Material solubility in, and rapid synthesis of, ionic liquids as a step towards efficient value recovery from waste

• Main Author: Gooding, Anna Claire
• Other Authors: Grimes, Sue
• Published: Imperial College London 2011
• Subjects: 628
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543312

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).