End-of-life or scrap Sm-Co permanent magnets are a valuable resource of cobalt, samarium, copper and iron. A solvometallurgical recovery route for indirect recycling of Sm-Co permanent magnets was developed by SIM² KU Leuven SOLVOMET researchers. The method is based on non-aqueous solvent extraction to minimize water consumption. The work is published in Separation and Purification Technology. (MO/PTJ, Leuven, 25/03/2019)

SmCo magnets

End-of-life or scrap Sm-Co permanent magnets are a valuable resource to recover cobalt, samarium, copper and iron. Interestingly, the most valuable metal from Sm-Co permanent magnets is not the rare-earth samarium, but cobalt, a transition metal. Indirect recycling allows to differentiate the end applications of the recovered metals, especially of cobalt whose demand for electric-vehicle batteries is rapidly increasing.

New solvometallurgical recovery route

A solvometallurgical recovery route (cf. position paper on this branch in extractive metallurgy) was developed with the aim to recycle Sm-Co permanent magnets, while minimizing the water consumption. In fact, the Sm-Co permanent magnets were leached in a 2 mol L^−1 hydrochloric acid solution in ethylene glycol, after a step of crushing and milling to powder size. Afterwards, cobalt, copper and iron were extracted from the leachate with 50 wt% Aliquat 336^® in toluene, which was pre-saturated with 37 wt.% hydrochloric solution.

Parameters optimized for the solvent extraction of the transition metals were: the temperature, the feed/solvent ratio and the hydrochloric acid concentration. The extraction kinetics were also studied as well as the required number of stages for upscaling in mixer-settlers, this last through the construction of McCabe-Thiele diagrams.

Cobalt was stripped from the loaded solvent by a 0.5 mol L^−1 aqueous hydrochloric acid solution. A 5 vol.% aqueous ammonia solution served to strip copper and to precipitate iron. whereas iron precipitated under these conditions.

The solvent could be reused after regeneration, i.e. evaporation of water and ammonia and reintegration of toluene and hydrochloric acid. Samarium was recovered from the hydrochloric acid-ethylene glycol raffinate by extraction with 20 vol.% Cyanex 272 in n-dodecane, followed by precipitation stripping with a 0.2 mol L^-1 aqueous oxalic acid solution. The purity of the recovered cobalt chloride was 98.3 wt% and that of samarium oxalate was 99.4 wt%.

Biography Martina Orefice

Martina Orefice graduated in Environmental Sciences (BSc) in 2010 and in Chemical Engineering (BEng) in 2012 and (MEng) in 2015 at the University Federico II of Naples (Italy), her birth-city. Passionate for environmental issues thanks to a board game in her childhood, Martina aims to be a professional in secondary raw materials and circular economy.

Acknowledgements

The research leading to these results received funding from the European Community’s Horizon 2020 Programme ([H2020/2014-2019]) under Grant Agreement no. 674973 (MSCA-ETN DEMETER) and from the European Research Council (ERC) under the European Union’s

Horizon 2020 Research and Innovation Programme: Grant Agreement 694078—Solvometallurgy for critical metals (SOLCRIMET). This publication reflects only the authors’ view, exempting the Community from any liability. The authors want to thank Magneti Ljubljana d.d. (Slovenia) for providing the SmCo permanent magnets, Tony Debecker and Kevin Wierinckx for crushing the magnets, Dr. Jeroen Jordens for the particle size measurements, Dr. Jeroen Sniekers for the SEM and EDS analysis, Dr. Nagaphani Kumar Batchu for the very helpful discussion and Dr. Bieke Onghena and Dr. Peter Tom Jones for reviewing and editing the manuscript.

On February 5-7, 2019, the DEMETER Concluding Symposium took place in Leuven. Around 70 experts from 38 organisations and 11 countries participated in the debate about the future of Electric Vehicles and the role of rare-earth permanent magnet phases and motors. They also discussed the criticality of rare earths. Presentations and photos are now available. (Peter Tom Jones, Leuven, 20/02/2019)

Presentations and photos

The presentations from the symposium can be found here: https://lnkd.in/dRFPvuP. Photos of the event are here: https://lnkd.in/e3crBTC. In the near future the DEMETER & SIM² KU Leuven teams will publish a Policy Brief on the Lessons Learned. Thanks to Allan Walton for moderating the debates and Asst. Prof. Kristina ŽuŞek RoŞman, Sofia Riano, Peter Rasmussen and Jose R. Garcia Santamaria for chairing the various sessions.

