Soil Washing

Description

Soil washing uses water to remove contaminants from soils. The process works by either dissolving or suspending contaminants in the wash solution. It is often used in conjunction with other physical separation techniques (see description of Separation).

Soil washing separates soil by particle size. Most organic and inorganic contaminants tend to bind and sorb to clay, silt, and organic soil particles. Most silt and clay are stuck to larger particles (i.e., sand and gravel). Washing separates the small particles from the large particles by breaking adhesive bonds. The separated material is smaller in volume and is more easily disposed of.

Limitations and Concerns

Soil washing is a technique of concentrating contaminants through separation. It does not destroy or immobilize the contaminants. Consequently, the resulting concentrated soil must be disposed of carefully.

The "clean" portion of separated soil must be analyzed for residual contamination before it is disposed of as clean material. Sites using soil washing often have an on-site capability to test samples of treated soil before it is released as clean. For example, see descriptions of X-Ray Fluorescence and Laser-Induced Fluorescence as characterization technologies.

Soil contaminated with both metals and organic compounds make formulating a single suitable washing solution difficult. In this case, sequential washing, using different wash formulations may be required.

High organic content of the soil may require pretreatment.

Wash water requires treatment before it can be discharged, as it is usually not completely free of smaller particles or organic particles.

Soil washing processes for soil contaminated with volatile organic compounds (VOCs) may require emission controls.

Applicability

Soil washing systems are used on soils contaminated with semi-volatile organic compounds (SVOCs), fuels, and heavy metals, including radionuclides. The technology can be used on selected VOCs and pesticides.

Technology Development Status

At the present time, soil washing is used extensively in Europe. Commercialization in the United States is not yet extensive.

Web Links

http://www.frtr.gov/matrix2/section4/4_21.html

Other resources

See technology description of Separation.