Performance assessment of five adsorbents based on fly ash for removal of cadmium ions

Five adsorbents based on fly ash treated with NaOH for the adsorption of cadmium ion from aqueous solutions were investigated. The materials were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the Brunauer-Emmett-Teller (BET) surface area methods. The results demonstrated that the specific surface area of fly ash was improved after NaOH treatment, and that the adsorption of cadmium by the new adsorbents reached equilibrium in less than 120 min. The results also confirmed that the materials treated with NaOH solution by direct activation had a higher adsorption capacity than untreated fly ash. The maximum adsorption capacities obtained were in the range of 9.18–48.5 mg/g. Also, SEM/EDS and FT-IR results of Cd(II) loaded adsorbents were performed. The obtained experimental data were used for kinetics determination using three model equations: a pseudo first-order model, a pseudo second-order model, and the intraparticle diffusion model. Was found that the adsorption of cadmium ions onto the adsorbents studied follows the pseudo second-order model. The adsorption isotherms of the adsorbent synthesized by direct activation for 15 h using 5 M NaOH at 90 °C with a ratio of 1:3 fly ash: NaOH (A5) was assessed in terms of the Langmuir (four types of linearization), Freundlich, Temkin, Harkin-Jura, and Halsey models. The effectiveness of the adsorbents was evaluated using the toxicity characteristic leaching (TCLP) procedure. Accordingly, the proposed methods in this study are recommended for advanced capitalization of fly ash, particularly as a potential adsorbent for the removal of cadmium ions from wastewater. [Display omitted] •The new adsorbents were synthesized by alkali activation of power plant fly ash.•An efficient and cost-effective approach for capitalization of fly ash was proposed.•The cadmium ions were successfully adsorbed by synthesized materials.•The experimental data were processed using different adsorption isotherms.