Stabilization/Solidification—Chemical

Description

Chemical Solidification/Stabilization (S/S) adds chemical reagents to contaminated soil to limit the waste’s 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 “weather” 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.

Applicability

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.

Web Links

http://www.sandia.gov/eesector/em/topics/remed/is-grcs/is-grcs.html

Other Resources and Demonstrations

See related descriptions of Solidification/Stabilization (S/S)—Physical and Solidification/Stabilization (S/S)—Vitrification.

See http://www.srs.gov/general/sci-tech/fulltext/ms2001092/ms2001092.html for Optimization of Remedial Design for Remediation of SRS’s Radioactive Seepage Basins by In-Situ Stabilization/Solidification.

See http://apps.em.doe.gov/ost/pubs/itsrs/itsr117.pdf for a description of DOE’s Argonne National Laboratory-East (ANL-E) development tests to validate the stabilization of salt-containing mixed wastes with a chemically bonded phosphate ceramics (CBPC) process. It is a stabilization process that involves reacting magnesium oxide and mono-potassium phosphate with a salt waste. It creates a dense ceramic monolith that makes a strong environmental barrier, and the metals are converted to insoluble, low leaching phosphate salts. The process has been tested on a variety of mixed waste streams, including soils, wastewater, flyash, and crushed debris.

See http://www.pimsnw.com/CSSESTCP/ for a demonstration of an Apatite-based system (Phosphate Induced Metal Stabilization) at Camp Stanley (lead).