Abstract:
Industrial waste materials have garnered increased attention as viable adsorbents that could be used for the extraction of heavy metals and organic pollutants from wastewater. This is primarily due to their abundant availability in large quantities and economical cost-effectiveness. Coal fly ash, bottom ash, and fly ash are examples of industrial waste generated from coal combustion in power plants, while petroleum coke is derived from oil refineries. These waste materials contain diverse functional groups, including carbon, calcium oxide, silicon dioxide, aluminium oxide, and iron oxide, which makes them ideal for the remediation of wastewater. Previous research studies have indicated that modified industrial waste materials possess greater adsorption capabilities. As a result, this study sought to modify coal fly ash (RCFA), bottom ash (RBA), fly ash (RFA), and petroleum coke (RPC) by adding iron oxide (Fe3O4) nanoparticles. This modification enables easy separation with an external magnet and enhances their effectiveness in adsorbing lead and efavirenz.
The following adsorbents Fe3O4@APC, Fe3O4@ACFA, Fe3O4@AFA, and Fe3O4@ABA were prepared in a two-step method. The first step was activation of the RPC, RBA, RFA, and RCFA with NaOH then followed by incorporating Fe3O4 nanoparticle. These mesoporous magnetic materials were successfully prepared and characterized using various techniques such as thermogravimetric analysis (TGA), scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDS), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller analysis (BET).
The Langmuir, Temkin, and Freundlich isotherm models were applied to analyse the equilibrium data. The maximum adsorption capacities for obtained for lead were 48.8, 15.63, 12.16, and 270.27 mg/g for Fe3O4@ACFA, Fe3O4@AFA, Fe3O4@ABA, and Fe3O4@APC, respectively. The maximum adsorption capacities for efavirenz obtained were 25.38, 37.64, 13.07 and 76.54 mg/g Fe3O4@ACFA, Fe3O4@APC, Fe3O4@ABA, Fe3O4@AFA respectively. Based on the adsorption isotherms for lead ions, both Fe3O4@ACFA and Fe3O4@AFA, are best described by the Temkin isotherm while Fe3O4@ABA and Fe3O4@APC were best described by the Langmuir and Freundlich isotherm, respectively. Additionally, adsorption of efavirenz was best described by the Langmuir isotherm for all prepared adsorbents.
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The kinetic data were also evaluated for the lead and efavirenz which revealed that the pseudo-second-order equation provided the best correlation for both lead and efavirenz. Thermodynamic parameters suggest that the adsorption process is endothermic and spontaneous for lead. However, for efavirenz it behaved differently on various adsorbents, revealing non-spontaneous adsorption. The adsorption process for lead was endothermic for all adsorbents, whereas for efavirenz it was found to be endothermic for Fe3O4@APC and Fe3O4@ACFA adsorbents, while exothermic for Fe3O4@ABA and Fe3O4@AFA adsorbents. The findings demonstrate that Fe3O4@ACFA, Fe3O4@APC, Fe3O4@ABA, and Fe3O4@AFA possesses the potential to effectively remove lead ions and efavirenz from aqueous solutions.
