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| CSIRO | SOLVE | Issue 9 | NOV 06 | |
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ARTICLE
LIGHT METALS:
Cooler Future for Smelting By Bianca Nogrady
The Light Metals Flagship is working with the minerals group Rio Tinto to lower the energy costs of producing aluminium.Aluminium producers, who consume as much as 15 per cent of Australia's electricity, are keenly watching research between the Light Metals Flagship and industry partner Rio Tinto on a new method for producing aluminium that could cut energy consumption and greenhouse gas emissions. The research involves the use of ionic liquids as 'designer solvents' that could reduce the high temperatures needed for aluminium smelting.
Designer solvents or ionic liquids could also be used as alternative media for reprocessing nuclear fuel and waste in the nuclear power industry, and as catalysts or solvents in a host of other industrial processes. CSIRO is also exploring their use as electrolytes in lithium batteries, because the organic solvents used in lithium battery manufacture are volatile and flammable. Other potential uses include carbon dioxide recapture in power plants, desulfurisation of fuels and even perfume production. The key to ionic liquids is their low melting point. Aluminium is currently produced through electrodeposition, where the alumina is dissolved in a molten cryolite bath at 1000°C and an electric current is applied to separate aluminium from oxygen. The high temperature needed to keep the cryolite in liquid form is the reason for the high energy consumption. By contrast, ionic liquids typically melt below 100°C. If they can be used instead of molten cryolite, they could dramatically reduce a smelter's energy needs. Rio Tinto's technology support general manager, Dr Ray Shaw, says that although research on ionic liquids is still in its early days, it is a novel approach that the company is monitoring closely. He says ionic liquids could reduce by 20–30 per cent the electricity used in aluminium production, based on the expectations of researchers in America. "Whether that's achievable or not is uncertain at this early stage. But if there's an opportunity to improve, then we're interested in exploring it."
The Flagship's ionic liquids research project leader, Dr Theo Rodopoulos, believes ionic liquids have significant commercial potential. "Their negligible vapour pressure eliminates the release of atmospheric pollutants, and because less of the solvent is lost to evaporation during processing, ionic liquids are more recyclable and economical than conventional industrial solvents," he says. Their capacity to remain liquid over a wide temperature range and their high thermal stability also allow chemical processes to operate at higher temperatures to improve reaction kinetics, without actually boiling or decomposing the solvent. Ionic liquids' electrochemical stability gives them a significant edge over conventional aqueous and organic electrochemistry in the electrodeposition of certain metals, Dr Rodopoulos says. "For example, aluminium electrodeposition is not possible in water due to the reduction of water to hydrogen at the cathode." They are often called designer solvents because they can be tailored to meet the needs of specific applications. Dr Rodopoulos says it all depends on the type of positively and negatively charged ionic components selected, with an almost infinite number of combinations possible. "You really need to consider the sort of application you're interested in and choose your cations and anions accordingly, to give you the desired properties such as lower viscosity, lower melting point or a particular solvation characteristic."
However, there are still issues to be resolved with ionic liquids – such as cost. Rio Tinto's Dr Shaw says the challenge is one of scale. "Until significant quantities are used, the cost will remain high. So they need to end up with a use that's sufficiently compelling to drive large-scale use." Dr Rodopoulos says that although ionic liquids are relatively easy to produce, they can vary in their purity. "They can be anything from colourless, which is typically what they are, to pale yellow and brown, which is usually an indication of impurities." However, this may not be an issue if the impurities do not interfere in the ultimate application, he says.For further information contact: |
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