Evaluation of Fillers for Magnesium Potassium Phosphate Cement (MKPC) for the Encapsulation of Low and Intermediate Level Metallic Radioactive Wastes

This study investigates the effect of coal fly ash (FA), wollastonite (WO), pumice (PM), and metakaolin (MK) as filler materials in the rheological, mechanical, chemical, and mineralogical properties of a magnesium potassium phosphate cement (MKPC), designed for the encapsulation of low and intermediate level radioactive wastes containing reactive metals. Workability, compression strength, dimensional stability, pH, chemical composition, and mineralogical properties were studied in different pastes and mortars of MKPC with a fixed molar ratio of MgO/KH2PO4 = 1. No new mineral phases were found with the addition of the fillers, denoting their low chemical impact on the MKPC system. Moreover, all formulations with a water/cement mass ratio of <0.65 presented compressive strengths higher than 30 MPa after 90 days, and pH values lower than 8.5, corresponding to the passivation zone of aluminum corrosion.

Automated summary

This study explores the influence of coal fly ash (FA), wollastonite (WO), pumice (PM), and metakaolin (MK) as fillers on the rheological, mechanical, chemical, and mineralogical properties of a magnesium potassium phosphate cement (MKPC) used for encapsulating radioactive wastes. Various pastes and mortars of MKPC were investigated, and parameters such as workability, compression strength, dimensional stability, pH, chemical composition, and mineralogical properties were analyzed. The results showed that the fillers had minimal chemical impact on the MKPC system, and all formulations with a water/cement mass ratio of <0.65 exhibited high compressive strengths and pH values in the passivation zone of aluminum corrosion after 90 days.