Simultaneous and efficient removal of Cd(II) and As(III) by a magnesium-manganese codoped biochar composite: Sorption performance and governing mechanisms

As(III) and Cd(II) co-existence results in co-contamination in soil and water. It is still a great challenge for As(III) and Cd(II) simultaneous removal in the aqueous medium due to their contrasting chemical behaviour. Herein, we prepared a novel magnesium-manganese modified biochar composite (Mg/Mn@BC) for simultaneous Cd(II) and As(III) elimination from contaminated water. The synergistic effect of Mg/Mn@BC composite on synchronous Cd(II) and As(III) removal was confirmed. In the mixed sorption system, the Langmuir sorption capacity of Mg/Mn@BC for As(III) and Cd(II) was 164 and 316 mg g−1, respectively, which was more than that in the single adsorption system (75 and 295 mg g−1). In the single sorption system, the Mg/Mn@BC sorption efficiency was > 61% and 100% for As(III) and Cd(II), respectively, while > 87% and 100% in the mixed adsorption system. The characterization results revealed that synergistic adsorption was mainly attributed to anion-bridging (Mn/MgO–As–Cd) and cation-bridging (Mn/MgO–Cd–As). The ion exchange, precipitation, Cd–π binding and inner-sphere surface complexation with functional groups were predominant in the sorption process, while hydrogen bonding force and ternary complexation were the primary pathways in mixed adsorption system to eliminate Cd(II) and As(III). The results suggested that Mg/Mn@BC composite can be a potential material for wastewater treatment.