Environmental Engineering Reference
In-Depth Information
The following three mechanisms govern the immobilization of radioactive and
hazardous contaminants in a stabilized Ceramicrete waste form: (1) chemical stabi-
lization, (2) microencapsulation, and (3) macroencapsulation. The first two mecha-
nisms work together to immobilize chemical constituents, while the third one is used
to physically encapsulate large objects. Chemical stabilization results from conver-
sion of contaminants in the waste to insoluble phosphate forms. This conversion
depends on the dissolution kinetics of these components. In general, if these com-
ponents are in a soluble or even in a sparsely soluble form, they will dissolve in the
initially acidic Ceramicrete slurry and react with the phosphate anions in the same
manner that MgO reacts. The resultant product will be an acid-phosphate that is
insoluble in groundwater. On the other hand, if a certain radioactive component is
not soluble in the acid slurry, it is already immobilized and will generally not dissolve
in groundwater, because such components are less soluble at the higher pH of
groundwater. Thus, the solubility of hazardous and radioactive components is key
to chemical immobilization as phosphates.
MKP is a dense material that coats the individual particles of both the contam-
inants and the fillers in the waste and forms an impermeable cover to particles. This
cover protects each particle from contact with groundwater and the surrounding
media. In addition, MKP consolidates loose particles into a leach-resistant mono-
lithic waste form.
6.2.4
S/S OF H AZARDOUS AND R ADIOACTIVE W ASTES WITH
C ERAMICRETE
Ceramicrete technology has been used to stabilize/solidify a range of waste streams
(both simulated and actual) containing hazardous and radioactive contaminants. 2,4-8
Table 6.2.1 lists waste acceptance criteria and corresponding studies demonstrating
compliance by Ceramicrete waste forms with those criteria. They are briefly described
in the subsections that follow.
6.2.4.1
Stabilization of Hazardous Contaminants
The effectiveness of the Ceramicrete matrix to stabilize ash was demonstrated by
simulating Pu-contaminated ash from the Rocky Flats site of DOE. 6 The simulated
waste contained oxides of aluminum, calcium, iron, magnesium, potassium, and
silicon, with silicon oxide comprising 41 wt% of the waste. The hazardous contam-
inants were Ba, Cr, Ni, and Pb, added as oxides at a concentration of several thousand
parts per million. CeO 2 was added as a surrogate of PuO 2 and formed 11.2 wt% of
the waste. In addition, carbon content was about 20 wt% of the waste.
The ash loading in the waste form was 54 wt%, dictated by a safeguard limit
of 5 wt% loading of Pu (simulated by Ce in the test) in the final waste form. The
density of the waste forms was 1.84 kg/l, open porosity was 4.4 vol%, and com-
pressive strength was 60.0 MPa (8700 psi). The toxicity characteristic leaching
procedure (TCLP) results in Table 6.2.2 list contaminant levels in the leachate well
below the Universal Treatment Standard (UTS) limit, indicating effective Cerami-
crete stabilization of the ash.
Search WWH ::




Custom Search