Ceramicrete process

The Ceramicrete process is based on the acid-base exothermic reaction. As a result, the exothermic heat evolution and its rate depend on the size of the waste forms produced. Larger forms generate more heat, which does not dissipate rapidly. Thus, the setting slurry heats up and accelerates the acid-base reaction, and the mixture is able to set even in cold surroundings. 

The acid-base reaction that forms the Ceramicrete waste forms also creates an oxidizing environment in which species of lower oxidation states are automatically converted to their fully oxidized states. Hence, pyrophoric components (such as PU2O3) should be converted to their most stable and fully oxidized forms (such as PUO2) that are no longer pyrophoric. Wagh et al. [10] have demonstrated such transformations in the Ceramicrete process by using surrogates of Pu (see the case study in Section 17.5.4). 

As shown in Table 17.9, the alpha activity in the leachate was 25 2 pCi/ml, and the beta activity was 98 lOpCi/ml. These activities are small when compared with the activities of their counterparts in the waste, which were in p-Ci/g. The very low activity in the leachate was attributed to the efficient stabilization of Ra as insoluble radium phosphate in the waste form. In particular, because Ra is water soluble, the leachate would provide a pathway for it, but the levels in the leachate are only in pCi/ml and, hence, much lower than the levels in the waste. This finding implies that radium and most other isotopes are stabilized in the waste forms. Thus, the Ceramicrete process is a good method to arrest leaching of even the most soluble Ra. 

Unlike Portland cement, the Ceramicrete slurry sets into a hard ceramic even in the presence of salts such as nitrates and chlorides hence, the Ceramicrete process has a great advantage over conventional cement technology with respect to the stabilization of some difficult waste streams, such as those from Hanford and Savannah River tanks. Wagh et al. demonstrated this advantage in several studies, wherein they produced monolithic Ceramicrete solids by using concentrated sodium nitrate and sodium chloride solutions in place of water to stabilize the waste streams. Details of some of these studies may be found in Ref. [21]. 

Researchers state that Ceramicrete technology is a low-cost, low-tech process. The technology nses almost the same eqnipment as that nsed in the cement indnstry. The binder powders are more expensive (approximately 50%) than cement, bnt ANL scientists estimate the cost of treating low-level mixed waste is less than 50 cents per ponnd (D177495, p. 5). 

The first deployment of CBPC for stabilization of Hg using Ceramicrete was reported by Singh et al. [58]. These authors used the CBPC process to stabilize crushed Hg light bulbs that were radioactively contaminated. Visual inspection of the waste revealed that 90 vol% of the waste was <60 mm in size. Typical size of the crushed glass ranged from 2 to 3 cm long by 1-2 cm wide down to fine particulates. Chemical analysis indicated... 

Wagh et al. [45] demonstrated stabilization of Cr, along with Cd, Pb, and Hg from contaminated soil and wastewater in the Ceramicrete waste form. Table 16.8 shows the contaminant levels in the waste and the wastewater, and the corresponding TCLP result for the stabilized waste. The wastewater in the Ceramicrete slurry was equal in amount to the stoichiometric water needed for the stabihzation process. Including this wastewater, the total waste loading was 77 wt%. The waste forms had open porosity of 2.7 vol% and a density of 2.17 g/cm. Compression strength was 34 MPa (4910 psi). 

Ceramicrete stabilization of Tc, partitioned from high-level tank wastes, was demonstrated by Singh et al. [11]. The waste stream was a product of a complexation-elution process that separates Tc from HLW, such as supernatant from salt waste tanks at Hanford and Savannah River. A typical waste solution generated during the complexation-elution process contains 1 M NaOH, 1 M ethylenediamine, and 0.005 M Sn +. 

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