Introduction - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 4

S/S. Inorganic binders, such as cement, are effective in immobilizing heavy metals
through chemical and physical containment mechanisms, but are not as effective in
immobilizing most organic contaminants. Many substances in the wastes significantly
affect the setting and hardening characteristics of binders, especially cement-based
cementing systems.

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A variety of processes and equipment were also developed. The mixing of wastes
and binders can be carried out through either an

ex situ or in situ process. For ex

situ mixing, pugmills, mortar mixers, or concrete mixers are often used. In situ

methods are widely used for remediation of contaminated sites and can be classified
into the following three categories: backhoe-based methods, drilling/jetting/auger-
ing/trenching methods, and shallow area methods. Selection of the mixing method
is based on the depth of the contamination and the characteristics of the contaminated
media.
The USEPA sponsored a series of seminars on S/S, known as the “Immobiliza-
tion Technology Seminars.” The American Society for Testing and Materials
(ASTM) sponsored a series of symposiums beginning in 1981, initially focusing on
test methods and later expanding to all aspects of S/S. Gilliam, with co-editors,

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edited three topics of the papers presented at three of these symposiums. Spence

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edited a similar topic of papers from an American Chemical Society meeting. An
extensive number of publications, reports, and presentations have been made on S/S,
plus websites covering S/S, its application, and items of interest for S/S professionals.
From roughly 1990 until the present time, S/S processes have been demonstrated
and have been reasonably accepted by regulators, industries, and environmentalists.
In 1999, the USEPA published a resource guide, which included recently published
materials such as field reports and guidance documents that address issues relevant
to solidification/stabilization technologies. This and other technology-related doc-

uments are available over the Internet at the Hazardous Waste Clean-Up Information
(CLU-IN) website at http://clu-in.org.
This topic is intended to provide the regulatory and scientific basis for the use
of S/S processes, a description of different S/S systems, a description of the testing
and evaluation of the materials before and after treatment, and finally a summary
of some previous field applications of S/S. Chapter 2 discusses the general guide-
lines for developing a waste form for a given application, giving two decision flow
path schematics. Chapter 3 discusses characterization and classification of waste,
an important preliminary step in treating waste or remediating sites. Binders are
discussed in Chapters 4 (cement), 5 (polymers), and 6 (phosphate, sulfur polymer
cement, gypsum, and hydroceramic). A variety of additives or sorbents are available
to minimize interference with the hydration of cement or to enhance the immobi-
lization of contaminants. Common additives or sorbents include activated carbon,
zeolites, clays, carbonate, oxidizing agent, reducing agent, sulfides, organoclays,
iron, and aluminum compounds. Chapter 7 discusses interactions between contam-
inants and binders, and Chapter 8 discusses some of the additives used to enhance
binder properties or contaminant stabilization. Chapter 9 discusses the microstruc-
ture of S/S waste forms. Chapter 10 discusses the leachability from S/S waste
forms. Chapter 11 discusses the evaluation of waste forms, their durability, and the
test methods used. Chapter 12 discusses QA/QC for S/S. Chapter 13 presents four

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