What type of residues remain in coal after it is combusted?

After coal is combusted, the type of residues that remain are inorganic residues. This residue primarily consists of ash, which is the non-combustible portion of coal that includes various minerals such as silica, alumina, iron oxides, and calcium. When the carbon-containing components of the coal burn, they release energy and produce gases such as carbon dioxide, but the inorganic materials do not combust and remain as ash.

Understanding this process is crucial in mining and energy production, as the presence of inorganic residues affects not only the efficiency of energy production but also has implications for waste management and environmental impact. Efficient disposal and handling of this ash are important considerations for operational practices in coal mining and combustion.