Soil washing is generally considered a media transfer technology.
Typical environmental problems involve contaminated soil, sludge, surface water, and groundwater, usually containing widely distributed contaminants such as heavy metals, organics and their byproducts/decomposition products, and low-level radioactive materials. To develop an effective treatment for a contact-contaminated soil or other waste, it is necessary to understand its physical and chemical characteristics, including the distribution of the contaminants. Soil washing process can be defined as a water-based process for scrubbing soils ex situ to remove contaminants. The process removes contaminants from soils in one of two ways:
The concept involves literally washing the contaminates from the soil using specially designed equipment.
1. By dissolving or suspending them in the wash solution (which can be sustained by chemical manipulation of pH for a period of time).
2. By concentrating them into a smaller volume of soil through particle size separation, gravity separation, and attrition scrubbing (similar to those techniques used in sand and gravel operations).
A novel soil washing process that is called Electrod Assisted Soil Washing (EASW) technology has been invented and demonstrated by Harry W. Parker, and the graduate student Ramesh Krishnan. These persons are working in the continued development of this process. EASW process technology is assigned to Toxic Environment Control Systems, Lubbock, Texas. This firm supplied the funding for the invention and development of the process over the past five years.
Advantage of the EASW Soil Washing Technology and Theory of Operation
Soil washing is frequently the most cost effective means of remediating soils contaminated with organics, or heavy metals. Commercial soil washing technologies are frequently ineffective on silts and clays due to their small particle sizes, and hence large specific surfaces. The EASW process causes boiling to be initiated on the surface of the particles. The violence of boiling being nucleated on particle surfaces directly dislodges contaminants from the particle surface. Such violent scrubbing of very small clay and silt particles can not be achieved by intense external mixing and shearing as practiced with other soil washing technologies. Intense mechanical shearing is not successful in washing small particles because the small particles move within the water film surrounding them during the mixing and shearing. In contrast, the EASW process initiates violent boiling on the particle's surface directly. Removal and destruction of a chlorinated hydrocarbon, pentachlorophenol.
Boiling is nucleated on the particle surface by superheating the liquid water surrounding the particles. Superheating is achieved by the flow of electric current through the soil slurry being washed. The local intensity of energy release is increased by the geometry of electrodes and insulating...