Adsorption of toxic mercury(II) by an extracellular biopolymer poly(γ-glutamic acid)

• Published in: Bioresource technology Vol. 100; no. 1; pp. 200 - 207
• Main Authors: Inbaraj, B. Stephen, Wang, J.S., Lu, J.F., Siao, F.Y., Chen, B.H.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 2009; [New York, NY]: Elsevier Ltd; Elsevier
• Subjects: adsorbents; Adsorption; Adsorption isotherms; Adsorption kinetics; Biological and medical sciences; biopolymers; Biopolymers - chemistry; Biosorption; Biotechnology; cadmium; calcium; Computer Simulation; copper; detoxification (processing); Fundamental and applied biological sciences. Psychology; glutamates; ionic strength; Kinetics; mathematical models; Mercury; Mercury - chemistry; Mercury - isolation & purification; mixing; Models, Chemical; poly(gamma-glutamic acid); Poly(γ-glutamic acid); Polyglutamic Acid - analogs & derivatives; Polyglutamic Acid - chemistry; potassium; reaction kinetics; sodium; sorption isotherms; temperature; Ultrafiltration - methods; waste treatment; zinc; Adsorption isotherms; Adsorption kinetics; Biosorption; Mercury; Poly(γ-glutamic acid); Toxicity; Adsorption isotherm; Mercury II; Extracellular; Adsorption; Biopolymer; Glutamic acid polymer; Kinetics
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2008.05.014

Adsorption of mercury(II) by an extracellular biopolymer, poly(γ-glutamic acid) (γ-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 γ-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 γ-PGA reuse for five cycles of operation showed a loss of only 6.5%. IR spectra of γ-PGA and Hg(II)-γ-PGA revealed binding of mercury(II) with carboxylate and amide groups on γ-PGA.