The influence of the aqueous media acidity on the electrokinetic potential, aggregation and adsorption properties of silica nanoparticles synthesized from metallurgical wastes

The main physicochemical characteristics of silica nanoparticles synthesized using such metallurgical wastes as copper-smelting slags and microsilica were analyzed and compared to fumed silica A-60. For silicas in the aqueous media, electrokinetic potential, morphology, particle size distribution, and adsorption activity with respect to low molecular weight solutes vs. the pH values were studied using quasi-elastic light scattering, scanning electron and optical microscopies, potentiometry, and infrared (IR) spectroscopy. It was found that the absolute value of the zeta potential for all the studied silicas does not exceed 30 mV that indicates certain instability of the aqueous suspensions. The value of the isoelectric point is within 2.98-3.30, at which the effective diameter of the particles has a maximum value. It has been determined that the synthesized silica has a sufficiently high sorption activity with respect to Methylene Blue and Congo Red at Qmax = 15 mg/g for MB and Qmax = 20 mg/g for CR. The efficiency of the dye adsorption greatly depends on the aqueous medium acidity since the maximum Methylene Blue extraction is observed in strongly alkaline media in contrast to Congo Red demonstrating maximal adsorption in strongly acidic media. According to the IR spectra, several possible mechanisms of interactions of dyes with the silica particles are considered, and the most probable scheme of such interaction is proposed.