Enhanced adsorption capacity of low-cost magnetic clinoptilolite powders/beads for the effective removal of methylene blue: Adsorption and desorption studies

Abstract

Clinoptilolite/Fe3O4 (Clin/Fe3O4) nanocomposite powders and Alginate/Clinoptilolite/Fe3O4 (Alg/Clin/Fe3O4) nanocomposite beads were prepared and used for methylene blue (MB) cationic dye removal from aqueous solution. The properties of the synthesized adsorbents were characterized by XRD, FTIR, SEM-EDX, dot mapping, VSM and BET analyses. Results confirmed that Fe3O4 nanoparticles were successfully placed in the structure of Clin/Fe3O4 nanocomposite powders and sodium alginate gelation method was effectively used to encapsulate the powders to Alg/Clin/Fe3O4 beads. The impacts of various parameters including pH, temperature, contact time, adsorbent dose, and initial MB dye concentration were investigated on the adsorbents’ performance towards MB dye removal. The maximum MB adsorption efficiency using Clin/Fe3O4 (97.57%) and Alg/Clin/Fe3O4 (93.62%) were obtained at an initial pH of 10. The results of the equilibrium study showed that the adsorption of MB using Clin/Fe3O4 and Alg/Clin/Fe3O4 followed the Langmuir isotherm model. The amount of monolayer adsorption capacity (qm) for Clin/Fe3O4 and Alg/Clin/Fe3O4 were determined as 45.662 mg/g and 12.484 mg/g, respectively. In addition, the values of n, RL, and E parameters derived from isotherm modeling showed that the MB dye adsorption process using both adsorbents was physically desirable. The kinetic data followed a pseudo-second order (PSO) kinetic model indicating that chemical mechanism was also effective in the adsorption process. The thermodynamic results showed that the adsorption process using both types of adsorbents was exothermic and spontaneous. Regeneration experiments performed in ethanol +0.5 M CaCl2 solution showed that the adsorption capacity of Clin/Fe3O4 and Alg/Clin/Fe3O4 was only decreased 7.92% and 9.76%, respectively after five cycles. This study demonstrated that Alg/Clin/Fe3O4 beads are efficient, very low-cost, environmentally friendly and fairly regenerable adsorbents for the removal of MB dye from the aquatic environment.