Immobilization of Cs and Sr in Geopolymers with Si/Al Molar Ratio of∼2

Geopolymers with Si/Al ∼ 2 were made by dissolving fly ash or metakaolinite in alkali solutions and polymerizing them by curing below 90°C. 1 and 5 wt% Cs and Sr were added as the nitrates or hydroxides separately. The geopolymers were characterized by X-ray diffraction analysis, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). PCT tests were carried out on selected materials which were heated to temperatures as high as 900°C. Many of the materials passed the PCT test and the most leachable ions were Na and K, with Cs and Sr being considerably more resistant. Fly ash-containing geopolymers can immobilize 1 wt% Cs and Sr effectively and this applies also when they are heated from ambient to as high as 900°C. The Na leach rates of the unheated samples just exceed the limit of 13.5 g/L specified in the PCT- B test. However, metakaolinite-based geopolymers have much lower leach rates for Na and K (< 6.9 g/L). Also the leach rates for Cs and Sr are also much lower (< 1.3 g/L) than than those for the fly ash based geopolymers. Most of the Cs was incorporated into the amorphous geopolymer matrix for the geopolymer with 5 wt% addition as shown by SEM/EDS.