G. Tenorio

Study of Cr (III) biosorption in a fixed-bed column

This research analyzes the potential use of the olive stone as a low-cost biosorbent for Cr (III) from aqueous solutions in a continuous system. First, experiments were carried out in fixed-bed column to test the influence of various parameters on breakthrough and saturation time. The breakthrough and saturation time increase with the decrease of the flow rate. The same effect is shown when the bed depth is increased. The olive stone sorption capacity, q(e), increases as the inlet Cr (III) concentration increases until a value close to 0.800 mg/g is reached, then q(e) remains constant. Column data obtained at different conditions were described using the Adams-Bohart, Thomas, Yoon and Nelson, and Dose-Response models. The breakthrough curve prediction by the Adams-Bohart and Dose-Response models were found to be very satisfactory. In particular, the Adams-Bohart model can be used to represent the initial region of breakthrough curve, whereas the Dose-Response model is the one which best reproduces the whole curve for all the inlet Cr (III) concentrations used. Finally, a study of pH evolution was carried out. The pH increases at the beginning, subsequently decreasing as time passes until practically reaching the initial value.

Biosorption kinetics of Cd (II), Cr (III) and Pb (II) in aqueous solutions by olive stone.

A by-product from olive oil production, olive stone, was investigated for the removal of Cd (II), Cr (III) and Pb (II) from aqueous solutions. The kinetics of biosorption are studied, analyzing the effect of the initial concentration of metal and temperature. Pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models have been used to represent the kinetics of the process and obtain the main kinetic parameters. The results show that the pseudo-second order model is the one that best describes the biosorption of the three metal ions for all the range of experimental conditions investigated. For the three metal ions, the maximum biosoption capacity and the initial biosorption rate increase when the initial metal concentration rises. However, the kinetic constant decreases when the initial metal concentration increases. The temperature effect on biosorption capacity for Cd (II) and Cr (III) is less significant; however, for Pb (II) the effect of temperature is more important, especially when temperature rises from 25 to 40oC. The biosorption capacity at mmol/g of olive stone changes in the following order: Cr>Cd>Pb. Thus, for an initial concentration of 220 mg/l, a maximum sorption capacity of 0.079 mmol/g for Cr (III), 0.065 mmol/g for Cd (II) and 0.028 mmol/g for Pb (II) has been obtained.

Sorption of Cr (VI) onto Olive Stone in a Packed Bed Column: Prediction of Kinetic Parameters and Breakthrough Curves

This paper investigates the ability of olive stone to remove chromium (VI) ions from aqueous solution in a packed bed up-flow column with an internal diameter of 1.5 cm. The experiments were performed with a bed height of 15 g (13.4 cm) and a flow rate of 2 mL/min. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Adams-Bohart, Thomas, Yoon-Nelson, and Dose-Response models were applied to the experimental data. All models were found suitable for describing the whole or a definite part of the dynamic behavior of the column. The simulation of the whole breakthrough curve was effective with the Dose-Response model, but the initial part of the breakthrough was best predicted by the Adams-Bohart model. On the other hand, the results indicated that, at pH values of this work, approximately 50% of Cr (VI) is biosorbed by olive stone and the other 50% is reduced to Cr (III), both processes being of equal importance. Therefore, a two-stage biosorption process was developed. The goal of these final experiments was to confirm that Cr (III) [the Cr (VI) reduction product] was also effectively sorbed by olive stone in a second column.

Effect of the presence of chromium (III) on the removal of lead (II) from aqueous solutions by agricultural wastes.

The influence of the presence of Cr (III) on the biosorption of Pb (II) by three olive wastes (olive stone, the two-phase olive mill solid, and olive tree pruning) was investigated in a batch system in terms of equilibrium isotherm and adsorption yield. The results show that the three olive wastes have greater affinity for lead than for chromium and the best results are achieved at pH=5. The presence of chromium in the solution reduces the percentage of lead removal suggesting that there is a competition between the two metals for the binding sites, and that the biosorbent retains both species presenting more affinity for lead. Simultaneous biosorption phenomena of Pb (II) and Cr (III) on the three solid wastes were expressed by multicomponent isotherms. The extended Freundlich-type and Sips-type models were found to exhibit good fit to the experimental data for olive stone and olive tree pruning, respectively.

Equilibrium Modelling Of Cr (VI)Biosorption By Olive Stone

In this study, Cr (VI) biosorption isotherms were investigated depending on temperature by employing batch biosorption technique and using olive stone as sorbent. To analyse the effect of the temperature in the equilibrium of the biosorption process, experiments were carried out by varying the concentration from 10 to 220 mg/L, at three temperatures: 25oC, 60oC and 80oC. The increase in temperature favoured biosorption and reduction processes, thus, for a specific initial Cr (VI) concentration, as temperature increases, the final Cr (VI) concentration that remains in the solution decreases, and the Cr (III) concentration increases. The experimental data were adjusted to Langmuir, Freundlich and RedlichPeterson models, the Langmuir model being the one that best reproduced the experimental results for all the chosen temperatures. From the results obtained it concluded that the maximum sorption capacity increases as the temperature increases, from a value of 1.728 mg/g at 25oC to 4.824 mg/g at 80oC. Similarly, the affinity parameter also increases with temperature, from 0.112 L/mg (25oC) to 0.472 L/mg (80oC). Finally, using the values obtained for the constant b of the Langmuir model, the changes in enthalpy, H, free energy, G, and entropy, S, were determined and it obtained that for Cr (VI) the process was endothermic, since the enthalpy had a positive value, and the negative free energy values, ∆G, showed the spontaneous nature of the process and that it was favoured by the increase in temperature.