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The ion-exchange equilibrium of Pb(II) and Cd(II) on clinoptilolite from different deposits was studied in this work. The Langmuir isotherm fitted the ion-exchange equilibrium data of both ions better than the Freundlich isotherm. The capacity of the natural zeolite to exchange Cd(II) and Pb(II) increased, augmenting the solution pH. This behaviour was attributed to the interactions between the ions in solution and the surface charge of the zeolite. Moreover, the capacity of the natural zeolite to exchange Cd(II) and Pb(II) was increased when the temperature was raised from 15 to 35• C. This tendency was explained by assuming that the ion exchange was an endothermic reaction. The selectivity of the zeolite for the metal cations decreased in the following order: Pb(II) > Cd(II). This order was not modified while reducing the solution pH, but the zeolite selectivity was increased. At pH 2 the selectivity of the zeolite for Pb(II) was nearly three times larger than at pH 4.

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Pyridine is a very toxic pollutant that has to be removed from wastewater. In this work, adsorption of pyridine on activated carbon cloth (ACC) is studied as a possible alternative for eliminating pyridine from aqueous solution. The ACC was produced from polyacrylonitrile. The adsorption equilibrium data of pyridine on ACC was obtained in a batch adsorber. The experimental data was interpreted with the isotherms of Langmuir, Freundlich, and Prausnitz-Radke (PR), and the PR isotherm better represented the experimental data. The capacity of ACC for adsorbing pyridine was favored increasing the solution pH from 3 to 6, and this effect was due to the p-p dispersive and electrostatic interactions between the pyridine species in solution and the surface complexes of ACC. The modified Langmuir model fitted reasonably well the influence of pH on the adsorption capacity. In this model was assumed that both neutral pyridine and pyridinium were simultaneously adsorbed on ACC accordingly to the experimental results. The adsorption capacity was almost independent of temperature. The reversibility study revealed that 75% of the pyridine can be desorbed from ACC indicating that part of the pyridine was irreversibly adsorbed, and possibly chemisorbed.

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The structural evolution, electronic, and magnetic properties of Pd-doped Cu n (n = 1–12) clusters and the dissociative chemisorption of H2 on the lowest energy structures are investigated on the basis of density functional theory. The Pd impurity occupies the surface site and changes the geometry of the pure copper clusters; i.e., a transition from 2D to 3D occurs at n = 5. The relative stability and chemical activity of the minimum energy structures are analyzed through the binding energy per atom, second-order energy difference, and energy gap. The results show that the stability of Cu n Pd containing an even number of Cu atoms is higher than that of Cu n+1, which is related to the closed-shell electronic structure. The electronic properties such as the ionization potential and electron affinity are calculated for Cu n Pd and Cu n+1 and compared with experimental data available. By studying the H2 chemisorption on the Pd-doped Cu n clusters, the results show that the doped clusters possess similar interactions with atomic H compared to the pure ones. Interestingly, the hydrogen dissociation pathway on Cu n Pd clusters shows that certain clusters possess significantly lower activation barriers than the pure ones. For Cu4–6Pd, the energy barriers for the release of chemisorbed hydrogen range from 0.63 to 0.75 eV, while from 1.19 to 2.53 eV on Cu5–7, suggesting that the doped clusters are more suitable for H2 dissociation and utilization. These results can be understood in terms of the localization of the spin-polarization density.

The production of lactic acid by Lactobacillus helveticus from a cheese whey residue obtained from a dairy was investigated. Batch fermentation experiments showed that the optimal temperature to carry out the process was 42°C and the optimum pH was 5.9, giving at these conditions a maximum concentration of lactic acid of 53 g/l. The addition of yeast extract to the cheese whey residue as a nitrogen source for L. helveticus did not increase the lactic acid production significantly. The results obtained in this work confirmed that it is possible to increase the value of residues from the dairy industry for the production of value-added products such as lactic acid, which has important industrial applications. Also, the effect of the addition of a nitrogen source to the culture media of the fermentation experiments did not present a costbeneficial improvement on lactic acid production as other authors have shown. The last finding could reduce the cost of the culture media used for lactic acid production when scaling up the process.