摘要
Maintaining the balance between the demand by the economic markets and the natural abundance of the rare-earth elements (REEs) in ores constitutes a major challenge for manufacturers of these elements. This is the so-called balance problem (or balancing problem). The ideal situation is a perfect match between the demand and (production) supply of REEs, so that there are no surpluses of any of the REEs. The balance problem implicates that the rare-earth industry has to either find new applications for REEs that are available in excess, or needs to search for substitutions for REEs that have limited availability and that are high in demand. Different solutions are proposed to solve the balance problem: diversification of REE resources, recycling and urban/landfill mining, substitution, reduced use and new high-volume applications. No single solution can solve the balance problem, but a combination of different strategies can. It is illustrated that the issue of thorium in REE ores is also directly related to the balance problem: presently, thorium is considered as radioactive waste, but this waste could be turned into a valuable resource by using thorium in a thorium-based nuclear fuel cycle. Keywords Lanthanides Permanent magnets Rare earths Recycling Substitution Thorium