Stabilization of hazardous ash waste with newberyite-rich chemically bonded magnesium phosphate ceramic

Abstract

A novel newberyite-rich magnesium-phosphate ceramic, intended for the stabilization of the US Department of Energy`s low-level mixed-waste streams, has been developed by an acid-base reaction between magnesium oxide and a phosphoric acid solution. The reaction slurry, formed at room temperature, sets rapidly and forms a lightweight hard ceramic with low open porosity and a high compression strength of {approx} 6,200 psi. It is a composite of stable mineral phases of newberyite, luenebergite, and residual Mg oxide. Using this matrix, the authors developed superior waste forms for a surrogate ash waste stream. The final waste form is a low-permeability structural-quality ceramic, in which hazardous contaminants are chemically fixed and physically encapsulated. The compression strength of the waste form is an order of magnitude higher than the land disposal requirement, even at high waste loading. The high compression strength is attributed to stronger bonds in the waste form that result from participation of ash waste in the setting reactions. Long-term leaching studies show that the waste form is stable in an aqueous environment. The chemically bonded phosphate ceramic approach in this study may be a simple, inexpensive, and efficient method for fabricating high-performance waste forms either for stabilizing waste streams or for developing value-added construction materials from high-volume benign waste streams.