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    An economic removal of Cu2+ and Cr3+ on the new adsorbents: Pumice and polyacrylonitrile/pumice composite
    (ELSEVIER SCIENCE SA, 2008) Yavuz, Mustafa; Gode, Fethiye; Pehlivan, Erol; Ozmert, Sema; Sharma, Yogesh C.
    In this article, the adsorption of Cu2+ and Cr3+ onto pumice (Pmc) and polyacrylonitrile/pumice (PAn/Pmc) composite has been investigated by using a batch method at room temperature and their adsorption properties were compared. To highlight their application, selected information on pH, initial metal concentration and adsorption capacity of the adsorbents is presented. Depending on the characteristics of the individual adsorbents viz. surface modification, initial concentration of adsorbates, and pH, their adsorption capacities were found to vary. The time required for the removal of metal ions (100-500 mg/g) from aqueous solutions was about 6 h. The experimental data have been analyzed using the Langmuir and Freundlich isotherm models. The results of adsorption were fitted to the Langmuir models and coefficients indicated favorable adsorption of Cu2+ and Cr3+ on the adsorbents. Adsorption of Cu2+ and Cr3+ in the solutions was in following order: (PAn/(Pmc) composite> Pmc). The adsorption capacity of the adsorbents Pmc and (PAn/Pmc) were determined from the isotherms equations and were found to be 0.055 and 0.065 mmol/g for Cu2+ and 0.031 and 0.268 mmol/g for Cr3+, respectively. More than 80% of studied cations were removed by Pmc and 87% (PAn/Pmc), respectively, from aqueous solutions in single step. Effective removal of metal ions was demonstrated at pH values of 8.0. The mechanism for cations removal by the Pmc and (PAn/Pmc) composite includes complexation and sorption. The process is very efficient especially in case of low concentrations of pollutants in aqueous solutions, where common methods are either economically unfavorable or technically complicated. (C) 2007 Elsevier B.V. All rights reserved.
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    Removal of chromium(III) from aqueous solutions using Lewatit S 100: The effect of pH, time, metal concentration and temperature
    (ELSEVIER SCIENCE BV, 2006) Gode, Fethiye; Pehlivan, Erol
    The removal of the Cr(III) ion from aqueous solutions with the Lewatit S 100 ion-excbange resin is described; and the performance of this resin was compared with Chelex-100 resin. The effect of adsorbent dose, initial metal concentration, contact time, pH and temperature on the removal of Cr(III) was investigated. Lewatit S 100 shows a remarkable increase in sorption capacity for Cr(III). The Batch ion-exchange process was relatively fast; and it reached equilibrium after about 150 min of contact. The ion-exchange process, which is pH dependent show maximum removal of Cr(III) in the pH range 2.8-4.0 for an initial Cr(III) concentration of 1.0 x 10-(3) M. The equilibrium constants were 36.67 at pH value 3.5 for Lewatit S 100 and 6.64 at pH value 4.5 for Chelex- 100 resin. Both of the resins had high-bonding constants. The equilibrium related to their ion-exchange capacity and the amount of the ion exchange was obtained by using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion-exchange capacity of 0.39 mmol of Cr(III)/g for Lewatit S 100 and 0.29 mmol of Cr(III)/g for Chelex-100 was achieved at optimum pH values of 3.5 and 4.5, respectively. The thermodynamic equilibrium constant and the Gibbs free energy flow were calculated for each system. The ion exchange of Cr(III) on these cation-exchange resins followed first-order reversible kinetics. The intra-particle diffusion of Cr(III) on ion-exchange resin represented the rate-limiting step. The rise in temperature caused a slight increase in the value of the equilibrium constant (K,) for the sorption of Cr(III) ion for both resins. (c) 2006 Elsevier B.V. All rights reserved.
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    Removal of Cr(VI) from aqueous solutions using modified red pine sawdust
    (ELSEVIER SCIENCE BV, 2008) Gode, Fethiye; Atalay, Elif Dincturk; Pehlivan, Erol
    The adsorption of Cr(VI) from aqueous solutions on sawdust (SD), base extracted sawdust (BESD) and tartaric acid modified sawdust (TASD) of Turkish red pine tree (Pinus nigra), a timber industry waste, was studied at varying Cr(VI) concentrations, adsorbent dose, modifier concentration and pH. Batch adsorption studies have been carried out. Sawdust was collected from waste timber industry and modified with various amount of tartaric acid (TA) (0.1-1.5 M). The batch sorption kinetics has been tested and the applicability of the Langmuir and Freundlich adsorption isotherms for the present system has been tested at 25 +/- 2 degrees C. Under observed test conditions, the equilibrium adsorption data fits the linear Freundlich isotherms. An initial pH of 3.0 was most favorable for Cr(VI) removal by all adsorbents. Maximum Cr(VI) was sequestered from the solution within 120 min after the beginning for every experiment. The experimental result inferred that chelation and ion exchange is one of the major adsorption mechanisms for binding metal ions to the SD. Percentage removal of Cr(VI) was maximum at the initial pH of 3.0 (87.7, 70.6 and 55.2% by TASD, BESD, and SD, respectively). Adsorption capacities range from 8.3 to 22.6 mg/g for SD samples. (c) 2007 Elsevier B.V. All rights reserved.
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    Sorption of Cr(III) onto chelating b-DAEG-sporopollenin and CEP-sporopollenin resins
    (ELSEVIER SCI LTD, 2007) Gode, Fethiye; Pehlivan, Erol
    In the present study, the removal of Cr(III) from aqueous solution was studied using a new chelate-resins (b-DAEG-sporopollenin and CEP-sporopollenin). Mechanisms including ion exchange, complexation and adsorption to the surface are possible in the sorption process. Adsorption analysis results obtained at various concentrations of Cr(III) showed that the adsorption pattern on the resin followed a Langmuir isotherm. Langmuir constant Gamma(max) and k for Cr(III) were found as 1.23, 84.84 mmol/g for b-DAEG-sporopollenin, 133.33, 10.39 mmol/g for CEP-sporopollenin at 20 +/- 1 degrees C, respectively. In addition, kinetic and thermodynamic parameters such as enthalpy (Delta H-0), free energy (Delta G(0)) and entropy (Delta S-0) were calculated and these values show that adsorption of Cr(III) on b-DAEG-sporopollenin and CEP-sporopollenin was an exothermic process and the process of adsorption was favored at high temperatures. Maximum Cr(III) removal was observed near a pH of 6. (C) 2006 Elsevier Ltd. All rights reserved.