Valorization of Silicomanganese Slag into Reusable Porous High-Performance Nanosilica for Recovery of Water from Methylene Blue Wastewater

The conversion of industrial wastes into advanced materials with environmental applications has always been one of the fascinating and promising research topics. This study investigates the removal of methylene blue dye using porous nanosilica obtained from silicomanganese slag. First, porous nanosilica was obtained from the silicomanganese slag using a facile and high-efficiency waste valorization path. The valorization path exhibited a dissolution efficiency of more than 96%. The obtained nanosilica possessed a specific surface area and total pore volume of 506 m(2)/g and 0.65 cm(3)/g, respectively, with the peak pore size of around 10 nm. The obtained nanosilica was then used to adsorb methylene blue dye from aqueous solutions. The results showed that a 96-98% dye adsorption efficiency could be achieved under the adsorbent dosage of 0.4 g/L, pH 7, contact time = 60 min, and ambient temperature. Fitting the isotherm models revealed that the Langmuir model could better predict the experimental adsorption data, meaning monolayer adsorption occurred. The maximum dye adsorption capacity of the porous nanosilica obtained from the Langmuir model constant was 256.41 mg/g. Also, the pseudo-second-order kinetic model could better fit the adsorption data, which meant the chemisorption of the dye on the adsorbent surface. Dye adsorption on the adsorbent microstructure was also confirmed by energy-dispersive X-ray spectroscopy, elemental mapping, and Fourier-transform infrared spectroscopy analyses. The reusability experiments indicated that the porous nanosilica could exhibit removal efficiency of higher than 90% until the fourth reuse. The overall results showed that by converting silicomanganese slag into an adsorbent with high dye removal performance, both a solution for slag management and dye removal from effluents could be proposed. These two paths can help to create a cleaner environment.