Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles

Abstract

In this study, magnetite-maghemite nanoparti- cles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy (XPS) studies showed the presence of arsenic on the surface of magnetite-maghemite nanoparticles. Theoretical multiplet analysis of the mag- netite-maghemite mixture (Fe3O4-cFe2O3) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite-maghemite mixture surface when arsenic was introduced. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on contact time and ini- tial concentration of arsenic. Equilibrium was achieved in 3 h in the case of 2 mg/L of As(V) and As(III) concen- trations at pH 6.5. The results further suggest that arsenic adsorption involved the formation of weak arsenic-iron oxide complexes at the magnetite-maghemite surface. In groundwater, arsenic adsorption capacity of magnetite- maghemite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 80 lmol/g and Gibbs free energy (DG 0 , kJ/mol) for arsenic removal was -35 kJ/mol, indicating the spontaneous nature of adsorp- tion on magnetite-maghemite nanoparticles.