# Multi-scale mechanistic approach to colloidal transport in porous media

Muqeet Iqbal, Sophie Roman, Catherine Noiriel, Cyprien Soulaine, Rémi Marsac, Khalil Hanna

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Muqeet Iqbal, Sophie Roman, Catherine Noiriel, Cyprien Soulaine, Rémi Marsac, et al. Multi-scale mechanistic approach to colloidal transport in porous media. 6th CARGESE school: FLOW and Transport In porous and fractured MEdia (FLOWTIME), Jun 2024, Cargèse, France. . [hal-04790083](https://hal.science/hal-04790083v1)

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Submitted on 19 Nov 2024

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Distributed under a Creative Commons Attribution 4.0 International License
# Multi-scale mechanistic approach to colloidal transport in porous media

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Muqeet Iqbal¹,² (muqeet.iqbal@cnrs-orleans.fr), S. Roman¹, C. Noiriel³, C. Soulaine¹, R. Marsac², K. Hanna⁴

¹Institut des Sciences de la Terre d'Orléans, UMR 7327 Université d'Orléans-BRGM-CNRS

²Géosciences Rennes, UMR 6118, Université Rennes, CNRS

³Géosciences Environnement Toulouse, Université de Toulouse

⁴Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226

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## Motivation

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Colloidal particles, including nanoparticles, bacteria, and fine particles, have significant potential to mobilize contaminants in porous media.¹

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Understanding the mechanisms controlling colloidal transport is limited, hindering their effective use in underground engineering, such as groundwater remediation and enhanced oil recovery.

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Therefore, a multi-scale approach combining laboratory experiments and numerical modeling is necessary to accurately predict retention and transport of colloids in porous matrices.

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## Role of colloids in contaminant transport

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Rare Earth Elements (REE), now recognized as emerging contaminants are shown to have strong interactions with natural colloids (Fe/Mn/Al (oxyhydr)oxides, and humic substances).²

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Limited knowledge is available on the impact of C- and Fe- rich colloids on REE mobility in subsurface systems under flow-through conditions.

## Experimental design

1. The sorption of REE under flow-through conditions was investigated using a liquid chromatography system (Äkta™ Pure) equipped with a fraction collector (F9-R).

2. A constant total metal ion concentration ($C_0$) of 0.7 µM was injected through fixed-bed columns packed with quartz sand. Colloids were injected until a complete breakthrough of HA was achieved.

3. The height of the porous bed was approximately 5 cm, the flow in the column was from bottom to top at a fixed rate of 0.5 mL min⁻¹, using 5 mM NaCl solution at pH 5.

4. The dissolved metal ions concentrations from the column outflow solutions (C) were measured using Triple Quadrupole ICP-MS.

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<figure><img src="image_11.png" /><figcaption>Breakthrough curve (BTC) of conservative tracer</figcaption></figure>

## Results

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In the absence of colloids, no breakthrough of REE was observed until 40 PV showing that REE are strongly adsorbed to the quartz.

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1D reactive transport model developed in Phreeqc for aqueous REE transport accurately describes the experimental breakthrough curves.³

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Colloids represented the dominant transport pathway for REE which otherwise would have remained immobile in the quartz column.

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Variability in REE patterns is an important tool to probe competitive adsorption in the context of transport from water to soils in porous media.

<figure><img src="image_16.png" /><figcaption>REE aqueous transport</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>REE with organic colloids</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>REE with mixed colloids</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>REE patterns in the column</figcaption></figure>

## On-going research / perspectives

Prediction of colloidal transport is not only dependent on scales but also on hydro-electro-chemical effects in geological porous media.

<figure><img src="image_20.png" /><figcaption>Pore clogging</figcaption></figure>

## 4D X-ray micro computed tomography

Time-resolved 3D non-invasive, non-destructive high resolution imaging technique which can be applied in-situ to observe colloid retention and transport processes directly inside the pore matrix.

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## Image processing

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## Goals to achieve

* Providing reference dataset validating continuum-scale models.

* Identification of key parameters controlling the distribution of colloids and the subsequent remobilization of fluids using 4D X-ray micro computed tomography.

* Understanding of dynamic processes → Pore clogging, wettability alteration and remobilization of fluids and particles (e.g. snap-off and Haines jump events).

<figure><img src="image_23.png" /><figcaption>Fluid / colloid redistribution</figcaption></figure>

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Pak et al. (2020)⁴

## Summary

* Colloids play a crucial role in mobilizing contaminants in subsurface systems.

* REE are emerging contaminants used in many modern-day technologies.

* Breakthrough curves show enhanced REE mobility in the presence of colloids.

* Limited knowledge on the mechanisms controlling colloid retention and transport hinders their widespread use in underground engineering, such as groundwater remediation and enhanced oil recovery. Therefore, a combined modeling-laboratory approach focused on multi-scale phenomena is necessary.

## References

¹Schiefler et al., Time Resolved Pore Scale Monitoring of Nanoparticle Transport in Porous Media Using Synchrotron X-Ray µ-CT. Environ. Sci.: Nano (2023)

²Pourret, et al., J. Colloidal Control on the Distribution of Rare Earth Elements in Shallow Groundwaters. Aquat Geochem (2010)

³Iqbal et al., A Mechanistic Surface Complexation Approach for the Prediction of Rare Earth Element Reactive Transport in Quartz Porous Media. Chemical Geology (2023)

⁴Pak et al., Pore-scale investigation of the use of reactive nanoparticles for in situ remediation of contaminated groundwater source. PNAS (2020)

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