Electrochemically modified adsorbents for treatment of aqueous arsenic: Pore diffusion in modified biomass vs. biochar

Abstract

Canola straw-based biomass and biochar adsorbents were electrochemically modified and used to remove arsenate (As(V)) from water. Studying the effects of the modification parameters on the As(V) adsorption capacity of the modified materials showed that the materials treated at lower pH (3) and drying temperatures (60 °C) had higher As(V) uptake. The modification conditions were optimized to obtain optimum modified biomass (OBM) and biochar (OBC) with the highest As(V) adsorption capacity. Characterization of the OBM and OBC indicated that the deposited iron oxide on the surface of the adsorbents was goethite. The adsorption isotherms and kinetic data suggested that a hybrid adsorption mechanism took place under the experimental conditions with a higher probability of heterogeneous multilayer chemisorption. Solid-phase speciation of the sorbed As(V) indicated a negligible reduction (2.5%) of As(V) to arsenite (As(III)) on OBM, while no reduction occurred on OBC. The liquid film mass transfer coefficient (kf) and effective pore diffusion coefficient (Dp) were estimated using a shrinking core model combined with a genetic algorithm. A higher tortuosity factor of 3.75 for the OBM was obtained as compared to 2.93 for the OBC. Overall, the applied electrochemical modification successfully enhanced the As(V) sorption capacity of both the biomass and biochar from 8 to 766 and 25 to 922 µg/g, respectively, indicating promising potential of this method for preparation of high performance adsorbents.