Cavitational activity in heterogeneous systems containing fine particles

Abstract

Ultrasound has been increasingly used in various processes containing a variety of homogeneous and heterogeneous systems. For largescale applications, a high energy efficiency of the process is required. With this view, the calorimetric energy and cavitational activity measurements were carried out in heterogeneous systems consisting of both liquid and solid phases (fine particles) in a 28-kHz double-bath sonoreactor. Ultrasonic soil washing for the remediation of clay-sized soils (similar to 75 mu m), contaminated with metals (Cu, Pb, and Zn), was used as a case study. As the liquid height/volume in the inner vessel increased under the same input electrical power, the inner vessel calorimetric energy also increased, whereas the total calorimetric energy between the inner vessel and the outer reactor remained approximately constant. No significant differences in calorimetric energies were observed for both with and without soil conditions. The chemical activity under similar experimental conditions was evaluated using sonochemiluminescence. Different sonochemiluminescence trends were observed depending up on the presence and size of beads. The highest total sonochemiluminescence intensity with a uniform spatial distribution was obtained from fine beads (#200, 75 mu m) suspended in the vessel. Ultrasound application significantly enhanced the removal efficiency of heavy metals when combined with mechanical agitation. The enhanced removal efficiency of the combined processes was attributed to a significant removal of metals from the residual (F5) fraction. It has been concluded that ultrasound has enough extraction power to be comparable to methods that employ extremely powerful acids for washing fine particles.