Adsorptive Removal of Lead and Chromate Ions from Water by Using Iron-Doped Granular Activated Carbon Obtained from Coconut Shells

In this study, a low-cost granular activated carbon doped with Fe₂O₃ nanoparticles (Fe–GAC) was prepared via a modified sol-gel technique and utilized for the elimination of lead (Pb(II)) and chromium (Cr(T)) ions from synthetic and actual brackish water. The effect of adsorption parameters on the removal of Pb(II) and Cr(T) ions from the water was evaluated in batch adsorption tests. The characterization results validated the distribution of well-defined Fe₂O₃ nanoparticles onto the GAC surface. GAC loaded with 5 wt.% of Fe₂O₃ (Fe–GAC 5) exhibited a maximum surface area of 848.2 m² g⁻¹. The equilibrium data of Cr(T) adsorption were in close agreement with the Langmuir and Sips models with R² values of 0.95 and 0.96, respectively. However, the R² values of the equilibrium data for Pb(II) adsorption were greater than 0.91 for all four models, i.e., Langmuir, and Sips, Freundlich and Redlich-Peterson. The maximum Langmuir adsorption capacities of Pb(II) and Cr(T) by Fe–GAC 5 at pH 5.6 and room temperature were 11.9 and 22.1 mg g⁻¹, respectively. Pseudo-second order (R²_Pb(II) = 0.99, R²_Cr(T) = 0.99) and Elovich kinetic models (R²_Pb(II) = 1, R²_Cr(T) = 1) were found the most suitable for describing the adsorption kinetics data of Pb(II) and Cr(T) using Fe–GAC 5. The adsorption/desorption studies illustrated that the Fe–GAC is reusable and can be regenerated using 1.0 M HCl. Moreover, the Fe–GAC 5 was found effective to reduce heavy metals loading in actual brackish water to the allowed international standards of drinking water. Accordingly, the Fe–GAC could be a promising material for large-scale applications for the elimination of heavy metals from water.