A novel oxalated zero-valent iron nanoparticle for Pb(II) removal from aqueous solution: Performance and synergistic mechanisms

A novel oxalated zero-valent iron nanoparticle (Ox-nZVI) was synthesized using one-step and two-step modification to investigate the performance and synergistic mechanisms for aqueous Pb(II) removal. Batch experiments showed the maximum removal capacity of Ox-nZVI toward Pb(II) reached 527 mg/g along with 7.87 mg/g Fe release (R2 = 0.989) at a pH of 7.0, contact time of 1440 min, initial Pb(II) concentration of 250 mg/L and temperature at 25 °C. The characterization results suggested reduction, adsorption and co-precipitation were synergistically realized between Pb(II) and Ox-nZVI. Oxalate modification favored steric stability by coverage of membrane-like flakes on the outer surface of nanospheres, leading to more Pb(II) reduced to Pb0 by capturing electrons from the oxidation of Fe0 into iron oxides including Fe3O4, Fe2O3 and FeOOH. The Pb(II) complexes existed on the active sites of Ox-nZVI surface via FeC2O4-, FeOOH and FeOH groups. The adsorption process was best fitted with pseudo-second-order kinetic model and Langmuir isotherm through surface mass transfer and interparticle diffusion. The existence of PbO, Pb3(CO3)2(OH)2 and PbFe12O19 was attributed to the co-precipitation of Pb(II) with hydroxyl ion and atmospheric CO2. This study provided a promising iron-based nanomaterial with surface modification strategy for effective and long-term treatment of Pb(II) from aqueous environment.