Fixed bed adsorption of As(III) on iron-oxide-coated natural rock (IOCNR) and application to real arsenic-bearing groundwater

This study examines the efficiency of the fixed-bed adsorption of As(III) on iron-oxide-coated natural rock (IOCNR) in a contaminated aquatic environment. We considered a column with a diameter of 2-cm and varying bed depths, including 10 cm, 15 cm, and 20 cm. The breakthrough (C/Co = 0.016) times were 31.0 h, 49.0 h, and 63.0 h, and the exhaust (C/Co = 0.90) times were 60.0 h, 90.0 h, and 110.0 h, with an up-flow rate of 8 mL/min, respectively. The volume of the contaminated water treated at the breakthrough points was 14.88 L, 23.52 L, and 30.24 L, and at the exhaust points 28.80 L, 43.20 L, and 52.80 L, respectively when As(III) concentration was 0.6 mg/L. The columns were designed using the logit method to evaluate the adsorption rate (K) and column efficiency (N). The 10-cm exhaust bed was regenerated with 4% NaOH, and its performance was evaluated. This study proposes an in situ two-step mechanism, oxidation of As(III) to As(V), and subsequent adsorption on IOCNR. A column (10 cm) performance of real arsenic-bearing groundwater was evaluated. Results indicate that the treated effluent water quality is suitable for domestic use. Moreover, the experimental results agreed well with the geochemical modeling using computer program PHREEQC.

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► As(III) removed column efficiency using IOCNR was evaluated by logit method.
► No oxidizing agent required to convert As(III) to As(V), in situ two step mechanism is proposed.
► Regenerated bed with NaOH could be re-usable.
► Effluent water quality of the treated real arsenic-bearing sample could be usable.
► Geochemical model, PHREEQC, accurately reflected the column experimental results.