Présentations Colloques

Oral Presentation
5.03
Session 5.03: CO2 storage in deep saline aquifers and potential impacts on shallow aquifers
Devau Nicolas
New insights on the changes induced by a potential CO2 leakage on the fate of trace metals in fresh groundwater- The case of the Albian aquifer
To mitigate CO2 emissions into the atmosphere, the geological storage of CO2 in deep saline aquifers is one of the main options. One potential risk associated with the geological storage is a potential leakage to fresh groundwater. The CIPRES project, co-funded by ANR, has been done to assess the impact of CO2 leakage to the Albian aquifer, a strategic water resource in the Paris basin, overlying deep saline formation suitable for potential geological storages. One task of the project aimed to determine how chemical properties of the Albian waters are affected by CO2 leakage, with a special focus on the fate of three trace metals (Zn, Ni and As(V)).**For this purpose, an approach combining long-term batch experiment (1 month) and modelling has been conducted. The batch reactor was filled with water and rocks issued from Albian aquifer and enriched by CO2 gas phase. Major and trace elements in water samples were analysed regularly during the experiment. The geochemical model accounts for various concomitant mechanisms including aqueous complexation, kinetically-constrained dissolution precipitation reactions for primary minerals, formation of secondary phases, protonation deprotonation and surface complexation reactions involving major and trace elements at the quartz surface sites and at the edge surface site of clay phases and cation exchange on the basal sites of the clay phases. **The simulations reproduce correctly the pH drops and the increase of alkalinity. The behavior of the main major elements was correctly simulated. The results highlight that the pH drop promotes the release of Zn and Ni initially sorbed onto glauconite. In contrast, the measured increase of As(V) concentration seems to be induced by the dissolution of fluorapatite. This work shows clearly that complex geochemical mechanisms control the fate of trace elements in water-rocks-CO2 systems.**
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