Valorization and remediation of tailings from W-ores – VARTA

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.

The work focused on the assessment, treatment, and valorization of tungsten-rich mining residues, particularly in France and at the Salau site. The use of historical data and archival documents enabled the development of interactive maps identifying former mining sites and their metalliferous potential. Each site was assigned an interest score, facilitating the identification of residual resources, associated environmental risks (arsenic, heavy metals, radioactivity), and opportunities for remediation or economic valorization.

Mineral processing studies show that scheelite recovery strongly depends on particle size and degree of liberation. Falcon UF-type centrifugal gravity separators enable the recovery of more than 70% of liberated scheelite, but exhibit limitations for very fine particles (< 5 µm). Good separation performances were achieved for arsenopyrite, in contrast to iron oxy-hydroxides, which limits arsenic recovery. The best processing flowsheets tested produced a WO₃-enriched concentrate with a recovery close to 60%.

An innovative probabilistic process simulation methodology based on automated quantitative mineralogy data was developed. It incorporates sampling and particle size uncertainties through bootstrap techniques and Monte Carlo simulations. The results show that conventional deterministic approaches tend to overestimate process performance, highlighting the value of explicitly accounting for uncertainties in decision-making.

In parallel, extractive chemistry studies demonstrated the effectiveness of layered double hydroxides and carboxylic acids for scheelite dissolution, with oxalic acid being the most reactive but also associated with arsenic release. Environmental assessments (LCA) indicate that residue reprocessing increases environmental impacts compared with leaving the residues inert, despite its benefits in terms of tungsten recovery. Economic analyses nevertheless show that the alkaline process is the most profitable, even under moderate APT price conditions.

Finally, studies on weakly oxidized residues confirm the need for preliminary washing steps and show that carbonate leaching achieves tungsten recoveries close to 50%, with fewer constraints than acidic processes.

Tests carried out using various separation techniques based on the physical properties of particles showed that these methods do not allow for the selective separation of arsenic-bearing minerals. In order to overcome this bottleneck, it appears relevant to conduct tests using a technique based on the physico-chemical properties of the particles. In particular, it would be of interest to assess flotation performance using equipment specifically designed for the flotation of ultra-fine particles. Indeed, as conventional flotation is not effective for separating particles smaller than 40 µm, it is essential to use dedicated devices such as the Imhoflot G-Cell reactor, which is designed for the flotation of particles smaller than 20 µm.

The perspectives identified regarding probabilistic simulation of mineral processing flowsheets based on automated quantitative mineralogy data focus on the full integration of the methodology into a process simulation software relying on advanced phenomenological models, as well as on the improvement of certain assumptions, particularly with respect to the detailed modelling of separators and stereological corrections of MLA data. In this respect, the project represents a structuring step toward realistic and robust probabilistic geometallurgical simulation.

With regard to tungsten purification in carbonate media, investigating separation either using ion-exchange resins or liquid–liquid extraction appears relevant, with the dual objective of process simplification and concentration during elution or stripping stages.

In addition to the phase separation models developed by LGC, it appears relevant to consider models in the various required technical domains: process optimization (PROSIM), life cycle assessment (a parametric model adaptable to target elements and encountered pollutants), and techno-economic analysis (the COUPRO tool currently being deployed at CEA), all of which could be adapted to different types of primary or secondary resources.

- 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.