Potential of magnesium silicate binders for the solidification / stabilization of contaminated soil
Soil contamination by radioactive substances represents a major challenge in terms of public health and environmental protection. Among the various strategies considered for managing such polluted soils, the excavation of contaminated materials offers a pathway to the safe reuse of the site. The excavated soils, when characterized by low to intermediate activity and short-lived radionuclides, must be stabilized prior to disposal. In this context, cementation is widely used due to its moderate cost, ease of implementation, and capacity to confine numerous pollutants. However, its application to soils rich in swelling clays presents two major limitations: poor workability of the fresh material and volumetric instability of the hardened product. To address these issues, this thesis aims to evaluate the potential of magnesium silicate cements as an alternative to conventional calcium silicate cements. These emerging binders are currently attracting growing interest, particularly in the fields of earthen construction and the development of low-carbon materials.
The first objective will be to study the influence of various formulation parameters on the reactivity and properties of magnesium silicate cements. This will be followed by an in-depth investigation of the interactions between the cement phases and the main constituents of contaminated soils. Finally, the long-term durability of the formulated materials will be assessed through leaching tests, which will serve as input for reactive transport modelling, with the aim of gaining a better understanding of the degradation mechanisms and the long-term behaviour of the materials.
This research project is intended for a PhD candidate interested in advancing his/her expertise in materials physical chemistry and contributing to the development of innovative solutions for contaminated soil management and low-impact binder technologies.
Elaboration and durability evaluation of water-permselective multilayer membranes for the CO2 conversion into e-fuels
The catalytic hydrogenation of CO2 into e-fuels is considered to decarbonize certain modes of transport that are difficult to electrify. However, some of the considered reactions are thermodynamically balanced (limited CO2 conversion efficiencies) and catalyst degradation by the produced water is observed. The use of membrane reactors, allowing water separation, is envisaged. For this, the development of water-permselective membranes, without defects and resistant to synthesis conditions, is necessary. Previous studies have targeted LTA and SOD zeolite membranes for this application. However, the presence of defects reduces their selectivity, and their performance deteriorates during operation. The objective of this thesis is therefore to study the sealing of membrane defects and the deposition of protective layers on their surface to improve their performance and durability. To achieve this, the deposition of permselective zeolite layers will first be carried out hydrothermally on suitable porous supports. The sealing of defects by impregnation/conversion of silica precursors in a supercritical CO2 environment will then be studied. Finally, different protective layers (zeolite, ceramic oxide, etc.) will be deposited on the membranes (sol-gel, supercritical CO2, hydrothermal methods). The coatings will be characterized (XRD, SEM, porosimetry, elipsometry, etc.) to ensure their chemical nature, thickness/homogeneity, and porosity. Gas permeation performance will be evaluated at the various stages of preparation, and the durability of the membranes will be studied in the presence of water vapor at different temperatures.
The candidate will work within the Supercritical Processes and Decontamination Laboratory (Marcoule), and will benefit from the laboratory's expertise in ceramic membranes. The student will interact with the laboratory's technicians, engineers, doctoral students and post-doctoral fellows and will exchange with the collaborators of the Reactors and Processes Laboratory (Grenoble). The doctoral student will be involved in the different stages of the project, the publication of results and the presentation of their work at conferences. They will develop solid scientific knowledge in the fields of environment and energy, as well as in project management.