Characterization and determination of the thermodynamic and kinetic properties of the adsorption of the molybdenum(VI)-calmagite complex onto active carbon

The extraction of the Mo(VI)-calmagite complex by adsorption onto active carbon is investigated in the present paper. Thermodynamic and kinetic properties and different adsorption isotherms were determined. The adsorption studies have shown that both the empirical Freundlich and the classical Langmuir isotherms successfully fit the experimental results. The overall adsorption process was exothermic and spontaneous in the temperature range from 283 to 323 K; namely, DeltaH(0) and DeltaS(0) values were found to be -8.15 kJ mol(-1) and -3.86 J mol(-1) K, respectively. The high activation energy demanded for desorption of the Mo(VI)-calmagite complex surface indicated that the overall process was controlled by the slow desorption, while a fast and low activated adsorption of the complex onto active carbon surface was fairly favored. These features indicate that active carbon may be very useful for preconcentration of molybdenum from diluted solutions. (C) 2003 Elsevier Inc. All rights reserved.