Yeşim Sağ

Kinetic studies on sorption of Cr(VI) and Cu(II) ions by chitin, chitosan and Rhizopus arrhizus

This work focuses on Cr(VI), Cu(II) sorption kinetics by chitin, a naturally occurring material, chitosan, the deacetylated form of chitin, and Rhizopus arrhizus, a filamentous fungus containing chitin and chitosan as a main cell wall component. The aim of this study is to understand the mechanisms that govern Cr(VI) and Cu(II) removal, and find an appropriate model for the kinetics of removal in a batch reactor. In order to investigate the mechanism of sorption and potential rate controlling steps, the pseudo-first, first, pseudo-second order kinetic models and the Elovich equation have been used to test experimental data. For all of the metal–biosorbent systems studied, the pseudo-second order rate expression provided the best fitting kinetic model.

The biosorpnon of copperod by C. vulgaris and Z. ramigera

Abstract The adsorption of copper(II) ions to dead cells of Chlorella vulgaris and Zoogloea ramigera was investigated. Optimum initial pH of the adsorption medium was found to be 4.0–4.5 for both microorganisms. In general, higher adsorptive uptake was observed at 25°C. The initial adsorption rate of metal ion increased by increasing metal ion concentration for C. vulgaris and Z. ramigera up to 150–200 mg l‐1 and 100–125 mg l‐1, respectively. Freundlich constants were determined from the Freundlich adsorption isotherms of two microorganisms.

The selective biosorption of chromium(VI) and copper(II) ions from binary metal mixtures by R. arrhizus

The uptake of copper(II) and chromium(VI) ions from binary mixtures by Rhizopus arrhizus is described as a function of ion concentration, pH and temperature.

Mass transfer and equilibrium studies for the sorption of chromium ions onto chitin

The kinetics and equilibrium of chromium sorption onto chitin were studied with respect to pH, particle size, initial metal ion concentration, sorbent concentration and stirring rate. In order to select the main rate-limiting step in the overall uptake mechanism, a single external mass transfer diffusion model and intraparticular mass transfer diffusion models were used. External film mass transfer coefficients gave a mean value of 1.16 10 3 cm s 1 . Chromium sorption onto chitin was mainly located on the surface. However, the stirring rate had no noticeable effect on the overall uptake rate of chromium. This observation led to the conclusion that external mass transfer resistance was not the major limiting phenomenon. Intraparticle diffusion coefficients gave a mean value of 2.7810 3 mmol g 1 s 0.5 (0.17 mmol g 1 h 0.5 ), indicating a poor intraparticular diffusion into the chitin or into the pores. The equilibrium isotherms were analysed using the monolayer and multilayer sorption models. Finally, the chromium binding capacity of chitin was compared with that of Rhizopus arrhizus, which possesses a high chitin content in the cell wall.

Application of equilibrium and mass transfer models to dynamic removal of Cr(VI) ions by Chitin in packed column reactor

Abstract The dynamic removal of hexavalent chromium by chitin flakes was studied in a packed column reactor. The values of column parameters were predicted as a function of flow rate, bed depth, particle size and inlet metal ion concentration. On evaluating the breakthrough curves, sorption isotherms were obtained and modelled according to the Langmuir, the Redlich–Peterson and the Freundlich models. Kinetic and mass transfer aspects of the dynamic removal of Cr(VI) ions by chitin were investigated using several mathematical models. Column studies showed a good correlation between the experimental data and the calculated breakthrough curves obtained by the Adams–Bohart or the Wolborska models and the Clark model. The simulation of the whole breakthrough curve was effective with the Clark model, but the breakthrough was best predicted by Adams–Bohart, or related derived models.

The simultaneous biosorption of Cu(II) and Zn on Rhizopus arrhizus: application of the adsorption models

The biosorption of two divalent metal ions—copper(II) and zinc—in single component and binary systems has been studied using Rhizopus arrhizus. The monocomponent equilibrium data have been analysed using the Langmuir, the Freundlich and the three parameter Redlich–Peterson isotherms. The non-competitive Freundlich isotherms have been found to have the highest regression correlation coefficients and the minimum average percentage errors between the predicted and the experimental values. The effects of the presence of Cu(II) and Zn ions together on the biosorption of Cu(II) and Zn ions have been investigated in terms of initial rates of biosorption and equilibrium isotherms. The competitive Freundlich model has also been demonstrated to provide the best correlation for the biosorption of the two metal ions on R. arrhizus.

