Adsorption of cadmium on different granulometric soil fractions: Influence of organic matter and temperature

Kinetic and thermodynamic studies are carried out at low initial cadmium concentration on a soil sample extracted from Aspach le Bas in Eastern France. It can be concluded from kinetic experiments that the implied process is of pseudo-second order. Rate constants, relaxation times and activation energy are calculated. The energy value determined in this study (40 kJ mol(-1)) shows that the process implies both physisorption and chemisorption. The influence of soil particle size (i.e. of the initial soil and its different fractions: sand, coarse silt, fine silt and clay), organic matter and temperature on the cadmium sorption capacity is also investigated. The Langmuir and the Dubinin-Radushkevich models are chosen to analyze these thermodynamic experiments. The isotherms have revealed that the Cd2+ sorption is enhanced by increasing temperature and organic matter for all the fraction but the sand (in this last case, no temperature or organic matter have changed Cd2+ sorption). Thermodynamics parameters (Delta G, Delta H and Delta S) are determined from experimental isotherms fitting following three methods used in the literature. It can be deduced from the different results that adsorption (exo or endothermic according to the fraction). Finally, a mean free energy of adsorption is obtained via Dubinin-Radushkevich model and confirms that the two types of sorption (physical and chemical) act in the whole process. (C) 2012 Elsevier B.V. All rights reserved.