General theme: In this Research Line the focus is on developing sustainable metallurgical processes that can be integrated into near-zero-waste flow sheets for the production, recovery and recycling of base and critical metals such as iron and steel, copper, zinc, nickel, cobalt, lead, rare earth metals and precious metals. The Research comprises both pyro/electrometallurgical and hydro/solvometallurgical unit processes. The experimental work covers the full range from lab to pilot and industrial scale and is supported by advanced characterisation techniques (cf. Research Line 1) and modelling approaches. The explicit goal is to develop processes with the lowest possible footprint in terms of CO2 emissions, energy, water and/or use of chemicals. To corroborate the advantages the processes are benchmarked with state-of-the-art industrial processes. This Research Line is fully synchonised with the clean energy and smart moblity targets set forth in the European Green Deal (EC,COM(2019)640) and A New Industrial Strategy for Europe (EC,COM(2020)102).
Slag is a partially or fully liquid oxidic phase that floats on top of the liquid metal in most pyrometallurgical processes. The slag acts as a thermal blanket, limiting heat losses from the metal to the environment, and also fulfils a refining function, by capturing unwanted impurities (e.g. specific desulphurisation slags used in steelmaking). The composition of the slag is strongly influenced by the gangue material, in case of primary processing, or the unwanted elements present in secondary raw materials. In addition, the composition can be tailored to the desired extent by adding specific fluxes.
SIM² KU Leuven targets the development of more efficient extraction and refining processes as well as recycling processes for various metals from new resources such as industrial wastes and by-products. This includes the development of novel pyrometallurgical processes using for instance plasma or microwave technology and carbon-free fuels to recover metals from metallurgical residues and slags.
Electrochemical processing has the advantage of using electrical energy to produce metals, potentially providing a clean and low-carbon production route. At SIM² KU Leuven we perform experimental and modelling investigation of the fundamentals of direct electrochemical reduction to recover iron from iron-rich metallurgical residues in aqueous solutions and reactive metals such as rare earth metals in molten salt or molten oxide systems.
SIM² KU Leuven develops both hydrometallurgical and solvometallurgical leaching processes. In solvometallurgical processes the aqueous phase of hydrometallurgical processes is partly or completely replaced by an organic solvent. One approach is “solvent leaching” in which the leaching is performed with a complexing agent (acting as an extractant) in an organic solvent. Lixiviants are often more reactive in organic solvents than in water. A second solvometallurgical method is “slurry solvent extraction”. Here, the finely crushed ore is wetted by a small volume of acid solution, and this slurry is contacted with a water-immiscible organic phase, containing an extractant. This approach is similar to conventional solvent extraction, but the volume of the aqueous phase is largely reduced.
Both aqueous and non-aqueous solvent extraction processes are developed for the separation of mixtures of rare earths and for the purification of other (critical) metals. In non-aqueous solvent extraction, the metals are distributed between two non-miscible organic phases (a less polar and more polar phase). Because the solvation of metal ions in polar organic solvents is different from that in water, other selectivities can be achieved in solvent extraction processes. The solvent extraction experiments are carried out in a small lab scale as well as in mini-pilot scale with mixer-settlers. The work in this topic also comprises the design and synthesis of new extractants. Traditional extractants are prepared in high purity for fundamental studies and at larger scale for mixer-settler studies. By combining 2 or 3 different extractants, synergistic solvent mixtures can be obtained with extraction behaviour that is different from that of the individual extractants. Special attention is paid to the active role of diluents in solvent extraction processes.
Metal ions are recovered from dilute aqueous waste streams and leachates by means of highly selective adsorbents. Two types of adsorbents are being considered: (1) adsorbents made by functionalisation of biopolymers such as chitosan or alginate, and (2) supported ionic liquid phases (SILPs). In SILPS an ionic liquid is immobilised on a solid support. SILP technology is very flexible, because both the type of ionic liquid and the solid support can be optimised independently. By the use of functionalised ionic liquids, very selective adsorbents can be obtained.
Different spectroscopic techniques (e.g. UV-VIS-NIR spectroscopy, NMR, FTIR, Raman, EXAFS, see also RL1) are used to determine what types of metal complexes are formed in aqueous and organic solutions under different conditions. The speciation studies give information on the composition and structure of metal complexes in solution: the number and type of ligands coordinated to the metal ion, the molecular mass, the number of coordinated water molecules. Knowledge of the speciation is essential for modelling the extraction process at a molecular level and as input for mechanistic studies of solvent extraction processes. Special emphasis is paid to speciation in highly concentrated solutions, with high metal concentrations and/or high salt concentrations. Understanding of the mechanism of solvent extraction at a molecular level is essential for the development of more efficient separation processes.
In dedicated waste-to-energy installations energy and materials are recovered from non-recyclable waste. SIM² researchers study how in these installations, from a chemical and process point of view, high energy efficiencies can be combined with advanced recovery of critical and valuable materials, while considering the trade-off with operational and maintenance costs.