Introduction - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 2

• Good self-shielding for radioactive wastes

• Long shelf life of cement powder

• No free water if properly formulated

• Rapid, controllable setting, without settling or segregation during cure

1.1 DEFINITION OF STABILIZATION AND

SOLIDIFICATION

“Stabilization” refers to techniques that chemically reduce the hazard potential of a
waste by converting the contaminants into less soluble, mobile, or toxic forms. The
physical nature and handling characteristics of the waste are not necessarily changed
by stabilization.
“Solidification” refers to techniques that encapsulate the waste, forming a solid
material, and does not necessarily involve a chemical interaction between the con-
taminants and the solidifying additives. The product of solidification, often known
as the waste form, may be a monolithic block, a clay-like material, a granular
particulate, or some other physical form commonly considered “solid.”
The terms solidification/stabilization and stabilization/solidification are often
used interchangeably and are referred to as S/S. Other commonly used terms were
fixation and chemical fixation, which have generally been replaced by S/S despite
some objections to the use of “monolith” in the USEPA definition of S/S.

3,5-7

Solidification and stabilization can be accomplished by a chemical reaction between
the waste and solidifying reagents or by mechanical processes. Contaminant migra-
tion is often restricted by decreasing the surface area exposed to leaching or by
coating the wastes with low-permeability materials.

1.2 A BRIEF SUMMARY OF THE ORIGIN OF S/S

TECHNOLOGY

The origin and development of S/S technology were described by Jesse Conner, first
in his benchmark topic in 1990, followed by the review in 1998 co-authored with
Steve Hoeffner. S/S technology was first used for treatment of radioactive wastes

in the 1950s. At early stages, liquid radioactive wastes were solidified using portland
cement in drums or other containers, then buried at government-controlled disposal
sites or at sea. High cement content was required to solidify the water in these liquid
wastes. Mineral adsorbents such as vermiculite were used with cement to help absorb
the high water content, reduce the amount of cement required, and prevent formation
of bleed water. The large volume increases from solidifying what was essentially
water led to subsequent high disposal costs. This led to calcination and vitrification
becoming the preferred techniques, because of the large mass and volume reductions
resulting from vaporizing the water and densifying the solids.
Prior to the Resource Conservation and Recovery Act (RCRA), disposal of liquid
waste, other than by underground injection, was regulated under the authority of the
Clean Water Act or controlled through state laws. Little documentation can be found
on S/S of hazardous wastes prior to 1970. From 1970 until the passage of RCRA

3,5