Chemical modification of Macadamia-derived activated carbon for remediation of selected heavy metals from wastewater

Abstract

In this study, Macadamia-derived activated carbon was utilized for the remediation of selected heavy metals from wastewater samples. The selected heavy metals include Pb (II), Fe (III), Cd (II), and Zn (II). The activated carbon used in the study was modified with KMnO4 and HNO3 to increase the content of the oxygen-containing functional groups on the adsorbent surface. Both the unmodified activated carbon (UAC) and modified activated carbon (MAC) adsorbents were employed throughout the study for comparative purposes in a multi-metallic system. The adsorbents were characterised using Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, and elemental (CHNS) analysis. Elemental analysis revealed an increased oxygen content from UAC to the MAC adsorbent from 8.34 % to 22.87 %. Scanning electron microscopy revealed a morphological contrast in the surfaces of both adsorbents. Optimal conditions for the carbon sorbents were observed at a pH 5, adsorbent mass of 0.2 g, initial concentration of 50 mg L-1, 4 h contact time, and a temperature of 298 K. Overall performance in removal efficiencies were recorded to be 74.74 % for UAC and 87.39 % for MAC. The MAC displayed superior removal efficiencies for Pb (II), and Fe (III) as compared to Cd (II) and Zn (II). Both adsorbents were applied in the treatment of acid mine drainage and leachate samples and the results indicated successful heavy metal remediation using the MAC adsorbent. Two-parameter and three-parameter adsorption isotherm models were fit to the experimental data, and it was found that the Langmuir model was better suited to the equilibrium data as opposed to the other models. The adsorption kinetics were best described using the pseudo-second-order model. Maximum adsorption capacities produced for UAC and MAC were found to be 3.00 and 3.50 mg g−1 respectively.