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SOLCRIMET Report Summary

Project ID: 694078
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - SOLCRIMET (Solvometallurgy for critical metals)

Reporting period: 2016-09-01 to 2018-02-28

Summary of the context and overall objectives of the project

The ERC Advanced Grant SOLCRIMET targets solvometallurgical solutions for the selective recovery of critical metals from end-of-life waste streams, using environmentally-friendly solvents. Solvometallurgy is the extraction of metals from ores, tailings, industrial process residues, production scrap and urban waste using non-aqueous solutions. Solvometallurgy differs from hydrometallurgy by the absence of a discrete water phase. The solvents are either organic or inorganic solvents (excluding water). Sustainable solvometallurgical processes must be based on green solvents. Therefore, toxic or environmentally harmful solvents must be avoided. Most of the unit processes in solvometallurgy are very similar to those in hydrometallurgy, with the main difference being that the water is replaced by a non-aqueous solvent. Solvometallurgy is complementary to pyrometallurgy and hydrometallurgy. However, this new approach offers several advantages. Firstly, the consumption of water is very limited offering a major advantage in regions where there is a shortage of water. Secondly, the leaching and solvent extraction can be combined in a single step, which leads to simplified process flow sheets. Thirdly, solvent leaching can be more selective than leaching with acidic aqueous solutions, leading to reduced acid consumption and less purification steps. Fourthly, solvometallurgy is useful for the treatment of ores that are rich in soluble silica (such as eudialyte) as no silica gel is formed. Hence, solvometallurgy is in a position to help develop near-zero-waste metallurgical processes, and with levels of energy consumption that are much less than with high-temperature processes.

SOLCRIMET Highlights:
• For most of its hi-tech applications (smart phones, electronics…) and cleantech applications (wind turbines, electric cars…) Europe is heavily dependent on countries like China who dominate the productions of the metals that are needed for these applications.
• In case a metal is economically very important and it suffers from a high supply risk (meaning that the easy supply of this metal can be blocked), such a metal is called a “critical metal”.
• To become less dependent on countries like China for these critical metals, Europe needs to develop novel technologies that are able to remove and recover the critical metals that are present in End-of-Life products that are available in Europe, such as End-of-Life electric cars, smart phones or wind turbines.
• SOLCRIMET develops new technology, based on environmentally-friendly, non-water nor acid-containing solvents that selectively recovers critical metals from a diversity of End-of-Life products.
• SOLCRIMET will make sure that the development and production of hi-tech and clean-tech products in Europe will become less dependent on the import of expensive, critical metals from countries like China.
• SOLCRIMET will contribute to the required transition from the present, fossil fuel based linear economy towards a climate-friendly, circular economy in Europe.

SOLCRIMET Objectives:
The overall objective of SOLCRIMET is to develop a new, metallurgical approach – i.e. solvometallurgy – that can be applied to different types of pre- and post-consumer waste in order to recover the following critical metals: the rare earths, tantalum, niobium, gallium, indium, germanium and antimony. This processing must be environmentally friendly, economically viable and produce metals of acceptable purity. The achievement of the main objective is built on four sub-objectives:
• New routes for dissolving metals and alloys in organic solvents;
• New ways to separate metal chlorides based on differential solubility in organic solvents;
• New paths to purify critical metals using two mutually immiscible organic solvents;
• New techniques for refining critical metals in an electrolytic cell using organic solvents.
Achieving these four sub-objectives will lead to a new paradigm in recy

