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MEI Online: Electrometallurgy: Latest News: July 4th 2011


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:: Ionic Solution for Metal Extraction

There is something about ionic liquids that attracts the interest of researchers seeking greater efficiency in electrical and chemical systems, from improved batteries to industrial catalysts and solvents.


Among them is Dr Theo Rodopoulos who leads a CSIRO Light Metals Flagship project investigating the use of ionic liquids to improve metal recovery processes, including reducing the energy required to produce aluminium. “Ionic liquids are fascinating media with enormous potential that is only limited by the experimentalists’ imagination," he says. “They are tunable, which allows us to design different ionic liquids for different applications. But we need to advance our understanding of ionic liquids and their chemistry to design better ionic liquids with improved applicability to industrial processes."

Dr Theo Rodopoulos and Dr Thomas Ruether consider the chemical make up of ionic liquids and their potential to improve metal recovery


He says ionic liquids are especially useful in metal processing because they can function as electrically conducting solvents that are so stable they can be used as a medium for reducing metals out of solution without decomposing or vaporising. He describes ionic liquids as ‘basically salts’ - positively and negatively charged ions whose electrical charge and chemical nature allows them to bond and arrange into materials like the common salt sodium chloride.

Ionic liquids are defined as salts which exist in the liquid form at, or near, room temperature. Common salts are solids at room temperature; sodium chloride has a melting point of more than 800°C. However, ionic liquids are formed from more complex ions (typically organic species), which have much lower melting points (typically below 100°C) because the relative electrostatic attraction between the ions and the relative packing density and efficiency in the crystal lattice is reduced.

Dr Rodopoulos says the potential for materials with these unique properties is enormous. His area of research focuses on metal processing applications of ionic liquids. “The electrochemical stability of ionic liquids allows you to apply a voltage to an ionic liquid solution containing metal ions and selectively reduce the target metal so that it deposits out of solution, allowing the recovery of the metal," he says. “They are especially useful for the more stable metals that require a large negative potential for their reduction and electrodeposition. For these metals, media such as water or traditional organic solvents start to reduce (decompose) before the metal."

In contrast, ionic liquids can be designed to be more stable than conventional solvents and allow electrochemistry to be performed over a broader voltage range. Furthermore, properties vital to electrochemistry like viscosity, melting point and conductivity can be modified by subtle changes to the chemical structure of the ionic liquid.

That means chemists can tune the properties of ionic liquids to suit specific applications. At CSIRO, Dr Rodopoulos and his team design and synthesise new ionic liquids for specific metals and applications. “To a large extent, the design and selection of ionic liquids involves understanding the chemistry of ionic liquids because they are reactive media," he says. “Since ionic liquids typically comprise organic ions, they can chemically react with added metal-containing solutes. In terms of electrochemistry, knowing what chemical species you have in solution allows you to optimise and improve the deposition process."




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