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.

Automated summary

This study developed a new type of iron-carbon composite using spent bleaching earth (SBE) to remove Cr(VI) from water. The adsorption and reduction mechanism of FexOy/SBE@C for Cr(VI) removal were investigated, and it was found that FexOy/SBE@C exhibited satisfactory performance in removing Cr(VI) through physical adsorption and chemical reduction.