Effect of the presence of metals on the adsorption and desorption of phenol on activated mangrove charcoal

Singular and competitive adsorption of phenol, Pb(II), Cr(III), and Cd(II) were studied using activated charcoal (AC) produced from mangrove charcoal, where KOH, ZnCl₂, and H₃PO₄ were used as activation agents. Raw and activated charcoal samples were characterized using elemental analysis, X-ray fluorescence, thermogravimetric, X-ray diffraction spectrometer, surface area analysis (Brunauer–Emmett–Teller), Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. According to the obtained results, showed that the best prepared AC sample had a specific surface area of 784.29 m²/g, when KOH was utilized at activation temperature and time of 600°C and 60 min, respectively. Effects of initial pH, adsorbent dosage, initial concentration, and contact time were studied in a singular system. The results showed that the maximum adsorption capacity at optimum conditions was around 41.5, 89.4, 34.2, and 25.2 mg/g of phenol, Pb, Cr, and Cd, respectively. In the binary system, phenol concentration, pH, and AC dosage were fixed at 50 mg/L, 5, and 1.25 g/L, respectively, where the AC was found to have a higher affinity to Pb (in phenol with Pb) and to phenol (in phenol Cr and Cd). Experimental data on the adsorption of phenol was found to fit the Freundlich isotherm model best, while heavy metals best fitted Langmuir isotherm. Furthermore, chemisorption was the attributed adsorption mechanism, since the equilibrium data best fitted the pseudo-second-order kinetic model. The regeneration study revealed that phenol removal efficiency dropped by 13.6% after three cycles using NaOH while using HCl the drop was 43.3%.