Description du sujet de thèse

Among the geochemical processes responsible for the production of natural hydrogen, serpentinization is a chemical reaction resulting from the interaction, in the subsurface, between a peridotite-type mantle rock and a hydrothermal solution. Hydration of the rock's anhydrous minerals increases the salinity of the interstitial solution, accompanied by anoxic oxidation of the rock's ferrous iron by reduction of the water to dihydrogen.
Although redox processes are at the heart of the serpentinization reaction, they remain poorly described in a hydrothermal context, i.e. under conditions of high salinity, of the order of several hundred grams per liter, temperatures approaching 250°C and pressures above 100 bar. Moreover, their experimental characterization is a scientific and technical challenge.
The main aim of the thesis project is to develop a methodology for characterizing the redox state and dynamics of hot saline systems, such as those found in the western part of the Pyrenean structure. Two main actions are envisaged to achieve this objective:
1) Implementation and modeling of interaction processes involving Fe(III)/Fe(II) and H2O/H2 redox couples in simplified synthetic aqueous brines that mimic hydrothermal brines from the Aquitaine Basin;
2) Application to experiments on H2 generation by serpentinization of natural rock.
The implementation and modeling of interaction processes will be carried out at BRGM, which has i) the equipment and expertise required to carry out the experiments and ensure operando kinetic monitoring of redox reactions using electrochemistry, and ii) the geochemical modeling tools and expertise to size the tests and interpret the results obtained. To this end, BRGM has hydrothermal reactors equipped with robust all-solid probes for operando measurement of physico-chemical parameters, and sampling cannulas to sample fluids and, where appropriate, solids for chemical analysis (speciation measurement of redox elements, physico-chemical characterization of balances by XRD and Raman spectroscopy). BRGM also uses the PhreeSCALE geochemical calculation code, developed in-house, to describe the chemical properties of brines and mineral-brine equilibria up to high salinities of several hundred grams per liter, and temperatures and pressures representative of hydrothermal conditions.
Experiments using natural rock will be carried out at ISTO, which has the expertise required to carry out water-rock interaction tests using a full range of autoclaves, and to characterize the physico-chemical properties of fluids and solids. In particular, ISTO has two sampling autoclaves designed to react high-salinity fluids with powdered rock up to 350°C and 500 bar.

Contexte de travail

The position is based on the Geosciences campus in Orléans and is shared between the Institut des Sciences de la Terre d'Orléans (ISTO) and BRGM. ISTO is a joint research unit of the University of Orléans, CNRS and BRGM. BRGM is the French national Geological Survey.
The PhD thesis is the fruit of a partnership between ISTO and BRGM, as part of the REDISH action of axis 12 " Bassin Aquitain " of the PEPR project "Sous-sol, bien commun". The thesis work includes laboratory tests and theoretical developments.
You have a Master's degree or equivalent with a major in experimental chemistry and electrochemistry. You have a strong theoretical background in chemical thermodynamics with some experience in numerical modelling.
To apply, send a CV, a cover letter, and one or two recommendation letters.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.