Thermodynamic and kinetic investigations of PO3−4 adsorption on blast furnace slag

The kinetics of adsorption of PO3−4 by blast furnace slag were found to be fast, reaching equilibrium in 20 min and following a pseudo-second-order rate equation. The adsorption behavior of PO3−4 on blast furnace slag has been studied as a function of the solution agitation speed, pH, and temperature. Results have been analyzed by Freundlich, Langmuir, BET, and Dubinin-Radushkevich (D-R) adsorption isotherms. The mean energy of adsorption, 10.31 kJ mol−1, was calculated from the D-R adsorption isotherm. The rate constants were calculated for 293, 298, 303, and 308 K using a pseudo-second-order rate equation and the activation energy (Ea) was derived using the Arrhenius equation. Thermodynamic parameters such as ΔH0, ΔS0, and ΔG0 were calculated from the slope and intercept of linear plot of lnKD against 1/T. The ΔH0 and ΔG0 values of PO3−4 adsorption on the blast furnace slag show endothermic heat of adsorption. But there is a negative free energy value, indicating that the process of PO3−4 adsorption is favored at high temperatures.