POSTMODEN ALCHEMY
Metallurgists at Saarland University aim to decarbonize aluminium production
Some things take time; some a lot more than others. In Isabella Gallino's case, the time between completing her doctorate and the practical application of her research has taken more than a few years. But it may all have been worth the wait, because Gallino's PhD thesis could potentially pave the way for a paradigm shift within the energy-intensive and environmentally challenging aluminium industry. The ultimate objective is nothing less than the carbon-neutral production of aluminium.
The conventional method of producing aluminium from its oxide alumina releases enormous amounts of the environmentally damaging greenhouse gas CO2. 'Smelting one tonne of alumina results in the emission of eight tonnes of CO2 if electricity from coal-fired power stations is used,' explained Ralf Busch, Professor of Metallic Materials at Saarland University. 'And,' added metallurgist Isabella Gallino, 'even if we were to use green electricity, smelting one tonne of alumina would still emit 1.5 tonnes of CO2.' The reason for this lies with how aluminium is produced industrially. The alumina (Al2O3) is electrolysed in the smelting furnace, where it is decomposed into its negatively and positively charged components, which are separated from one another by the anode and cathode of the electrolytic cell. Up until now, the oxygen from the alumina is separated from the aluminium metal by means of a graphite anode. The carbon of the anode combines with the oxygen from the alumina to produce CO2, with 1.5 tonnes of CO2 emitted into the atmosphere for every tonne of alumina processed. What's left is mostly pure aluminium, a highly valuable raw material that finds use in many industrial sectors, ranging from automotive manufacturing to the beverages industry. Germany's largest aluminium producer is the company Trimet, which now has access to the scientific expertise of Isabella Gallino and Ralf Busch as part of a major research project. To get some idea of the dimensions involved, just one of Trimet's plants contains 300 smelting cells (or 'pots’ as they are often known), each of which houses table-sized graphite anodes that need to be replaced on a monthly basis. According to the industry body that represents the aluminium sector, around 63 million tonnes of primary aluminium are produced annually[1] – a fact that clearly underscores the need to introduce more climate-friendly means of producing aluminium.
This is where Isabella Gallino's PhD thesis comes into play. She was awarded her doctorate some 20 years ago at Oregon State University in the USA. In it she demonstrated that so-called inert anodes do in fact work in practice. Put simply, she replaced the conventional graphite anode by one made from an alloy of iron, copper and nickel. When this anode is used, the gas produced at its surface is not CO2 but oxygen (O2) and, unlike the graphite anode, the metallic anode does not get consumed as electrolysis progresses. 'Unfortunately, from an environmental policy position, the situation in the USA in the early 2000s was not good,' said Isabella Gallino. The US government under Republican President George W. Bush had already rolled back support for environmentally friendly industrial reforms. However, with the introduction of the European Green Deal, a set of carbon-reduction policy goals adopted by the European Commission in 2019, conditions in Europe are now excellent for implementing this type of climate-positive change. Remodelling a heavy industry like the aluminium production sector does not come cheap. 'But if our goal really is to achieve carbon neutrality, then this is the only way forward,' said Isabella Gallino.
Gallino is part of a consortium for the CO2-free production of aluminium whose lead partner is Trimet. Her goal over the next three years will be to develop inert metallic anodes that are capable of delivering an efficient and carbon-neutral production process. Once suitable anodes are available, the other industrial partners will develop a prototype electrolysis system and test the new carbon-neutral production process. If all goes well, a small industrial smelting facility would then be built to produce smaller quantities of CO2-neutral aluminium.
Metallurgist Isabella Gallino is also looking at another option that could be exploited in future should the production of carbon-neutral aluminium become reality. 'Aluminium is an excellent material for storing energy if it's produced using green electricity. Aluminium is a chemical element that is able to donate three (valence) electrons at once, so its energy density is higher than that of other elements. And there is a method of generating electricity and hydrogen gas by which elementary aluminium is oxidized back to Al2O3 by letting molten aluminium react with water in a controlled manner.'
Electric power from aluminium rather than from burning coal? It's an idea that could indeed become reality if we are able to produce aluminium in a carbon-neutral, climate-compatible way.
The project has received funds from the Ministry of Economic Affairs, Industry, Climate Action and Energy of the State of North Rhine-Westphalia.
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