OPERATIONS •
RECOVERING REE FROM COAL FLY ASH
The ash produced by coal-fired power stations may hold recoverable trace amounts of Rare Earth Elements critical for renewable energy devices , writes Dr Nicolaas C Steenkamp .
There has been a significant amount of debate about the future of coal in the past year , with the mantra of “ Coal is dead , long live Coal ” being echoed at a number of conferences and on many stages . At the moment there is no real economic and fast replacement for the effective electricity generation by coal-fired power stations and in the shadow of the global energy crises , especially in the West , the need for coal remains the foundation to being able to survive , produce and remain globally significant .
The generation of waste products from coal-fired power stations is mainly ash . In effective systems where the correct thermal coal is supplied , around 20 % is bottom ash and 80 % is fly ash . The ash , if handled correctly , is for the most part stored on ash dumps , close to the power station . There have been several attempts at utilising the ash from these dumps , such as producing bricks or other predominantly industrial applications .
Research in the last couple of years has revealed that the fly ash component , derived from certain formations , contain recoverable trace amounts of Rare Earth Elements ( REE ) which is utilised in the production of renewable energy devices . The REE contained in the fly ash is dependent on the presence of the REE in gangue mineral phases contained within the coal prior to burning . Aluminium ( Al ), silicon ( Si ), calcium ( Ca ), and iron ( Fe ) are the major gangue elements .
It is suggested that the REE is contained in the clay minerals associated with the coal . Various studies have been conducted , with variable results for the recovery of REE from the fly ash . It was found that the largest portion of the REE is found in the smaller fraction of the ash . Cerium , Lanthanum , Neodymium , and Yttrium are the most common of the REEs detected . The economical recovery is heavily dependent on the type and volumes and ratio of critical REE which is present and can be recovered and not lost to the tailings .
The use of floatation proved to be the most effective of the methods , but further upgrading can be achieved by a selective combination of magnetic or gravity separation methods . These developments could place the coal fly ash within a potentially economic range if feasible beneficiation methods could be developed to selectively recover and upgrade REE values . The other advantage of processing coal fly ash is that it would carry no mining and comminution costs .
There has also been research into utilising citric acid to separate the REE from the fly-ash in an environmentally-friendly solution .
Recovery of economically viable volumes of REE from CFAs is still a long way into the future , with characterisation of the CFA and tailings facilities with the highest potential and developing more effective means of recovery . There is , however , very clear potential . •
Pexels | Pixabay www . africanmining . co . za African Mining Publication African Mining African Mining • October 2023 • 23