CERZOS   05458
CENTRO DE RECURSOS NATURALES RENOVABLES DE LA ZONA SEMIARIDA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The dissolution kinetics of humic acid particles.
Autor/es:
M. BRIGANTE; G. ZANINI; M. AVENA
Lugar:
Kyoto. Japan
Reunión:
Conferencia; 5th International Conference Interfaces Against Pollution.; 2008
Resumen:
Humic acids (HA) are a very active fraction of the refractory organic
matter in soils, sediments and natural waters. Their molecules can bind solid
surfaces, metal ions and organic molecules such as pesticides or other
contaminants. As a consequence of this binding HA can affect significantly the
distribution and transport of contaminants in the environment. In fact, when HA
molecules are in the dissolved state, they are rather mobile and can be
transported by water flows (rivers, groundwaters), transporting with them the
attached pollutants. On the contrary, when they are in the solid state forming
part of the soil or sediment matrix, they are rather immobile, limiting the
mobility of the attached pollutants.
A study of the dissolution kinetics of solid HA particles is presented
here, and the ability of HA to become solubilized in aqueous media by different
substances and conditions is evaluated. Thus, the effects on the dissolution
rate of pH, temperature, concentration of inorganic and organic cations, organic
acids and pesticides are investigated. The results show that the dissolution
rate is strongly dependent on the pH of the aqueous solution; there is a
400-fold increase in the dissolution rate by increasing the pH from 4 to 11.
Cations, either organic or inorganic, usually decrease the dissolution rate
whereas organic acids and anionic pesticides increase that rate at constant pH.
Dissolution appears to be controlled by sorption-desorption processes at the
solid HA-water interface. These sorption-desorption processes are believed to
modify the attractive forces that hold HA molecules together in the solid,
modifying their rate of detachment from the surface.