[Mechanism and Surface Fractal Characteristics for the Adsorption of p-nitrophenol on Water-quenched Blast Furnace Slag]

In the present study, the removal of p-nitrophenol (p-NP) from aqueous solution through the adsorption on water-quenched blast furnace slag (WBFS) was investigated. The physicochemical properties of the slag were characterized by SEM, XRD, FTIR and BET. Batch experiments were conducted to investigate the mechanism, kinetics and thermodynamics of adsorption process. The results showed that the experimental data could fit to Freundlich model. The enthalpy change (ΔH) and entropy change (ΔS) were 3.29 kJ·mol^-1 and 4.66 J·(mol·K)^-1, respectively. It indicated that the adsorption of p-NP on WBFS was an endothermic and entropy-increasing process. The values of ΔG decreased with increasing temperature, indicating the spontaneous adsorption proportional to the temperature. The adsorption could be divided into two parts, one was high-speed surface coverage, and the other was slow-speed internal diffusion adsorption. It was also found that the adsorption process followed the pseudo-second-order kinetic model. The fractal dimensions of WBFS surface calculated by Freundlich adsorption fractal model were 2.78, 2.80, 2.84 and 2.87 at different temperatures, respectively. It indicated the existence of fractal phenomenon with higher fractal dimension of WBFS at higher temperature.