University of Poitiers, IC2MP institut

The Institute of Chemistry of Media and Materials in Poitiers (IC2MP) is a multidisciplinary Joint Research Unit (UMR) affiliated with the University of Poitiers and the CNRS (Chemistry and Earth & Universe institutes). It specializes in the fields of chemistry and surface geosciences. The institute brings together five research teams, including the HydrASA team (Hydrogeology, Clays, Soil, Alterations), which will host the phD student. The HydrASA team has internationally recognized expertise in clay reactivity and in the alteration of various geological systems. The team’s researchers are also working on developing digital autoradiography techniques to localize radionuclides within mineral phases.

Homepage: https://ic2mp.labo.univ-poitiers.fr/

CONTEXT

Scandinavian alum shales are fine-grained sedimentary formations rich in organic matter, deposited from the Middle Cambrian to the Lower Ordovician. They represent complex geochemical systems characterized by high concentrations of trace elements and redox-sensitive metals (U, V, Mo, Ni). Their formation under anoxic conditions favored the preservation of organic matter and the incorporation of these elements into various mineral phases, including sulfides (notably pyrite), organic matter, and clay minerals.

These formations crop out along a broad belt extending across Norway, Sweden, and Finland. They are of both geological and economic interest, as they may host polymetallic ore deposits.

However, these shales also raise significant environmental concerns. When exposed to oxidizing surface conditions, they become highly reactive, mainly due to sulfide oxidation, which generates acidity and promotes the mobilization of associated metals.

These meteoric weathering processes involve coupled mechanisms of mineral dissolution, oxidation, and phase transformation, strongly influencing the speciation and mobility of trace elements.

In mining contexts, these processes are further intensified by extraction, crushing, and waste storage, which increase reactive surface area and modify physicochemical conditions (pH, redox potential, oxygen and water availability). This leads to enhanced acid mine drainage and the dispersion of contaminants into surrounding environmental compartments.

In this framework, understanding the reactivity of these materials under both natural weathering and post-mining conditions requires a multiscale approach combining field observations, mineralogical and geochemical analyses, and techniques such as alpha autoradiography. The aim is to better constrain the mechanisms controlling element release and transport, in order to improve predictive models and environmental management strategies.

DESCRIPTION

Upon exposure to oxidizing surface conditions, alum shales undergo strong geochemical destabilization driven primarily by sulfide oxidation reactions. This triggers acid generation and the subsequent mobilization of associated trace elements. These meteoric weathering processes involve tightly coupled reaction networks encompassing mineral dissolution, redox transformations, secondary mineral precipitation, and sorption processes, collectively controlling element speciation and mobility.

In anthropogenically disturbed systems, particularly mining environments, these processes are markedly amplified. Mechanical disaggregation, increased reactive surface area, and perturbation of physicochemical parameters (pH, Eh, fluid circulation, oxygen availability) significantly enhance reaction kinetics. This often results in intensified acid mine drainage and long-range dispersal of contaminants across environmental compartments (soils, surface waters, and groundwater systems).

Despite their significance, the mechanistic understanding of alum shale reactivity remains incomplete, particularly regarding the role, stability, and transformation pathways of uranium-bearing phases under coupled weathering and mining-induced perturbations. Addressing this gap requires an integrated, multiscale approach bridging field- scale geological variability with mineralogical and molecular-scale processes.

This PhD aims to establish a predictive framework for the reactivity of Scandinavian alum shales under natural and anthropogenic perturbations. The objectives are to :

1) resolve the mineralogical and geochemical controls governing metal(loid) distribution and reactivity across contrasting geological settings ;

2) quantify reaction pathways and kinetics under meteoric weathering conditions, with emphasis on redox-driven transformations and acid generation potential ;

3) evaluate the impact of mining-related mechanical and chemical processing on system reactivity and contaminant mobility ;

4) assess long-term environmental risks through the integration of process-based understanding into broader geological and environmental contexts.

The project will rely on a multiscale methodological strategy combining field-based sampling, advanced mineralogical and geochemical characterization, and targeted identification of U-bearing phases (e.g., alpha autoradiography). Ultimately, this work aims to improve predictive capabilities for element release and transport, and to support evidence-based environmental management and resource evaluation strategies in alum shale-bearing regions.

METHODOLOGY

To answer these questions, the work of the PhD position will consists to obtain :

(1) a mineralogical and petrological characterization of alumshales inhereted from different areas of Scandinavia according to their nature and geological context ;

(2) a geochemical characterization focusing on the reactivity to weathering, by investigating the mineral transformations, the potential for acid mine drainage and the mobility of metals and other trace and ultratrace elements ;

(3) a comparison of this same reactivity in post-mining samples after they have undergone physicochemical treatment ;

(4) a risk assessment of the long-term reactivity of alumshales, after placing these results within a broader geological context, thereby enabling the identification of the optimal management strategy.

Field sampling campaigns will be part of the study.

OTHER INFORMATIONS

PhD of 36 months. Expected date of employment: 1 October 2026.

Applicants should have a Master or an Engineer degree in a field related to Earth Science and/or Physico-Chemistry of Materials, with a strong interest in characterization and experimental activities. The candidate is expected to be proficient in English.

Fieldwork is planned

Sent to sophie.billon@univ-poitiers.fr and michael.descostes@orano.group a report with:

-CV

-copies of the university or engineer school marks (Master level)

-a motivation letter for this proposal

-letters of two referees