Contaminated soils particle-size separation

Phenanthrene dissolved in Triton X-100 solution was separated by sorption with three GACs with different particle size (4 12,12 20, and 20 40 mesh). The highest adsorption selectivity was obtained with the 20 40 mesh over a wide concentration range of phenanthrene and Triton X-100. The results demonstrate that the selective adsorption is potentially effective to reuse surfactants in a soil-washing process for the remediation of contaminated soils. 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

The BioTrol soil washing system is a patented, water-based volume reduction process used to treat excavated soil. It separates slightly contaminated, coarse, washed soil particles from heavily contaminated fine soil particles. The process operates on the premise that (1) contaminants tend to be concentrated in the fine size fraction of soil (sUt, clay, and soil organic matter) and (2) contaminants associated with the coarse soil fraction (sand and gravel) are primarily surficial. The BioTrol soil washing system can be used to treat soils contaminated with petroleum hydrocarbons, pesticides, polychlorinated biphenyls (PCBs), various industrial chemicals, and metals. 

The BESCORP Soil Washing System (BSWS) is a water-based unit for the volume reduction of coarse/sandy soils contaminated with lead or other heavy metals. It uses a combination of trommel agitation, attrition scrubbing, high-pressure washing, and separation by particle size and density to remove heavy metals and heavy-metal compounds from soil. 

Aqueous soil washing cannot handle viscous materials such as tars, and it cannot separate contaminants if they have the same size and specific gravity as the soil particles. 

Physical processes separate contaminants from uncontaminated material by exploiting differences in their physical properties (e.g. density, particle size, volatility, by applying some external force (e.g. abrasion) or by altering some physical characteristic to enable separation to occur (e.g. flotation). Depending on the nature and distribution of the contamination within the soil, physical processes may result in the segregation of differentially contaminated fractions (for example a relatively uncontaminated material and a contaminant concentrate based on a size separation) or separation of the contaminants (for example oil or metal particles) from the soil particles. Table 6 summarises the main advantages and disadvantages of physical processes. 

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