Sustainable RECovery of vALuable metaLs in bauxite residue – RECALL

The RECALL project relies on an integrated methodology structured into six interconnected work packages (WPs), combining experimental, technological and socio-economic approaches.

WP0 ensures project coordination, integration of disciplines and interactions between academic and industrial partners. It guarantees coherence between the different scientific tasks and facilitates knowledge transfer.

WP1 provides the scientific foundation of the project through multi-scale characterization of bauxite residues and detailed speciation of target elements (REEs and Fe). Advanced analytical techniques (XRD, electron microscopy, X-ray spectroscopy) are used to identify mineral phases, hosting phases and local atomic environments. This step is essential to guide downstream extraction strategies.

WP2 focuses on the selective extraction of critical metals using innovative and environmentally friendly approaches. Leaching is performed under mild conditions (aqueous media, moderate pH and temperature) using organic acids inspired by biological processes. Process parameters (pH, concentration, temperature, kinetics) are optimized to enhance selectivity. The resulting leachates are treated using solid–liquid separation techniques, including functionalized resins, to concentrate and purify REEs.

WP3 addresses the valorization of iron contained in bauxite residues. Hydrothermal processes are developed to convert iron into value-added materials such as ferrites. Two process routes are investigated: extraction of REEs before or after iron valorization, allowing optimization of the overall process performance.

WP4 implements a Social Cost–Benefit Analysis (SCBA) to evaluate the environmental, health and economic impacts of the developed processes. By integrating externalities and uncertainties, this WP provides a framework to compare innovative routes with conventional technologies and to guide process optimization through feedback loops.

WP5 is dedicated to dissemination and outreach, including communication to stakeholders and the general public, to promote awareness of resource scarcity and sustainable alternatives.

Together, these WPs enable the development of selective, low-impact and adaptable processes, integrating fundamental understanding, technological innovation and socio-economic evaluation.

This project made it possible to identify the main barriers and levers for the valorization of rare earth elements (REEs) and iron contained in bauxite residues (BR), by integrating speciation, extraction, and purification processes within a sustainable and holistic approach.

The results show that REE speciation is a key factor controlling their extractability, mainly governed by the origin of the bauxite (lateritic vs. karstic). In lateritic BR, heavy REEs are predominantly present as highly stable phosphate phases (e.g., xenotime), while light REE speciation is more complex and diverse. In contrast, in karstic BR, heavy REEs are adsorbed onto or incorporated into secondary phases (iron oxyhydroxides, hydroxyapatite), and the presence of CeO₂ was observed. This variability explains the differences in extraction behavior. The study demonstrates that extraction processes at moderate pH using weak organic acids enable selective dissolution controlled by speciation. For example, up to 80% of light REEs from lateritic BR can be extracted at pH 2.7–4.5, with good selectivity relative to heavy REEs, Fe, and Al. Conversely, heavy REEs are more soluble in karstic BR, with extraction yields reaching up to 60%.

Downstream, bio-based ligands and resins were developed for leachate treatment. Phenol-formaldehyde resins exhibit adsorption capacities ranging from 0.38 to 0.75 mmol/g, fast kinetics, and pH-dependent selectivity, enabling efficient lanthanide recovery from complex media. An additional purification step based on selective calcium precipitation, notably using alginate beads in batch and continuous modes, was successfully validated.

Furthermore, the results show that BR valorization can be coupled with iron recovery: hydrothermal transformations enable the formation of ferrites (up to 77 wt% for NiZn), although some limitations remain in terms of purity and functional properties.

Finally, an integrated cost–benefit analysis at the value-chain scale highlights the potential of REE recycling from BR to reduce environmental and health impacts compared to primary extraction. These results demonstrate the feasibility of “tailor-made” extraction strategies adapted to BR speciation, paving the way for low-impact, selective processes compatible with a circular economy for rare earths.

