Adsorption of toxic mercury(II) by an extracellular biopolymer poly(gamma-glutamic acid).
Adsorption of mercury(II) by an extracellular biopolymer, poly(gamma-glutamic acid) (gamma-PGA), was studied as a function of pH, temperature, agitation time, ionic strength, light and heavy metal ions. An appreciable adsorption occurred at pH>3 and reached a maximum at pH 6. Isotherms were well predicted by Redlich-Peterson model with a dominating Freundlich behavior, implying the heterogeneous nature of mercury(II) adsorption. The adsorption followed an exothermic and spontaneous process with increased orderliness at solid/solution interface. The adsorption was rapid with 90% being attained within 5 min for a 80 mg/L mercury(II) solution, and the kinetic data were precisely described by pseudo second order model. Ionic strength due to added sodium salts reduced the mercury(II) binding with the coordinating ligands following the order: Cl(-) >SO(4)(2-) >>NO(3)(-). Both light and heavy metal ions decreased mercury(II) binding by gamma-PGA, with calcium(II) ions showing a more pronounced effect than monovalent sodium and potassium ions, while the interfering heavy metal ions followed the order: Cu(2+) >> Cd(2+) > Zn(2+). Distilled water adjusted to pH 2 using hydrochloric acid recovered 98.8% of mercury(II), and gamma-PGA reuse for five cycles of operation showed a loss of only 6.5%. IR spectra of gamma-PGA and Hg(II)-gamma-PGA revealed binding of mercury(II) with carboxylate and amide groups on gamma-PGA.
Inbaraj
B Stephen
BS
Department of Food Science, Fu Jen University, Taipei 242, Taiwan.
Wang
J S
JS
Lu
J F
JF
Siao
F Y
FY
Chen
B H
BH
D000327:Adsorption; D001704:Biopolymers / Q000737:chemistry*; D003198:Computer Simulation; D007700:Kinetics; D008628:Mercury / Q000737:chemistry* / Q000302:isolation & purification*; D008956:Models, Chemical; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D014462:Ultrafiltration / Q000379:methods*
D001704:Biopolymers; C511775:poly(gamma-glutamic acid); D011099:Polyglutamic Acid; D008628:Mercury