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641.
The thermal behaviour and the structural properties of three important industrial phyllosilicates, such as kaolinite, talc and Ca-rich montmorillonite, have been examined after mechanical treatment in a specifically built planetary ball mill working in vacuum (P = 0.13 Pa) at room temperature (25 °C). It is found that, on increasing the grinding time, the temperature of the dehydroxylation reaction decreases linearly as a result of a decrease of the crystallite size and structural order. To be noted that the mechanical treatment in our milling conditions did not induce significant amorphization. The temperature at which there is the maximum of dehydroxylation and the weight losses of the intralayer OH are linearly related to the increase of the FWHM of the 001 basal plane. These results are useful for predicting the thermal behaviour of layer silicates to be subjected to mechanical processing in industrial application. 相似文献
642.
Giancarlo Capitani Nobuyoshi Miyajima Roberto Sulpizio Maria D’Addabbo Lucia Galimberti Massimo Guidi Giovanni B. Andreozzi 《Environmental Earth Sciences》2018,77(13):521
In this study, we performed leaching experiments for timescales of hours-to-months in deionized water on fresh volcanic ash from Mt. Etna (Italy) and Popocatépetl (Mexico) volcanos to monitor Fe release as a function of ash mineral chemistry and size, with the aim of clarifying Fe release mechanisms and eventually evaluating the impact of volcanic ash on marine and lacustrine environments. To define sample mineralogy and Fe speciation, inclusive characterization was obtained by means of XRF, SEM, XRPD, EELS and Mössbauer spectroscopies. For Etna and Popocatépetl samples, glass proportions were quantified at 73 and 40%, Fe2O3 total contents at 11.6–13.2 and 5.8 wt%, and Fe3+/FeTot ratios at 0.33 and 0.23, respectively. Leaching experiments showed that significant amounts of iron, ~?30 to 150 and ~?750 nmol g?1 l?1 for pristine Etna and Popocatépetl samples, respectively, are released within the first 30 min as a function of decreasing particle size (from 1 to 0.125 mm). The Popocatépetl sample showed a very sustained Fe release (up to 10 times Etna samples) all along the first week, with lowest values never below 400 nmol g?1 l?1 and a maximum of 1672 nmol g?1 l?1 recorded after 5 days. This sample, being composed of very small particles (average particle size 0.125 mm) with large surface area, likely accumulated large quantities of Fe-bearing sublimates that quickly dissolved during leaching tests, determining high Fe release and local pH decrease (that contributed to release more Fe from the glass) at short timescale (hours-to-days). The fractional Fe solubility (FeS) was 0.004–0.011 and 0.23% for Etna and Popocatépetl samples, respectively, but no correlation was found between Fe released in solution and either ash Fe content, glass/mineral ratio or mineral assemblage. Results obtained suggest that volcanic ash chemistry, mineralogy and particle size assume a relevant role on Fe release mostly in the medium-to-long timescale, while Fe release in the short timescale is dominated by dissolution of surface sublimates (formed by physicochemical processes occurring within the eruption plume and volcanic cloud) and the effects of such a dissolution on the local pH conditions. For all samples, a moderate to sustained Fe release occurred for leaching times comparable with their residence time within the euphotic zone of marine and lacustrine environments (variable from few minutes to few hours), revealing their possible contribution to increase Fe bioavailability. 相似文献
643.
Mahmudova Ayisha Borsi Iacopo Porta Giovanni Michele 《Computational Geosciences》2022,26(5):1119-1134
Computational Geosciences - Damage in subsurface formations caused by mineral precipitation decreases the porosity and permeability, eventually reducing the production rate of wells in plants... 相似文献