Vincenzo Leone

Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: Thermodynamic aspects

Sorption isotherms from water solutions for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol and cyclohexanol onto a humic acid-zeolite adduct were determined at 4, 14, 24 and 34 °C and utilized to calculate the isosteric enthalpy (ΔadsHi) and isosteric entropy (ΔadsSi) of the process. For hydrocarbon compounds, toluene, cyclohexane and o-xylene, both ΔadsHi and ΔadsSi were negative, the process was exothermic. In contrast, for hydroxyl compounds, benzyl alcohol, phenol and cyclohexanol, ΔadsHi and ΔadsSi were positive, the increase in entropy possibly reflecting the release of water molecules during sorption. The results suggest that sorption/desorption of either class of compounds could be controlled by operating on the temperature.

A novel organo-zeolite adduct for environmental applications: Sorption of phenol

A novel organo-zeolite adduct has been synthesized by sorbing humic acids (HA) onto zeolitic tuff and then heating the resulting complex at 330°C for 1.5h. Desorption tests showed that this procedure effectively immobilized HA on the tuff. The crystal structure of the zeolitic tuff and the chemical structure of HA were not altered during the preparation. Phenol sorption analysis demonstrated that the HA-zeolite adduct had good sorbing properties; moreover, the sorbed amount markedly decreased with increased ionic strength. These results point to prospective application of the HA-zeolite adduct as a low-cost and environmentally friendly sorbent for water purification from phenol and possibly other neutral organic pollutants.

Sorption of humic acids by a zeolite-feldspar-bearing tuff in batch and fixed-bed column

The sorption of humic acids (HA) on zeolite-feldspar-bearing Phlegraean Yellow Tuff enriched with calcium ions has been investigated at neutral pH both on fixed-bed columns and in batch. A two-step sorption kinetics and a relatively long time to reach the equilibrium were observed in batch. In line with this behaviour, the breakthrough curves and shipping curves from exhaust columns showed distinctive properties that cannot be easily modelled by the common mass balance equations; noteworthy, the breakthrough curves were dependent on the space velocity also for very slow processes and the bed sorption capacity decreased linearly with the space velocity. Moreover, after an initial high-rate burst, HA desorption from exhausted columns proceeded at a very slow rate, particularly so for columns loaded with higher amounts of HA.

Modelling the biphasic sorption of simazine, imidacloprid, and boscalid in water/soil systems

The sorption kinetics of simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine), imidacloprid (1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine), and boscalid (2-chloro-N-(4′-chlorobiphenyl-2-yl)nicotinamide), three pesticides of wide use in agriculture, was determined in five different water/soil systems over a time interval from the initial few seconds to about 1 month. In all the experiments, sorption kinetics showed a biphasic pattern characterized by an initial, relatively short phase with a high sorption rate and a later phase with much a lower sorption rate. Initial sorption capacity increased with soil organic carbon content and with sorbate hydrophobicity. We postulate that the first phase of the process involves a fast second-order sorption reaction on superficial sites of soil particles, whereas the second phase depends on diffusion-controlled migration to internal binding sites. A kinetic equation based on this hybrid model accurately fitted all data sets. Less satisfactory results were obtained employing the pseudo-first order, pseudo-second order, Elovich, two site non-equilibrium, or Weber-Morris equation. The superior performance of the hybrid model for describing boscalid sorption probably reflects the high hydrophobic character and consequent low diffusion rates of this compound. The accuracy of modelling was in any case strongly dependent on the time interval considered.

Use and Misuse of Sorption Kinetic Data: A Common Mistake that Should be Avoided

Numerical simulation of sorption dynamics showed that the use of data recorded at (or very close to) equilibrium in the search for the kinetic equation that best describes the process frequently leads to incorrect conclusions. Notably, it has been demonstrated that the fit of the adsorption data at equilibrium (t/qt versus t) is a straight line irrespective of the sorption kinetics. In order to distinguish pseudo-first-order from pseudo-second-order sorption kinetics, the data near the equilibrium should be omitted from the least-squares fit and the result confirmed by a different method. A straightforward method based on Δ(qt/qe)/Δt versus 1 – qt/qe and versus (1 – qt/qe)2 plots is suggested. Some recent papers reporting incorrect sorption kinetic analyses are discussed.

Sorption of non-ionic organic pollutants onto immobilized humic acid

AbstractSorption isotherms from water solution onto immobilized humic acid have been determined at 4, 14, 24, and 34°C for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol, and cyclohexanol. The experimental data were well described by the Freundlich sorption equation. The higher values of K constant were obtained for the two aromatic hydrocarbon compounds, toluene (924 mmoln−1u2009Lnu2009kg−1) and o-xylene (1,350 mmoln−1u2009Lnu2009kg−1). The isosteric sorption enthalpy (ΔistH) and the standard enthalpy were negative for all compounds analyzed, and the absolute values of ΔistH decreased with increasing sorbate loading. Comparisons with data for a humic acid-zeolitic tuff adduct supports the conclusion that the sorption properties of combined materials may not be the sum of the components, thus strengthening the rationale for research of novel adducts.

Contribution of vehicular traffic and industrial facilities to PM10 concentrations in a suburban area of Caserta (Italy)

PM10 levels have been recorded in the suburban area of Caserta (Italy) from February to October 2012. The daily limit was exceeded in 13xa0% of the determinations, with no significant difference between weekdays and weekends. Benzo[a]pyrene concentrations were in the range 0.01–0.46xa0ng/m3, thus, never exceeding the National Standard. The B(a)P-eq was 0.20xa0ng/m3. PM10 peaks were associated with wind from east–northeast. The same was observed for Ca concentrations, whereas no relation with wind direction was observed for organic pollutants. The results point to a local limestone quarry and cement factory as the likely major source of PM10 pollution in the area investigated.

Sorption of a Cationic Surfactant Benzyldimethyldodecyl Ammonium Chloride onto a Natural Zeolite

The presence of surfactants in groundwater and in drinking and superficial waters is a major public health concern. Recently, various treatment technologies have been studied to remove these pollutants; among them, the treatments based on the sorption onto natural adsorbing materials appear more eco-friendly and with very interesting removal efficiencies. The sorption of the cationic surfactant benzyldimethyldodecyl ammonium chloride (BDC-12) onto zeolitic tuff (Si/Al ratiou2009=u20092.4) was well described by a pseudo-second-order equation with a kinetic constant not depending on the exchangeable cationic form of the zeolite. The isosteric enthalpies and entropies (∆istH and ∆istS) obtained from sorption isotherms were negative, and their absolute values increased with decreasing amounts of BDC-12 bound at the equilibrium (qe). Zeolite sorbitivity (qe/unit dry mass sorbent) for BDC-12 increased with NaCl concentration in the batch solution, suggesting that the sorption process does not involve cation exchange.

Sorption Equilibrium of Aromatic Pollutants onto Dissolved Humic Acids

The adsorption of some benzene derivatives—o-xylene, toluene, phenol, and benzyl alcohol onto dissolved humic acids (HA) was analyzed by equilibrium dialyses experiments. HA were extracted from compost and from leonardite. The humification index (E4/E6 ratio) and the distribution coefficient between ammonium sulfate/polyethylene glycol solutions show that HA from compost have a higher hydrophobicity. Assuming that the binding sites onto HA molecules are energetically equivalent, the binding curves were analyzed, and the amount of ligands bound per unit weight of HA and the association constants were derived. The binding capacity was higher for the HA from compost and for more hydrophobic ligands.