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Metals and alloys can be dissolved in organic solvents by first oxidising them with chlorine gas to metal chlorides. The choice of chlorine as a halogen, rather than bromine or iodine, is justified by the lower price and wide availability of chlorine, its higher reactivity and the fact that the critical metals of interest form more stable chloride than bromide or iodide complexes. Chlorine gas is much more soluble in organic solvents than in water, and especially in polar aprotic solvents such as DMF or acetonitrile. Due to its high reactivity, chlorine can react with organic solvents, so that the dissolution tests need be carried out at low temperatures. Alternatively, halogenated organic solvents such as tetrachloroethylene can be used, although this is not the best choice from an environmental point of view. For this reason, SOLCRIMET is focusing on trichloride ionic liquids, i.e., ionic liquids with the Cl3- anion. Ionic liquids are special solvents that consist entirely of ions. These trichloride ionic liquids are very interesting because of their high concentration of dissolved chlorine and because they are more reactive towards metals than tribromides and triiodides. Trichloride ionic liquids can ensure the safe storage of chlorine gas at atmospheric pressure, yet they are reactive towards metals. A series of trichloride ionic liquids with different cations have been synthesised and characterised in order to find the systems with the lowest melting points and viscosities. The trichloride ionic liquids could conveniently be prepared by bubbling chlorine gas through the corresponding chloride ionic liquids. The most promising ionic liquid was found to be tributyl(tetradecyl)phosphonium trichloride, [P444,14][Cl3]. A total of 12 metals were selected for dissolution tests: iron, copper, indium, zinc, gallium, antimony, gold, platinum, germanium, tantalum, samarium and dysprosium. Most of these metals, including gold, dissolved fast in the ionic liquid. Other metals such as tantalum and platinium could not be dissolved in these ionic solvents, so that selective dissolution can be used for separation of metals. Also gallium arsenide and indium arsenide (important semiconductor compounds used for instance in LEDs) could be dissolved in the trichloride ionic liquids. Further research on the dissolution in the metals and alloys in the trichloride ionic liquids is ongoing.
Solvent extraction is a very important technique in hydrometallurgy for the separation and purification of metals, such as the rare earths, platinum-group metals, cobalt, nickel, copper and uranium. In conventional solvent extraction, metal ions are distributed between an aqueous phase and a water-immiscible organic phase. At equilibrium, the ratios of the concentrations of the metal ion in the organic phase and the aqueous phase are different for different metal ions. This is the basis for the separation of mixtures. SOLCRIMET extends solvent extraction to non-aqueous solvent extraction in which the metals are distributed between two immiscible organic phases. Non-aqueous solvent extraction can offer some important advantages. There is the opportunity to carry out extractions that cannot be done efficiently in an aqueous solution. An example is the extraction of rare-earth ions from chloride solutions. These ions cannot be extracted by anion-exchange extractants, because rare-earth ions do not form anionic chloro complexes in water, even with very high chloride concentrations. In contrast, anionic chloro complexes do form in polar organic solvents. The extraction mechanisms are often different in aqueous and non-aqueous solvent-extraction systems. These differences in the mechanisms can be exploited to develop new, highly selective separation processes. A large series of different solvent pairs have been tested for use in non-aqueous solvent extraction. The solvent pairs must fulfil the following requirements: (1) the formation of two phases after mixing and s

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

From a science/technology point of view, SOLCRIMET challenges existing paradigms and explores uncharted territory for the recycling of critical metals. SOLCRIMET creates new metallurgical systems for the recovery of critical metals from urban mines. The work can inspire other researchers to enter the field of solvometallurgy and invent other, complementary, solvometallurgical methods. Chemical engineers can further develop the processes to continuous closed-loop processes and work on the recycling of the solvents. The project gives new insights into the fundamental chemistry of polyhalide ionic liquids and polyhalide compounds in general, in the solvation of metal ions in organic solvents, and the coordination chemistry in non-aqueous solvents. SOLCRIMET explores the field of non-aqueous solvent extraction, i.e., solvent extraction with two mutually immiscible organic phases. This offers opportunities for designing new separation and purification methods for many metals, not only the critical metals targeted in this study. The project is developing other methodological approaches than the non-aqueous solvent extraction, such as electrorefining in organic solvents, the use of liquid electrodes, as well as high-pressure electrolysis cells. The success of the project will open up new horizons for the recycling of critical metals. By focusing on these critical metals – which are also essential for the transition to a low-carbon economy – SOLCRIMET comprehensively addresses the “Climate action, environment, resource efficiency and raw materials” Grand Societal Challenge of the EU, while it also assists in addressing the Grand Societal Challenges related to clean energy and transport. Given the present major concerns about the supply of critical metals in Europe, a project focusing on the development of new approaches to the recovery of metals from production scrap and end-of-life consumer goods is timely.

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