Hydro- and solvometallurgical processes
General theme: Innovative, efficient hydrometallurgical and solvometallurgical processes are developed for the recovery of base metals (Cu, Zn, Ni) and critical metals (REEs, PGMs, Ge, In, Sb, Ga, Co, Ta) from End-of-Life consumer goods, industrial process residues and low-grade ores. The recovery of the metals is part of larger flow sheets, which target near-zero-waste valorisation of the metal-containing residues.
Solvometallurgical leaching and preconcentration of metals.
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
Solvent extraction for separation and purification of metals
Undiluted ionic liquids are used in solvent extraction processes for the separation of mixtures of rare earths and for the purification of other metals. Undiluted ionic liquids offer in solvent extraction the advantage of a very high extractant concentration, allowing for high metal loadings in the organic phase. Additionally, non-aqueous solvent extraction processes are developed. 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.
Metal recovery from dilute aqueous waste streams
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
Design of extractants and solvent formulation
New extractants are designed, synthesised and characterised. 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.
Mechanistic and speciation studies
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 (stoichiometry) and structure of metal complexes in solution: the number and type of ligands coordinated to the metal ion, the molecular mass (and the degree of oligomerisation), the number of coordinated water molecules (hydration number). 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.
The leading members in this research line are: