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    Removal of As(V) from aqueous solutions by iron coated rice husk
    (ELSEVIER, 2013) Pehlivan, E.; Tran, T. H.; Ouedraogo, W. K. I.; Schmidt, C.; Zachmann, D.; Bahadir, M.
    A lignocellulosic material extracted from rice husk (Oryza sativa), Vietnam, was modified as a new adsorbent for the removal of As(V) ions from aqueous solution. Iron was coated onto this adsorbent by hydrolization of ferric nitrate while adding an alkaline solution drop wise into the batch type reactor. The adsorption of As(V) ions from aqueous solution on coated rice husk was then studied at varying pH, As(V) concentrations, contact times, ionic strength, and adsorbent amounts. The minimum contact time to reach equilibrium is about 6 h. The adsorption of As(V) anions on the coated rice husk was found to be highly pH dependent due to Coulomb interactions between As(V) species in solution and positively charged surface groups RH-FeOOH, as well as formation of chelate complexes with naturally occurring carboxyl and carbonyl functional groups in the matrix. As(V) adsorption on Fe(III)-coated rice husk (RH-FeOOH) from aqueous solution was studied in the pH range 2-10. The main effects of pH on adsorption are estimated by considering both the behavior of As(V) ions (hydrolysis and hydroxide precipitation) and the effect of pH on coordination. A strong effect of pH was demonstrated at pH 4.0 with a maximum percentage for removal of As(V) ions 94%. Although both Langmuir and Freundlich isotherms have been used to characterize the adsorption of As(V), the Langmuir model fitted the equilibrium data better than Freundlich model and confirmed the surface homogeneity of adsorbent. The maximum adsorption capacity is determined as 2.5 mg/g of adsorbent at pH 4.0 for the Fe(III)-coated rice husk. It is concluded that initial As(V) concentration has an effect on the removal efficiency of RH-FeOOH. Higher adsorption of As(V) was observed at lower initial concentrations. RH-FeOOH as a low cost material is effective for the removal of As(V) ions and may become a valuable adsorbent to improve the ground water quality in Vietnam. (C) 2012 Elsevier B.V. All rights reserved.
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    Sugarcane bagasse treated with hydrous ferric oxide as a potential adsorbent for the removal of As(V) from aqueous solutions
    (ELSEVIER SCI LTD, 2013) Pehlivan, E.; Tran, H. T.; Ouedraogo, W. K. I.; Schmidt, C.; Zachmann, D.; Bahadir, M.
    The mechanism of As(V) removal from aqueous solutions by means of hydrated ferric oxide (HFO)-treated sugarcane bagasse (SCB-HFO) (Saccharum officinarum L.) was investigated. Effects of different parameters, such as pH value, initial arsenic concentration, adsorbent dosage, contact time and ionic strength, on the As(V) adsorption were studied. The adsorption capacity of SCB-HFO for As(V) was found to be 22.1 mg/g under optimum conditions of pH 4, contact time 3 h and temperature 22 degrees C. Initial As(V) concentration influenced the removal efficiency of SCB-HFO. The desorption of As(V) from the adsorbent was 17% when using 30% HCl and 85% with 1 M NaOH solution. FTIR analyses evidenced two potential binding sites associated with carboxyl and hydroxyl groups which are responsible for As(V) removal. Adsorption, surface precipitation, ion exchange and complexation can be suggested as mechanisms for the As(V) removal from the solution phase onto the surface of SCB-HFO. (C) 2012 Elsevier Ltd. All rights reserved.
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    Use of modified wheat bran for the removal of chromium(VI) from aqueous solutions
    (ELSEVIER SCI LTD, 2014) Kaya, K.; Pehlivan, E.; Schmidt, C.; Bahadir, M.
    Novel adsorbents, wheat bran (WB) and modified wheat bran (M-WB) with tartaric acid were developed and Cr(VI) adsorption was investigated by changing various parameters. The adsorption increased with contact time and become optimum at 180 min for WB and 200 min for M-WB. When the pH of the solution phase increased, some of toxic Cr(VI) reduced into less toxic Cr(III) on the WB surface. The maximum removal of Cr(VI) from the solution having an initial Cr(VI) concentration of 200 mg L-1 was obtained at pH 2.0 as 51.0% and 90.0% for WB and M-WB, respectively. Isotherm data of Cr(VI) adsorption on WB and M-WB was described by the Freundlich adsorption model. The adsorption capacity of 4.53 mg of Cr(VI)/g for WB and 5.28 mg of Cr(VI)/g for M-WB was obtained at pH 2 and 2.2 respectively. (C) 2014 Elsevier Ltd. All rights reserved.