Rationale for the Symposium

The DEMETER Symposium featured a high-quality, “beyond-science-only” programme on rare-earth permanent-magnet motors and the e-mobility revolution. The three-day Symposium provided the floor to invited international experts from industry, academia and the European Commission, as well as the early-stage researchers from the ETN DEMETER project who will present their final results (watch the DEMETER video here). The Symposium included two exciting panel discussions, which stimulated a wider societal debate about the transition to a low-carbon mobility system, the requirement of critical metals (incl. rare earths), the Social License to Operate to mine and/or recycle critical metals, as well as the geopolitical aspects of rare earth sourcing. The Symposium was a co-organisation of DEMETER, SIM² KU Leuven and GloREIA.

Within the EU H2020 REMAGHIC project, KU Leuven developed a process to recover yttrium and europium from a mixed oxide obtained by the processing of lamp phosphor waste based on solvent extraction with undiluted thiocyanate ionic liquids. The work is published in the Journal RSC Advances. (Leuven, 18/2/2019)

Spent fluorescent lamps contain a significant amount of the rare earths yttrium and europium, which are present, in particular, in the red phosphor YOX as oxides (Y₂O₃:Eu³⁺). Because the market demand for phosphors has moved to LED lamps, a lot of waste phosphor becomes available and the mutual separation of yttrium and europium is required for their use in other applications.

In this paper we propose an alternative approach compared to the conventional solvent extraction to separate yttrium and europium which is based on the use of undiluted ionic liquids, namely Cyphos IL 101 and Aliquat 336 thiocyanate. The main advantages of this approach are the use of non-volatile and non-flammable organic solvents and the limited number of process steps required to the desired separation.

We observed that the best extraction performances are obtained with [C101][SCN], by using four counter-current extraction stages. The loaded organic phase was afterwards subjected to scrubbing (with a solution of CaCl₂ and NH₄SCN) to remove the co-extracted europium. Yttrium was then stripped by deionised water. Yttrium and europium were finally recovered as hydroxides by precipitation with ammonia and then calcined to the get the corresponding oxides.

The process was first developed by using synthetic solutions and afterwards applied on a leachate obtained from the dissolution of a real mixed oxide. The research presented in this manuscript is relevant also for the recovery of rare earths from end-of-life cathode-ray tube (CRT) phosphors.

Figure 1: Yttrium and europium are separated from a mixed oxide through solvent extraction with undiluted thiocyanate ionic liquids.

Full reference paper

R. Banda, F. Forte, B. Onghena, K. Binnemans, Yttrium and europium separation by solvent extraction with undiluted thiocyanate ionic liquids, RSC Advances, 2019, 9, 4876.

Biography Raju Banda

Raju Banda worked as postdoctoral fellow at (SOLVOMET) KU Leuven, Department of Chemistry. His main interests are in the field of hydrometallurgy and ionometallurgy. In particular, he was involved in the development of solvent extraction processes for rare earths recovery from lamp phosphor waste.

Acknowledgements

This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No 680629 (REMAGHIC: New Recovery Processes to produce Rare Earth-Magnesium Alloys of High Performance and Low Cost) (project website: http://www.remaghic-project.eu).

More info?

More information about REMAGHIC, can be found in this interview here.

Researchers at SIM² KU Leuven have developed a new method to recover metals from spent samarium-cobalt magnets. The procedure involves oxidative dissolution of these metals in trichloride ionic liquids, followed by metal removal from the leachate with a series of stripping steps. The ionic liquids can be reused for the next cycles after their regeneration. The work is published in the Journal ACS Sustain. Chem. Eng. (PTJ/SL, Leuven 28/1/2019)

SmCo magnets

SmCo magnets are used mainly for high-temperature applications due to their high coercivity (resistance to demagnetisation), good corrosion resistance and excellent thermal stability. the global SmCo magnets market is growing thanks to new applications in consumer electronics, automotive and medical technology, aerospace and military equipment. Recycling of SmCo magnets can lower the supply risk of samarium and cobalt, close the materials loop (circular economy), and reduce the environmental issues associated with primary mining and ore processing.

New method to recover metals from spent SmCo magnets

In this work, a trichloride ionic liquid trihexyltetradecylphosphonium trichloride, [P_666,14][Cl₃], which can safely store chlorine gas in the form of the trichloride anion, was synthesized and employed as a reactive solvent for the recycling of SmCo magnets. The dissolution efficiency has been studied by varying the volume fraction of [P_666,14][Cl₃] in [P_666,14]Cl (the latter as an additional source of coordinating chloride ions), the solid-to-liquid ratio and the temperature.

Stripping of metals from the loaded IL was studied with different aqueous solutions, followed by a reusability study of the ILs. In the end, a conceptual process flow sheet (Figure 1) was developed for the recovery of metals from SmCo magnet using a trichloride ionic liquid in which single-element aqueous streams are obtained and the IL is recycled.

Oxidative dissolution of metals in trichloride ILs is easily transferable to the recycling of valuable metals from other end-of-life products such as neodymium−iron−boron magnets and nickel metal hydride batteries.