The key strength of RECALL lies in demonstrating that REE speciation—strongly controlled by bauxite origin—is the primary driver of extractability, enabling the design of “tailor-made” extraction strategies adapted to resource variability. By combining low-impact leaching processes under mild conditions with advanced separation techniques and a Social Cost–Benefit Analysis (SCBA), the project goes beyond conventional approaches focused solely on technical efficiency, integrating environmental and societal dimensions.

Future work will focus on scaling up the most promising processes to pilot level, improving the recyclability of organic extractants, and refining process optimization under realistic conditions. In parallel, assessing the variability and stocks of bauxite residues will be essential to evaluate their industrial potential. Ultimately, these developments aim to support the emergence of circular and resilient supply chains for critical raw materials, while providing decision-support tools for industry and policy makers.

1. Arrachart, G.; Couturier, J.; Dourdain, S.; Levard, C.; Pellet-Rostaing, S., Recovery of rare earth elements (REEs) using ionic solvents. Processes 2021, 9, (7), 1202.
2. Lallemand, C.; Ambrosi, J. P.; Borschneck, D.; Angeletti, B.; Chaurand, P.; Campos, A.; Desmau, M.; Fehlauer, T.; Auffan, M.; Labille, J.; Roche, N.; Poizat, L.; Collin, B.; Rose, J.; Levard, C., Potential of Ligand-Promoted Dissolution at Mild pH for the Selective Recovery of Rare Earth Elements in Bauxite Residues. ACS Sustainable Chemistry & Engineering 2022, 10, (21), 6942-6951.

In the context of a circular economy, the RECALL project (Sustainable RECovery of vALuable metaLs in bauxite residue) aims to extract valuable metals from an industrial waste with the overall goal of reducing the pressure on natural mineral resources and scrutinizing all consequences in terms of human well-being

With a predicted world population of over 9 billion people in 2050, the demand for raw materials is growing fast especially in newly industrialized countries. Because of limited reserves and the exponential increase of the demand for raw materials, there is an urgent need for a change of paradigm to identify alternative sources and more sustainable extraction strategies. In particular, the European Commission has identified a number of materials and sectors facing specific challenges. Among them, access to certain raw materials (including critical metals) has been identified as a growing worldwide concern in the face of complex geostrategic conflicts or technological obstacles. Due to the economic importance of critical metals (they are present in many emerging applications including renewable energies) and their high supply risk, production from secondary resources appears to be the only way to sustain these new economic sectors.

In this context, the interdisciplinary and intersectoral RECALL project aims to develop sustainable processes (in aqueous media at relatively low temperature and without the use of solvents and strong mineral acids) to recover iron and critical metals (rare earth elements, gallium and scandium) from industrial waste and to value the economic impact of this technological change in terms of social welfare in which potential environmental and health impacts are taken into account.

In addition to a WP dedicated to project coordination, the RECALL project consist in five WPs that aim to develop sequential extraction processes for critical metals (WP2) and iron (WP3) based on thorough characterization of the initial and intermediate residues (WP1). Proxies of naturally occurring biomolecules will be used as extractant in mild conditions. WP4 will quantify the reduction in negative externalities (e.g. environmental and health impacts of the process we will develop) compared to traditional hydro-pyro metallurgy protocols, and guide the processes developed in WP2 and WP3 through retroaction loops. We believe that considering social well-being, which goes far beyond the technical performance of the process, will pave the way for the industrial valorization of a controversial waste that is currently little or not valorized. In particular, we think that this tight interdisciplinary approach will enable us better anticipate market issues that could prevent up scaling of the technology.

Finally, WP5 proposes an innovative outreach action, in particular toward society with the conception and construction of an exhibition module on urban mining in the framework of a public exhibition on circular economy that will be held in 2022 near Marseille.

This research project will be a springboard for this research topic identified as strategic by the CEREGE lab and for initiating other collaborative projects (EU calls, Horizon Europe). This project, not only of scientific interest, but also of economic and societal interest, is supported by the French Institute of Circular Economy