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 ßCe,HAapp=5.2.

Synthesis of MnO2 on Activated Carbon and its Potential Application in the Adsorption of As(V) and Pb(II) in Aqueous Solutions.

The conditions for the synthesis of a material with MnO2 (OMD) on activated carbon (AC) were studied. These conditions were: reaction time, temperature, stirring speed, concentrations of AC, H2SO4, and O3 in solution, and particle size. Agglomerates on AC were observed by means of scanning electron microscopy (SEM) and microanalysis by energy dispersive spectroscopy (EDS) and revealed the presence of OMD deposited on the surface. The activation energy and the factor of frequency for the reaction were determined as Ea = 1.2 kcal/mol and A = 2.2. The value of Ea indicates that the precipitation of OMD on the AC was controlled by mass transfer in aqueous solution and the order of reaction was zero. The adsorption capacities of AC were q = 14 mg Pb(II)/g AC and q = 9.1 mg As(V)/g AC. Whereas, for the OMD/AC obtained in the following conditions: [AC] 1 or 2 g/L, particle size of AC of +0.59 mm, [H2SO4] 1 or 2 mol/L, 25 °C, stirring speed 600 rpm, and [O3] 1.35 mol/L, the adsorption capacities were q = 90.5 mg Pb(II)/g OMD/AC and 25.4 mg As(V)/g OMD/AC. Therefore, the fixing of OMD on the surface of the AC greatly improved the removal of both Pb(II) and As(V) from aqueous solutions.