Enhanced adsorption and reduction of Pb(II) and Zn(II) from mining wastewater by carbon@nano-zero-valent iron (C@nZVI) derived from biosynthesis

Heavy metal ions containing Pb(II) and Zn(II) in mining wastewater are dangerous contaminants because of their genotoxicity and carcinogenicity. Here, a green sustainable carbon@nano-zero-valent iron composite (C@nZVI) derived from biosynthesis was used to simultaneously remove Pb(II) and Zn(II) with the removal capacities of 98.37 and 26.38 mg·g−1 for Pb(II) and Zn(II), respectively. Advanced characterization confirmed that both Pb(II) and Zn(II) were adsorbed onto carbon and iron oxides via electrostatic force and complexation, and subsequently Pb(II) was reduced to Pb(0) by nZVI, where biomass-derived carbon promoted the reduction of Pb(II) by accelerating electron transfer. Adsorption of both Pb(II) and Zn(II) best fit the Langmuir model with R2 of 0.991 and 0.994, respectively and both followed the non-linear pseudo-second-order kinetic model with R2 of 0.995 and 0.959, respectively, indicating that the removal process was dominated by monolayer and chemical adsorption. Reduction kinetics of Pb(II) conformed to the pseudo-first-order kinetic model (R2 > 0.990), where the apparent activation energy was 31.39 KJ mol−1, suggesting that Pb(II) reduction was dominated by chemical reaction. Finally, C@nZVI not only removed 98.7 % of Pb and 99.4 % of Zn from mining wastewater, but also exhibited similar removal efficiencies for As (82.9 %), Cd (91.6 %), and Sb (92.7 %), demonstrating that C@nZVI has great potential for environmental remediation applications.