Investigating the Replicability of Geopolymer Formulations for Industrial-Scale HYPEX® Radioactive Waste Immobilization– 25513

This research presents a comprehensive investigation of the factors influencing geopolymer quality, offering a pathway to standardize and optimize geopolymer production for industrial applications, particularly when used as conditioning matrices for Low Level Waste (LLW) and Intermediate Level Waste (ILW) for instance in the HYPEX process. The focus here is on the chemical and mechanical characterization of commercially available metakaolins with the goal of establishing standards for industrial replication. The chemical characterization was performed estimating the concentrations of oxides such as Si, Al, Na, K, and Ca in metakaolin using techniques like X-Ray Fluorescence. The mechanical characterization was performed analysing the specific surface area of each metakaolin powder using the BET method. The specific surface area resulted a key factor in the dissolution process of metakaolin in alkaline solutions. A lower specific surface area slows down the dissolution process, while an excessively high surface area requires a large amount of water, which can be detrimental to the geopolymer formation and its final properties. Furthermore, the thermal profile of the geopolymer during the first 24 hours of formation under adiabatic conditions was studied, varying the batch of metakaolin, fundamental atomic ratios, and water content. The results showed that metakaolins developing different temperature profiles tend to produce geopolymers with different mechanical characteristics. This analysis helps identify the optimal temperature profile for geo-polymerization, that maximizes mechanical strength and minimizes leachability, while keeping the temperature below 95°C to prevent excessive water evaporation and ions volatility.