Improved Removal of Quinoline from Wastewater Using Coke Powder with Inorganic Ions

In this paper, laboratory batch adsorption tests were performed to study the adsorption behavior of coke powder in a quinoline aqueous solution with the absence and presence of inorganic ions (K+ and Ca2+). Adsorption isotherms, thermodynamic parameters, and kinetic models were used to understand the sorption mechanism, and zeta potential measurements were performed to elucidate the effect of the inorganic ions on the adsorption. The results showed that coke powder exhibited a reasonably good adsorption performance due to its pore structure and surface characteristics, and the presence of K+ and Ca2+ could further improve the adsorption. Without inorganic ions, the adsorption capacity of coke powder for quinoline and the removal efficiency of quinoline were 1.27 mg/g and 84.90%, respectively. At the ion concentration of 15 mmol, the adsorption capacity of coke powder and quinoline removal efficiency in the presence of K+ reached 1.38 mg/g and 92.02%, respectively, whereas those in the solutions with Ca2+ reached 1.40 mg/g and 93.31%, respectively. It was found that the adsorption of quinoline onto coke powder in the absence and presence of inorganic ions fit the Freundlich isotherm. Changes in the Gibbs free energy, the heat of adsorption, the entropy, and the activation energy of adsorption suggest that the adsorption was spontaneous and exothermic, which was dominated by physical adsorption, and that the added K+ and Ca2+ would favor the adsorption. In addition, the pseudo-second-order kinetic model was found to provide the best fit to the adsorption kinetic data, and K+ and Ca2+ increased the rate of quinoline adsorbed onto coke power. This improved adsorption due to inorganic ions was found to be a consequence of the decrease in the surface potential of coke powder particles, which resulted in a reduced thickness of water film around particles, as well as a decreased electrostatic repulsion between coke powder particles and quinoline molecules.