Improvement of the sorption capacity of methylene blue dye using slag, a steel by product

A steel by-product, the slag collected from the blast furnace, was exploited as an adsorbent to remove methylene blue dye in solution by batch adsorption under the impact of contact time, mass of solid, agitation speed, pH, temperature, particles size, and initial concentration. The slag is mainly composed of silica, alumina and lime with a considerable specific surface (320.46 m2/g), which increased its adsorbent power. The experimental data revealed that the methylene blue (MB) dye adsorption on the slag is favorable (R = 93.3%) and the maximum adsorbed capacity after 50 min of contact amounts to 140.44 mg/g. The adsorption isotherms revealed that the adsorption of methylene blue dye was performed on a homogeneous monolayer surface, and their parameters confirmed that the process is favorable and physically achievable. The kinetic study specified that the methylene blue dye sorption is more adapted to the pseudo-second-order kinetic model (R2 = 0.99). In accordance to the diffusion investigation, exterior diffusion under the diffusional and kinetic regimes and internal diffusion under the diffusional regime alone successively controlled the passage of the pollutant from solution to adsorbent. According to the values of free energy, enthalpy, and entropy, the MB dye adsorption is spontaneous, exothermic, and less entropic. Additionally, the free energy and enthalpy values suggest that this process was performed physically (physical adsorption) under the influence of electrostatic interactions. Based on the results of the desorption investigation, the slag could potentially be recycled four times in a row using hydrochloric acid (0.5 M) as a desorbent.