Removal of Cr(III), Ni(II) and Cu(II) by poly(γ-glutamic acid) from Bacillus subtilis NX-2

Poly(γ-glutamic acid) (γ-PGA) derived from Bacillus subtilis NX-2 was investigated as a sorbent for heavy metal ions in batch adsorption experiments. The results showed that the heavy metal adsorption capacity of γ-PGA enhanced with the increase of pH, in the following order: Cr(III)>Cu(II)>Ni(II), within the pH range 3-5. The Langmuir sorption model effectively described the metal sorption of γ-PGA through the experiments of isotherm sorption, and it was deduced that the affinity of γ-PGA for metals was following the sequence: Cr(III)>Cu(II)>Ni(II). γ-PGA was also used to trap trace amounts of heavy metals from the electroplating wastewater, which were difficult to be entirely removed by the traditional hydroxide precipitation method. The results showed that Cr(III) and Ni(II) in the electroplating effluent decreased from 3.07 and 9.46 mg/l to 0.15 and 1.01 mg/l, respectively, and the treated solutions reached the effluent standard. Therefore, γ-PGA is satisfactory as a well biosorbent for the removal of heavy metals. The adsorption mechanism of γ-PGA binding heavy metals was also studied using HyperChem simulation and FT-IR.