1,721,096 research outputs found
Adsorption–Desorption Process to Separate Dyes from Tanning Wastewaters
Full text linkWastewater production is a major environmental issue for the leather and textile industries: in a modern plant, several synthetic dyes are used in separated coloring batches whose wastewaters are usually mixed, diluted with other process water streams, and sent to a unique wastewater treatment plant. This includes specific physical and biochemical tertiary treatments to remove dyes efficiently. One of the main difficulties of these processes is the presence of multiple dyes, which cannot be treated with the same efficiency as a “wide-spectrum” process. This work explores the possibility of using conventional granular activated carbon (GAC) and a new polyurethane foam (PUF) for the adsorption of an acid red dye in the wastewater of a specific coloring batch of the tanning industry. The aim of this work is twofold: on the one hand, we aim to explore the performance of the new PUF sorbent; on the other hand, we aim to explore the possibility of using adsorption as an optimized pre-treatment for single-dye batches, which may take advantage of the presence of a single type of target dye and its higher concentration. The effluent is then sent to the wastewater treatment plant for further depuration
Adsorption of heavy metals on silica-supported hydrophilic carbonaceous nanoparticles (SHNPs)
No full textThis paper reports experimental results on the removal of Cd(II), Ni(II) and Pb(II) ions using hydrophilic carbon nanoparticles (HNPs) supported over silica beads to enhance their separation from treated water. The supported HNPs (SHNPs) exhibit high removal efficiencies especially at neutral pH and low temperature (10 °C), conditions that commonly occur for natural water remediation and for some types of industrial wastewater. The maximum adsorption capacity of the SHNPs at a reference concentration of 0.2 mM is 0.042 mmol g−1, 0.027 mmol g−1 and 0.055 mmol g−1 for Cd(II), Pb(II) and Ni(II) ions, respectively. Modelling analysis on the adsorption isotherms revealed that the free Gibbs’ energy of interactions between the sorbent and Ni(II) and Pb(II) ions is higher than that of Cd(II) ions indicating that the sorbents are more affine to intermediate acids, as Ni(II) and Pb(II) ions, than to soft acids, as Cd(II) ions. The sorbents exhibit appreciable adsorption capacities per gram of active phase (0.54 mg g−1 for Cd(II) ions, 13.48 mg g−1 for Ni(II) ions and 8.87 mg g−1 for Pb(II) ions) at the corresponding quality limit admitted by Italian regulations on wastewater, suggesting their possible use in water treatment plants
Recovery of platinum from diesel catalysts by combined use of H2O2/HCl leaching and adsorption
No full textSpent automotive catalysts are industrial non-hazardous wastes of high added values because of the presence of platinum group metals, whose recovery is gaining increasing attention in European countries. This paper proposes a hydrometallurgical process to recover platinum from diesel catalysts, based on a first leaching step with aqueous solutions of H2O2 (up to 0.2 M) and mild HCl concentrations (0.4 M), followed by a refining step in which platinum is deposited over a granular activated carbon. Tests were carried out at different H2O2 content, temperatures, and sizes of granulated catalyst. The use of H2O2 and low HCl content allows higher sustainability than conventional hydrometallurgical processes by reducing safety risks associated with the use of concentrated HCl and the emissions of NOx deriving from the use of nitrogen species in conventional leaching. Besides, the use of an adsorbent avoids the utilization of cyanides or other toxic organic solvents for the refining of the leaching solution. Experiments revealed that the low HCl concentration results in longer leaching times; however, process conditions can be tuned to completely recover platinum with negligible extraction of other metals on the catalyst, minimizing on the subsequent adsorption process. Optimal conditions appear as leaching at 20 °C with a 0.13 M H2O2 0.4 M HCl solution followed by an adsorption step at 20 °C using an activated carbon with high BET surface area and high content of reducing surface groups. These findings suggest that the proposed recovery process can be a suitable candidate for future technology implementations
Manifestazioni cliniche da papilloma-virus in donne HIV positive: il ruolo della terapia antiretrovirale (HAART).
No full textManifestazioni cliniche da papilloma-virus in donne HIV positive: il ruolo della terapia antiretrovirale (HAART)
A model for the absorption rate in electrically charged droplets
Full text linkCharged droplets are produced by electrosprays or sometimes generated by natural phenomena, and nowadays their application is also investigated as a tool for process intensification in heat and mass transfer processes typical of chemical engineering. This paper analyses the absorption of slightly soluble trace gases into electrically charged droplets: it reports a new mass transfer model taking into account the electrophoretic motion of gas molecules and the possible alteration of the interfacial properties induced by the imposed electric charges. The model is successfully validated against existing experiments on the absorption of SO2 into electrified water droplets. These experiments are useful both for the robustness of data available for the SO2-air-water system and for its significance in atmospheric chemistry and physics, and chemical engineering applications. Considering the same SO2-air-water system as a case study, the model predicts that the absorption rate for a droplet produced with a conventional electrospray is up to 42% faster than that of an uncharged droplet with the same size and morphology, while the electrophoretic drift provides an improvement of the gas-side mass transfer coefficient mainly for droplets finer than 500 μm
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