Microstructure and leaching durability of glass composite wasteforms for spent clinoptilolite immobilisation

Simulated spent Cs-clinoptilolite waste was immobilised in a monolithic glass composite material (GCM) produced by a pressureless sintering at 750 °C for 2 h duration. The effects of waste loading from 1:1 up to 1:10 glass to waste volume ratio (37 up to 88 wt%) on the GCM wasteform microstructure and leaching properties were analysed. The open porosity ranged between 0.84 and ∼13.2 % for the highest waste load. Significant changes occurred in the microstructure, phases present and wasteform durability at different waste loading. At waste loading up to 73 wt% of spent clinoptilolite, the GCM microstructure consists of several crystalline phases (clinoptilolite, sodalite, wollastonite and CsCl) that were fully encapsulated by a glass matrix. This leads to a low normalized leaching rate of Cs (remaining below 6.35 × 10−6 g/cm2 day in a GCM with 73 wt% waste) during a leaching test for 7 days conducted using ASTM C1220-98. In GCM’s with waste loading exceeding 73 wt%, the crystalline phases present (clinoptilolite and CsCl) were not fully encapsulated by the glass matrix hence the normalized leaching rate of Cs was as high as 9.06 × 10−4 g/cm2 day at waste loading of ⩾80 wt%.