Recovery of metal values from metal-containing wastes and low-grade ores is important in
reducing consumption of metals from primary sources. The potential for ionic liquids (ILs) to
be used to recover valuable constituents from waste by selectively dissolving target materials
and then recovering them from the IL prior to regeneration and use of the IL in further
extraction is demonstrated.
A literature review shows the different types of ILs, their syntheses and applications as
solvents in extraction procedures. The use of rapid synthesis methods (particularly, open- and
closed-vessel microwave-assisted methods) to prepare ILs, of suitable purity for extracting
value from wastes and low-grade ores, is described, with the benefits of more rapid synthesis,
more efficient reagent conversion, higher purity product, reduced loss of starting materials
and less use of volatile organic solvents, all of which contribute to a more environmentally-sound
synthesis methodology.
The solubilities of a range of metals and metal compounds, in the prepared ILs, show
selective dissolution of metals can be achieved with the recovery of these metals, from IL
solution also being reported. Testing the use of ILs as solvents to recover metals from alkali
battery black mass waste and the mineral, malachite, as model systems, was studied, with
recovery of zinc and manganese from the battery waste being achieved using HBetNTf2 and
recovery of copper, from malachite, using protomimBr and protomimCl.
Crystals have been isolated from solutions of Zn, ZnO, ZnS, CuO, CoCl2, Mn and MnO2 in
protomimBr and their crystal structures determined, which show that complex formation
between components of the IL and the metal ions provides the mechanism for the dissolution
of metals from solids into the ILs. The complex formation can, however, involve either the
nitrogen atom of the imidazolium-IL cation (for zinc, copper and manganese) or the IL halide
anion (for cobalt).