What are the conventional treatment options for site remediation?

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The Environmental Protection Agency, other federal government agencies, States, and Tribes have been managing investigations and cleanup activities at mining and mineral processing sites for over twenty years. A large number of cleanup technological innovations have been successfully utilized in the removal and handling of mining waste .

There are three major categories of technology used for environmental remediation and site remediation projects. These technologies are: Conventional, Innovative/Emerging, and Institutional Controls. 

Conventional Treatment Technologies

  • Chemical Treatment
    In chemical treatment, reagents are used to eliminate or chemically
    change organic and inorganic contaminants, changing hazardous constituents into less
    environmentally destructive forms.
  • Stabilization
     Stabilization points to steps that lower the hazard posed by a waste by
    changing the contaminants into a less soluble, less mobile, and, consequently, less harmful type without always modifying the actual physical nature of the waste.
  • Solidification
    Solidification pertains to procedures that encapsulate waste in a monolithic solid of
    high-structural integrity.
  • Thermal Desorption
    Thermal desorption pertains to treatment solutions that use high temperatures to
    remediate contaminated soils, sediments, and sludges.
  • Thermal Destruction
    Thermal destruction typically uses higher temperature ranges to actually break down the contaminants, potentially with no hazardous
    contaminant residues requiring further management.
  • Vapor Extraction
    Vapor extraction is an in-situ procedure that uses vacuum technologies and
    subsurface retrieval systems to eliminate contamination in its gas-phase.
  • Solvent Extraction
    Solvent/chemical extraction is an ex-situ separation and concentration
    process in which a nonaqueous liquid reagent is used to remove organic and/or inorganic
    contaminants from wastes, soils, sediments, sludges, or water.
  • Soil Washing
    The ex-situ procedure of soil washing uses chemical and physical removal
    and detachment techniques to remove a broad range of organic, inorganic, and radioactive contamination from soils.
  • Soil Flushing
    The in-situ procedure of soil flushing uses water, enhanced water, or gaseous
    combinations to increase the mobilization of contaminants from a contaminated soil for recovery and treatment.
  • Decontamination of Buildings
    Decontamination of buildings and other structures through
    various extraction and treatment techniques may be necessary at certain mining and mineral processing sites. Decontamination may be as easy as pressure washing a structure or more complicated, involving partial removal practices.

Chemical Treatment

For this site remediation treatment, you use reagents to destroy or modify the contaminants. This method can be used to neutralize acid rock drainage or to enhance a subsequent process. Lime treatment for acid rock drainage is one of the most common forms of chemical treatment.

Site Remediation by Stabilization

This is changing the contaminants to a less mobile or soluble form thereby making it less hazardous to the environment. For example, stabilization could be used to treat soil pollution found in a sludge slurry by changing the pH of the sludge to make it less mobile. Another form often used for stabilization is the capping of soil pollution. In this case, a clean cap of soil is placed over the polluted soil to protect it from running into streams and rivers.

Solidification of Contaminants

This process involves making the pollution solid, such as capping or mixing the pollution into a concrete block. The contaminant migration is restricted vastly by decreasing the surface area exposed to leaching or runoff from rain or stormwater.

Decontamination of Buildings

When a mine site or industrial operations are complete, there is often a desire to preserve the historical significance of the buildings. When this occurs, the structures themselves will need to be decontaminated. Site remediation by decontamination could be as simple as washing the building or as complicated as removing asbestos from the interior walls and ceilings.

Thermal Desorption

Thermal desorption is using heat to remediate contaminated soils, sediments, and sludges. Using heat the contaminated is turned to the gas-phase with further treatment of the off-gas required. This technique is generally not used at mine sites as the main contaminants of metal are difficult to change to a gas-phase.

Thermal Destruction

Thermal destruction uses high temperatures in an attempt to decompose the contaminants. For mining, it is generally unsuccessful as the process does not actually destroy the metal. 

Vapor Extraction

Vapor extraction uses vacuum technology and subsurface retrieval systems to remove contaminant material in the gas-phase. It is mostly used to remove volatile compounds from permeable soils. With metal being the most common contaminant on mine sites it is generally not used for metal contamination. Vapor extraction is however very common for hydrocarbon and solvent removal at sites where the fluid has leaked into the subsurface.

Solvent Extraction

This process uses a nonaqueous liquid reagent to remove organic and/or inorganic contaminants from waste, soils, sediments, sludges, or water. An example of this technology in mining is leaching. With leaching, the solvent can be targeted to remove the soil contaminants in the soil.

Soil Washing

This method uses a combination of chemical and physical extraction and separation techniques to remove contaminants from the soil. The process begins with extraction, separation for coarse and fine grain fractions. The fine-grained fractions are generally then separated further with additional washing and processing. The fines from this material are generally the most contaminated and require another remedial action.

Soil Flushing

Flushing uses water, enchanted water, or gaseous mixtures to accelerate the mobilization of contaminants from the contaminated soil via adsorption/desorption, acid/base reactions, and biodegradation. The fluids could be introduced to the contaminated soil via flooding, sprinklers, or subsurface leach fields. The contaminated fluids are then recovered and treated. With this method, it is possible the bulk of the soil could be left in place after treatment.

Note: This page is produced as educational content to assist our clients and engineers in gaining a better understanding of environmental remediation. Portions of the content of this page are summarized and copied from the EPA Abandoned Mine Site Characterization and Cleanup Handbook. 

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