Steve Bennett and Barbara Breeze.
The Platinum Group metals (Pt, Pd, Rh, Ru, Ir and Os) are used in a wide range of applications ranging from fine jewellery all the way through to catalysts in large chemical plants. The largest consumer of these precious metals today is the automotive industry in which they are used to make catalysts which are fitted to the exhaust pipes of millions of vehicles worldwide to abate the emissions of NOx, carbon monoxide, soot particles and unburnt fuel that would otherwise be emitted into the atmosphere. Johnson Matthey started making auto catalysts in 1974 and since then has supplied one in three of all auto catalysts ever sold in the world and prevents 40 tonnes of pollutants from entering the air we breathe every minute.1
Platinum group metals (PGMs) are classified as critical raw materials (CRM) by many governments due to their limited availability in nature (geographical occurrence and concentration), their wide-ranging applications and the difficulty to substitute them in these key technologies. As such PGMs hold a high financial value and have an established circular economy with global networks to recycle PGM containing products at the end of life. For instance, global demand for palladium for auto catalysts alone in 2022 was 262.2 tonnes of which about a third (82 tonnes) came from metal which had been recovered and recycled from a previous application.2 As the uses for these critical metals increases in the global transition to net zero then the volume of material requiring recycling will increase.
Over many decades of working with PGMs JM has developed routes to efficiently recycle them and now has highly efficient recycling processes, with over 95% of the PGMs that enter into our metal refineries recovered into forms that can be used to make fresh products.3 However, that leaves small quantities of highly precious metals in the by-products generated from our process.
As well as recycled material the PGM market is of course also made up of metal obtained from mining activities. The refining processes from these are also not 100% efficient and results in waste streams which contain low concentrations of PGMs that are trapped and uneconomical to recover. 78 million tonnes per year of these refinery tailing are produced in South Africa alone (which is the main global PGM producer from primary ore) and these contain 37.4 tonnes of Pt, 14.8 tonnes of Pd and 2.3 tonnes of Au which cannot be accessed by any conventional routes.4
The route being developed by the BIORECOVER project offers a way to recover some of the PGMs from the dilute waste streams generated from both the recycling of the end-of-life products and also the tailings from the treatment of primary PGM ores. This will improve the supply of PGMs in the UK/EU and make them less reliant on other countries and regions on the supply of these critical elements.
Of particular interest to JM is the possibility that the BIORECOVER route could be used in the early stages of our existing routes used extract PGMs from spent catalysts. This could allow lower amounts of the strong acids and other chemicals that are currently used to extract PGMs from these waste streams and so help lower the environmental impact of the recycling process. With further development it could be that a process developed from the results from the BIORECOVER project could even completely replace some of the steps in the current recycling process. This is some way off at the moment, but the potential is there.
1- JM Clean air marketing presentation, https://matthey.assetbank-server.com/assetbank-matthey/action/downloadFile
2- JM PGM Market Report 2023, https://matthey.com/documents/161599/404086/PGM+Market+Report+May23.pdf/2f048a72-74a8-8b23-f18e-c875000ed76b?t=1684144507321
3- Recycling the Platinum Group Metals: A European Perspective, C. Hagelüken, Platinum Metals Rev., 2012, 56 (1), 29
4- Investigation of the potential for mineral carbonation of South African PGM tailings. J. Vogeli et al. UCT (2011).