Simultaneous adsorption of Cd(II) and As(III) by a novel biochar-supported nanoscale zero-valent iron in aqueous systems

Biochar-supported nanoscale zero-valent iron (nZVI-BC) is a promising material for Cd(II) and As(III) removal from aqueous systems. In this study, simplified nZVI-BC composites were successfully synthesized and characterized via scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectroscopy (FTIR) to understand the underlying adsorption mechanism. SEM and FTIR confirmed that nZVI particles were distributed evenly on the biochar surface. XRD and XPS revealed that metal ions were separated from solutions via electrostatic adsorption, complexation, oxidation, precipitation/co-precipitation, and the formation of type B ternary surface complex. Batch experiments showed that nZVI-BC (1:1) had a high removal efficiency in a wide pH range of 5.0-8.0 for Cd(II) and 3.0-8.0 for As(III), the maximum Cd(II) and As(III) adsorption capacities were 33.81 and 148.5 mg/g within 2 and 1 h, respectively. Additionally, synergisticeffects considerably enhanced the adsorption capacity of nZVI-BC(1:1) in mixed adsorption systems, the adsorption capacities of Cd(II) and As(III) reached 179.9 and 158.5 mg/g, respectively. Hence, nZVI-BC(1:1) is an ideal candidate for Cd(II) and As(III) pollution treatment.