Antimony (Sb) is an element in the group XV that has allotropic modifications and two main oxidation states as Sb(III) and Sb(V) in nature. Antimony is a pollutant of concern for its carcinogenic and bioaccumulation effects. Sb presence in drinking water or wastewater is strictly regulated worldwide. Removing Sb(V) from water is a challenging task. In this study, we aim to develop a simple method to produce a highly reactive iron-based reactive media mixture, namely, the activated iron media (AIM), and to evaluate the AIM technology as a potential solution for treating Sb-contaminated water. For the purpose, batch tests were conducted to evaluate the optimum recipe, conditions and procedures to synthesize the AIM and to evaluate the performance of the AIM for removing Sb(V).
Batch tests using serum vial as reactors showed that aeration of Fe^2+ under alkaline condition could result in formation of mixed Fe(II)-Fe(III) oxide crystalline (FeOx). The composition and structure of resulting FeOx varies greatly with the dosage of Ov2. With a stoichiometric dosage of Ov2/Fe(II) at 1:6, magnetite (Fe3O4) was the product from the oxidative precipitation of Fe(OH)v2 by Ov2, which was corroborated by a ratio of Fe(III)/Fe(II) at 2:1 as well as an inverse-spinel structure identified by X-ray diffraction (XRD) spectroscopy. When zero-valent iron (ZVI) was added into a Fe(OH)v2 system, ZVI could consume some of the introduced Ov2, which resulted in a lower Fe(III)/Fe(II) ratio in the formed FeOx than the one without ZVI. With aeration, ZVI surface was corroded and formed a FeOx coating similar to those FeOx formed from
oxidative precipitation of Fe(OH)v2 in term of crystal structure and composition. When the dosage of Ov2 to Fe^2+ was doubled to 1:3, the Fe(III)/Fe(II) ratio in the resulting FeOx was near 2.3:1, close to the desired ratio of FeOx in the mixture of the AIM. The batch tests and scaled-up pilot test showed that with appropriate dosage and intensity of Ov2 aeration, the mixture of ZVI and Fe^2+ with controlled alkalinity could be converted to form a mixture of highly reactive media with a magnetite-like FeOx in form of a coating on ZVI or discrete crystalline.
Batch tests using the activated iron media to treat Sb-contaminated water was conducted to evaluate effectiveness of the media for Sb removal under various conditions. Under an anaerobic condition, Sb(V) removal consists of rapid removal within the initial 15 min, followed by a slower phase before entering a stagnant phase, which could be better modelled as a chemisorption. Both externally supplied Ov2 and Fe^2+ would somewhat help Sb(V) removal by the AIM, but with the co-presence of Ov2 and Fe^2+, Sb(V) removal by the AIM could be greatly enhanced, in which a treatment of 50 mg/L with 10 g/L AIM could decrease Sb(V) to below 6 ug/L, the EPA drinking water maximum contaminant level (MCL). Sequential dosing test showed that such high removal of Sb(V) could be sustained in a continuous flow treatment system.
This study has expanded our knowledge of the AIM water treatment system for industrial wastewater treatment, in particular with applications involving extremely high concentration of Sb(V)
