Thèses dans notre équipe

Emilie THOMASSOT

Origine et formation des diamants et de leurs inclusions de sulfure :
contribution à l’étude des processus géochimiques, des cycles (C, N et S) et de leur évolution dans le manteau supérieur terrestre.

sous la direction de Pierre Cartigny : soutenue le 7 décembre 2006

Nelly ASSAYAG

Traçage isotopique des sources et des puits de CO₂ dans les réservoirs géologiques

sous la direction de Pierre Agrinier : soutenue le 4 décembre 2006

Le lac Pavin

Fabien DUFAUD

Etude expérimentale des réactions de carbonatation minérale du CO₂ dans les roches basiques et ultrabasiques

sous la codirection d'Isabelle Martinez et de Guillaume Fiquet (Minéralogie) : soutenue le 8 novembre 2006

Mineral storage of CO₂ is the process that converts gaseous CO₂ into a carbonate phase stable over geological timescales. Carbonate formation upon interaction of CO₂ with basic and ultrabasic rocks is an interesting option due to the good repartition of these rocks at the surface of the Earth and to the strong thermodynamic disequilibrium between the CO₂-rich fluid and the constitutive minerals of these rocks.

échantillon d'olivine qui a réagit a 500°C et 1 kbar dans une presse hydraulique pendant 4 heures. On voit des carbonates globuleux qui se sont formés dans une matrice riche en silice et des olivine résiduelles.

We have carried out carbonatation experiments on olivine, serpentine and orthopyroxene under various conditions. Powders of these minerals are in contact with oxalic acid (H₂C₂O₄ used as a source of CO₂) in platinum capsules and then react at high pressure and temperature in an hydraulic press. Water and brines are introduced in some of the experiments to test their influence on the carbonatation reaction. After experiments, capsules are opened under vacuum to separate and quantify the different gases that were in contact with the silicates.

The amounts of carbonate formed were measured by decarbonatation of the reacted material. Chemical and isotopic mass balance calculations were also done in order to provide precise monitoring of carbonatation rates. Mineralogical study of the reacted samples using SEM and TEM allowed the identification of the mechanisms of carbonatation and the observation of magnesite crystals. Strong differences in carbonate textures and carbonatation rates were reported between NaCl-containing and NaCl-free samples. The measured carbonation rates in these systems strongly depend on the initial magnesium rich mineral. Pressure, temperature and molar fraction of CO₂ in the gas phase are also key parameters. Additions of brines and water in the system increase the yield of the reactions. The conditions of temperature and pressure of these experiments, although far from planned CO2 storage conditions, allow to discuss thermodynamic aspects of these reactions.