Abstract
AbstractThe determination of reliable weathering/dissolution rates for cement phases is of fundamental importance for the modelling of the temporal evolution of both radioactive waste repositories and CO2 geological storage sites (e.g. waste matrix, plug in boreholes). Here, the dissolution kinetics of AFm-Cl (hydrated calcium aluminates containing interlayer Cl) has been studied using flow-through experiments conducted at pH values ranging from 9.2 to 13. Mineralogical (XRD) and chemical (EPMA, TEM) analyses have been performed to determine the evolution of the phases during the dissolution experiments. For pH values between 10 and 13, the dissolution of AFm-Cl is congruent (i.e. Ca/Al ratios close to 2 both for solids and outlet concentrations). In contrast, the precipitation of amorphous Al-phases and possibly amorphous mixed Al/Ca phases is observed at pH 9.2, leading to Ca/Al ratios in the outlet solutions higher than those of the initial solid. Therefore, at pH 9.2, even if Cl–/OH– exchange occurs, estimation of dissolution rate from released Cl appears to be the best proxy. Dissolution rates were normalized to the final specific surface areas (ranging from 6.1 to 35.4 m2 g−1). Dissolution rate appears to be pH-independent and therefore the far-from-equilibrium dissolution rate at room temperature is expressed as: logR(mol m–2 s–1) = –9.23 ± 0.18
Highlights
IN most of the designs of deep underground radioactive waste disposal, cementitious materials will be used to build access structures, galleries, vaults and packages for wastes
The present study focuses on the stability of hydrated calcium aluminates (AFm), which are phases found in most hydrated cement pastes
Àq(coi ut where Ni is the amount of the atom i, t is the time (s), q is the flow rate (L s–1), coi ut À ciin is the difference between inlet and outlet concentrations, ε is the stoichiometry of the atom inside AFm-Cl, A is the total reactive surface of the mineral (m2), and R is the dissolution rate
Summary
IN most of the designs of deep underground radioactive waste disposal, cementitious materials will be used to build access structures, galleries, vaults and packages for wastes. In such contexts cement materials have essentially a mechanical function (e.g. low permeable barriers that retard radionuclide migration), but can sorb radionuclides. Some authors highlight a possible long-term stabilization of the sorbed elements, if phases remain at equilibrium with the surrounding pore water (Cornelis et al, 2012). Cement materials that will be present in situ may be in direct contact with the surrounding rock formation, and with rock pore water. The chemical gradient between the cement pore water and the pore water in the host rock will induce mineralogical transformations whose impact must be evaluated in the framework of repository long-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
