Behaviour of cerium(III) in the presence of components of soils and its humate complex.

The behaviour of cerium, as a prototype of the lanthanide group, against the inorganic components of two types of soils (one from an Abisreligiosa forest (IM-F) and the other from a semiarid zone (IM-S)) was investigated. The pseudo-second order model applied to the kinetics adsorption data for both soils indicated chemical adsorption; the equilibrium was reached in less than 4 h, the adsorption of Ce(III) in these conditions were 15.6 and 3.5 mg g-1 for IM-F and IM-S respectively. The adsorbents showed a buffer effect in alkali conditions, the adsorption was highest at 5 > pHeq < 6 for both adsorbents. The adsorption isotherms showed that the IM-F surface is homogeneous with a maximum adsorption capacity of 15.7 mg g-1 and that of IM-S is heterogeneous. IM-F is more efficient at low adsorbent dosage, whereas this parameter virtually does not affect the IM-S efficiency but the adsorption percentage increases as the dosage increases. The thermodynamic parameters showed an exothermic and chemical adsorption process using IM-F (ΔH0 = -96.6 KJ mol-1) and an endothermic and physicochemical process using IM-S (ΔH0 = 29 KJ mol-1). Finally, the competition of the adsorption by IM-F and the formation of the complex with humic acids showed the complex formation of Ce:(HA)n, (1:1) with a log βCe,HAapp=5.2.