Proceedings ION4RAW final workshop: Exploring Raw Material Insights and Industrial Prospects

2 January 2024 Zahra

Article written by Ioana Pristavu | PNO Innovation

On 30 November 2023, the ION4RAW project organised its final event – “Exploring Raw Material Insights and Industrial Prospects”, which marked a pivotal moment as it opened its exploitation event to the public. Introduced by Nader Akil (Operations manager at PNO Innovation Belgium) and Maria Tripiana Serrano (Division Manager in the Chemical department at IDENER and coordinator of the ION4RAW project), the event focused on two objectives. Firstly, it aimed to present the outcomes and the findings derived from the extensive research work carried out in the framework of the project. Secondly, the event facilitated in depth discussions on the perspectives and challenges associated with the application of Deep eutectic solvents (DES) in Metallurgy.

Following the coordinator’s introduction, which outlined the main objective of ION4RAW – to develop a new energy- and material-efficient mineral processing technology to recover by-products from primary sources by means of innovative Deep Eutectic Solvents (DES) ionic liquids and advanced electro-recovery using a one-reactor system, the event dived into the technical presentations providing a comprehensive overview of ionometallurgical process development, and an outline of the upscaled process.

Outcomes of the ION4RAW project

Leaching

Ainhoa Unzurrunzaga, researcher at TECNALIA (Spain) explained the main objective of collaborative research focused on investigating and fine tuning of the leaching, the separation and the purification processes to selectively recover targeted metals [silver (Ag), tellurium (Te), cobalt (Co), selenium (Se), indium (In), antimony (Sb) or bismuth (Bi)] using ionometallurgical processes. The process development was divided in specific tasks, from the mineralogical characterisation of the product materials, to assessing dissolution behaviour and kinetics in DES, establishing the solution speciation and effects on contaminants, and finally exploring various recovery methodologies.

Ainhoa outlined the main characteristics of DES and their advantages in comparison to conventional metallurgical processes, mentioning here reduced resources usage (energy, water), rapid preparation, availability of commercial precursors, electrochemical stability, and often lower toxicity. The various types of DES prepared by TECNALIA were based on choline chloride, mixing with different hydrogen bond donors (HBD). Their research involved nine materials (in the form of sulphide concentrates rich in Cu, Pb, Zn, Au and Ag) sourced from five different mines.

The research team at TECNALIA tested various DES with diverse chemistries and with diverse ores, focusing their presentation on the results obtained with concentrate extracted from Peru’s El Porvenir mine. With this ore, apart from different DES chemistries, researchers studied the addition of an additive and oxidant and the effect of the DES/solid ratio, amongst other parameters. Their findings revealed that the composition of DES, along with other parameters, significantly influence metal dissolution. Adding an oxidant and an additive improved the recovery rates, but simultaneously rendered the extraction process less selective. This conclusion opened further investigations into adjusting different parameters, such as the quantity of additives.

The DES-system displaying the most promising balance between recovery and target metals concentration, and showing low amount of main metals and suitability for subsequent electrowinning process, was later optimised. Under the most suitable operating conditions, researchers reported the following recovery rates: over 81% Ag and Te, 97% Bi, around 30% Sb and In.

Electrochemical recovery

During the ION4RAW exploitation event, Gøril Jahrsengene, Research Scientist at SINTEF (Norway), explained the electrowinning process using DES with dissolved metals post-leaching. The objective lay in determining the electrochemical stability window by identifying the range of electroactive species and redox behaviour occurring during the process. Researchers established the process limitations, mainly contingent on the oxidation state in DES, the presence of numerous metals with different concentrations, and the anode reaction, ensuring the solvent can be further recycled. Initial leaching experiments conducted at TECNALIA’s premises at small scale, followed by small scale electrolysis experiments conducted at SINTEF’s facilities at 60 °C, aimed to improve the electrochemistry. The results showed high concentrations of Ag ad Bi in the produced metal at this scale.

