Why in News
India and Norway discussed industrial-waste reuse in construction and hazardous-waste treatment in cement kilns on 10 November.
Prelims Pointers
Participants included India’s Council of Scientific and Industrial Research (CSIR), Norway’s SINTEF and the Research Council of Norway.
The waste materials discussed come from several industrial processes.
Fly ash is fine ash generated by coal combustion in thermal power plants.
Red mud is the residue from extracting alumina from bauxite.
Steel slag is a by-product of steelmaking.
Construction and demolition waste consists of debris from building, renovation and demolition, including concrete and masonry.
Processed wastes can supply bricks, roads, aggregates and concrete. Fly ash can partially replace Portland cement.
Cement-kiln co-processing substitutes suitable waste for fuel or raw materials, with controlled treatment, emission monitoring and regulatory compliance.
Cement production releases carbon dioxide through fuel combustion and calcination.
Fuel combustion supplies heat to the kiln.
Calcination releases carbon dioxide when limestone is converted into lime: CaCO₃ → CaO + CO₂.
Prelims Traps
“Fly ash contains only silica and calcium oxide.” This is incorrect. It can contain other compounds and toxic elements. (UPSC Prelims 2015)
“Clean energy eliminates all cement-production CO₂.” This is incorrect. Limestone calcination also releases CO₂. (UPSC Prelims 2025)
“Red mud is a residue of coal combustion.” This is incorrect. It arises from alumina production from bauxite.