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

H.I Adegoke,A.L Yaqub,I.T Olowookere,F.A Adekola

doi:10.4314/jasem.v21i3.5

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

Highlights

The origin of the large quantities of aqueous effluents that contain high level of heavy metals is as a result of the extended use of metals and chemicals in the process industries and agricultural activities, which tends to pose difficult environmental disposal problems (Antunes et al, 2003)
Results of Batch Adsorption Experiments: Effect of initial concentration: the plots of the amount of Pb (II) ion adsorbed on the adsorbents (0.5 g each) from 20 ml solutions for different initial concentrations (100-500ppm) of Pb (II) ion is shown in fig
The positive values of heat of adsorption ∆H for Magnetite and composite suggested that the adsorption of metal ions is endothermic, which is supported by the increased adsorption of metal ions with increase in temperature

Summary

Introduction

The origin of the large quantities of aqueous effluents that contain high level of heavy metals is as a result of the extended use of metals and chemicals in the process industries and agricultural activities, which tends to pose difficult environmental disposal problems (Antunes et al, 2003). Heavy metals, which are not biodegradable (Vijayaraghavan et al, 2004) are of great concern because they are being added to water, soil and air in increasing amounts They are toxic to human health when consumed at relatively high amounts and may cause serious health problems upon long term exposures. This makes their effective removal from water sources within a reasonable cost, an important issue (Bready and Weil, 1999). Other conventional technologies which have been used ranged from granular activated carbon to reverse osmosis These processes are not economically feasible for small scale industries prevalent in developing economies due to large capital investment (Horsfall and Spiff, 2004). Adsorption capacity of activated carbon, magnetite and their composites were investigated in the adsorption of Pb (II) ion from aqueous solution

Methods

Results

Conclusion