Ceramicrete slurry

The pumping time is very sensitive to MgO content in the Ceramicrete slurry. A slight increase in MgO accelerates the acid-base reaction, and the slurry sets faster. Figure 15.5 shows the effect of excess MgO on the pumping time at 200 °F (93°C). Excess MgO provides additional surface area for dissolution. It also provides additional nucleation sites... 

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). 

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]. 

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. 

Because MgO has high solubility even at room temperature, Ceramicrete compositions are suitable for permafrost and shallow wells only. Boric acid is used to retard the reaction in these formulations. The amount of water used in these formulations is also higher than normally needed for the acid-base reaction. This excess water and a minimum amount of boric acid (0.125 wt% of the powder blend) are needed to reduce the initial Be (or reduce the yield stress and the initial viscosity) of the slurry. 

Five-gallon size waste forms were fabricated. Typical waste loading was 35-40 wt%. A small amount of potassium sulfide was added to the Ceramicrete binder mixture for stabilization of Hg, and dense and hard ceramic waste forms were produced. Just before solidification, TCLP results were obtained on small aliquots of the mixing slurry that was separated and allowed to set. Mercury levels in the leachate were found to be 0.05 /rg/1, well below the LfTS limit of 0.025 mg/1. The entire waste was treated, removed from the inventory, and sent to the Radioactive Waste Management Complex at the Idaho National Engineering and Environmental Laboratory for disposal. 

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