CHARACTERIZATION OF MAGNESIUM POTASSIUM PHOSPHATECEMENT WITH IRON OXIDES ADDITIVES FOR IMMOBILIZATIONOF RADIOACTIVE WASTE

The effects of adding fine Fe2O3 (<5.0 µm) and larger Fe3O4 (~44 µm) powders on the hydration, phase composition, microstructure and compressive strength of magnesium potassium phosphate cement (MKPC) was investigated. It was shown that the addition of Fe2O3 and its mixture with Fe3O4 prolongs the setting time of MKPC paste. The compressive strength of MKPC specimens increased with the increase of Fe2O3 content at all curing times. In MKPC with the addition of Fe2O3 and Fe3O4 mixture, the strength was higher than in the case of the addition of Fe2O3 only. XRD analysis revealed that K-struvite MgKPO4·6H2O was the main phase in the obtained MKPC for all specimens. It was found that the optimized MKPC formulation contained 5 wt.% Fe2O3 together with 15 wt.% Fe3O4 contributed to the dense microstructure and maximum strength, which are important characteristics to provide long-term waste forms stability.