| Summary: | Iron oxides/oxyhydroxides, namely maghemite, iron oxide-silica composite, akaganeite, and ferrihydrite, are studied for As<sup>V</sup> and As<sup>III</sup> removal from water in the pH range 2–8. All sorbents were characterized for their structural, morphological, textural, and surface charge properties. The same experimental conditions for the batch tests permitted a direct comparison among the sorbents, particularly between the oxyhydroxides, known to be among the most promising As-removers but hardly compared in the literature. The tests revealed akaganeite to perform better in the whole pH range for As<sup>V</sup> (max 89 mg g<sup>−1</sup> at pH<sub>0</sub> 3) but to be also efficient toward As<sup>III</sup> (max 91 mg g<sup>−1</sup> at pH<sub>0</sub> 3–8), for which the best sorbent was ferrihydrite (max 144 mg g<sup>−1</sup> at pH<sub>0</sub> 8). Moreover, the study of the sorbents’ surface chemistry under contact with arsenic and arsenic-free solutions allowed the understanding of its role in the arsenic uptake through electrophoretic light scattering and pH measurements. Indeed, the sorbent’s ability to modify the starting pH was a crucial step in determining the removal of performances. The As<sup>V</sup> initial concentration, contact time, ionic strength, and presence of competitors were also studied for akaganeite, the most promising remover, at pH<sub>0</sub> 3 and 8 to deepen the uptake mechanism.
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