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Sorption and desorption of Cr(VI) ions from water by biochars in different environmental conditions.

Tytłak A, Oleszczuk P, Dobrowolski R - Environ Sci Pollut Res Int (2014)

Bottom Line: The Langmuir model has better fitting of adsorption isotherms than the Freundlich model.The sorption process can be described by the pseudo second-order equation.The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Skłodowska Square 3, 20-031, Lublin, Poland.

ABSTRACT
In the present research, the potential of two biochars produced by the thermal decomposition of wheat straw (BCS) and wicker (BCW) for Cr(VI) ions removing from wastewater was investigated. The pH and the presence of chlorides and nitrates were also investigated. The Freundlich and Langmuir models were applied for the characterization of adsorption isotherms. The Langmuir model has better fitting of adsorption isotherms than the Freundlich model. The sorption process can be described by the pseudo second-order equation. The optimal adsorption capacities were obtained at pH 2 and were 24.6 and 23.6 mg/g for BCS and BCW, respectively. X-ray photoelectron spectroscopy (XPS) studies confirmed that Cr(III) ions were the most abundant chromium species on the biochars' surface. The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

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Desorption of Cr(VI) from BCS and BCW in respect to 1 nitric acid and 2 hydrochloric acid concentration; m = 0.008 g, V = 2 mL, ACr(BCS) = 14 mg/g, ACr(BCW) = 11 mg/g, t = 24 h, T = 25 °C
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Fig7: Desorption of Cr(VI) from BCS and BCW in respect to 1 nitric acid and 2 hydrochloric acid concentration; m = 0.008 g, V = 2 mL, ACr(BCS) = 14 mg/g, ACr(BCW) = 11 mg/g, t = 24 h, T = 25 °C

Mentions: Batch desorption experiments were conducted in order to investigate whether chromium adsorption on investigated biochars is reversible or not. The desorption studies of Cr(VI) ions in relation to HCl and HNO3 concentrations were performed. The desorption kinetics of chromium forms was similar for both materials and does not exceed 20 min (Fig. 7). The maximum desorption of Cr(VI) ions from the biochars’ surface cannot be achieved even if concentrated HCl or HNO3 was applied. Additionally, for nitric acid as a desorptive agent, the lowest desorption is observed for BCW (51 %) and the greatest for BCS (79 %). A different effect is observed for hydrochloric acid, wherein the lowest desorption is for BCS (39 %) and greatest for BCW (47 %). This study confirmed that even the application of concentrated hydrochloric or nitric acid does not cause the total desorption of Cr(VI) ions from the biochar surface. Moreover, it should be noticed that chromium(VI) adsorption process onto BCs is irreversible, which can be caused by the surface precipitation of Cr(OH)3. The differences between desorption obtained in the case of both desorptive agents can be related to the fact that the adsorption of Cr(III) species proceeds by different functional groups, acidic and basic, on the BCS and BCW surfaces. Furthermore, the different structures of studied biochars (different SBET) (Table 1) can be responsible for uncompleted desorption.Fig. 7


Sorption and desorption of Cr(VI) ions from water by biochars in different environmental conditions.

Tytłak A, Oleszczuk P, Dobrowolski R - Environ Sci Pollut Res Int (2014)

Desorption of Cr(VI) from BCS and BCW in respect to 1 nitric acid and 2 hydrochloric acid concentration; m = 0.008 g, V = 2 mL, ACr(BCS) = 14 mg/g, ACr(BCW) = 11 mg/g, t = 24 h, T = 25 °C
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig7: Desorption of Cr(VI) from BCS and BCW in respect to 1 nitric acid and 2 hydrochloric acid concentration; m = 0.008 g, V = 2 mL, ACr(BCS) = 14 mg/g, ACr(BCW) = 11 mg/g, t = 24 h, T = 25 °C
Mentions: Batch desorption experiments were conducted in order to investigate whether chromium adsorption on investigated biochars is reversible or not. The desorption studies of Cr(VI) ions in relation to HCl and HNO3 concentrations were performed. The desorption kinetics of chromium forms was similar for both materials and does not exceed 20 min (Fig. 7). The maximum desorption of Cr(VI) ions from the biochars’ surface cannot be achieved even if concentrated HCl or HNO3 was applied. Additionally, for nitric acid as a desorptive agent, the lowest desorption is observed for BCW (51 %) and the greatest for BCS (79 %). A different effect is observed for hydrochloric acid, wherein the lowest desorption is for BCS (39 %) and greatest for BCW (47 %). This study confirmed that even the application of concentrated hydrochloric or nitric acid does not cause the total desorption of Cr(VI) ions from the biochar surface. Moreover, it should be noticed that chromium(VI) adsorption process onto BCs is irreversible, which can be caused by the surface precipitation of Cr(OH)3. The differences between desorption obtained in the case of both desorptive agents can be related to the fact that the adsorption of Cr(III) species proceeds by different functional groups, acidic and basic, on the BCS and BCW surfaces. Furthermore, the different structures of studied biochars (different SBET) (Table 1) can be responsible for uncompleted desorption.Fig. 7

Bottom Line: The Langmuir model has better fitting of adsorption isotherms than the Freundlich model.The sorption process can be described by the pseudo second-order equation.The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Skłodowska Square 3, 20-031, Lublin, Poland.

ABSTRACT
In the present research, the potential of two biochars produced by the thermal decomposition of wheat straw (BCS) and wicker (BCW) for Cr(VI) ions removing from wastewater was investigated. The pH and the presence of chlorides and nitrates were also investigated. The Freundlich and Langmuir models were applied for the characterization of adsorption isotherms. The Langmuir model has better fitting of adsorption isotherms than the Freundlich model. The sorption process can be described by the pseudo second-order equation. The optimal adsorption capacities were obtained at pH 2 and were 24.6 and 23.6 mg/g for BCS and BCW, respectively. X-ray photoelectron spectroscopy (XPS) studies confirmed that Cr(III) ions were the most abundant chromium species on the biochars' surface. The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

Show MeSH