Sustainable RECovery of vALuable metaLs in bauxite residue – RECALL

In addition to a WP dedicated to the coordination of the project, the RECALL project is based on five WPs which aim at developing sequential extraction processes for critical metals (WP2) and iron (WP3) based on a thorough characterization of the residues at different stages of the process (WP1). Natural biomolecule proxies will be used as extractants under mild conditions. WP4 will quantify the reduction of negative externalities (e.g. environmental and health impacts of the process we will develop) compared to traditional hydro-pyro-metallurgical protocols, and will guide the processes developed in WP2 and WP3 via feedback loops. We believe that the consideration of social welfare, 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 believe that this interdisciplinary approach will allow us to better anticipate the market problems that could prevent the technology from gaining momentum.

Finally, WP5 proposes, an innovative awareness-raising action towards society with the design and construction of an exhibition module on the concept of «urban mine« as part of a general public exhibition on the circular economy.

The work performed in the first 18 months has advanced the objectives of WPs 1, 2 and 3:

WP1. Characterization/speciation of bauxite residues
A multi-scale analysis of bauxite residues from the Altéo company (Gardanne, France) has allowed to determine the chemical composition, the mineralogy and the speciation of heavy rare earths in the residues. If the chemical composition and mineralogy are in accordance with what has been described in the literature for this type of tailings (presence of iron oxyhydroxides in majority with a total rare earths concentration of 712 mg/kg), we were able to characterize for the first time the speciation of heavy rare earths by X-ray absorption spectroscopy. The latter are present in the form of rare earth phosphate particles of 5 µm in diameter.

WP2. Selective extraction of critical metals
First tests of selective leaching of rare earths have been performed by ligand-assisted dissolution using bio-inspired organic acids with low molecular weight and moderate pH (between 2 and 5). First promising results published this year (Lallemand et al. 2022) were obtained with citric acid in particular which allows a certain selectivity of the dissolution towards major elements such as Fe and Ti for example. The understanding of the dissolution mechanisms is being investigated with the use of a series of organic ligands with functional groups and variable physico-chemical properties. The solid-liquid extraction part will be carried out in the coming months at the ICSM within the framework of a post-doctoral contract currently being recruited.

WP3. Iron valorization
First experiments of transformation of bauxite residues into nano-magnetites have been carried out by the partner Hymag'In (track 1) under mild hydrothermal conditions and in the presence of ferrous co-waste. The first results show a partial transformation of iron oxyhydrooxides (goethite is transformed into magnetite contrary to hematite). A chemical analysis of the different products obtained after reaction (nano-magnetites and solid residues) does not show any rare earth concentration phenomenon in either product. Concerning the valorisation of iron, the efforts will now focus on the initially proposed way 2 (valorisation of iron after selective extraction of rare earths).

WP5. Valorization, communication.
Two scientific articles of rank A have been published.
Conferences on the theme «Mineral resources and transition: a need for sobriety« were given to the general public

The understanding of the dissolution mechanisms is under investigation with the use of a series of organic ligands with variable functional groups and physicochemical properties. The solid-liquid extraction part will be carried out in the coming months at the ICSM within the framework of a post-doctoral contract currently being recruited.

Concerning the iron recovery (WP3), the efforts will now focus on the initially proposed route 2 (iron recovery after selective extraction of rare earths).

Finally, the economic evaluation of the process will be developed within the framework of a PhD which starts on 01/10/2022 at AMSE.

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