RSM-CCD optimization approach for the adsorptive removal of Eriochrome Black T from aqueous system using steel slag-based adsorbent: Characterization, Isotherm, Kinetic modeling and thermodynamic analysis

The waste from the steel industries is disposed of in landfills or used in construction and improvement of the soil. Since these wastes are reported as adsorbents for water pollutants, two steel dust/slag wastes, Alrhaji (AL) and Arab (AR) materials, were applied for Eriochrome Black T dye (EBT) removal from the aqueous system. The materials were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), N₂ adsorption/desorption analysis, transmission electron microscopy (TEM), Fourier transform-IR (FTIR), and X-ray diffraction (XRD). The performances of adsorbents (i.e., q = 34.82 mg/g for AL and q = 38.88 mg/g for AR at 45 °C) result in promising values compared to other adsorbents reported for EBT removal. The equilibrium data provided good fit for Sips model (AL) and Langmuir model (AR) showed the highest values of R² and lower values of average relative error (ARE). The kinetic data was best represented by the pseudo-second order model for both adsorbents. The thermodynamic studies indicate a physisorption adsorbent/adsorbate interaction with slight structural modifications in AR surface and the randomness reductions at the adsorption surfaces for AL adsorbent. Considering the results of the present investigations, the Alrhaji and Arab steel slags are promising adsorbents for EBT removal from the aqueous system.