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4.3 Management of Spent Materials 351

using oxygen or air as oxidant at a relatively low temperature (150–325 °C) and high pres-
sure (2069—20,690 kPa gauge pressure) (Freeman, 1998). A more recent development is the
wet oxidation process utilizing hydrogen peroxide as oxidant. The oxidation can be carried
out at 100 °C under atmospheric pressure. The application of peroxide wet oxidation at low
temperatures for the treatment organic waste and ion-exchange resins has been studied exten-
sively in the United Kingdom (Wilks et al ., 1991).
Barix pr ocess: Barium is first added to the resin in the form of a liquid hydroxide.
Subsequently, the resin is heated in the absence of oxygen and broken into its original
components. Barium plays the role of catalyst in this depolymerization process and reacts
with the sulfur in the cationic functional groups to form barium sulf which in turn acts ate,
as a binder for the metallic species in the waste. Moreo the barium hydroxide adjusts v , er
the pH so that the metals contained in the resins stay in the residue after the steps of dry-
ing and destruction (IAEA, 2002).

Direct immobilization and encapsulation of spent materials
Immobilization is the process of incorporating waste into a matrix material for solidif ica-
tion, or directly into a storage and/or final disposal container. More specif solidif , ically i-
cation can be defined as encapsulation of a waste in a solid of high structural inte grity
(Freeman, 1998). At the same time, the goal of the solidification process is the stabiliza-
aste,
tion of the w which means that the risk posed by the waste is reduced by con erting v
it into a less soluble and less mobile form (Freeman, 1998).
It is possible that a pretreatment step is required for organic ion-exchange materials
before immobilization, although it is not definitely the case. The immobilization matrices
currently used are cement, bitumen, and some polymers.

Cement immobilization Another way to treat the spent materials is to immobilize them
by adding cement or a cement-based mixture (EP 1996). A monolithic block of w aste,
A,
,
er
v
which is very stable, is the result of this treatment. Moreo the resulting waste forms
grity
ustible,
, exhibit high structural inte are noncomb and are resistant to radiation as well
as to leaching (IAEA, 2002). wing: ypes of solidifying/stabilizing agents include the follo T
portland, gypsum, modified sulfur cement, and grout. With the exception of VOCs and
pesticides, cement immobilization may be used for any kind of spent materials, especially
for radioactive waste (EPA, 1996).
Cement has many adv antages:
• high aailability, v
• inexpensive raw material,
• conventional well-known technology.

However, there are also some disadv the faste has a v antages. First of all, ery high inal w
volume compared to the initial one. Grinding before cementation may partially solve this
problem. Furthermore, when organic ion-exchange materials are stored via cementation,
,
swelling of the resin beads may occur in contact with w which may lead to cracking ater
of the cement. So, the cementation of such material should be preceded by an appropriate
pretreatment step.