Adsorption of arsenate from groundwater through a fixed bed using iron-coated natural fibres: reusability and sorbent characterisation

Abstract

ABSTRACT Arsenic in groundwater is a severe problem, especially in rural areas. This research developed a novel sorbent (Fe-kapok) by hydrothermal surface treatment of natural fibres with iron for As(V) removal from groundwater in a column-fixed bed. The Fe-kapok was extensively characterised using various high-technology instruments and methods. Results showed higher specific surface area BET (3.272 m2/g) and pore volume (0.032 cm3/g) for Fe-kapok than raw kapok (0.976 m2/g and 0.021 cm3/g), indicating its higher As(V) adsorption capacity. Fe-kapok was effective at As(V) adsorption despite the presence of competing ions, such as sulphate, with its high interference capacity in the groundwater. Nonetheless, the As(V) adsorption efficiency declined with increasing flow rate and As(V) initial concentration. By contrast, the As(V) removal efficiency increased with increasing adsorbent dosage and groundwater temperature, and the optimal adsorption was achieved at neutral pH. The Thomas model predicted an adsorption capacity of 6.63 mg.g−1 at 25°C, 3 g adsorbent dose, and 100 µg.L−1 As(V) concentration for Fe-kapok. However, the Bohart and Adams correlation coefficient (R2 = 0.88–0.99) was higher than the Thomas R2 (0.89–0.98). Regeneration and reusability of Fe-kapok were demonstrated after eight adsorption cycles, and it could run for up to 600 minutes before saturation at the last reuse round.