CE04 - Innovations scientifiques et technologiques pour accompagner la transition écologique

Valorization and remediation of tailings from W-ores – VARTA

Valorization and remediation of tailings from W-ores

Mine tailings often have a dramatic environmental impact on the surrounding environment, rivers and groundwater. The treatment and recovery of tailings could be combined, with effective soil decontamination carried out at the same time as the extraction of metals from these secondary mines.

Innovative approach to recovering recoverable metals and managing arsenic

VARTA's key objective is to develop an innovative approach based on a dedicated treatment of mine tailings combined with a new hydrometallurgical process enabling the recovery of tungsten and potentially other valuable metals (gold, copper...), and the management of a hazardous element (arsenic) from the tailings of a former mine located in France. Firstly, reprocessing the tailings would enable the residual fraction to be recovered and purified to some extent. A first challenge lies in the surface alteration of the tailings following storage for several years, which could have a negative impact on the flotation concentration process. A second challenge is the very fine particle size of the residues, whereas current processes work for coarser particles.<br />An innovative process to extract both toxic (As) and recoverable (W) elements will be developed using double lamellar hydroxides (LDH), specific materials with anion exchange properties. The chemical properties of LDHs open the way to new treatment strategies combining leaching and separation in a single step, while improving separation performance. In particular, the possibility of extracting W and As by LDH in weakly acidic solution is a major advance that simplifies and reduces the footprint of chemical processes by combining leaching and separation steps, limiting the number of individual operations and improving recovery performance. Finally, the industrialization potential of the entire process will be assessed by combining residue economic value assessment, scaling-up of the complete process scheme, life cycle assessment (LCA) and techno-economic analysis (TE).

The project is structured into different tasks, each corresponding to a complementary approach: (1) sampling and characterization of residues, (2) production of a concentrate, (3) hydrometallurgical approach to extract tungsten and manage arsenic, (4) design of a process scheme including a techno-economic analysis.

Samples from a previous project were characterized in terms of chemical and mineralogical composition (phase quantification), particle size distribution and acid and neutralization potentials. Sulfide alteration and carbonate consumption processes with precipitation of new phases were documented. Sorting tests were then launched at BRGM's Pilot Hall, with the aim of concentrating tungsten and arsenic phases in an experimental design. The techniques tested to date are hydrocycloning and Falcon centrifugal gravimetric concentration, following the development of a sample preparation methodology. Initial results show fairly limited concentration rates, which will need to be improved by testing new parameters and protocols.
The leaching of pure scheelite, using either a commercial product or a ground mineral, was investigated. To dissolve this mineral in a weakly acidic medium and thus avoid the use of conventional processes with a high environmental footprint, the use of an anionic exchanger (LDH) was tested, either alone or in synergy with a calcium complexing agent. In both cases, the strategy was to shift the solubility equilibrium of scheelite. The use of a complexing agent (EDTA) had a noticeable effect, but also reacted with LDH. Conversely, proof-of-concept for LDH-assisted scheelite leaching in the absence of complexing agent was obtained, through the results of several pH-stabilized experiments. A literature study on the behaviour of arsenic under leaching conditions was also carried out, highlighting its leaching in the presence of EDTA, supporting our efforts to avoid the use of complexing agents.

Concentration tests will be continued in the coming months to optimize concentrate preparation and with material balance calculations.
The leaching conditions for scheelite and the composition of LDH remain to be optimized, along with additional characterizations to highlight the reactions taking place at the interface. Finally, tests on concentrates will be carried out to identify the role of accessory minerals on leaching performance.

- F. Ajami, D. Giaume, G. Lefèvre, « Extraction of tungsten from mine tailings: LDH- and EDTA-assisted scheelite dissolution », Goldschmidt 2023, 10-14 juillet 2023, Lyon (France)
- F. Ajami, D. Giaume, G. Lefèvre, « Utilisation d’un Hydroxyde Double Lamellaire pour l’extraction du tungstène des résidus miniers », Journées de l’Association Française de l’adsorption, 26-27 janvier 2023, Nancy
- G. Lefèvre, F. Ajami, M. Rakotomalala, « Extraction de métaux critiques à partir de ressources secondaires : complexité et opportunité de la chimie en solution des polyoxométallates », Journées Scientifiques du GDR Prométhée, 15-16 juin 2023, Nîmes

Mine tailings often have dramatic environmental impacts into the near environment, river and ground waters. Unfortunately, most of them were generated many years ago and historical mining companies do not exist any more to take responsibility for the remediation of soils. However, in some cases, treatment and valorization of the tailings could be smartly combined with an efficient ground depollution and such tailings could be upgraded as secondary mines of strategic metals, with an easier access to the ore compared to primary mines and lower energy consumption since already milled. VARTA aims to simultaneously meet both these goals in the case of the tailings of the Salau mine. Salau is a world class deposit which has been partially exploited between 1975 and 1986. The tailings (about 1 Mt) are stored in two piles, coming from a tungsten skarn-type or a vein-type ore. Arsenopyrite is present and could be a source of arsenic which can be leached out and contaminates the surface waters, especially from the oxidized part of the tailings. These tailings still contain about 0.4% of WO3 due to the initial richness of the ore, a higher grade than most of current tungsten mines, and gold between 1 and 3 g/t. Tungsten is on the EU 2020 list of Critical Raw Materials due to its growing world consumption and poorly substitutable nature and the valorization of old tailings could help Europe to be less dependent.
The key objective of the VARTA project is to develop an innovative approach based on a dedicated mineral processing treatment combined with a new hydrometallurgical process allowing the recovery of tungsten and potentially other strategic metals (gold, copper…) and the management of a hazardous element (arsenic) of the Salau mine tailings. First, the reprocessing of tailings would make it possible to recover value on one side and to purify the residual fraction to a certain extent on the other side. A challenge lies in the surface weathering of the tailings due to their stockpiling for several years, which could have a negative impact for the concentration process based on flotation. Then, an innovative process to extract both toxic (As) and valuable (W) elements with the use of layer double hydroxides (LDHs), specific materials with anion-exchange properties, will be developed. The chemical properties of LDHs open the door to new process strategies combining leaching and separation in a one-step operation, and at the same time improving the separation performances. In particular, the possibility to extract W and As by LDH in mild acid solution is a major breakthrough that simplifies and reduces the footprint of chemical processes by combining leaching and separation steps, limiting the number of individual operations and improving recovery performances. At last, the industrialization potential of the whole process will be assessed by combining the evaluation of the economic value of the tailings, the up-scaling of the whole process flowsheet, life-cycle analysis (LCA) and techno-economics (TE).
The valorization potential of the tailings, as a whole, will be provided to confirm the interest of the future management of these tailings. Such an approach could be mirrored on many old historical W mines and lead to satisfy both strategic metal recycling priorities and environmental restoration objectives, and contribute to developing new, more efficient mining strategies with fewer processing steps and reduced environmental impact.

Project coordination

Grégory LEFEVRE (Institut de Recherche de Chimie Paris)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

BRGM BUREAU DE RECHERCHE GEOLOGIQUE ET MINIERE
LGC Laboratoire de Génie Chimique
E-Mines E-Mines / Recherche et Développement
IRCP Institut de Recherche de Chimie Paris
CEA - ISEC/DMRC Commissariat à l'Energie Atomique et aux Energies Alternatives - Centre de Marcoule

Help of the ANR 714,534 euros
Beginning and duration of the scientific project: March 2022 - 42 Months

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