1,721,256 research outputs found
“Studio dei processi di desolforazione spray-dry dei fumi prodotti da centrali termoelettriche ad olio combustibile. Parte I"
No full text“Calcium bisulfite oxidation rate in the wet limestone–gypsum flue gas desulfurization process”
No full textIn this paper oxidation of calcium bisulfite in aqueous
solutions was studied, in connection with the limestone -
gypsum flue gas desulfurization process. Experimental
measurements of the oxidation rate were carried out in a
laboratory scale stirred reactor with continuous feeding
of both gas and liquid phase. A calcium bisulfite clear solution
was used as liquid phase, and pure oxygen or mixtures
of oxygen and nitrogen were used as gas phase. Experiments
were carried out at
T
) 45 ° C varying the composition
of the liquid phase and the oxygen partial pressure.
Manganous sulfate was used as catalyst. The analysis of
the experimental results showed that the kinetics of
bisulfite oxidation in the presence of MnSO 4 follow a parallel
reaction mechanism, in which the overall reaction rate
can be calculated as the sum between the uncatalyzed rate
( 3 / 2 order in bisulfite ion) and the catalyzed reaction rate
(first order in manganous ion)
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
"Mass Transfer between a Fixed Bed of Limestone Particles and Acid Solutions"
No full textLimestone dissolution in acid solutions was experimentally studied by means of a fixed-bed reactor. A diffusive model was proposed to describe experimental results. The model, based on the film theory, takes into account the effect of the electric potential of diffusion on the dissolution rate. In order to validate the model, experiments were carried out to study the effect of both particle size and liquid-solid relative velocity on the dissolution rate. Furthermore, the limestone dissolution rate in aqueous solutions of SO2(aq), HC1, and H2SO4 was measured at different acid concentrations. The results showed that the diffusive model, associated with the correlation proposed by Chu et al. [Chu, J. C.; Kalil, J.; Wetteroth, W. A. Chem. Eng. Prog. 1953, 49 (3), 141] for the evaluation of the liquid-solid mass-transfer coefficient, is capable of describing the dependence of the dissolution rate on both the size of the limestone particles and the liquid-solid relative velocity. In addition, it was found that, in agreement with the physical meaning of the film theory, the thickness of the liquid film is not dependent on the kind of acid present in the solution nor on its concentration but only on the fluid dynamic conditions of the liquid-solid system
“A Real Adsorbed Solution Theory for the adsorbition of PCE and TCE from aqueous solution”
No full text
- …
