NEW RECYCLING DIRECTIONS FOR ASH RESULTING FROM LOW GRADE COAL DEPOSITED IN ASH DUMP SITE.

Low-grade coal (lignite or brown coal) produces a significant impact upon the environment through multiple vectors (during mining, combustion and disposal and treatment of combustion by-products). With a power generation industry in which coal has still a significant weight a lot of research effort has been dedicated to identifying solutions to mitigate the impact upon the environment and place coal on the roadmap of circular economy. The paper discusses comparatively and present research data on two directions of recycling ash resulting from lignite combustion in Romania: (i) re-burning in mixture with coal in adequate proportions (due to the high content of unburned carbon, this has been proven to be possible) and (ii) obtaining highly valued raw materials for various industrial uses, such as graphite. Although completely different, each of the two recycling directions has particular advantages over the other one. The key property of the ash that both technologies exploit is the content of organic matter in the form of unburned carbon. The paper describes the two technologies, particular conditions for their applicability supported by experimental data and presents, comparatively, the advantages and disadvantages. A multi-criteria analysis is performed in order to point out the main differences between the two technologies. It is emphasized that a general solution does not exist and the most advantageous recycling direction depends on particular factors. [ABSTRACT FROM AUTHOR]