Enhanced sorption of hexavalent chromium [Cr(VI)] from aqueous solutions by diluted sulfuric acid-assisted MgO-coated biochar composite

摘要

Metal oxide-Carbon composites have aroused great interesting towards specific anionic contaminants removal from the polluted environment. In this study, aiming at removing toxic chromate ion [Cr(VI)] from aqueous solutions, a novel approach was developed to produce surface-enhanced MgO-coated biochar adsorbent from sugarcane harvest residue (SHR). It was found that sulfuric acid hydrolysis and MgO-coating both facilitated the removal of Cr(VI) by biochars, and the maximum sorption capacities for the pristine biochar (SHR550), MgO-coated biochar (MgSHR550), and acid-assisted MgO-coated biochar (MgASHR550) that derived from the Langmuir isotherm model were 20.79, 54.64, and 62.89 mg g−1, respectively. Additionally, the Cr(VI) removal was a pseudo-second-order kinetic model controlled process with equilibrium reached within 24 h. The mechanism investigation revealed that Cr(VI) ions was directly sorbed by the MgO-coated biochars via the chemical interaction between MgO and Cr(VI), whereas the sorption-coupled reduction of Cr(VI) to Cr(III) governed the sorption of Cr(VI) on the SHR550. Although the increases of solution pH (>2.0) and KNO3concentration (>0.05 mol L−1) reduced the Cr(VI) removal by biochars, while there were lower secondary pollution risks in MgO-coated biochar treatments due to the suppressed release of Cr(III) in solutions. This work could provide guidance for the production of efficient biochar for the removal of Cr(VI) from wastewater.