Removal of Cr (VI), As (V), Cu (II), and Pb (II) using cellulose biochar supported iron nanoparticles: A kinetic and mechanistic study

Abstract

Abstract Magnetic iron-carbon nanoadsorbents synthesized using cellulose biochar as the carbon support have demonstrated great potential for removal of heavy metals (Cr (VI), As (V), Cu (II), and Pb (II)). The effects of initial solution pH, adsorbent dosage, contact time, initial concentration and different iron mass loadings on metal ion adsorption were examined. In an attempt to avoid the capital and operating costs associated with mixing, all the adsorption experiments were conducted under no mixing conditions. Non-linear regression analysis was used to determine kinetic and isotherm parameters. The kinetics of Cr (VI), As (V), and Pb (II) uptake followed pseudo-second order while Cu (II) adsorption best fit pseudo-first order model. Weber intraparticle diffusion model applied to heavy metal uptake revealed multiple rate limiting steps representing different adsorption stages. The adsorption isotherms of all four heavy metals in this study were well fitted by three-, four- and five- parameter models indicating carbon encapsulated iron nanoparticles (CEINPs) possessed a heterogeneous surface. 40 wt% iron loaded CEINPs showed a maximum Langmuir adsorption capacity of 688.6 mg g−1 for the uptake of As (V), a significantly high value when compared to all previously tested iron-based adsorbents in literature. X-ray photoelectron spectroscopy measurements on the CEINPs before and after metal ion adsorption confirmed that heavy metal adsorption process involved interactions with the metallic iron core. Further, a detailed adsorption mechanism for each metal was postulated based on the observed results.