Antonello Marocco

Cyclic process of simazine removal from waters by adsorption on zeolite H-Y and its regeneration by thermal treatment

Removal of the agrochemical simazine from polluted waters through adsorption by zeolite Y in its protonic form was studied. The investigated parameters were: pH, time, initial simazine concentration and solid/liquid ratio. An iterative process of simazine removal from waters is proposed, featuring: (i) final agrochemical concentration well below 0.05 mg/dm(3), the maximum concentration allowed by Italian laws in wastewaters; (ii) regeneration of the adsorbent by a few minutes thermal treatment in air at about 500°C, which results in the combustion of simazine without damage of the adsorbent; (iii) destruction of the agrochemical compound by combustion.

Effect of the mineralizer solution in the hydrothermal synthesis of gadolinium-doped (10% mol Gd) ceria nanopowders

Background Gadolinium-doped ceria is an attractive electrolyte material for potential application in solid oxide fuel cells (SOFCs) operating at intermediate temperatures typically with 10%-20% substitution of Ce+4 by Gd+3. In particular, 10% gadolinium-doped ceria seems to have the highest values of conductivities among the other dopant compositions. Methods Nanosized powders of gadolinium-doped ceria were prepared by hydrothermal treatment using coprecipitate as a precursor and in the presence of 3 different mineralizer solutions. The powders obtained were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and thermal analysis, while the electrical behavior of the corresponding pellets were ascertained by AC impedance spectroscopy. Results Nanocrystalline gadolinium-doped ceria powders with fluorite cubic crystal structure were obtained by hydrothermal treatment. Independent of the mineralizer used, these powders were able to produce very dense ceramics, especially when selecting an optimized sintering cycle. In contrast, the electrical behavior of the samples was influenced by the mineralizer solution, and the samples synthesized in the neutral and alkaline solutions showed higher values of electrical conductivity, in the range of temperatures of interest. Conclusions By the coprecipitation method, it has been possible to synthesize nanosized gadolinium-doped cerium oxide in a fluorite structure, stable in a wide range of temperatures. Hydrothermal treatment directly on the as-synthesized coprecipitates, without any drying step, had a very positive effect on the powders, which can be sintered with a high degree of densification, especially with an optimized sintering cycle. Furthermore, the electrical behavior of these samples was very interesting, especially for the samples synthesized using neutral mineralizer solution and basic mineralizer solution.

Parameters Expediting the Thermal Conversion of Ba-ExchangedZeolite A to Monoclinic Celsian

Four samples of Ba-exchanged zeolite A, bearing small residual amounts of Na (0.27, 0.43, 0.58, and 0.74meq/g), were thermally treated in the temperature range 200–1500 ◦ C for times up to 28 hours. The same samples were pressed at 30 and 60MPa to form cylindrical pellets which were thermally treated at 1300 ◦ C for 5 hours. All materials were characterized by room temperature XRD. The sequence of thermal transformations that Ba-exchanged zeolite A undergoes (zeolite → amorphous phase → hexacelsian → monoclinic celsian) and the strong mineralizing action developed by Na are confirmed. Pressing the Ba-exchanged zeolite A powder-like samples to obtain cylindrical pellets is found to expedite the sluggishfinal phase transitionhexacelsian → monoclinic celsian. The optimum residual Na content of Ba-exchanged zeolite A for transformation into monoclinic celsian is assessed to be between 0.27 and 0.43meq/g.

Effect of residual Na on the low temperature synthesis of monoclinic celsian from zeolite Ba-A

Publisher Summary This chapter presents the effect of residual Na on the low temperature synthesis of monoclinic celsian from zeolite Ba-A. Monoclinic celsian is used as a refractory, high temperature electrical insulator, or as substrate for integrated circuits on account of its good thermal and electrical properties, although its synthesis gives rise to considerable problems. A long term study on the thermal transformation of Ba-exchanged zeolites into monoclinic celsian was undertaken. This study started from the work of Subramanian who crystallized alkaline-earth and alkaline framework aluminosilicates by thermal treatment of cation exchanged zeolites at temperatures slightly higher than 1000 °C for some hours. This technique seemed to avoid the drawbacks arising in the traditional syntheses of monoclinic celsian. Interesting results were obtained in studying the thermal transformation of Ba-exchanged zeolites in monoclinic celsian. It was found that, upon thermal treatments at temperatures >1000 °C, zeolite Ba-A gave rise to the following transformations: zeolite → amorphous phase → hexacelsian → monoclinic celsian. It was found that thermal treatments at 1100 °C for 6 hours and 1300°C for 22 hours were sufficient to transform samples of zeolite Ba-A, containing 0.58 and 0.20 meq/g Na residual amount, respectively, into fully monoclinic celsian. These data reveal that zeolite Ba-A does appear a very reactive precursor as the full conversion into monoclinic celsian was obtained in far milder conditions than those reported in the literature.

Application of highly porous materials for simazine removal from aqueous solutions

ABSTRACT The removal of simazine from both pure water and solute-bearing well water was studied by adsorption on two solids: zeolite H-Y from the commercial Na form and porous silica tailored by the sol–gel technique. The pH dependence of the amount adsorbed in a closed system at constant total simazine content as well as the apparent isotherms of adsorption was measured in all four cases. The low ion content of natural water suffices to alter the adsorption features in the case of silica, but not with zeolite H-Y. Iteration of the adsorption process onto constant amounts of solid allowed bringing the residual simazine concentration below 0.05 mg/L, the value allowed by Italian laws in wastewaters.

Adsorption of simazine on zeolite H-Y and sol-gel technique manufactured porous silica: A comparative study in model and natural waters.

In this work, we studied the removal of simazine from both a model and well water by adsorption on two different adsorbents: zeolite H-Y and a porous silica made in the laboratory by using the sol–gel technique. The pH dependence of the adsorption process and the isotherms and pseudo-isotherms of adsorption were studied. Moreover, an iterative process of simazine removal from both the model and well water, which allowed us to bring the residual simazine concentration below the maximum concentration (0.05 mg L−1) of agrochemicals in wastewater to be released in surface waters or in sink allowed by Italian laws, was proposed. The results obtained were very interesting and the conclusions drawn from them partly differed from what could reasonably be expected.

Use of Sawing Waste from Zeolitic Tuffs in the Manufacture of Ceramics

This paper investigates the thermal transformation of powders of volcanic tuffs that are used as building stones and aims at thermally transforming them into ceramics. The following positive indications concerning this thermal transformation were found: (1) the structural evolution which brings products similar to traditional ceramics, (2) the good ability to give rise to dense and compact final products, and (3) the good mechanical properties and the lovely appearance of the final products. Nevertheless, the high values of linear shrinkages recorded in this work seem to strongly hinder the thermal transformation of this powder-like waste into ceramics. However, mixing this by-product with other powder-like waste exhibiting higher-dimensional stability, such as those deriving from sawing of granites, appears proper.