SoS RARE: Multidisciplinary research towards a secure and environmentally sustainable supply of critical rare earth elements (Nd and HREE) Rare earth elements (REE) are the headline of the critical metals security of supply agenda.  All the REE were defined as critical by the European Union in 2010, and in subsequent analysis in 2014. Similar projects in the UK and USA have highlighted 'heavy' REE (HREE - europium through to lutetium) as the metals most likely to be at risk of supply disruption and in short supply in the near future. The REE are ubiquitous within modern technologies, including computers and low energy lighting, energy storage devices, large wind turbines and smart materials, making their supply vital to UK society. The challenge is to develop new environmentally friendly and economically viable, neodymium (Nd) and HREE deposits so that use of REE in new and green technologies can continue to expand.  The principal aims of this project are to understand the mobility and concentration of Nd and HREE in natural systems and to investigate new processes that will lower the environmental impact of REE extraction and recovery.  By concentrating on the critical REE, the research will be wide ranging in the deposits and processing techniques considered. It gives NERC and the UK a world-leading research consortium on critical REE, concentrating on deposit types identified in the catalyst phase as most likely to have low environmental impact, and on research that bridges the two goals of the SoS programme.  The project brings together two groups from the preceding catalyst projects (GEM-CRE, MM-FREE) to form a new interdisciplinary team, including the UK's leading experts in REE geology and metallurgy, together with materials science, high/low temperature fluid geochemistry, computational simulation/mineral physics, geomicrobiology and bioprocessing. The team brings substantial background IP and the key skills required. The research responds to the needs of industry partners and involves substantive international collaboration as well as a wider international and UK network across the REE value chain.  The work programme has two strands. The first centres on conventional deposits, which comprise all of the REE mines outside China and the majority of active exploration and development projects. The aim is to make a step change in the understanding of the mobility of REE in these natural deposits via mineralogical analysis, experiments and computational simulation. Then, based on this research, the aim is to optimise the most relevant extraction methods. The second strand looks to the future to develop a sustainable new method of REE extraction. The focus will be the ion adsorption deposits, which could be exploited with the lowest environmental impact of any of the main ore types using a well-controlled in-situ leaching operation.  Impact will be immediate through our industry partners engaged in REE exploration and development projects, who will gain improved deposit models and better and more efficient, and therefore more environmentally friendly, extraction techniques. There will be wider benefits for researchers in other international teams and companies as we publish our results. Security of REE supply is a major international issue and the challenges tackled in this research will be relevant to practically all REE deposits.  Despite the UK not having world class REE deposits itself, the economy is reliant on REE (e.g. the functional materials and devices industry is worth ~£3 Bn p.a.) and therefore the UK must lead research into the extraction process. Manufacturers who use REE will also benefit from the research by receiving up to date information on prospects for future Nd and HREE supply. This will help plan their longer term product development, as well as shorter term purchasing strategy. Likewise, the results will be useful to inform national and European level policy and to interest, entertain and educate the wider community about the natural characters and importance of the REE. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.