A mobile extraction plant for recycling of copper and indium
28 August 2017
There is as yet no commercially viable method of salvaging all valuable metals from the dust generated during the production of copper and zinc. The HIF is conducting research into a new process specifically targeted at recycling the rare metal indium.
“A plant for deriving copper and indium solutions from industrial residues,” muses Philipp Rädecker, PhD student at the HIF, “What a great idea!” It may sound like an admirable recycling fantasy, but it has the potential to unlock considerable value.
While the bulk metal copper is indispensable as an electrical conductor, the rarer indium in combination with tin is an important raw material for flat screens and touch screens. These two elements occur together in nature: indium is primarily obtained as a by-product from zinc and copper ores. A worthwhile secondary source is so-called ‘flue dust’ – particles released during the processing of metal-containing concentrates into pure metals, which are cooled down in off-gas and collected. They are made up of many valuable as well as pollutant substances.
Valuable flue dust
“Previously, the dust particles were simply dumped,” explains Philipp Rädecker. “Today, nobody would do that because the content is too valuable and the costs are too high.” Rädecker studied Material Science and Technology at TU Bergakademie Freiberg and joined the HIF Division of Metallurgy and Recycling two years ago as a doctoral student. The team here have been working in collaboration with TU Bergakademie on concepts for the recycling of flue dust since 2013.
The samples being used by Philipp Rädecker in his research project are taken from an old slag heap containing several thousand tonnes of dust particles. While new ionometallic approaches are being tested at TU Bergakademie, Rädecker at HIF is applying the so-called solvent or liquid-liquid extraction technique. To this end, he first dissolves the waste material in acid. The aim is to transfer the solutes to a second liquid containing an extracting agent, by causing both solutions to flow past each other as a counter current. The problem is that, in addition to the elements copper, zinc and indium, the initial solution also contains lead and iron, all of which must be extracted individually.
Valuable substances and pollutants
In the laboratory, the separation of copper and indium already works well under simple conditions: both elements can be extracted almost completely from synthetic solutions. Mineral Projekt, a partner company in the endeavour, is evaluating the research results for commercial viability. Rädecker tells that the prospects are currently looking good.
His task becomes more challenging when he uses the complex composite initial solution. While the separation rate for copper is also high, the extraction of the valuable indium has so far always been impeded by the problematic presence of iron. Philipp Rädecker is currently looking into ways of cracking this particular nut. Soon he will be able to carry out his experiments on a pilot scale using an extraction column approximately two metres tall.
How exactly does he imagine the finished recycling plant? “It should be transportable and consist of different modules for the various substances to be recycled. Companies operating at multiple sites could adjust their production cycles so that the plant can be used on a rotating basis.” In light of the forecast by associate HIF scientist Dr Max Frenzel that the technological availability of indium is unlikely to keep pace with rising demand, this new technique could help to assure the continuing supply of this coveted metal.