Surface modification of petroleum residue-activated carbon using citric acid for enhanced cobalt removal from an aqueous solution

Although the amount of petroleum residues produced from oil refinery processes has increased, there has been limited research for the residues. In this work, we developed petroleum residue-activated carbon (PAC) by chemical modification with citric acid as a novel adsorbent The optimal concentration of citric acid for PAC was chosen as the 6 M (named PAC-CA6) and the adsorption behavior of Co(II) was investigated. The experimental data were analyzed using various isotherm and kinetic models. The maximum adsorption capacity of 12.50 mg/g was determined using the Langmuir model. The pseudo-second-order model was found to be the most suitable for describing the adsorption kinetics. PAC-CA6 was characterized by using various instrumental analyses including FE-SEM, FTIR, and XPS. The Boehm titration method indicated the presence of multiple oxygen groups in PAC-CA6. Conclusively, the mechanism of Co(II) adsorption onto PAC-CA6 involved electrostatic interactions between Co(II) ions and carboxylic groups present on the surface of PAC-CA6. From the result, the PAC-CA6 could be sufficiently used as a potential adsorbent for the removal of cobalt from aqueous solutions.