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350 4. Adsorption and Ion Exchange

In general, pyrolysis has less environmental impact than other thermal conersion routes v
(Freeman, 1998).
Incineration : The incineration in an oxygen-rich atmosphere results in the oxidation of
the initial feed material and produces a volume reduction factor ranging from 30 to 100.
Incineration systems include, among others, rotary kiln and fluidized-bed incinerators (US
DOE, 1998).
Ion-exchange resins contain significant amounts of sulfur and nitrogen, and thus their
heating at high temperatures leads to the formation of SO 2 ,SO 3 , and small amounts of
f
NO x . Therefore, an eficient scrubbing system is required for the remoal of these sub- v
stances from the off-gases. Additionally, the presence of radionuclides, such as cesium and
ruthenium, which are volatile at temperatures aboe 800 °C, makes the off-gas treatment v
more complex. The incineration of resins loaded with radionuclides has been used in pilot
and commercial scale at the Technical Research Centre in Finland, in Japan, and at the
Austrian Research Centers of Seibersdorf (V 1982; yri, alkiainen and Nyk Abe, ahata and Y
1982; Neubauer, 1996).
Vitrification : Various molten-glass processes are commercially aailable for the
v
destruction and/or immobilization of hazardous wastes (Freeman, 1998). The vitrif ication
method destroys the combustible and some toxic portions of the waste while at the same
time incorporating residuals into a glass form.
Vitrification involves a heating step under extremely high temperatures, from 1100 to
3000 °C, follothe v wed by a cooling step to form a solid mass. During the cooling step, ar-
ious contaminants are trapped into the dense glassified mass formed. Plasma torches or
electric arc furnaces can be used in vitrification. It is possible that some inorganic com-
pounds will v while some organics may be destroyed during this heating step.
olatilize,
Consequently, a system to treat these off-gases may be needed (EP 1996). A,
The main advantage of vitrification is that the glass waste formed exhibits excellent
,
v
leach resistance. Moreo the ash coming from incineration or pyrolysis may be immo-
er
itrif
bilized by this method (IAEA, 2002; Jantzen et al ., 1995). Vication can be held at
similar or lower temperatures than incineration, depending on the addities that ha v v e
been used during glass forming. Commercial ion-exchange resin vitrification suppliers
v
have emerged in the United States oer the last few decades (Cicero and Herman, 1998;
Place, 1992).
Nonthermal pr ocesses There are a number of chemical treatment methods de eloped v
and used for the processing of hazardous chemical wThese methods are briefly dis- aste.
cussed in the next sections.
Acid dig estion : Sulfuric and nitric acids are applied at 250 °C to combustible waste in
order to convert it into carbon dioxide and water. Although this is a very promising method
for the treatment of spent ion-e it has some serious disadv xchange resins, The use antages.
of concentrated acids at eleated temperatures may lead to off-gases containing nitrogen v
, and sulfur oxides that hae to be treated. Moreo very resistant materials are needed to v er v
stand the corrosion from acids, which adds to the cost of the process (Cooley and Lerch,
1974; Ha wkings et al ., 1980).
Wet oxidation : The wet oxidation process inolves the reaction of a waste with an oxidant v
in excess water in the presence of a catalyst (IAEA, 2002). Wet oxidation can be carried out