Effective removal of Cr(VI) from aqueous solution by iron-carbonized solid waste composite: behavior mechanism and factor analysis

BACKGROUND: The spent bleaching earth (SBE) is a solid waste produced during the refining of vegetable oil, with features of high residual oil and difficult disposal. At present, pollution control by the treatment of waste is a hot issue to attract more and more attention. This study used SBE as the raw materials and developed a new type of iron-carbon composite (FexOy/SBE@C) by loading iron on spent bleaching earth carbon (SBE@C) to remove Cr(VI) in water. SBE@C was obtained by the pyrolysis of SBE. RESULTS: The behavior mechanism and factor analysis of FexOy/SBE@C for Cr(VI) removal in water were investigated for the first time. At first, one-factor experiments in the preparation process were adopted to obtain FexOy/SBE@C with optimal performance. By characterization analysis of the optimal FexOy/SBE@C before and after Cr(VI) removal, it was found that the Cr(VI) removal mechanism was adsorption followed by reduction. Specifically, the adsorption kinetic and isotherm behaviors of FexOy/SBE@C for Cr(VI) belong to the pseudo-second-order kinetic model and Langmuir isotherm, respectively. Cr(VI) removal by FexOy/SBE@C is spontaneous (Delta G<0) and endothermic (Delta H>0). The presence of coexisting anions (i.e., BrO3- < SO42- < PO43-) and the increase of pH (only adsorption at pH>7) are not conductive to Cr(VI) removal by FexOy/SBE@C. Fortunately, N-2 atmospheres can promote Cr(VI) removal (similar to 100%) that is significantly higher than those in air atmosphere (63.34%) and natural conditions (82.25%). CONCLUSION: Overall, FexOy/SBE@C has the satisfactory Cr(VI) removal performance through physical adsorption and chemical reduction, and exhibits great potential application value in Cr(VI) elimination from water. (C) 2022 Society of Chemical Industry.