|
Content:
|
Redox and complexation reactions are part of many metallurgical processing chains. Redox
potentials of metals are strongly influenced by the coordination of the solution species, which is
controlled through the composition of the solvent. Ionic liquids and brines provide a high level of
control over metal speciation through judicious choice of potential ligands in the solvent [1].
However, actual design is only possible if the link between solvent composition, metal speciation
and redox behaviour is thoroughly understood.
We investigate metal complexation with spectroscopic methods such as EXAFS or Raman
spectroscopy and try to connect speciation to electrochemical behaviour of metals in ionic liquids
with various anions [2,3]. These results are compared to aqueous solutions containing a range
of concentrations of the same complexant, illustrating the high level of reactivity control in ionic
liquids. Fig.1 shows a simple example from the redox chemistry of copper, where the stability
window of the monovalent oxidation state is controlled by chloride activity. Using examples from
chemically very different metals, we compare the electrochemical series with its ionic liquids
equivalents. We are currently transferring electrochemical methods to determine equilibrium
constants [4] from aqueous systems to ionic liquids, with the aim to model solution speciation
ionic media. Results can be applied to metal plating and mineral processing [5-7].
In aqueous solutions, modelling of leaching solutions and mechanistic studies into leaching and
bioleaching reactions for sulfidic ores have been performed. Our data show e.g. that copper can
play an important role in the iron-mediated sulfide oxidation chain (Fig.2), which is also part of
microbial leaching mechanisms. In abiotic leaching, we aim to design new mineral processing
techniques using other redox shuttles such as iodine/iodide (Fig.3).
|