Upscaling experiments using 1 kg of concentrate (pre-leaching) aimed to obtain a Ag-Sb-Bi-Te alloy with small contribution of Cu, and no Pb, after electrowinning. Researchers improved the current efficiency from 30-40% to 50-55% while maintaining similar levels of metal depletion, by optimising the leaching conditions. The resulting alloy contained high amounts of Bi (~ 50-60%) in contrast to other metals (around 20% Ag, 5% Sb, 3% Te, 5-20% Cu), with minimal lead detected (2% Pb).

Looking at the opportunities window, researchers concluded that batch electrolysis using this specific concentrate could yield metal alloys with more than 80% of target elements (Ag, Sb, Bi, Te) along with traces of Cu. This significant improvement indicated the potential to produce metal alloys with relatively high concentrations of target metals from low initial concentrations present in metal sulphide ores. Further altering the current density, researchers produced additional alloys with higher Ag concentrations compared to Bi.

Moreover, different ores may yield different combinations of metals and DES concentrations after leaching. Understanding the electrochemical reactions for the relevant metals enables replication across other systems. Gøril outlined several optimisation scenarios with potential to produce single metal or simpler alloys, highlighting a pool of opportunities for future research initiatives.

Chemical recovery and residual solid valorisation

Cristina Salazar Castro, chemist at LUREDERRA (Spain) focused her presentation on the diverse input materials and their varying elemental compositions, particularly highlighting the outputs extracted from Peru’s El Porvenir mine. Cristina described the sequential chemical steps aimed at recovering various target metals like Ag, Te and Bi. The methodology involved initial precipitation steps, followed by a two-step separation process using additional sodium hydroxide (NaOH) to adjust the pH, and a subsequent precipitation step using thiosulfate. This phase facilitated a premature separation of various metals present in the solution, notably Te and Bi. Subsequent rounds of precipitation processes revealed presence of Bi compounds (oxides or hydroxides), but also traces of Cu and Cd. By describing this multi-step separation chemical process, Cristina emphasised the potential of this complementary route for recovering Ag, Te and Bi.

Additional to the chemical route, LUREDERRA’s focus extended beyond chemical recovery; researchers explored valorising the residual solids obtained post-filtration by repurposing them as concrete fillers. Tests conducted during the revalorisation processes confirmed that all particle ranges can be further exploited in the construction sector, without altering the curing concrete process.

To underscore ION4RAW’s commitment to sustainability and circularity, researchers at LUREDERRA and TU Freiberg have been optimising the solvent’s recyclability by removing the leached metals and reducing the amount of water in the DES. These conclusions align with ION4RAW’s overarching goals supporting sustainable mining solutions – recovery of valuable elements from secondary sources by chemical routes, solid waste valorisation and DES reuse.

Pilot plant advances and overview of the upscaled process

After introducing the specific objectives of the process upscaling, Laura Sanchez Cupido, researcher at TECNALIA, revisited the main stages of the ION4RAW process development, highlighting the progression from TRL 3 to TRL 5. During this last stage of the project, partners are designing and building the pilot plant, working on the optimisation and validation of leaching and electrochemical recovery process, alongside products characterisation.

The innovative aspect of the ION4RAW project lies in its objective to design a process using one main reactor that could cater to a diversity of streams and could perform both the leaching and the electrowinning processes. Initial pilot-scale leaching tests processed seven batches (24 kg) of the concentrate extracted from Peru’s El Porvenir mine in 180 L of leaching media. Progress in parameter optimisation ensured controlled temperature (around 45°C) and a filtration time up to 15-20 minutes; optimisation of other parameters in the pilot plant set up allowed also a significant reduction of oxidant usage without compromising efficiency. Promising initial results showed satisfactory recovery rates for Ag, Bi and Te.

Anticipating the electrowinning tests, joint efforts of TECNALIA and SINTEF focused firstly on the leachates’ characterisation to identify electrodeposition potentials and current densities. Initial electrowinning trials reported deposits of Ag, Bi, Te, Sb and Cu in ranges similar to the lab scale. Researchers’ work is now focused primarily on optimising the conditions to improve the recovery rates, with a final objective to produce 100 L leachate and electrowinning of target metals at optimum conditions.

Finally, Laura provided an overview of the ION4RAW process outlining the advantages, but also the challenges that research still needs to address to optimise DES application in extractive metallurgy. Pilot scale trials showed various benefits of using DES over conventional processes, including low temperature atmospheric pressure, milder leaching medium for sulphide ores, compatibility with existing components and chemicals, as well as acceptable viscosity levels which allow the use of same equipment and same processing times and losses as when aqueous media are used. Looking at improvement opportunities, certain challenges persist, notably the need to reduce the oxidant and additive quantities and improve the partial selectivity, which is highly dependent on the composition of the raw material.

Applications of Deep Eutectic Solvents in Metallurgy – Perspectives and Challenges session

The second part of the event gathered esteemed speakers from the research and academic backgrounds, not only with proven expertise in DES, but also with practical examples of successful EU-funded projects. This session was inaugurated by Univ.Prof.in Dipl.-Ing. Dr.in techn. Katharina Schröder, who presented “Critical raw material recovery: TU Wien’s approach in the PLATIRUS project”. Officially declared a success story by the European Commission in 2022, PLATIRUS developed a business plan based on its novel flowsheet for the recovery of platinum group metals (PGMs) from secondary resources, such as spent autocatalysts. These PGMs recovered from waste, using a combination of innovative technologies (such as microwave assisted leaching, ionic liquid-based liquid-liquid extraction and gas-diffusion electrocrystallisation), can be used to manufacture new autocatalysts with similar or better performance than commercial ones. TU Wien’s role in the project was to develop a leaching process with alternative solvents. The research team investigated various solvents, like ionic liquids (IL), DES, supercritical fluids. Finally, the team at TU Wien pursued further research on PGM leaching with choline-based DES [More information about the results of the research can be found in open access in the scientific paper “Benign recovery of platinum group metals from spent automotive catalysts using choline-based deep eutectic solvents”], Liquid-Liquid separation using DES and IL combined processes, and Solid-Liquid separation. Within the latter process, researchers investigated further the development of selective sorbent materials on solid phase for the recovery of Pt, Pd and Rh under relatively mild conditions and the development of a strategy to separate these materials in an aqueous solution, with the final target to remove all interfering elements and simultaneously reduce the use of IL. The most benign leaching route used a mix of hydrochloric acid (HCl) and hydrogen peroxide (H₂O₂), working at 65°C for approx. 3 hours. The Pd-rich leachate was later loaded on the support material developed in the project, under various parameters, with the aim to enhance the retention of target elements. Finally, two consecutive striping steps allowed initially to remove the interfering metals (Al in large quantities), and consequently to separate Pd and Pt from the solid material, to obtain high purities.

The event featured a second success story of: CROCODILE – showcasing innovative metallurgical systems based on advanced technologies for the recovery of cobalt (Co) and the production of Co metal and upstream products from a wide variety of secondary and primary European resources. Introduced by Dr. Lourdes Yurramendi, experienced chemist at TECNALIA, the presentation focused on the chemical treatment, phase that facilitated the pilot scale-up. At lab scale, CROCODILE flowsheet involved the black mass treatment using DES leaching, liquid/liquid extraction using solvometallurgy, and finally electrowinning to achieve the final metallic Co. Dr Yurramendi underlined CROCODILE’s success in employing advanced technologies to optimise Co recovery and metal production, while enhancing sustainability through comprehensive LCA and LCC assessments and efficient resource utilisation:

DES recycling was achieved for up to ten cycles
Low operation temperatures (up to 55°C) while maintaining high stability
Viscosity concerns were addressed by using a DES-based leaching system mixed with water

Based on the breakdown of the operating expenditure (OPEX) at lab scale, 90% of the expenses were allocated to raw materials, with 7% attributed to energy consumption. Additionally, 36% of the raw materials were released to the DES leaching process. During the validation of the pilot at TRL7, a total of 1000 kg black mass containing 25% Co content underwent testing. The daily production yielded over 6 kg Co, with a purity exceeding 97%. Considering the comparatively slower development pace of the recycling industry in contrast to the European battery sector, the DES-based CROCODILE technology stands as a promising route. It offers an opportunity for further optimisation, positioning itself as an encouraging recycling technology on the European market.