Akademik Veri Yönetim Sistemi
Journal of Molecular Liquids, cilt.438, 2025 (SCI-Expanded, Scopus)
In this study, the adsorption characteristics of fly-ash modified with anionic surfactant sodium-dodecyl-sulfate have been investigated for the removal of cationic-surfactant cetyl-pyridinium-chloride from aqueous solutions by means of sequential adsorption method. Three fly-ashes loaded from 1.0·10−5, 2.0·10−4, 5.0·10−3 mol dm−3 sodium-dodecyl-sulfate solutions absorb more cetyl-pyridinium-chloride than the bare fly-ash at three temperatures in 298–318 K range. Fly-ash loaded with sodium-dodecyl-sulfate above the critical-micelle-concentration (4.0·10−3 mol dm−3 in water equilibrated with fly-ash at 298 K) removes 0.820·10−4 mol g−1 of cetyl-pyridinium-chloride after seven adsorption-cycles at 298 K, which is close to its Langmuir-capacity of 0.853·10−4 mol g−1. Under similar conditions, 0.662·10−4 and 0.527·10−4 mol g−1 of cetyl-pyridinium-chloride are adsorbed on fly-ashes at low and medium sodium-dodecyl-sulfate loadings, respectively, which are considerably lower than their Langmuir capacities of 3.731·10−4 mol g−1 and 1.374·10−4 mol g−1. We have derived a new equation for modeling their L-S shaped curves by combining Langmuir and Liu equations, considering hemimicelle and maximum adsorption capacity. A model has been proposed for surfactant orientations on the bare and sodium-dodecyl-sulfate loaded fly-ashes by using the number of the cetyl-pyridinium-chloride in the ad-micelle evaluated from the equation. The polynomial dependence of adsorption-constants on the temperature is also reflected on the Gibbs free-energy vs temperature plots. The enthalpy and entropy changes derived from the curves are well consistent with the proposed orientation model of the surfactants.