Highly competitive multicomponent adsorption of organic and heavy metals using activated mangrove charcoal

Abstract

Multicomponent competitive adsorption of phenol, Pb(II), Cr(III), and Cd(II) were studied using activated carbon produced from mangrove charcoal that was activated using potassium hydroxide with a specific surface area of 784 m2/g. Effects of initial pH, adsorbent dosage, initial concentration variation, thermodynamic, and contact time were investigated. Results of the investigation showed that the maximum removal efficiency in the multicomponent system was around 76%, 92%, 47%, and 31% of phenol, Pb, Cr(III), and Cd, respectively. Those values were obtained at pH 5, adsorbent dosage of 2.5 g/L, contact time of 120 min, and an initial concentration of 50 mg/L for phenol and 30 mg/L of each heavy metal. The highest achieved adsorption capacity obtained was 46, 32, 11, and 3.8 mg/g of phenol, Pb, Cr(III), and Cd, respectively. Moreover, the results showed that the competition between phenol, Pb, and Cr(III) was fierce due to the similar adsorption mechanism. Freundlich isotherm well-fitted phenol, while Cd data were well fitted by Redlich– Peterson isotherm. On the other hand, Langmuir was found to well-fit results of Pb and Cr(III). The pseudo-second-order was the best match for the four pollutants, which indicated that chemisorption was the adsorption mechanism. Intraparticle diffusion indicated that the diffusion happened in the micro and macro levels for most of the pollutants, except for Cr(III), where it happened at the macro levels only. The thermodynamic study concluded that the nature of multicomponent adsorption was exothermic in nature, except for Cr(III), which was endothermic. Also, the highest achieved removal efficiency from the thermodynamic study was 60%, 59%, 42%, and 13% of phenol, Pb, Cr(III), and Cd, respectively at 30°C. Adsorption–desorption for the multicomponent system showed that HCl was better for heavy metals desorption due to the addition of hydrogen ions, while NaOH was better for phenol desorption due to interactions between phenol and NaOH.