Projet Impact of tailings on environment : Example of transfers of elements from spoil tips in the North of France

Type of project :ANR JCJC Jeune Chercheur Jeune Chercheuse
Dates :01/01/2021 – 31/12/2024
Research team concerned :ER4
Project manager :Emily LLORET
Centers concerned :Lille University
Partners :LOG (Laboratoire d’Océanologie et de Géosciences) Université de Lille, CNRS UMR 8187
IMPMC (Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie) – Paris Sorbonne, CNRS UMR 7590
GéoRessources – Université de Lorraine, CNRS UMR 7359

Project description

To meet his needs, man is constantly increasing mining capacity. This operation has a strong impact on the environment, especially during the storage of non-recoverable mining residues. These tailings are generally accumulated in the form of domes modifying the landscape, and are subject to weathering and leaching processes. Consequently, potentially toxic and/or polluting elements can be transferred from these residues to their immediate environment, and constitute a risk for human health and ecosystems.

Faced with these societal, economic and environmental issues, the interactions between mining waste rock and the environment, as well as the associated transfer processes, must be well understood and their impacts quantified in an attempt to minimize them.

In France, this problem is particularly present in the former mining regions, particularly in the Nord and Pas-de-Calais, where one of the largest coal mining areas in the country was located. The slagheaps – nearly 300 domes formed by the cumula of residues and waste from coal mining – can be the source of transfers of elements from the parent geological material (trace elements, metals, sulphur, organic compounds, etc.) towards adjacent ecosystems and hydrosystems. However, to date, very few studies have quantified the risks associated with these transfers.

Despite their potential polluting power and their apparent sterility, the slag heaps present on their surface a new soil and vegetation by pioneer species. Thus, the slag heaps become the support of original and unique ecosystems in the region, and must therefore be protected.

This project aims to characterize the interactions and transfers of the heap/water/environment, to establish the flows of mobile elements, and to identify the potential risks of pollution. To do this, we plan to follow three axes of research: (1) a geological axis, in order to characterize the parent material and the weathering processes (characterization of the source of the mobile elements), (2) a pedological axis, to study neo-soil formation and its role in element transfers, and (3) a geochemical axis, to determine and quantify element transfers to the surface environment. By combining the results of these three areas of research, we will be able to help develop strategies for the rational management of waste dumps and their ecosystems. Although centered on the slag heaps of northern France, our results will be transposable to similar systems throughout the world (Wallonia (Belgium), Russia, England, etc.). To carry out this project, we will combine geological, geophysical, hydrological, ecological and biogeochemical approaches. Several sampling, measurement and analysis protocols will be specially developed for this project. Thus, to characterize the processes of alteration of the geological material, composition analyzes at the nanometric scale will be carried out (STXM-XANES for the study of the oxidation state of iron), the GPR (Ground Penetrating Radar) will be deployed to study the internal hydrological system of the heaps and laboratory leaching tests will be used to establish links between the release of the elements of the geological material and the neo-soil and the in situ composition of the runoff water and percolating. This project relies on the expertise of collaborators in mineralogy, biogeochemistry, hydrology and geophysics.

Scientific contributions from the laboratory

This project is perfectly in line with the themes of the ER4 team of the LGCgE laboratory, addressing the rehabilitation of anthopized and/or polluted environments. This project echoes the GESIPOL project (ADEME) led by Francis Douay (Junia) which aims to refunctionalize various multi-contaminated soils near former metallurgical industries and at the foot of mining waste storage.

This project will make it possible to create synergies, strengthen existing collaborations and equip a new geochemistry laboratory. Although the subject of the study is a regional concern, the expected results must make it possible to understand the processes at work in other contexts, thus giving an international scope to the project.