A preliminary investigation of the mechanism of hexavalent chromium removal by corn-bran residue and derived chars

Abstract

In this study, biochars were prepared from corn-bran residue (CBR) at a low pyrolysis temperature range from 300 to 600 °C. The CBR and CBR-derived chars were characterized and utilized to remove Cr(VI) from the aqueous solution. CBR-chars produced at higher temperatures have larger specific surface area and lower content of functional groups. The Cr(VI) removals by CBR and CBR-chars were mainly achieved by the reduction from Cr(VI) to Cr(III) through SO₃²⁻ or oxygen-containing functional groups from these adsorbents. The amount of Cr(VI) removed by the adsorbents ranged from 8.18 to 86.49 mg g⁻¹ at the initial Cr(VI) concentration range of 50–500 mg L⁻¹ (pH 2). The SO₃²⁻-rich CBR was demonstrated to be more economical and effective for Cr(VI) removal than others, with a Cr(VI) removal efficiency of 96.02%. The results can be modeled by Freundlich isotherm at pH 2, indicating that the Cr(VI) adsorption process was complex and related with solution pH and adsorbent properties. Reduction-coupled with adsorption was the mechanism of Cr(VI) removal by CBR and CBR-derived chars.