Efficient Removal of Cr(VI) from Aqueous Solution by Fe-Mn Oxide-Modified Biochar

Removal of Cr(VI) is of great concern due to its high mobility and toxicity in the natural environment. In this study, Fe-Mn oxide-modified biochar composite (FMBC) was prepared by impregnation to remove Cr(VI) from aqueous systems. The effect of Fe/Mn ratio, adsorbent dosage, solution pH, initial Cr(VI) concentration, and temperature were investigated on the Cr(VI) removal efficiency. Results showed that F1M3BC (with an Fe/Mn ratio of 1:3) had the maximum Cr(VI) adsorption capacity of 118.03 mg g−1 at pH 2.0. The removal efficiency of Cr(VI) by F1M3BC (91.79%) was higher than that by the pristine BC (32.17%). Experimental data fitted well with the Langmuir model and the pseudo-second-order kinetics equation. Thermodynamic studies showed that the adsorption process was endothermic and spontaneous. Multiple techniques including BET, SEM, FTIR, and XPS were used to analyze the possible adsorption mechanisms. It was found that the increased adsorption of Cr(VI) on F1M3BC, mainly occurred due to electrostatic attraction and Cr(VI) reduction, together with Cr(III) complexation. Furthermore, regeneration studies indicated that F1M3BC could be recycled for up to six cycles without loss of activity. Therefore, F1M3BC may be promising for environmental applications removing Cr(VI) from aqueous systems.