Search results for "DSO"
showing 10 items of 1609 documents
Oxidation of oxalate ion in aqueous suspensions of TiO2 by photocatalysis and ozonation
2005
Abstract Oxalate anion has been oxidized in aqueous alkaline solution by using ozonation and photocatalysis in the presence of TiO 2 . A batch annular reactor has been used for carrying out reactivity runs in the presence of air/ozone, air/ozone/near UV irradiation, air/ozone/TiO 2 , air/near UV-irradiated TiO 2 and air/ozone/near UV-irradiated TiO 2 . The Langmuir–Hinshelwood kinetic model adequately describes the photocatalytic results obtained at different reaction conditions and allows determining the values of the kinetic and equilibrium adsorption constants. The contemporary presence of photocatalysis and ozonation shows a significant improvement of the process performance as the oxid…
Sorption characteristics of heavy metal ions by a natural zeolite
2005
Zeolites have been shown to be effective adsorbents for the removal of heavy metals from aqueous solutions. A natural material from Cuba, containing zeolite, has been used for the removal of several metal ions, namely Cu2+, Zn2+, and Ni2+, to evaluate its potential use as a low-cost adsorbent. Batch experiments have been conducted to evaluate the process kinetics and the removal equilibrium at different pH values, metal and zeolite concentrations. Pseudo-second order kinetics and Freundlich equilibrium parameters have been obtained. Results suggested that this natural zeolite has a high potential for heavy metal retention. The selectivity of the studied metals was determined as Cu2+ ≫ Zn2+ …
A calcined clay fixed bed adsorption studies for the removal of heavy metals from aqueous solutions
2021
Abstract A natural clay material from southern Tunisia was used as a low cost sorbent in a column-wise removal of metal pollutants. This is fundamentally important for a sustainable wastewater treatment strategy. This work has been performed within the framework of a project aiming to the valorization of natural geomaterials, from Tunisia, in several environmental applications. Column adsorption experiments were carried out for a better production of cleaner effluents and further understanding of the main mechanisms involved in the removal process, through a dynamic methodology, that would allow an industrial scale treatment. A calcined clay sample was used as an adsorbent for the removal o…
Removal of drugs in aqueous systens by photoassisted degradation
2005
Aqueous solutions of tetracycline, lincomycin and ranitidine were irradiated with UV light in homogeneous and heterogeneous systems. Two commercial polycrystalline TiO2 powders (Degussa P25 and Merck) were used as photocatalysts. After 5A h, an appreciable photolytic degradation of tetracycline and ranitidine was observed while the degradation of lincomycin was noticeably lower. As far as the mineralization is concerned, a small decrease of the TOC values was measured in the case of tetracycline whereas negligible variations were found for lincomycin or ranitidine. The presence of the photocatalysts greatly enhanced the degradation rates of the drugs with respect to those observed during th…
Some working principles of heterogeneous photocatalysis by semiconductors
1993
The present paper outlines some of the principles which are the working base for the photocatalytic processes: we refer to those photocatalytic processes performed using irradiated semiconductors. The steps related to the photoproduction of electron-hole pairs and their separation are discussed. It is also shown how the step of pair separation induces the formation of various chemical species, some of which are useful for the oxidation reactions. It is also shown that in order to reach a detailed description of photocatalytic processes it is necessary to have the knowledge of both the electronic and the physicochemical features of the semiconductors. The paper finally reports a case study r…
Sorption of argon and nitrogen on network types of zeolites and aluminophosphates
1991
Abstract Synthetic zeolites and aluminophosphates comprising 10- and 12- membered ring openings, unidimensional and network type of pore systems (MFI, MEL, ERI, LTA, AEL, AFI and FAU) were used as model adsorbents to examine the impact of micropore structure on the sorption properties. Argon and nitrogen were employed as adsorptives. Adsorption measurements were carried out on gravimetric and volumetric sorption devices and also monitored by microcalorimetry. From the low coverage regime of the isotherm Henry's constants and isosteric heats of adsorption were derived. Both quantities allowed the discrimination between 10- and 12- membered ring systems. Unidimensional 10- and 12- membered ri…
High Resolution Sorption Studies of Argon and Nitrogen on Large Crystals of Aluminophosphate AlPO4-5 AND ZEOLITE ZSM-5
1989
High resolution adsorption (HRADS) with argon and nitrogen at 77 K in the pressure range of 10−6 < p/p° < 0.5 were performed on large crystals of zeolite ZSM-5 (180 μm) and aluminophosphate AlPO4-5 (150 μm) using a novel volumetric device. Multi-step isotherms of both adsorptives on ZSM-5 could be observed for the first time. The adsorption followed by low temperature microcalorimetry resulted in distinct exothermic signals at the steps in the adsorption isotherms. Based on the results of atom-atom potential energy calculations (AAP) as well as independent model building it was shown that 24 ‘kinetic’ adsorbate molecules can be filled into a ZSM-5 unit cell. Experimental results are reasona…
High-resolution sorption studies of argon and nitrogen on large crystals of microporous zeolite ZSM-5
1989
High resolution adsorption (HRADS) with argon and nitrogen at 77 K were performed on large crystals of zeolite ZSM-5 using a novel volumetric device. Multi-step isotherms for both adsorptives could be observed for the first time. The micropore filling was followed by low temperature microcalorimetry. Exothermic heats of adsorption were found to be correlated with steps in the adsorption isotherms. Based on results from atom-atom potential energy calculations (AAP) as well as from independent model building it is shown that 24 kinetic adsorbate molecules can be situated in a ZSM-5 unit cell. Localized adsorption is presented as possible filling mechanisms. Experimental results are reasonably…
Memory effects and coverage dependence of surface diffusion in a model adsorption system
1999
We study the coverage dependence of surface diffusion coefficients for a strongly interacting adsorption system O/W(110) via Monte Carlo simulations of a lattice-gas model. In particular, we consider the nature and emergence of memory effects as contained in the corresponding correlation factors in tracer and collective diffusion. We show that memory effects can be very pronounced deep inside the ordered phases and in regions close to first and second order phase transition boundaries. Particular attention is paid to the details of the time dependence of memory effects. The memory effect in tracer diffusion is found to decay following a power law after an initial transient period. This beha…
Speciation and oxidation kinetics of arsenic in the thermal springs of Wiesbaden spa, Germany.
2001
Since 1886 arsenic has been known to be present as a trace component in the Wiesbaden thermal waters at concentrations of over 100 microg L(-1). In this study for the first time molecular level speciation of arsenic was measured both in the water (by HG-AAS) and in wellstone scale deposits (by XANES). Most of the arsenic in the anoxic NaCl-type waters is in the reduced arsenite form. Hydrous ferric oxide (HFO) precipitates in the scale deposits scavenge only the minor dissolved arsenate portion which is, however, accumulated up to 3% w/w. Isothermal precipitation experiments at in-situ temperatures showed a difference between the progress of both arsenic and iron oxidation and precipitation…