Chitosan and biochar synergize the efficient elimination of lead from wastewater by sulfidised nano-zero-valent iron

The safety of drinking water and food has been threatened by Pb2+ pollution. A chitosan and biochar synergistically-modified sulfurized nano-zero-valent iron was synthetized by NaBH4 reduction and tested for Pb2+ efficient removal from aqueous solution. The synthesized compound was characterized with X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Zeta potential, Brunauer-Emmett-Teller (BET), X-ray powder diffraction (XRD), and scanning electron microscope (SEM). The optimized synthesis parameters of CS@S-nZVI/TB were determined as a 0.14 molar ratio of S/Fe and a 4 mass ratio of Fe/biochar. The removal of Pb2+ increased with the increase of the initial solution pH from 2 to 6, but it decreased slightly with the increasing ionic strength of NaCl in the solution. The removal processes fitted well with pseudo-second order, Langmuir, and Freundlich models, which indicated that both monolayer chemical and multilayer physical adsorption occurred during Pb removal. The removal process for Pb2+ was exothermic, with a maximum removal of 281.97 mg/g of Pb2+ at 25 degrees C. The removal mechanisms involved mainly adsorption, reduction reaction, and complexation reactions. Overall, these findings provide new ideas for the modification of Fe-0 and reveal the mechanism for the removal of heavy metals from wastewater by CS@S-nZVI/TB.