Simultaneous removal of arsenite and cadmium by a manganese-crosslinking sodium alginate modified biochar and zerovalent iron composite from aqueous solutions

Abstract

Biochar (BC) pyrolyzed using solid waste has attracted increasing attention for wastewater treatment, while pure BC has limitations in the simultaneous removal of arsenite (As(III)) and cadmium (Cd(II)). Herein, a novel manganese-crosslinking sodium alginate modified biochar and zerovalent iron composite (Mn/SA-BC@nZVI) was prepared for the simultaneous removal of As(III) and Cd(II) from contaminated water. Mn/SA-BC@nZVI allowed for the simultaneous removal of As(III) (20 mg L⁻¹) and Cd(II) (20 mg L⁻¹), with efficiencies of >90% and >80% within 10 min, which were 17.18% and 28.23% higher than those of single As(III) and Cd(II) solution, respectively. Principally, this is attributed to the production of anion-bridged (MnO/FeO–As–Cd) and cation-bridged surface complexes (MnO/FeO–Cd–As) via surface multiple complexation, multiple H-bonds, electrostatic attraction, and precipitation. The Langmuir adsorption capacities of Mn/SA-BC@nZVI towards As(III) and Cd(II) were 121 and 120 mg g⁻¹, respectively. The graphitized structure of Mn/SA-BC@nZVI promoted electron transfer and free radical production. As a result, part of As(III) was oxidized to arsenate (As(V)). The inner-sphere surface complexation of As(III) or As(V) with iron and manganese oxides was the main mechanism of As(III) removal. However, Cd–π binding with aromatic carbon components, surface complexation with oxygen-containing groups, and precipitation with CO₃²⁻ were predominant in Cd(II) removal. Moreover, the current research provides an efficient adsorbent for the synchronous removal of As(III) and Cd(II) in wastewater treatment.