Here, a dual-modification strategy using KMnO4 (potassium permanganate) and AlCl3·6H2O (aluminum chloride, hexahydrate) as co-modifiers to improve the Cr(VI) removal capacity of K2CO3 activated biochar is introduced. As a result, the dual-modified biochar with KMnO4 and AlCl3·6H2O has the calculated adsorption energy of -0.52 eV and -1.64 eV for HCrO4-, and -0.21 eV and -2.01 eV for Cr2O72-. The Al2O3 (aluminum oxide) and MnO (manganese oxide) embedded on the surface of dual-modified biochar bring more Cr(VI) absorption sites comparing to single-modified biochar, resulting in a maximum Cr(VI) saturated adsorption capacity of 152.86 mg g-1. The excellent removal performance is due to the synthetic effect of electrostatic attraction, reduction reaction, complexation reaction, and physical adsorption. The experimental results also indicated that the spontaneous adsorption process agreed well with the pseudo-second order and Langmuir models. This dual-modification strategy is not limited to the treatment of Cr(VI) with biochar, and may also be incorporated with the treatment of other heavy metals in aqueous environment.
Keywords: Al/Mn modification; Cr(VI) absorption; biochar; removal mechanism; wastewater treatment.