Adsorptive Removal of Arsenic by Synthetic Iron-loaded Goethite: Isotherms, Kinetics, and Mechanism

Abstract Arsenic contamination in the groundwater is a worldwide concern. Therefore, this study was designed to use synthetic iron-loaded goethite to remove arsenic. Adsorption was significantly pH-dependent; hence, pH values between 5.0 and 7.0 resulted in the highest removal of arsenate and arsenite. Langmuir and Freundlich isotherms were almost perfectly matched in terms of strong positive coefficient of determination “R2” arsenate – 0.941 and 0.992 and arsenite – 0.945 and 0.993. The adsorption intensity “n” resulted as arsenate – 2.542 and arsenite – 2.707; besides separation factor “RL” found as arsenate – 0.1 and arsenite – 0.5, respectively. However, both “n” and “RL” leads to a favourable adsorption process. Temkin isotherm yielded in equal binding energies “bt” showing as 0.004 (J/μg) for both arsenate and arsenite. Jovanovic monolayers isotherm was dominated by the Langmuir isotherm. This resulting in maximum adsorption capacity “Qmax” of arsenate – 1369.877 and arsenite – 1276.742 (μg/g), which approaches to the saturated binding sites. Kinetic data revealed that adsorption equilibrium was achieved in 240 – arsenate and 360 – arsenite (minutes), respectively. Chemisorption was found effective with high “R2” values 0.981 ­– arsenate and 0.994 – arsenite, respectively, with the best fitting of pseudo-second order. Moreover, Brunauer Emmett Teller (BET), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were used to determine the morphological content, surface area, crystalline structure, and chemical characteristics of the adsorbent. It is anticipated that optimal arsenic removal was achieved by the porosity, chemical bindings, and surface binding sites of the adsorbent.