Removal of Heavy Metals from Wastewater Using Multiwalled Carbon Nanotubes

Abstract

Recently, carbon nanotubes have been employed as new adsorbent for the removal of many pollutants. In this study, raw multiwalled carbon nanotubes (MWCNTs) were firstly tested for the removal of lead from aqueous solutions. Then, sodium lauryl sulfate modified multiwalled carbon nanotubes (SLS-MWCNTs) were produced, characterized and used for lead removal. Surface characterization using energy dispersive X-ray spectroscopy (EDS), thermogravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR) showed that surface modification has been achieved successfully. Adsorption results revealed that the surface modification has increased the adsorption capacity from 3.84 mg/g for raw-MWCNTs to 141 mg/g for SLS-MWCNTs. On the other hand, the optimum values of some important parameters were determined. Optimum values of adsorbent dosage, contact time, pH and temperature using raw-MWCNTs were found to be 15.0 g/L, 50 min, 6.5 and 25 °C, respectively and for the SLS-MWCNTs the optimum parameters were found to be 3.00 g/L, 30 min, 5.3 and 25 °C, respectively. Fitting equilibrium data on different isotherm models showed that adsorption on raw-MWCNTs follows Langmuir model with qm = 3.84 mg/g and KL = 0.29 L/mg, while adsorption on SLS-MWCNTs is best described by Freundlich model with n = 2.50 and KF = 15.40 (mg0.6. L0.4)/g. Furthermore, kinetics study results revealed that both raw and SLS-MWCNTs follow the pseudo second order model with rate constants 0.11 g/mg.min and 0.06 g/mg.min, respectively. Thermodynamics study showed that mode of adsorption is physisorption on both raw and SLS-MWCNTs with ∆G values -0.45 and -9.21 kJ/mol at 25 °C, respectively. In order to get higher density particles with more granular structure to enhance column operation, magnetite pellets of SLS-MWCNTs were prepared and used in packed bed column. Column data were found to fit well by the modified dose response model with parameters values qmdr = 28.4 mg/g and a' = 3.47 mg-1.