Adsorptive removal of arsenic ions from contaminated water using low-cost schwertmannites and akaganéites

Abstract

Schwertmannite and akaganéite have potential in treatment of arsenic contaminated waters. In this work, schwertmannite and akaganéite were synthesized by chemical and biological methods. Characterization and analysis results showed about 120 m2/g for schwertmannite spheres with a diameter of 2–5 μm (Sch-Chem) and about 0.5 μm (Sch-Bio) and 240–280 m2/g for akaganéite rod with a length of about 300–500 nm (Aka-Chem) and 150 nm (Aka-Bio). Agglomerated particle average diameters (μm) of synthesized products in solutions were 32.5, 20.6, 0.480 and 26.4, respectively. Schwertmannite and akaganéite were used to investigate arsenic adsorption behaviors in aqueous solutions by batch experiments, under various reaction times, initial arsenic and adsorbent levels, pH values, and anions (Cl−, NO3−, H2PO4−, CO32−, and SO42−). Adsorption data well fitted to pseudo-second-order rate model (R2 = 0.999), and Langmuir (R2 = 0.977–0.998) and Freundlich (R2 = 0.948–0.998) isothermal models at pH 7.0. Maximum adsorption capacities of As(III)/As(V) were 102/98.3, 110/115, 6.40/7.03 and 30.3/34.8 mg/g, respectively. Anions of SO42− and H2PO4− can affect arsenic removal efficiency. Adsorbents with pHZPC of 4.0–5.0 still had a good arsenic removal ability at pH 3.0–9.0, due to a main adsorption mechanism of anionic exchange between hydroxyl group (or sulfate) and arsenic ions. Further, schwertmannite candidates were used in arsenic removal from polluted groundwater. Breakthrough points (bed volume, mL) for Sch-Bio/Sch-Chem were about at 90/120, 70/(100–110) and 80/110 for As(III), As(V), and total As, respectively. It demonstrated that akaganéite and schwertmannite could be potentially applied in treatments of arsenic-polluted waters.