Kilogram-scale synthesis of iron oxy-hydroxides with improved arsenic removal capacity: Study of Fe(II) oxidation–precipitation parameters

Various iron oxy-hydroxides were synthesized in a continuous flow kilogram-scale production reactor through the precipitation of FeSO4 and FeCl2 in the pH range 3–12 under intense oxidative conditions to serve as arsenic adsorbents. The selection of the optimum adsorbent and the corresponding conditions of the synthesis was based not only on its maximum As(III) and As(V) adsorption capacity but also on its potential efficiency to achieve the arsenic health regulation limit in NSF challenge water. As a result, the adsorbent prepared at pH 4, which consists of schwertmannite, was selected because it exhibited the highest adsorption capacity of 13 μg As(V)/mg, while maintaining a residual arsenic concentration of 10 μg/L at an equilibrium pH 7. The high surface charge and the activation of an ion-exchange mechanism between SO42− adsorbed in the Stern layer and arsenate ions were found to significantly contribute to the increased adsorption capacity. Adsorption capacity values observed in rapid scale column experiments illustrate the improved efficiency of the qualified adsorbent compared to the common commercial arsenic adsorbents.

► Low-cost synthesis of iron oxy-hydroxides in kilogram-scale for arsenic adsorption.
► Optimum precipitation pH for maximum arsenic removal is 4.
► Adsorption capacity for residual As at 10 μg/L reaches 13 μg As(V)/mg.
► Schwertmannite formation enables sulfate-arsenate exchange.
► Breakthrough tests illustrate improved properties compared to commercial products.