ISTOPore Seminar by Mohamadou Sarr

Abstract

Most of the world’s drinking water supply comes from groundwater aquifers. These sources, however, are susceptible to contamination (hydrocarbon, chlorinated solvents, nitrates…). Environmental engineering applications foreseen the usage of charged colloidal particles for groundwater remediation or for sealing damaged geological confinement barriers. However, the injection of colloidal particles into the area of interest in a geological formation using conventional mechanisms such as pressure gradients or gravity is challenging. Using solute concentration gradients, it is possible to induce the particles to flow into or out of the pores under controlled conditions. This phenomenon is known as diffusiophoresis. In geological porous media, local concentration gradients arise from a number of physico-chemical processes such as salt or crystal dissolution, drying, precipitation, interphase mass transfer, chemical reactions, and can lead to diffusiophoretic transport of colloidal particles. The present study assesses the magnitude and spatial distribution of local concentration gradients generated in situ during the dissolution of calcite crystals, and evaluate their potentiel to deliver colloidal particles to regions of interest. We developed an approach that combines microfluidic devices with Raman spectroscopy, a non-invasive, non-destructive technique that allows the in situ identification of chemical species and their transformation during a reaction [1]. We perform Raman spectroscopy in real time during calcite dissolution under dynamic conditions. From Raman spectra we obtain the calcite and solute compositions, thus providing new insights into hydro-geochemical coupling in porous media. The experimental results will extend the numerical models developed that simulates the dissolution of calcite at the pore-scale [2]. In a second step, more complex reactive micromodels will be considered, like flow-through reactors to localize concentration gradients generated by dissolution/precipitation. The anticipated outcomes aim to contribute significantly to the understanding of local concentration gradients in geological porous media, paving the way for improved predictions and management of subsurface processes.