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

Abstract

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.