doi:10.1016/j.jhazmat.2008.02.122 
Copyright © 2008 Published by Elsevier B.V.
Equilibrium and thermodynamic studies on biosorption of Pb(II) onto Candida albicans biomass
Zübeyde Baysal
, a, 
, Ercan Çinara, Yasemin Buluta, Hüseyin Alkana and Mehmet Dogrua
aDepartment of Chemistry, Faculty of Science–Art, Dicle University, Diyarbakır, Turkey
Received 31 January 2007;
revised 21 November 2007;
accepted 29 February 2008.
Available online 20 March 2008.
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Abstract
Biosorption of Pb(II) ions from aqueous solutions was studied in a batch system by using Candida albicans. The optimum conditions of biosorption were determined by investigating the initial metal ion concentration, contact time, temperature, biosorbent dose and pH. The extent of metal ion removed increased with increasing contact time, initial metal ion concentration and temperature. Biosorption equilibrium time was observed in 30 min. The Freundlich and Langmuir adsorption models were used for the mathematical description of biosorption equilibrium and isotherm constants were also evaluated. The maximum biosorption capacity of Pb(II) on C. albicans was determined as 828.50 ± 1.05, 831.26 ± 1.30 and 833.33 ± 1.12 mg g−1, respectively, at different temperatures (25, 35 and 45 °C). Biosorption showed pseudo second-order rate kinetics at different initial concentration of Pb(II) and different temperatures. The activation energy of the biosorption (Ea) was estimated as 59.04 kJ mol−1 from Arrhenius equation. Using the equilibrium constant value obtained at different temperatures, the thermodynamic properties of the biosorption (ΔG°, ΔH° and ΔS°) were also determined. The results showed that biosorption of Pb(II) ions on C. albicans were endothermic and spontaneous. The optimum initial pH for Pb(II) was determined as pH 5.0.
FTIR spectral analysis of Pb(II) adsorbed and unadsorbed C. albicans biomass was also discussed.
Keywords: Candida albicans; Pb(II); Biosorption; Kinetic; Thermodynamic
Fig. 1. Effect of time and initial metal ions concentration on the biosorption of Pb(II). Biomass concentration: 25 mg, volume: 50 ml, pH 5.0. The bars represent the standard error of the mean (p < 0.05).
Fig. 2. Pseudo second-order kinetics for biosorption of C. albicans on Pb(II) at 25 °C.
Fig. 4. Effect of microorganism concentration on initial adsorption rates. pH 5.0, initial metal concentration: 100 mg ml−1, agitator speed: 200 rpm. The bars represent the standard error of the mean (p < 0.05).
Fig. 5. Effect of initial pH on initial adsorption rate. Initial metal ion concentration: 100 mg l−1, biomass concentration: 50 mg ml−1, T: 25 °C, agitator speed: 200 rpm. The bars represent the standard error of the mean (p < 0.05).
Fig. 6. Adsorption isotherms of Pb(II) on C. albicans at different temperatures.
Fig. 7. Plot of ln b versus 1/T.
Fig. 8. IR spectra of C. albicans (a) before metal was loaded and (b) after metal was loaded.
Table 1.
Effect of initial Pb(II) concentration on kinetic parameters for biosorption of Pb(II) on C. albicans
pH 5.0, dose of C. albicans: 50 mg ml−1, temperature: 25 °C, agitator speed: 200 rpm.
Table 2.
Kinetic parameters for biosorption of Pb(II) on C. albicans at different temperatures
pH 5.0, biomass concentration: 25 mg, volume: 50 ml, initial Pb(II) concentration: 100 mg l−1, agitator speed: 200 rpm.
Table 3.
Isotherm parameters for Pb(II) biosorption on C. albicans
pH 5.0, biomass concentration: 25 mg; volume: 50 ml, initial Pb(II) concentration: 100 mg l−1, agitator speed: 200 rpm.
Table 4.
The thermodynamic constants of adsorption obtained for Pb(II)
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