Thermodynamic studies on adsorption of lead (II) Ion from aqueous solution using magnetite, activated carbon and composites

Abstract

Magnetite nanoparticles, activated carbon and their composite were synthesized in the laboratory and their adsorption capacities were tested for the removal of Pb (II) ion from aqueous solutions. Magnetite was prepared using co-precipitation method and the activated carbon prepared by chemical activation. The prepared adsorbents were characterized by some physico-chemical and spectroscopic methods. The instrumental techniques used for characterizing the adsorbents include Fourier Transform Infrared (FTIR), X –ray Fluorescence (XRF) and Scanning Electron Microscopy coupled with energy dispersive X-ray (SEM-EDX). The comparative adsorption of Pb (II) ion from aqueous solution onto different adsorbents was investigated using batch adsorption experiment at room temperature. The effects of initial metal ion concentration, contact time, adsorbent dosage, and temperature were evaluated. The activated carbon shows a structure like a honeycomb with a pattern of hollows and ridges, while the EDX shows an abundance of carbon. The results showed that maximum removal of Pb (II) ions was achieved with magnetite nanoparticles at a concentration of 100 mg/L within 60 minutes. The adsorption of Pb (II) on the all adsorbents best fitted the Langmuir adsorption isotherm based on its better regression coefficient. Kinetics result showed that the adsorption followed pseudo-second order perfectly implying chemisorption. Thermodynamic result revealed ΔG values of (-6.73 to -0.502 kJ/mol), depicting that the adsorption is feasible and spontaneous. Also, the reaction is endothermic as evident in the positive value of ΔH (0.779 to 22.815 kJ/mol) and positive value of ΔS means there is an irregular increase in the randomness at the solid-solution interface of the adsorbents. The results obtained revealed that the adsorbents prepared can be used for the treatment of Pb (II)-based effluents.

Keywords: Adsorption, Pb (II) ion, Kinetics, Thermodynamics