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Multi-isotope monitoring of enhanced weathering of glauconitic sands under controlled high pCO2 conditions

Abstract : Enhanced water-rock interaction in aquifers overlying CO2 storage sites in deep saline formation can be expected in the case of CO2 leakage, leading to a release of geogenic compounds into freshwater resources. Our study investigates the use of trace elements and several isotope systematics (B, Li, C, O, D, Sr) as monitoring tools to detect CO2-leaks in aquifers. For this, we develop batch experiments under controlled pCO2 conditions. The glauconitic Albian greensands of the Paris Basin were chosen as interacting solid phase because i) the Paris Basin contains aquifers identified as CCS targets and ii) the Albian aquifer is a deep freshwater resource of strategic national importance. The selected greensand sample consists mainly of quartz with presence of glauconitic minerals and traces of apatite, rutile, ilmenite. The water used for the experiments was pumped from the confined part of the Albian aquifer. PTFE reactors (liquid/solid ratio of 10, pCO2= 2 bar; room temperature, continuous pH measurements) were run simultaneously, over 1 day, 1 week, 2 weeks and 1 month. A pH drop from 6.6 to 4.9 was noticeable immediately after the injection, due to CO2 dissolution (ΔHCO3 = 0.8 mmol/L). Cations and silica increased by a factor of 2 (Ca), 2 (SiO2), 1.5 (K), 1.3 (Mg), 1.5 (Sr), 3.7 (Li), 4.2 (B) for t=1 month. From 1 day to 1 month of contact with CO2, the δ13CDIC decreased from -15.7 ‰ to -21 ‰ vs. PDB suggesting a proton-consuming process which entails supplementary CO2 dissolution. Weathering reactions and surface complexation consume acidity and account for the observed chemical variations. Glauconitic minerals being the main B-bearing phase, the evolution of the aqueous B concentrations indicates their implication in the water-gas-mineral interactions. This is supported by a shift of δ11B towards more negative values in the presence of CO2. The δ11B is different according to the origin of the B (surface or structural), which gives additional information of the actual processes at stake during the evolution. We focus here on the complex weathering behavior of glauconitic minerals, as poorly defined phases with regards to its mineral structure, under pCO2 and low-pH conditions, constraining e.g. dissolution rates and surface complexation models through isotope and geochemical data.
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https://hal-mines-paristech.archives-ouvertes.fr/hal-00777747
Contributeur : Vincent Lagneau <>
Soumis le : vendredi 18 janvier 2013 - 09:13:12
Dernière modification le : samedi 19 septembre 2020 - 04:29:30

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  • HAL Id : hal-00777747, version 1

Citation

Pauline Humez, Julie Lions, Vincent Lagneau, Philippe Négrel. Multi-isotope monitoring of enhanced weathering of glauconitic sands under controlled high pCO2 conditions. Goldschmidt 2012, Jun 2012, Montreal, Canada. ⟨hal-00777747⟩

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