Adsorption of aqueous methylene blue, NH4+, Co(II) or As(III) with alkali-activated glass wool: isotherms, kinetics and thermodynamics

An alkali-activated glass wool (AAGW) adsorbent was synthesized using sodium aluminate to remove methylene blue (MB), ammonium (NH 4 + ), cobalt (Co(II)), and arsenic As(III) from water. X-ray diffraction, infrared spectroscopy and scanning electron microscopy evaluated the adsorbent and raw glass wool. In alkali-activated glass wool, there were more surface hydroxyl groups and a more negative surface charge. This improved its affinity for cationic adsorbates (MB, NH 4 + and Co(II)) but decreased its uptake of neutral As(III) (H 3 AsO 3 at pH 7). Alkali-activated glass wool (AAGW) adsorbs 82, 30, 5 and 3 mg g −1 for MB, Co(II), NH 4 + and As(III) respectively under the chosen experimental conditions (1 g L −1 adsorbent dosage, 24 h contact period, pH 7, 100 mg L −1 , 22 °C). The adsorbate capacity of raw glass wool was 0-2 mg g −1 . The adsorption kinetics of MB, Co(II), As(III) and NH 4 + pollutants were modeled with pseudo-first-order and Elovich models. The negative Gibbs free energy (ΔG°) values for MB, NH 4 + , and Co(II) indicate a thermodynamically beneficial adsorption process. The entropy and enthalpy changes (ΔS° and ΔH°) were greater than zero for all adsorbates except for NH 4 + . Thermodynamic investigations showed that temperature greatly affected adsorption. Co(II), As(III), and MB adsorption increased with temperature, likely due to entropy. In contrast, NH 4 + adsorption decreased, suggesting an exothermic interaction and partial conversion to volatile NH 3 at high pH (9-10). FTIR pyridine, diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed desorption tests characterized the AAGW surface's chemical properties. The measurements revealed Brønsted and Lewis acid sites on a silanol-rich surface, which critically influenced the adsorption efficiency of alkali-activated glass wool.