RESUMEN
The sorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol by a allophanic soil was studied in a series of batch experiments. Chlorophenol sorption behavior was evaluated as a function of reaction time (0-96h) and input concentration at a fixed ionic strength (0.1mol L(-1) KCl) at 25, 35, and 45 degrees C. Sorption results for the various reaction temperatures were used in calculating thermodynamic parameters. Chlorophenol sorption increased with temperature, suggesting an endothermic process. The Elovich equation was used to describe the kinetic data. Data from the isotherm experiments were described by the Triple-Layer Model in which monodentate outer- and inner-sphere complexes were formed between deprotonated organic molecules and active sites on the variable-charge soil. The calculated thermodynamic parameters suggest that chlorophenol sorption is a spontaneous (DeltaG<0), endothermic (DeltaH>0) and entropy-driven reaction (DeltaS>0).
Asunto(s)
Clorofenoles/química , Contaminantes Ambientales/química , Suelo , Adsorción , Cinética , Concentración Osmolar , Pentaclorofenol/química , Temperatura , TermodinámicaRESUMEN
The adsorption of 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) by a variable-charge soil from southern Chile was studied in a series of batch equilibration experiments. 2,4-DCP and PCP adsorption behavior was evaluated as a function of pH (pH values of 4.5, 6.0 and 7.5) in a 0.1M KCl (25 degrees C) background solution for soil material collected at three different depths (0-20 cm, 20-40 cm, and 40-60 cm). 2,4-DCP and PCP adsorption decreased with increasing soil pH, suggesting that the undissociated species were adsorbed more readily and that electrostatic repulsion may inhibit partitioning as pH increases. The PCP adsorption was greater than observed for 2,4-DCP and decreased with soil depth. Multiple regression analysis between K(d) and various soil properties indicated that the soil organic carbon content is a strong indicator of chlorophenol adsorption, and in addition to organic carbon, the soil pH is an important property controlling adsorption behavior.
Asunto(s)
Clorofenoles/química , Pentaclorofenol/química , Contaminantes del Suelo/análisis , Adsorción , Fenómenos Químicos , Química Física , Chile , Cromatografía Líquida de Alta Presión , Interpretación Estadística de Datos , Concentración de Iones de Hidrógeno , Análisis de Regresión , TermodinámicaRESUMEN
The sorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol by a variable-charge soil from southern Chile was studied in a series of batch experiments. The chlorophenol sorption behavior was evaluated as a function of pH (pH range 4-8) at two different ionic strengths, 0.01 and 0.1 M KCl (25 degrees C). Chlorophenol sorption depended on pH and a downward shift in the soil PZC was observed with increasing chlorophenol concentration. Chlorophenol sorption decreased with increasing pH, suggesting that the undissociated species is sorbed more readily and that electrostatic repulsion may inhibit partitioning as pH increases. Data from the sorption experiments were fitted by the triple-layer model, in which monodentate outer- and inner-sphere complexes were formed between deprotonated organic molecules and active sites on the variable-charge soil.