Evaluation of Iron(III) Chelated Polymer Grafted Lignocellulosics for Arsenic(V) Adsorption in a Batch Reactor System

Abstract

A novel adsorbent, iron(III) chelate of an amino-functionalized polyacrylamide-grafted coconut coir pith (Fe(III)-A-PGCP) was prepared and used for the removal of arsenic(V) from aqueous solutions. The adsorbent was prepared by graft copolymerization of acrylamide onto coconut coir pith, CP (a lignocellulosic residue) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent followed by treatment with ethylenediamine and ferric chloride in acid (HCl) medium. The adsorbent was characterized using Fourier transform infrared (FTIR) spectroscopy, Raman analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), surface area analysis, determination of amine and iron moieties on the surface of the adsorbent, and batch adsorption experiments were carried out under a variety of operating conditions such as contact time, initial sorbate concentration, pH, adsorbent dose, presence of interfering ions, and temperature. The results showed a maximum adsorption (>99.9%) at pH 7.0. Kinetic data were modeled using pseudo-first-order, pseudo-second-order, and Ritchie-modified second-order models. The kinetic data were best described by a pseudo-second-order equation. Adsorption equilibrium data were correlated with Langmuir, Freundlich, and Sips isotherms. The results showed that the Langmuir isotherm model seemed to successfully simulate the adsorption isotherm curve and the maximum adsorption capacity was estimated to be 107.8 mg/g at 30 °C. The reusability of the spent adsorbent for several cycles was demonstrated using 0.1 M HCl. The residual arsenic concentration was brought down from 1.0 mg/L to 0.01 mg/L (more than 99.0%) was achieved with a Fe(III)-A-PGCP dose of 150 mg in a 50-mL sample. A counter-current batch adsorber was designed using operating lines.