The effect of incorporating Cs, Sr and Eu nitrates on the matrix development of Fe-rich polymers

Abstract

Radionuclides like 137 Cs, 90 Sr and 152+154 Eu need to be immobilised from liquid radioactive waste to a suitable final encapsulation matrix. Alkali-activated Materials (AAMs) have the potential to be more effective in immobilising Cs + and Sr 2+ than Portland cement because they can produce stable phases and incorporate them into their structure. Less explored in AAMs is their capacity to immobilise Eu-ions. Nanoparticles are investigated for extracting radionuclides from liquid radioactive waste. CeO 2 nanoparticles have exhibited great potential in their ability to sorb Eu 3+ but after several adsorption/desorption cycles also these need to be immobilised into a final encapsulation matrix. In this work, AAMs were prepared from synthetic Fe-rich slag. Two sodium silicate ratios were examined and the AAMs were doped with various mixtures of CsNO 3 , Sr(NO 3) 2 , Eu(NO 3) 3 , and CeO 2 nanoparticles. Contaminants added to the AAM matrices can change the properties of the encapsulation system. To understand the impact on the AAM structure and to determine whether the effects are derived from the simulated radioactive Cs + , Sr 2+, and Eu 3+ , the presence of the CeO 2 nanoparticles or the presence of the nitrate ions, samples were examined during their matrix development using isothermal calorimetry, and investigations were made on their microstructural and physicochemical characteristics. The introduction of Cs + to the matrix showed no notable impact on the activation kinetics, but Eu 3+ seems to form Eu(OH) 3 similarly to Sr 2+ which forms Sr(OH) 2 reducing the available hydroxides during the activation and ultimately hindering the polymerisation.