Ultrasound assisted extraction and decomposition of Cl-containing herbicide involved in model soil

This work focused on ultrasound assisted extraction and decomposition of MCPA [(4-chloro-2-methylphenoxy) acetic acid] from model soil under argon atmosphere. In the experiments, 10 g model soil containing 1.75 x 10(-5) mol MCPA mixed with 90 g of de-aired water was used. For a comparison, the experiments were also carried out using MCPA aqueous solution of which the concentration was adjusted to 1.75 x 10(-4) mol/l. The results showed that complete MCPA decomposition was achieved after 120 min in the case of MCPA aqueous solution. Meanwhile, in the case of model soil, the MCPA decomposition ratio of 0.9 was obtained after 600 min. This result was attributed to combined effect of MCPA adsorption on kaolin and to attenuation of ultrasound by solid particles of kaolin. To evaluate ultrasound attenuation in the presence of solid particles, experiments with slurry consisting of alumina particles and MCPA solution were carried out at alumina particles concentration range of 0.1-100g/l. The results showed that the MCPA initial decomposition rate significantly decreased with an increase in alumina particles concentration. Thus, it was concluded that the solid particles reduced the MCPA decomposition ratio by reducing the formation of reactive species such as hydroxyl radicals which are know to be necessary for MCPA decomposition.