Adsorption of Pb~(2+) and Ni~(2+) Ions by Montmorillonite: Isotherm,Kinetic and Thermodynamic Studies

摘要

The adsorption of Pb~(2+) and Ni~(2+) ions from aqueous solution onto montmorillonite (MMT) has been investigated at 293 K, 303 K, 313 K and 323 K using batch equilibrium experiments. In order to optimize the adsorption conditions, the effects of contact time, solution pH and initial metal ion concentrations were tested thoroughly. The adsorption isotherms were best described by the Langmuir model at lower temperatures, while the Freundlich model gave a better fit at higher temperatures. The theoretical saturated adsorption capacities of MMT for Pb~(2+) and Ni~(2+) ions at 293 K as calculated via the Langmuir isotherm were 133 g/kg and 56 g/kg, respectively. The kinetic data were poorly correlated by the pseudo-first-order model and the intraparticle diffusion equation, but were fitted perfectly by the pseudo-secondorder kinetic model. For Pb~(2+) ions, the thermodynamic parameters ?_(ads) G~0, ?_(ads)H~0 and ?_(ads)S~0 were determined as —3.08 kJ/mol (at 293 K), 4.83 kJ/mol and 26.95 J/(mol K), respectively. For Ni~(2+) ions, the values of ?_(ads)G~0,?_(ads) H~0 and ?_(a d s )S~0 were —1.10 kJ/mol (at 293 K), 23.77 kJ/mol and 84.63 J/(mol K), respectively. The experimental results indicated that the adsorption processes for both Pb~(2+) and Ni~(2+) ions onto MMT were favourable, spontaneous and endothermic.