The arsenic contamination of surface and groundwater represents a worldwide environmental issue, mainly caused by arsenic mobilization from soils due to anthropogenic activities. Among various technologies, adsorption is a promising method for the removal of As(III)/As(V) due to its low cost, high efficiency, simplicity, and the possibility of regeneration.
Iron oxyhydroxide nanopowders exhibit remarkable adsorption capabilities due to their high surface area, abundant hydroxyl groups, strong arsenic affinity, low toxicity, and facile green synthesis.
In this study, three iron oxyhydroxides—akaganeite, ferrihydrite, and feroxyhyte— were synthesized via eco-friendly precipitation and characterized using XRD, TGA, N₂ physisorption, ELS, TEM, FTIR, Mössbauer spectroscopy, and DC magnetometry. Adsorption tests evaluated As(III) and As(V) removal under identical conditions, varying pH (2–8), arsenic concentration (10–500 mg/L), contact time (10–960 min), and competing ions. Total arsenic concentrations before and after adsorption were determined by ICP-OES.
Akaganeite removed nearly 100% of As(V) (C₀ = 100 mg/L) across all pH levels. Ferrihydrite showed high As(V) removal at pH 2 and 3 (100% and 94%), but performance dropped to 23% at pH 8. Feroxyhyte performed well at pH 2 (99%) and maintained 77–80% efficiency up to pH 6, then decreased sharply to 50% at pH 7 and 38% at pH 8. For As(III), akaganeite showed limited removal at pH 2 (64%) but improved (~80%) from pH 3 to 8. Ferrihydrite and feroxyhyte both maintained high As(III) removal (~90–96%). Per unit surface area, feroxyhyte had the highest As(III) uptake, followed by ferrihydrite and akaganeite; for As(V), akaganeite was most active, followed by feroxyhyte and ferrihydrite.
Due to the higher toxicity and mobility of As(III), its oxidation to As(V) combined with adsorption is a promising approach. Manganese-doped iron oxyhydroxides were synthesized to provide both oxidation and adsorption capabilities, and preliminary tests are ongoing.
These findings support the further development of Fe-oxyhydroxide and Mn-doped Fe-oxyhydroxide hybrid materials for practical application in real-world scenarios.