Surface Cleaning of Particles

Many conventional soil vashing processes are based on the principle that pollutants adsorb onto very small particles fine fractions of the soil such as silt, clay and humic matter ivhich tend to be attached to coarser sand and gravel particles. These larger particles make up the majority of the soil content. A primary aim in soil washing is therefore to dislodge and separate these fine components from the bulk soil. If the pollutant materials can be detached from the bulk, possibly together with some other surface contamination, a concentrated volume of polluted soil can be produced. This can then be treated or disposed of and a large volume of residual soil which requires relatively little treatment and can be returned to the site as back fill. 

A comparison has been made of the efficiencies of conventional and ultrasonically assisted pollutant extraction procedures using model soil samples (granular pieces of brick) which had been deliberately contaminated with copper oxide at 51 ppm [50]. Analysis of the brick particles after 30 min sonication on a Vibrating Tray [51] revealed an average reduction in copper content to 31 ppm, a reduction of about 40%. Using a conventional mechanically shaken tray for the same time period the residual contamination was 48 ppm representing a reduction of only 6% (Tab. 4.6). 

The Vibrating Tray has been used to enhance the clean-up of soil contaminated with PCB s (Fig. 4.3). 

Brick remaining after v ashing Particulate material 20 mesh Fines Aqueous wash 

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