Agricultural bio-waste for adsorptive removal of crude oil in aqueous solution

In this study, an agricultural bio-waste, corncob, was used as an effective adsorbent for the removal of crude oil in aqueous solution. The adsorption efficiency of crude oil in natural corncob (NCC) and powdered corncob (PCC) was examined. In addition, the crude oil adsorption behavior is discussed, and the kinetic models used suggest that the sorption process occurs via a surface reaction. Equilibrium isotherm data were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich isotherms. Based on the regression coefficients, the Langmuir isotherm shows a better fit to the data. The maximum adsorption capacities were 4.21g/g and 7.80g/g for NCC and PCC, respectively. The adsorption energy obtained was 5.143kJ/mol for NCC and 5.768kJ/mol for PCC. Based on these results, crude oil adsorption using corncob was a physical process. Moreover, the value of 1/n was 0.462 for NCC and 0.359 for PCC; hence, the adsorption of crude oil using corncob was very favorable. The thermodynamic analysis showed that Gibbs free energy (G) and enthalpy (H) were both negative, and the adsorption process was exothermic and spontaneous. Due to its low cost, biodegradability, and high adsorptivity, corncob could be considered as a new alternative adsorbent.