Efficiency of iron-based oxy-hydroxides in removing antimony from groundwater to levels below the drinkingwater regulation limits

Abstract

This study evaluates the efficiency of iron-based oxy-hydroxides to remove antimony from groundwater to meet the requirements of drinking water regulations. Results obtained by batch adsorption experiments indicated that the qualified iron oxy-hydroxide (FeOOH), synthesized at pH 4 for maintaining a high positive charge density (2.5 mmol OH-/g) achieved a residual concentration of Sb(III) below the EU drinking water regulation limit of 5 μg/L by providing an adsorption capacity of 3.1 mg/g. This is more than twice greater compared either to similar commercial FeOOHs (GFH, Bayoxide) or to tetravalent manganese feroxyhyte (Fe-MnOOH) adsorbents. In contrast, all tested adsorbents failed to achieve a residual concentration below 5 μg/L for Sb(V). The higher efficiency of the qualified FeOOH was confirmed by rapid small-scale column tests, since an adsorption capacity of 3 mg Sb(III)/g was determined at a breakthrough concentration of 5 μg/L. However, it completely failed to achieve Sb(V) concentrations below 5 μg/L even at the beginning of the column experiments. The results of leaching tests classified the spent qualified FeOOH to inert wastes. Considering the rapid kinetics of this process (i.e., 85% of total removal was performed within 10 min), the developed qualified adsorbent may be promoted as a prospective material for point-of-use Sb(III) removal from water in vulnerable communities, since the adsorbent's cost was estimated to be close to 30 ± 3.4 €/103 m3 for every 10 μg Sb(III)/L removed.