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The adsorption performance and mechanism of extracellular polymeric substances (EPS) extracted from Klebsiella sp. J1 for soluble Pb (II) were investigated. The maximum biosorption capacity of EPS for Pb (II) was found to be 99.5 mg g−1 at pH 6.0 and EPS concentration of 0.2 g/L. The data for adsorption process satisfactorily fitted to both Langmuir isotherm and pseudo-second order kinetic model. The mean free energy E and activation energy Ea were determined at 8.22– 8.98 kJ mol−1 and 42.46 kJ mol−1, respectively. The liquid-film diffusion step might be the rate-limiting step. The thermodynamic parameters (ΔGo, ΔHo and ΔSo) revealed that the adsorption process was spontaneous and exothermic under natural conditions. The interactions between EPS system and Pb (II) ions were investigated by qualitative analysis methods (i.e Zeta potential, FT-IR and EDAX). Based on the strong experimental evidence from the mass balance of the related elements participating in the sorption process, an ion exchange process was identified quantitatively as the major mechanism responsible for Pb (II) adsorption by EPS. Molar equivalents of both K+ and Mg2+ could be exchanged with Pb2+ molar equivalents in the process and the contribution rate of ion exchange to adsorption accounted for 85.72% (Δmequiv = −0.000541).

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Microbial extracellular polymeric substance (EPS) is a complex high molecular weight compound secreted from many organisms. In this work, magnetic nanocomposite Fe 3 O 4 @EPS of Klebsiella sp. J1 were first synthesized for silver ions (Ag + ) wastewater remediation, which synergistically combined the advantages of the easy separation property of magnetic Fe 3 O 4 nanoparticles and the superior adsorption capacity of EPS of Klebsiella sp. J1. The physical and chemical properties of Fe 3 O 4 @ EPS were analyzed comprehensively. Fe 3 O 4 @EPS exhibited the well-defined core−shell structure (size 50 nm) with high magnetic (79.01 emu g −1 ). Batch adsorption experiments revealed that Fe 3 O 4 @EPS achieved high Ag + adsorption capacity (48 mg g −1 ), which was also much higher than many reported adsorbents. The optimal solution pH for Ag + adsorption was around 6.0, with the sorption process followed pseudo-second-order kinetics. Ag + adsorption on Fe 3 O 4 @EPS was mainly attributed to the reduction of Ag + to silver nanoparticles (AgNPs) by benzenoid amine (−NH−), accompanied by the chelation between Ag + and hydroxyl groups, ion exchange between Ag + and Mg 2+ and K + , and physical electrostatic sorption. The repeated adsorption−desorption experiments showed a good recycle performance of Fe 3 O 4 @ EPS. This study has great importance for demonstrating magnetic Fe 3 O 4 @EPS as potential adsorbent to remove Ag + from contaminated aquatic systems.

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