Waste walnut shell valorization to iron loaded biochar and its application to arsenic removal

Abstract

Iron loaded biochar (ILB) was prepared from waste walnut shell by microwave pyrolysis and its application for arsenic removal was attempted. The ILB was characterized using X-ray diffraction, scanning electron microscopy and BET Surface area analyzer. The adsorption isotherm of As (V) in ILB covering a temperature range of 25 to 45 °C, as well as the kinetics of adsorption at 25 °C were experimentally generated. The adsorption isotherms were modeled using Langmuir and Freundlich isotherm models, while the kinetics of adsorption was modeled using the pseudo-first-order, pseudo-second-order kinetic models, and intra particle diffusion model. The ILB had a surface area of 418 m2 /g with iron present in the form of hematite (Fe2O3) and magnetite (Fe3O4). The arsenic adsorption isotherm matches well with Langmuir isotherm model with a monolayer adsorption capacity of 1.91 mg/g at 25 °C. The adsorption capacity of As (V) well compares with other porous adsorbents widely reported in literature, supporting its application as a cost effective adsorbent.