title: Adsorption capacities of poly-γ-glutamic acid and its sodium salt for cesium removal from radioactive wastewaters.
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)-1at pH 6.0 and 290 mg-Cs(g-γ-PGANa)-1at pH 9.0, respectively. At lower pH < pKa, the carboxyl groups of γ-PGA primarily remained in the protonated form and adsorption of Cs only slightly occurred. At higher pH > pKa, 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.
authors.affiliation: Research Center for Biochemical and Environmental Engineering, Department of Applied Chemistry, Toyo University, 2100 Kujirai, Kawagoe, Saitama, 350-8585, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Sakamoto
authors.affiliation: Research Center for Biochemical and Environmental Engineering, Department of Applied Chemistry, Toyo University, 2100 Kujirai, Kawagoe, Saitama, 350-8585, Japan. Electronic address: ykawase@toyonet.toyo.ac.jp.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kawase
mesh_terms: D065966:Absorption, Physicochemical; D002588:Cesium Radioisotopes / Q000032:analysis* / Q000737:chemistry; D007700:Kinetics; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D012964:Sodium; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000737:chemistry; D014875:Water Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry
chemical_list: D002588:Cesium Radioisotopes; D011099:Polyglutamic Acid; D012964:Sodium; D062065:Wastewater; D014875:Water Pollutants, Radioactive; C511775:poly(gamma-glutamic acid)
keywords: Adsorption capacity; Biosorption; Cesium; Poly-γ-glutamic acid; Surface characterization