# The Role of Clean Coal Technologies in the Development of Renewable Energy Sources
## 1 Introduction
### The Impact of CCT on the Development of Renewable Energy Sources
#### 1.2.2 Fly Ash as a Source of REEs  
The rare earth elements (REEs) are a group of 17 metals including yttrium, scandium, promethium, samarium, terbium, cerium, neodymium, praseodymium, gadolinium, holmium, erbium, thulium, lanthanum, ytterbium, lutetium, europium and dysprosum [19]. REEs are metals without which technological development would be impossible. This applies to both renewable energy sources and technological achievements that accompany people in everyday life and without which it would be impossible to lead life as we know it. They are used in the production of high-intensity lighting, automotive catalytic converters, magnets, cameras, lasers, cell phones, computers, X-ray machines, magnetic resonance imaging equipment, nuclear reactors, medicine and many other technologies [20; 21].  
Taking into account the subject of the research conducted here, the most important consideration is the role of rare earth elements in the energy transformation. Because the demand for REEs is huge and constantly growing, and the sources are limited, they have been placed by the European Union on the list of critical raw materials [22]. Limited access to REEs means that their prices are very high and tend to increase rapidly [23]. Almost the entire demand for REEs in the EU is covered by elements imported from China, which dominates the market for these raw materials [24; 25]. Even though REE deposits are also located in India, Brazil, Russia, the United States and Australia, approximately 90% of imports to the EU come from China [26]. Such a large share of one source in the supply of raw materials poses a threat to the EU's energy security. It is believed that in order to properly diversify the supply of raw materials, the share of one source should not exceed 30% [27]. Therefore, it seems necessary to look for new sources of REEs. The problem deepens when REEs' contribution to energy transition is taken into account. 30% of REEs produced in 2020 were used in the production of permanent magnets and 15% in the production of electric vehicles. In total, 10% of the magnets made were used in the production of wind turbines [28]. Due to the further development of renewable energy sources, it is estimated that in 2030 the number of electric vehicles sold will increase by ten times and the number of wind turbines will double. Since this development is a global trend, there may soon be a shortage of elements on the market, without which the expansion of renewable energy sources will be impossible. Therefore, it is necessary to look for alternative sources of obtaining REEs. Since the Polish energy system is still based on coal, Poland has access to large amounts of fly ash. This constitutes a waste product of the coal combustion process in the production of electricity and heat. REEs are contained in coal, but their amount is usually so small that it is economically unjustifiable to obtain REEs from this raw material. Ashes, in turn, are a concentration of substances that have not been degraded during the combustion of organic matter. REEs are present in ashes resulting from the combustion of Polish coal in the following amounts: light REEs--neodymium, lanthanum, cerium, praseodymium--0.03% and heavy elements 0.015% [29]. Such concentrations make the REE separation process profitable, as does the fact that it eliminates the need to mine REE-rich ores, and also provides many elements at the same time, which is usually not the case during traditional mining.