Oxidative adsorption of arsenic from water environment by activated carbon modified with cerium oxide/hydroxide

Abstract

Arsenic contamination at high concentration frequently occurs in nature water environments and poses a great risk to human health. In this study, a cerium oxide/hydroxide-modified activated carbon was synthesized via a simple co-precipitation process as an adsorbent for the removal of arsenic from aqueous systems. Analysis of the cerium oxide/hydroxide-modified activated carbon by field emission scanning electron microscopy and X-ray photoelectron spectroscopy showed that cerium was mainly coated on the surface of activated carbon as cerium (IV) hydroxide. The arsenic adsorption performance of the adsorbent was investigated via batchwise adsorption and using a chromatographic system with a fixed bed column. Neutral pH conditions were optimal for removal of arsenic. Kinetic experiment data were described by a diffusion–chemisorption model. The adsorption isotherm followed the Langmuir model, and the maximum adsorption capacity of cerium oxide/hydroxide-modified activated carbon was 0.220 and 0.284 mmol g−1 for As(V) and As(III), respectively. Regeneration trials showed that cerium oxide/hydroxide-modified activated carbon could be regenerated with 0.1 mol L−1 NaOH solution as regenerant. During adsorption, redox reactions occurred in the aqueous and solid phases. As(III) was oxidized to As(V) by reduction of surface functional groups (CO, C-O, and cerium oxide/hydroxide) in the solid phase and by dissolved organic matters and surface functional groups in the aqueous phase. Chromatographic treatment with a fixed bed column of cerium oxide/hydroxide-modified activated carbon showed high arsenic adsorption efficiency. The repeated use of cerium oxide/hydroxide-modified activated carbon by chromatographic operation was also achieved.