Thermodynamic and kinetic investigations of PO43- adsorption on blast furnace slag

The kinetics of adsorption of PO43 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 PO43- 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 W 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 (E-a) was derived using the Arrhenius equation. Thermodynamic parameters such as DeltaH(0), DeltaS(0), and DeltaG(0) were calculated from the slope and intercept of linear plot of In K-D against 1/T. The DeltaH(0) and DeltaG(0) values of PO43- adsorption on the blast furnace slag show endothermic heat of adsorption. But there is a negative free energy value, indicating that the process of PO43- adsorption is favored at high temperatures. (C) 2004 Elsevier Inc. All rights reserved.