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The removal of phosphorous from wastewater in metal-orthophosphate systems typically occurs by simultaneous adsorption on poorly soluble metal hydroxides and by precipitation reactions between metal ions and orthophosphates in solution. To understand the individual contribution of these mechanisms to the removal of phosphorus, the main aim of this study was to determine the kinetics of consumption of contaminant orthophosphates by the precipitation reaction with aluminium ions in a solution free of insoluble aluminium hydroxide. To define the amount of aluminium and phosphorous compounds to be dissolved in water to have this desired reacting condition at a given pH, the solubilities of KH2PO4(s), Al(OH)3(s) and AlPO4(s) were examined at 25 °C in the pH range ∼2.6 to 7.9. pH-solubility diagrams for these ionic solids were made by solving a system of nonlinear algebraic equations involving dissolution, dissociation and hydrolysis reactions at equilibrium. The kinetics of the reaction between aluminium and orthophosphate ions at a reacting condition free of solids except for the product AlPO4(s) was investigated in a well-stirred batch reactor at pH ∼3.1 and 3.5 at 25 °C. A detailed kinetic model involving ten species, seven reversible reactions of hydrolysis of soluble aluminium and orthophosphate species and one reversible precipitation reaction between aluminium and phosphate ions revealed a rate constant for the latter reaction of 5.968 × 1010 L mol−1 s−1 (p = 0.191). XRD, TGA/DTGA and EDX analyses of the filtered and dried reacting mixture confirmed that the only solid product of the precipitation reaction was hydrated AlPO4(s). [ABSTRACT FROM AUTHOR]

The main aim of this manuscript was to investigate the effect of amine (MEA, DEA and TEA) functionalization of high surface area supports (Amberlite IR120H, Ambersep 252H, Amberlite 200CNa and Amberlite XAD7HP) on adsorption of CO2 from gases streams. A saturated factorial design of experiments was initially applied to determine the influence of four amine impregnation variables on amine loading. Except for the amine concentration whose effect was significantly positive on the amount of ethanolamine impregnated in Amberlite XAD7HP (p ≤ 0.05), the other factors had negligible importance. Kinetic experiments of CO2 adsorption were performed in a fixed bed at different inlet concentrations of CO2 and temperatures. The amounts of adsorbed CO2 on the DEA enriched Ambersep 252H, Amberlite 200CNa and Amberlite XAD7HP at bed saturation were ~ 40–400 times as high as those obtained with the same adsorbents without impregnation. DEA enriched Amberlite IR120H and TEA functionalized resins presented small capacities to adsorb CO2 at the investigated conditions, while MEA enriched resins were effective as CO2 adsorbents in the case of impregnation in Amberlite 200CNa. A classical fundamental model described correctly the breakthrough curves for CO2 adsorption–desorption at concentrations of CO2 in the gas feed stream of 1%, 3% and 5% at 40 °C and 60 °C. [ABSTRACT FROM AUTHOR]

An initial set of 12 kinetic experiments was carried out to remove naphthalene from an aqueous effluent by photo-Fenton involving Fe0 and Fe2+ at two different concentrations of H2O2 (150 and 300 mg L−1) and three different pHs (3, 5, and 7) (22×31 experiments). The rate constants (k) for the reaction of naphthalene degradation by involving Fe2+ as reactant were in general higher than those with Fe0, but the use of Fe2+ increased the concentration of naphthalene at equilibrium (Ce) when compared with the same response obtained with Fe0 at analogous conditions. A second set of twelve kinetic experiments of photo-Fenton degradation was also performed with persulfate as additive at the conditions already reported, but at a constant concentration of H2O2 of 150 mg L−1 (21×31 experiments with NaCl +21×31 experiments without NaCl). In almost all the runs in which only the source of iron was varied, k from the kinetic data involving Fe2+ was higher than that involving Fe0, but no difference was observed in terms of Ce that was always zero. The addition of persulfate to treat the effluent either containing or not containing salt enhanced the chemical kinetics, and shifted the equilibrium toward the full removal of naphthalene. A final set of nine experiments of UV photo degradation of naphthalene by involving persulfate without iron, with Fe0 and Fe2+ in the pH range from 3 to 7 (32 experiments) mainly showed that the use of H2O2 may be avoided to remove rapidly and completely naphthalene from wastewater. [ABSTRACT FROM AUTHOR]

A large set of results of concentration of hydrogen sulfide in the feed and bottom product streams of a sour water stripper found in a typical oil refinery was experimentally obtained. The readings of H2S concentrations were at several different operating conditions in terms of the main process variables that classically have significant effects on the efficiency of H2S removal (E). In particular, the considered factors were the mass flow rate, and temperature of sour water fed into the stripper, the mass flow rate of external steam injected into the reboiler, the difference between the temperature of the product stream leaving and entering the reboiler, and the difference of pressure at the two ends of the tower. Three different soft-sensor models were suggested to describe the observed variation in E from 63 to 97%, namely, an equilibrium, statistical and an artificial neural network model. The best of them was the neural network one with three input variables, four neurons in the one-hidden layer, and a hyperbolic tangent function for both the output and one-hidden layers. The mean absolute relative deviation between measured and calculated E by involving this model was only approximately 2.5% with negligible tendency for the residuals. It confirms the reliability of this approach as a tool to inferential estimation of the efficiency of removal of H2S from the sour water by stripping. [ABSTRACT FROM AUTHOR]