Leaching of Pollutants from within Particles

Ultrasonically assisted extraction is particularly useful for the environmental analytical chemist because it facilitates a more complete extraction of absorbed chemicals e. g. the extraction of pesticides [57, 58] and of heavy metals from soils [59[. 

Although there is plenty of experimental evidence that ultrasound improves leaching the exact mechanism is not fully understood. Swamy and Narayana [60] have suggested models for leaching in the presence and absence of ultrasound (Fig. 4.4). Normal leaching takes place as the solvent front moves inward and a steady state diffusion occurs through the depleted outer region and is equal to the rate of reaction within the reaction zone itself (Fig. 4.4a). 

Under the influence of ultrasound, normal leaching occurs but several additional factors contribute towards improvements in the efficiency. These include  

Asymmetric cavitation bubble collapse in the vicinity of the solid surface leading to the formation of high speed microjets targeted at the solid surface. The microjets can enhance transport rates and also increase surface area through surface pitting. 

Particle fragmentation through collisions will increase surface area. 

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