FULLY COMPETITIVE BIOSORPTION OF CHROMIUM(VI) AND IRON(III) IONS FROM BINARY METAL MIXTURES BY R. ARRHIZUS : USE OF THE COMPETITIVE LANGMUIR MODEL

Abstract The uptake of heavy metal ions by microbial biomass has been extensively studied but very little attention has been given to the biosorption of multi-component systems. In this study, a process of fully competitive biosorption of chromium(VI) and iron(III) ions to Rhizopus arrhizus from binary metal mixtures is described and compared to single metal-ion situations in solution. Effects of the presence of chromium(VI) and iron(III) ions together on the biosorption of chromium(VI) and iron(III) ions were investigated in terms of initial rates of biosorption, maximum uptake capacity and equilibrium isotherms. Both chromium(VI) and iron(III) were more effectively adsorbed to the biomass at very low values of pH. The optimum initial pH for the biosorption of chromium(VI) and iron(III) ions by R. arrhizus was determined as 2·0. The initial biosorption rates and the adsorptive capacity of the biomass for chromium(VI) and iron(III) ions increased with increasing temperatures in the range 25–45°C and 25–35°C, respectively. These properties were used in the bioremoval of chromium(VI) and iron(III) ions simultaneously from binary mixtures. The instantaneous, equilibrium and maximum uptake of chromium(VI) and iron(III) was reduced by the presence of increasing concentrations of the other metal. In particular, the long-term uptake of chromium from the solution in the presence of iron was greater than the uptake of iron under the same conditions. In the single-ion situation, the adsorption isotherms were developed at different pH and temperature values and it was seen that the adsorption equilibrium data fit the non-competitive Langmuir model. The ‘best fit’ parameters for the non-competitive chromium(VI) and iron(III) biosorption at pH 2·0 and at 25°C were determined to be q s = 58·12 mg g −1 and b = 0·047 litre mg −1 ; q s = 34·73 mg g −1 and b = 0·066 litre mg −1 , respectively. For the multi-component adsorption equilibrium, the competitive adsorption isotherms were also developed and the competitive Langmuir model was shown to be consistent with the observed uptake of multi-metal ions.

Ternary biosorption equilibria of chromium(VI), copper(II), and cadmium(II) on Rhizopus arrhizus

A process of competitive biosorption of Cr(VI), Cu(II), and Cd(II) ions to Rhizopus arrhizus from ternary mixtures was described. Three-dimensional biosorption isotherm surfaces were used to evaluate the three-metal biosorption system performance. Triangular equilibrium diagrams, which could incorporate all the experimental data of the ternary system, were also constructed. The multimetal biosorption equilibria were described by the multicomponent Langmuir and Freundlich models. Of the two models examined, the Langmuir-type model showed the best fit for the three-metal biosorption data, whereas the Freundlich-type multicomponent model did not adequately describe the biosorption results of Cr(VI) ions on R. arrhizus from ternary mixtures. The multimetal biosorption results indicated that Cr(VI) and Cu(II) significantly inhibited the biosorption of Cd(II). The Cr(VI)+Cu(II)+Cd(II) combination showed synergistic interaction on the biosorption of Cr(VI) ions.

A comparative study for the simultaneous biosorption of Cr(VI) and Fe(III) on C. vulgaris and R. arrhizus: application of the competitive adsorption models

A process of fully competitive biosorption of Cr(VI) and Fe(III) ions to C. vulgaris and R. arrhizus from multi-component systems is described and compared to single metal ion situations in solution. The effects of the presence of Cr(VI) and Fe(III) ions together on the biosorption of Cr(VI) and Fe(III) ions were investigated in terms of initial rates of biosorption and equilibrium isotherms. Since initial biosorption rates and equilibrium metal removal decreased with increasing concentrations of the other metal ion, the combined action of Cr(VI) and Fe(III) ions on C. vulgaris and R. arrhizus was generally found to be antagonistic. In the single ion situation, the adsorption isotherms were developed for optimum conditions and adsorption equilibrium data fitted both the non-competitive Langmuir and Freundlich models. For the multi-component adsorption equilibrium, competitive adsorption isotherms were also developed. The competitive Freundlich model for binary metal mixtures was satisfactory for most adsorption equilibrium data of Cr(VI) and Fe(III) ions on C. vulgaris, while the competitive Langmuir model and the modified Langmuir model were used successfully to characterize competitive adsorption of Cr(VI) and Fe(III) ions from two component systems by R. arrhizus.

Determination of the biosorption activation energies of heavy metal ions on Zoogloea ramigera and Rhizopus arrhizus

Abstract The activation energies of Fe(III) and Pb(II) ions on Zoogloea ramigera and Fe(III), Cr(VI) and Ni(II) ions on Rhizopus arrhizus were determined using the Arrhenius equation. Batch adsorption kinetics was described by the Langmuir–Hinshelwood model. The applicability of the Langmuir–Hinshelwood model for the metal–microorganism systems was tested at different temperatures in the range 15–45°C. With respect to the magnitude of the activation energy of biosorption, the dominant adsorption mechanism in the whole biosorption process was proposed for each metal–microorganism system.