Bio lead author

Xiaohua Li is a postdoctoral researcher working with Prof. Koen Binnemans in the SOLVOMET Group at KU Leuven. She obtained her doctor degree from university of Twente in the Netherlands in February 2017 and started her work on ERC SOLCRIMET project in KU Leuven from November 2016. Her main research interests include separation technology, solvent extraction, leaching, solvometallurgy and ionic liquids.

Full reference paper

Li, X.; Li, Z.; Orefice, M.; Binnemans, K. Metal Recovery from Spent Samarium–Cobalt Magnets Using a Trichloride Ionic Liquid. ACS Sustain. Chem. Eng. 2019, 7 (2), 2578-2584.

Acknowledgements

The research leading to these results received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme: Grant Agreement 694078 – Solvometallurgy for critical metals (SOLCRIMET) and from the European Community’s Horizon 2020 Programme ([H2020/2014-2019]) under Grant Agreement 674973 (MSCA-ETN DEMETER).

New PhD on innovative technologies for REE recovery from bauxite residue

On January 23^rd, 2018, Rodolfo Marin Rivera obtained his PhD degree in Chemical Engineering. He successfully defended his PhD thesis entitled ‘Innovative technologies for rare earth element recovery from bauxite residue‘. (Leuven, 23/01/2019)

The research was supervised by Prof. Tom Van Gerven (promoter), Prof. Koen Binnemans (co-promotor) and Dr. Ghania Ounoughene (co-promotor). Dr. Marin Rivera obtained his degree in the framework of the European Training Network for Zero-Waste Valorisation of Bauxite Residue (REDMUD). A list of the peer-reviewed papers published in the framework of his PhD can be found below. The full text of the thesis will become available once all research results have been officially published in the peer-reviewed literature. Dr. Marin Rivera is continuing his research career as a postdoc in the group of Prof. Tom Van Gerven, where he works on the synthesis of precipitated calcium carbonate from waste materials.

Abstract

Bauxite residue is a by-product in the Bayer process of alumina production from bauxite mineral ores. Disposal and long-term storage of this waste volumes occupy a lot of land. Additionally, the high alkalinity of bauxite residue is the main environmental concern. Some treatments already exist to further utilize this bauxite residue. However, bauxite residue also contains valuable metals such as rare-earth elements (REEs), in minor but non-negligible concentration.

Different studies have already been performed to consider a possible recovery of REEs, scandium in particular. Direct acid leaching is a commonly applied method with differences in the specific operational conditions. However, these methods have demonstrated low extraction yields and/or selectivity, which limit their application at an industrial scale. Thus, the main objective of this PhD Thesis was the development of innovative hydrometallurgical methods in order to overcome the main disadvantages of leaching processes reported in the literature, i.e. consumption of large amounts of acid during neutralization of the alkaline bauxite residue, the high co-dissolution of major metals that affects the efficiency of the separation process (e.g., solvent extraction or ion exchange), and the decomposition of silicate compounds that leads to the polymerization of amorphous silica.

The treatment of bauxite residue by dry digestion with multi-stage circulation of the leach solution appears to be economically the most interesting leaching alternative. The process allows to reduce significantly the volume of effluents due to the low amount of water required for the process. Gel formation does not occur and titanium can be recovered simultaneously with the REEs. High-pressure acid leaching of slag from bauxite residue smelting also avoids the polymerization of silica gel, but titanium remains in the solid residue after leaching. These processes must be studied further as part of an integrated extraction-separation process, so that a comprehensive cost analysis can be obtained to assess the feasibility and viability of the processes for the recovery of REEs from bauxite residue.

Publications by Rodolfo Marin Rivera in the framework of his PhD

M. Rivera, B. Xakalashe, G. Ounoughene, K. Binnemans, B. Friedrich, T. Van Gerven. High pressure acid leaching of slag from bauxite residue smelting in view of selective rare-earth elements recovery. Hydrometallurgy, In press.

R.M. Rivera, G. Ounoughene, A. Malfliet, J. Vind, D. Panias, V. Vassiliadou, K. Binnemans, T. Van Gerven. A study of the occurrence of selected rare-earth elements in neutralised-leached bauxite residue and comparison with untreated bauxite residue. Journal of Sustainable Metallurgy, In press.

R.M. Rivera, B. Ulenaers, G. Ounoughene, K. Binnemans, T. Van Gerven (2018). Extraction of rare earths from bauxite residue (red mud) by dry digestion. Minerals Engineering, 119, 82-92.

R.M. Rivera, G. Ounoughene, C.R. Borra, K. Binnemans, T. Van Gerven (2017). Neutralisation of bauxite residue by carbon dioxide prior to acidic leaching. Minerals Engineering, 112, 92-102.