Washing of oiled sediment and soil

(also known as “Chemical extraction” if solvent are used).

Soil washing uses water to remove contaminants from soils. The process works by either dissolving or suspending contaminants in the wash solution (using hot water, 30° to 50°C and solvent/ dispersant chemical agent when required). It is often used in conjunction with other physical separation techniques (see decantation, centrifugation etc.).

Contaminated sediment and soil.

Equipment may exist in public works, construction industry, mining etc. or mobile units may be imported.

Soil washing starts by the separation of soil by particle size. Most organic and inorganic contaminants tend to bind and sorb to clay, silt, and organic soil particles. This fine sediment is separated from the remaining soil during the washing by scrubbing, water and possible solvant.
Washing does not treat the pollution but also helps removing the pollutants bound to the finer sediments from the coarser sediments and concentrates them in a small volume of oily water, easier to treat and dispose of afterwards.

The pollutants must be dilutable with solvent (adsorbed to the fine sediment).
Soil washing is a technique of concentrating contaminants through separation. It does not destroy or immobilize the contaminants. Consequently, the resulting concentrated contaminated soil and/ or effluents must be disposed of carefully.

The "clean" portion of the separated soil must be analyzed for residual contamination before it is disposed of as clean material.
Sand and gravel are relatively easy to wash. However, mud and clay retain, by adsorption, some oil and will require an additional treatment (Source: Bocard).
Wash water requires treatment before it can be discharged, as it usually contains smaller particles or organic particles.

Limited if wash waters are managed adequately and treated material is analysed before further treatment or disposal.

Refer to those applying to polluted soil and groundwater and to the management of oily water.

Depending on the installation, may treat from few 10's of tons of waste per day to few 100's of tons.

OPEX: around 150 Euros / m3 (Source: KOLLER)