Capacity and mechanism of arsenic adsorption on red soil supplemented with ferromanganese oxide-biochar composites.

Two ferromanganese oxide-biochar composites (FMBC1 and FMBC2) were prepared by an impregnation method to promote the adsorption of As on red soil. Maximum adsorption capacities (Qm) of 0.687 and 0.712 mg g-1 were observed for FMBC1 and FMBC2, respectively, corresponding to increases of 104 and 111% relative to the control treatment (Qm = 0.337 mg g-1). Treatment with FMBC1 increased the pH of red soil, whereas a reverse trend was observed for FMBC2. A variety of analytical techniques were used to explain the differences between FMBC1 and FMBC2, revealing that the oxidation of As(III) to As(V) by Mn and Fe oxides was aided by interactions with the oxygen-containing functional groups of the ferromanganese oxide-biochar composites. Thus, red soil supplemented with the ferromanganese oxide-biochar composites mainly adsorbed As by chemisorption, thereby projecting ferromanganese oxide-biochar composites as potential absorbents for effectively remediating As-polluted red soil.