Analysis and optimization of the adsorption of lead ions on a new material based on silica synthesized from blast furnace slag

A novel silica-based material (SBM), synthesized from chemically-, thermally-, and mechanically-treated blast furnace slag (TBFS), was examined for its batch-mode lead adsorption capacity based on various parameters. Physicochemical examinations revealed that the formulation of the new SBM consisted mainly of silica, which represented 81.79% of its total composition. After modification, the measured specific surface area changed significantly, from 275.8 to 480.13 m2/g, with a point of zero charge (PZC) of approximately 3.4 on the pH scale. The experiment revealed that the driving factors (contact time, stirring speed, solution pH, temperature, and initial concentration) greatly influenced improvement of the lead adsorption capacity, which reached 164.84 mg/g after 40 min of interaction. The adsorption isotherms demonstrated that the lead adsorption took place on a homogeneous surface and in a single layer, which was confirmed by the correlation coefficient and the ability of the Langmuir model to adsorb. The separation factor (RL) and heterogeneity factor (1/n) demonstrated that adsorption was favorable, while the Temkin parameter (bt) revealed that removal occurred through physical adsorption. According to the kinetic analysis, this process followed a pseudo-second-order kinetic model and was regulated by both external diffusion and intraparticle diffusion. Thermodynamic parameters demonstrated that lead adsorption was a spontaneous, exothermic, less entropic, and physical process, driven by electrostatic interaction. Activation energy revealed that the lead removal process occurred through physical adsorption. Desorption analysis demonstrated that SBM can be reused up to four consecutive times.