Aqueous leachability of metakaolin-based geopolymers with molar ratios of Si/Al = 1.5–4

The leachability in water of metakaolin based geopolymers with molar ratios of Na/Al = 1 and Si/Al = 1.5–4.0 has been investigated in order to optimise the composition for the immobilisation of nuclear waste. Formulations with Si/Al of around 2 are the most suitable using the ASTM/PCT leach test method. The variability of the leach results is discussed with reference to the microstructure, compressive strength and the degree of polymerisation of the geopolymers as observed here by solid state nuclear magnetic resonance, XRD and infrared measurements.