Chemical Solidification/Stabilization (S/S) adds chemical reagents to contaminated soil to limit the wasteÕs solubility and mobility. The soil is mixed with a chemical that reacts with the contaminants and chemically absorbs and immobilizes the contaminant materials, or lowers their toxicity. It is accomplished either in-situ, by injecting a solidifying/stabilizing agent into contaminated materials, or ex-situ, by excavating and machine-mixing the materials with the solidifying/stabilizing agent and then placing the solidified soil in containers or burying it on site. Chemical S/S agents include thermoplastic polymers (asphalt bitumen, paraffin, polyethylene), thermosetting polymers (vinyl ester monomers, urea formaldehyde, epoxy polymers), and other proprietary additives. Some in-situ systems, sometimes referred to as soil fixation, use auger/caisson systems and injector head systems. After boring into the soil, chemicals are injected into the soil, trapping or immobilizing contaminants. These agents bind to the soil mass or encapsulate contaminants.
Limitations and Concerns
Although Chemical S/S may effectively reduce the mobility of contaminants, it may not affect volume or toxicity.
This technology usually requires capping or covering, engineering controls, and/or institutional controls. If the solidified material contains radioactive contaminants, a soil cover sufficiently thick to absorb gamma radiation is required.
Chemical S/S processes require that potentially large volumes of bulk reagents and additives be transported to project sites. The future site use may ÒweatherÓ the materials and affect the ability to keep contaminants stabilized.
Some processes result in a significant volume increase (up to double the original).
For in-situ applications, the following limitations exist: The depth of contaminants may limit some types of application; reagent delivery and effective mixing are difficult; confirmatory sampling can be more difficult than for ex-situ treatments.
For ex-situ applications, the following limitations exist: Environmental conditions may affect long-term contaminant immobility; volatile organic compounds (VOCs) are generally not immobilized; long-term effectiveness has not been demonstrated for many contaminant/process-reagent combinations.
Chemical S/S can apply to many contaminants, including all classes of radioactive waste, organics, inorganics, heavy metals, and mixed waste. These processes may not be effective on some organics (e.g., Semi-Volatile Organic Compounds and pesticides) that can inhibit the chemical bonding of stabilizers or the mechanical bonding of solidifying agents.
Technology Development Status
Chemical S/S uses conventional materials handling equipment, and it is widely available for some contaminants. Some techniques are commercial, and others are being field tested. The Auger/Caisson and Reagent/Injector Head Systems processes are well demonstrated; they can be applied to the most common site and waste types.
See http://www.frtr.gov/matrix2/section4/4-21.html for adescription of ex-situ stabilization (includes physical, chemical and vitrification).
https://portal.navfac.navy.mil/portal/page/portal/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/ENVIRONMENTAL/ERB/STAB-SOL/ (in-situ: physical and chemical)
https://portal.navfac.navy.mil/portal/page/portal/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/ENVIRONMENTAL/ERB/SOLID-EXSITU (ex-situ: physical and chemical)
Other Resources and Demonstrations
See related descriptions of Solidification/Stabilization (S/S)—Physical and Solidification/Stabilization (S/S)—Vitrification.
See http://www.clu-in.org/download/remed/solidstab.pdf for a matrix and description of various solidification and stabilization projects, both physical and chemical.
See http://sti.srs.gov/fulltext/ms2001092/ms2001092.html for ÒOptimization of Remedial Design for Remediation of SRSÕs Radioactive Seepage Basins by In-Situ Stabilization/Solidification.Ó
See http://sti.srs.gov/fulltext/ms9900314/ms9900314.pdf for a description of Savannah River Site (SRS) solidification of radioactive incinerator wastes. Also see http://sti.srs.gov/fulltext/tr2001526r1/tr2001526r1.pdf for a description of PUREX (plutonium/uranium extraction fluids) solidification at SRS.