Cationic Surfactant (HDTMA)-Loaded Fly Ash for Effective Removal of Benzene Derivatives from Wastewater

S. Mushtaq, U. Aslam, R. Ali, S. Naseem, M. Ashraf, Z. Aslam and A. Tariq

Abstract
In this study, the cationic surfactant hexadecyl trimethylammonium bromide (HDTMA) was loaded onto coal fly ash and subsequently utilized for wastewater treatment. The surfactant-treated ash was characterized to investigate its porosity, surface morphology, thermal stability, and the presence of surface functional groups. Experimental studies were conducted under varying solution pH, adsorbent dosage, temperature, time, and initial pollutant concentration to obtain data for isothermal, kinetic, and thermodynamic analysis. The equilibrium uptake capacities of chlorobenzene (CB) and nitrobenzene (NB) using HDTMA-modified coal fly ash (HCFA) were found to be 214 mg g–1 and 74 mg g–1, respectively. Kinetic analysis revealed that the pseudo-second-order model accurately described the adsorption kinetics for both benzene derivatives, while isotherm model investigations demonstrated multilayer adsorption on the HCFA surface. The isotherm data of CB and NB conformed to the Koble Corrigan and Khan Isotherm models, respectively. Thermodynamics parameters such as ΔG° (Gibbs free energy), ΔH° (enthalpy), ΔS° (entropy) and ∆Hx (isosteric heat of adsorption) were also evaluated. The results indicated that the adsorption of chlorobenzene was exothermic, spontaneous, and feasible, whereas nitrobenzene exhibited endothermic behavior and followed the non-spontaneous process. Furthermore, variations in ∆Hx values indicated the heterogeneous nature of HCFA. Overall, the prepared adsorbent demonstrated good affinity for benzene derivatives and could be considered for the treatment of wastewater containing these pollutants.

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Keywords
coal fly ash, hexadecyltrimethylammonium bromide (HDTMA), adsorption, wastewater treatment, chlorobenzene, nitrobenzene