Comparison of As removal efficiency and health risks from aqueous solution using as-synthesized Fe0 and Cu0: modelling, kinetics and reusability

Abstract

Batch scale removal of arsenic (As) from aqueous media was explored using nano-zero valent iron (Fe⁰) and copper (Cu⁰) particles. The synthesized particles were characterized using a Brunauer-Emmett-Teller (BET) surface area analyzer, a scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). The BET result showed that the surface area (31.5 m²/g) and pore volume (0.0415 cm³/g) of synthesized Fe⁰ were higher than the surface area (17.56 m²/g) and pore volume (0.0287 cm³/g) of Cu⁰. The SEM results showed that the morphology of the Fe⁰ and Cu⁰ was flowery microspheres and highly agglomerated with thin flakes. The FTIR spectra for Fe⁰ showed broad and intense peaks as compared to Cu⁰. The effects of the adsorbent dose (1-4 g/L), initial concentration of As (2 mg/L to 10 mg/L) and solution pH (2-12) were evaluated on the removal of As. Results revealed that effective removal of As was obtained at pH 4 with Fe⁰ (94.95%) and Cu⁰ (74.86%). When the dosage increased from 1 to 4 g L^-1, the As removal increased from 70.59 to 93.02% with Fe⁰ and from 67 to 70.59% with Cu⁰. However, increasing the initial As concentration decreased the As removal significantly. Health risk indices, including estimated daily intake (EDI), hazard quotient (HQ), and cancer risk (CR) were employed and a significant decline (up to 99%) in risk indices was observed in As-treated water using Fe⁰/Cu⁰. Among the adsorption isotherm models, the values of R² showed that isothermal As adsorption by Fe⁰ and Cu⁰ was well explained by the Freundlich adsorption isotherm model (R² > 0.98) while the kinetic experimental data was well-fitted with the Pseudo second order model. The Fe⁰ showed excellent stability and reusability over five sorption cycles, and it was concluded that, compared to the Cu⁰, the Fe⁰ could be a promising technology for remediating As-contaminated groundwater.

Keywords: Aqueous electrons; Arsenic; Reductive pathways; Surface chemistry; Wastewater; Zerovalent nanoparticles.