UC warns of risks in the self-combustion of mining waste

As published in the Diário de Coimbra on May 30, 2023, self-combusting coal mining waste has a negative impact on the environment, concluded an investigation by the University of Coimbra, released yesterday.
The study was carried out by the Department of Earth Sciences (DCT) of the Faculty of Science and Technology of the University of Coimbra (FCTUC).
The researchers explained that self-combusting coal mining waste has a negative impact on the environment due to the production of acid drainage which, as a result, can affect soils and ecosystems
of the surrounding area, the UC informed in a statement.
The work on self-combustion mining waste in Portugal, which began in 2007, in addition to focusing on the identification of self-combustion mining waste resulting from coal mining in the past,
aims to identify and understand the impacts of this process on the environment, particularly on soil, water and the atmosphere.
According to Joana Ribeiro, DCT professor and author of the study, the most significant impact may be related to volatile organic compound emissions during combustion.
«Substances were detected, namely polycyclic aromatic hydrocarbons and other organic compounds, which are emitted into the atmosphere and are harmful to human health. This situation
it can be particularly worrying when self-combusting heaps are found close to inhabited areas", she revealed.
According to the researcher, in Portugal there are three known cases of heaps of coal mining waste whose ignition began in 2005 due to forest fires.
One of these heaps, in São Pedro da Cova, Gondomar, has been in self-combustion for almost two decades, being a source of contamination to the atmosphere due to the emission of volatile organic compounds
that result from the combustion of coal, and also into the surrounding environment, due to acid drainage.
In 2017, two other heaps combusted, for the same reason, but in these cases the Mining Development Company (EDM) implemented a rehabilitation project that allowed the extinction of the combustion.
«There are always ways to resolve situations like that of the São Pedro da Cova heap, however, they are expensive and complex», assured Joana Ribeiro, adding that
there are solutions, such as the one applied by EDM, which includes the remobilization of material from the site, cooling with water and a temperature retarding agent, replacement and compaction on site. “This compaction is fundamental since it restricts the access and circulation of oxygen inside the heap, which feeds the combustion process”, she explained.
For the scientist, this is a process that happens all over the world and that has not only an environmental and health impact, but also an economic one, since it can occur in a coal mine and in the coal layers themselves, altering and making it unfeasible the geological resource.

Therefore, it is very important to carry out an inventory of the coal heaps that exist in Portugal, the respective characteristics and conditions of deposition, as well as the situation in relation to the framework in forest areas. In this way, the risk of ignition and consequent self-combustion of coal heaps could be minimized through proper forest and land management, Joana Ribeiro considered.
D.R. (05/30/2023)