Enhancing adsorption efficiency for environmentally-friendly removal of As(V) and Pb(II) using a biochar-iron oxide composite

In this study, we aimed to develop an absorbent for efficient removal of heavy metals. We developed a composite (BC-IOx) using biochar (BC) obtained by carbonizing rice hull, a type of biomass, and iron(III) nitrate nonhydrate (IO). The bonding strength between BC and IO was increased through ultrasonication with high energy at 25 ℃ and a 2-h heat treatment process at 350 ℃. Brunauer-Emmett-Teller analysis showed that BC-IOx had an increased specific surface area, which was proportional to iron loading and provided an abundance of active heavy metal adsorption sites. This composite effectively removed Pb(II) and As(V). The addition of BC-IO3 to Pb(II)-contaminated water for 120 min increased Pb(II) absorption capacity to 90.21 mg/g from 18.12 mg/g with unmodified BC. The As(V) adsorption capacity increased from 8.33 mg/g for unmodified BC to 65.34 mg/g for BC-IO10. In addition, the potential adsorption mechanism was discussed using detailed chemical and physical analyses. The synthesis of a composite from biochar and iron oxide can inspire the cost-effective and straightforward production of heavy metal absorbents that can be utilized on a large scale.