INERTIZATION OF CADMIUM ENRICHED HAZARDOUS RESIDUE: AN INERT APPROACH - Management of Hazardous Residues Containing Cd - page 142

liquids. Solidification and stabilization are each distinct technologies, as
described below (EPA, 1997):

 S olidification refers to the processes that encapsulate a waste to form

a solid material and to restrict contaminant migration by decreasing
the surface area exposed to leaching and/or by coating the waste with
low-permeability materials. Solidification can be accomplished by a
chemical reaction between a waste and binding (solidifying) reagents
or by mechanical processes. Solidification of fine waste particles is
referred to as microencapsulation, while solidification of a large block
or container of waste is referred to as macroencapsulation.

 Stabilization refers to processes that involve chemical reactions that

reduce the leachability of a waste. Stabilization chemically
immobilizes hazardous materials or reduces their solubility through a
chemical reaction. The physical nature of the waste may or may not
be changed by this process.

Solidification/stabilization techniques are akin to locking the contaminants
in the soil. It is a process that physically encapsulates the contaminant. This
technique can be used alone or in combination with other treatment and
disposal methods.
The most common form of solidification and stabilization is a cement
process. It simply involves the addition of cement or a cement-based mixture,
which thereby limits the solubility or mobility of the waste constituents. These
techniques are accomplished either in-situ , by injecting a cement based agent
into the contaminated materials or ex situ , by excavating the materials,
machine-mixing them with a cement-based agent, and depositing the solidified
mass in a designated area. The goal of the S/S process is to limit the spread,
via leaching of contaminated material. The end product resulting from the
solidification process is a monolithic block of waste with high structural
integrity.
Types of solidifying/stabilizing agents include the following:
Portland; gypsum; modified sulfur cement, consisting of elemental sulfur
and hydrocarbon polymers; and grout, consisting of cement and other dry
materials, such as acceptable fly ash or blast furnace slag. Processes utilizing
modified sulfur cement are typically performed ex situ .
Portland cement, Pozzolans, Bentonite, Lime, Plaster of Paris,
Thermoplastic Resins and ion exchange resins (Zeolites) are some of the
commonly used solidifying agents. Of these, the most important agents for