Adsorption capacities of poly-γ-glutamic acid and its sodium salt for cesium removal from radioactive wastewaters. (December 2016)

• Record Type: Journal Article
• Authors: Sakamoto, Shigeki; Kawase, Yoshinori
• Is Part Of: Journal of environmental radioactivity. Volume 165(2016:Dec.)
• Page Start: 151
• Page End: 158
• Publication Date: 2016-12
• Subjects: Cesium -- Biosorption -- Poly-γ-glutamic acid -- Adsorption capacity -- Surface characterization; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2016.10.004
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: Cesium removal from radioactive wastewaters was examined using water-insoluble poly-γ-glutamic acid (γ-PGA) and water-soluble sodium salt form poly-γ-L-glutamic acid (γ-PGANa) as biosorbents. The maximum adsorption capacities at equilibrium of γ-PGA and γ-PGANa for Cs were 345 mg-Cs(g-γ-PGA) −1 at pH 6.0 and 290 mg-Cs(g-γ-PGANa) −1 at pH 9.0, respectively. At lower pH < p K a, the carboxyl groups of γ-PGA primarily remained in the protonated form and adsorption of Cs only slightly occurred. At higher pH > p K a, the adsorption of Cs was significantly facilitated due to ionization of carboxyl groups to carboxylate ion. Adsorption of Cs at pH > 9.0 was inhibited due to the hydrolysis of Cs. The Langmuir model could successfully describe the isotherm data. For γ-PGA and γ-PGANa, the maximum adsorption capacities at equilibrium in the Langmuir model were 446 and 333 mg-Cs(g-adsorbent) −1, respectively. The high adsorption capacities confirmed a potential utilization of γ-PGA and γ-PGANa for Cs removal. The adsorption of Cs by both γ-PGA and γ-PGANa attained the equilibrium within 0.5 min. The very quick equilibration is a benefit from the viewpoint of practical application. The spectra of FT-IR and XPS before and after adsorption confirmed the adsorption of Cs onto γ-PGA and γ-PGANa via electrostatic interaction with carboxylate anions. Graphical abstract: Deprotonation and conformational change of α-carboxylic acid group in γ-PGA and γ-PGANa. Highlights: Cs removal from radioactive wastewater by poly-γ-glutamic acid was studied. High adsorption capacity of poly-γ-glutamic acid for Cs removal was obtained. Langmuir model could successfully represent the isotherm data of Cs removal. The adsorption of Cs by γ-PGA attained the equilibrium very quickly. Potential utilization of poly-γ-glutamic acid for Cs removal was confirmed.