tavola, la gamba e lo stivale
No full textBreve ricostruzione dei modelli con i quali la poenisola italiana è stata concepita nel cosrso della stori
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lithium iron phosphate batteries recycling: An assessment of current status
No full textIn this paper the most recent advances in lithium iron phosphate batteries recycling are presented. After discharging operations and safe dismantling and pretreatments, the recovery of materials from the active materials is mainly performed via hydrometallurgical processes. Moreover, a significant number of works are currently being focused on direct regeneration processes. Both approaches are currently applied only at laboratory scale. The main challenges to be faced when dealing with upscaling these technologies (for example mechanic vs manual dismantling, valuable elements recovery strategy vs all-components recovery strategy) are here presented and discussed
Magnesium recovery from seawater desalination brines: a technical review
Full text linkExisting desalination technologies produce large amount of waste brines with higher salinity concentration than feed seawater, the disposal of which pose serious environmental problems. At the same time, waste brines represent a valuable source of strategic materials—such as magnesium—and therefore their valorization offers the opportunity to overtake both the environmental and the economic issues. Current needs are to identify gaps and challenges to recover secondary magnesium in order to bring recovery technologies closer to the market for potential commercial applications. In this technical review, the available methods for magnesium recovery from seawater desalination brines are described and compared in details, to provide the readers with a wide overview to better address their research efforts towards resources valorization, in accordance with the circular economy principles. Graphical abstract: [Figure not available: see fulltext.
Materials recovery from end-of-life wind turbine magnets
No full textNeodymium–iron–boron permanent magnets are increasingly used in green energy technologies, such as wind turbines and electric vehicles. In the near future, an increasing amount of magnets will reach their end-of-life stage, andtherefore, it is imperative to develop proper recycling routes aimed at the valorization of this waste fraction. In this work, a room temperature hydrometallurgical process was developed aimed at the recovery of both iron and rare earths contained in end-of-life wind turbine magnets. The process is based on a leaching step with nitric acid, followed by two precipitation steps and calcination. Iron hydroxide(III) and rare earth oxide with purity grade equal to 98% and 99%, respectively, were obtained. Based on these results, a process flowsheet was proposed for industrial implementation
- …
