Fast removal of methylene blue by modified sorel cement using manganese(VII) as an additive: kinetics, thermodynamics, and equilibrium studies

ABSTRACT

In this study, Sorel cement (SC) was doped with Mn⁷⁺ to develop a cost-effective adsorbent that can quickly remove methylene blue (MB) dye from aqueous solutions. The characteristics of the prepared adsorbents were examined using X-ray diffraction, atomic force microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The examinations confirmed the formation of SC and the successful doping of manganese. Batch adsorption experiments were also performed to investigate and to optimise the operational parameters such as Mn⁷⁺ ion concentration, contact time, dosage, MB concentration, pH, and temperature. The modified adsorbent revealed a significant adsorption improvement when compared with pure SC. A small addition of 0.01 g of Mn⁷⁺ exhibited 100% removal efficiency up to a dye concentration of about 100 mg/L, whereas about 64% removal efficiency was obtained with pure SC using 36.5 mg/L of the MB solution. Furthermore, the modified adsorbent revealed rapid equilibrium times of around 1 and 3 minutes using 36.5 and 100 mg/L of the MB solution, respectively. An experimental adsorption capacity of up to 246 mg/g was obtained, and the equilibrium data were consistent with the Freundlich isotherm and were well fitted with a pseudo-second-order kinetic model. The thermodynamic values indicated a physisorption, exothermic (ΔH° = −7.7 kJ/mol), and spontaneous (ΔG° = −9.4 kJ/mol) nature of the adsorption process with enhanced feasibility and comparable regeneration efficiency for up to five cycles. Therefore, the results indicate that the modified sorbent can possibly be utilised as a potential fast method for the removal of MB dye from wastewater.

KEYWORDS:

• Sorel cement
• adsorption
• methylene blue
• manganese
• removal

Acknowledgments

The authors are thankful to King Abdulaziz City for Science and Technology (KACST) for funding this work under project number ((14-WAT2227-07) 1851-38).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research leading to these results received funding from King Abdulaziz City for Science and Technology [14-WAT2227-07(1851-38)].