Reduction and Removal of Chromium VI in Water by Powdered Activated Carbon.

Yanan Chen,Linping Qian,Jiayi Gao,Sainan Sun,Dong An

doi:10.3390/ma11020269

Abstract

Cr adsorption on wood-based powdered activated carbon (WPAC) was characterized by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The highest Cr(VI) adsorption (40.04%) was obtained under acidic conditions (pH 3), whereas Cr removal at pH 10 was only 0.34%. The mechanism of Cr(VI) removal from aqueous solutions by WPAC was based on the reduction of Cr(VI) to Cr(III) with the concomitant oxidation of C-H and C-OH to C-OH and C=O, respectively, on the surface of WPAC, followed by Cr(III) adsorption. Raman spectroscopy revealed a change in the WPAC structure in terms of the D/G band intensity ratio after Cr(VI) adsorption. SEM-EDS analysis showed that the oxygen/carbon ratio on the WPAC surface increased from 9.85% to 17.74%. This result was confirmed by XPS measurements, which showed that 78.8% of Cr adsorbed on the WPAC surface was in the trivalent state. The amount of oxygen-containing functional groups on the surface increased due to the oxidation of graphitic carbons to C-OH and C=O groups.

Highlights

Chromium (Cr) is a common heavy metal pollutant in water, where it mainly exists in two stable oxidation states, i.e., hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) [1]
wood-based powdered activated carbon (WPAC) surface was in the trivalent state
The Cr(VI) adsorption capacity of WPAC was investigated at pH 3, 7, and 10

Summary

Introduction

Chromium (Cr) is a common heavy metal pollutant in water, where it mainly exists in two stable oxidation states, i.e., hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) [1]. Toxicity studies have shown that Cr can enter the human body through the respiratory tract and skin, and has significant carcinogenic and mutagenic effects. Cr(VI) is about 100 times more toxic than Cr(III) because of its higher solubility and easy absorption and accumulation in kidneys, stomach, and liver [2]. Cr-containing compounds are widely used in various industries such as leather, electroplating, textile dyeing, and metal fabrication and finishing. Cr-containing wastewaters are one of the major pollutants of the environment [3]. According to the World Health Organization, the permissible limit of Cr(VI) in drinking water is

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