Ceramic-matrix fixation of medium-level concentrated liquid waste

Medium-level concentrated liquid waste (MLLW), containing sodium nitrate as a base component, can be immobilized in the form of alkaline aluminosilicate ceramics at 900 degrees C, using urea, fluorides, and natural aluminosilicates, The process was studied with both model and real MLLW. With model samples the maximal load by the total of chlorides and sulfates was found to be up to 9 wt %. With real MLLW it was demonstrated that 24-40 wt % of dry salts can be incorporated. In this case the load by chlorides and sulfates is 3.2-5.4 wt %. The X-ray diffraction analysis showed the formation in ceramics of network- and chain-structure silicates such as feldspathoids, pyroxenes, albite, and quartz and also hematite. The resulting ceramics was tested for the strength and open porosity. The true and apparent densities of the ceramics varied from 2.7 to 3.6 and from 1.3 to 1.7 g cm(-3), respectively. The chemical resistance of the ceramic matrix was evaluated by the leaching rates of radionuclides, Na+, F-, Cl-, and SO42-. The rate of Cs-137 leaching from the ceramics containing real MLLW from a nuclear power plant was no more than 6.0 x 10(-3) g cm(-2) day(-1).