In parts of India, you can tell what colour a factory dyed its fabric that week just by looking at the river next to it. One such dye is Methylene Blue. It is widely used by industries and can be difficult to remove once it enters water. 

But researchers at the National Institute of Technology (NIT) Rourkela have now found a way to clean it up, using two materials that industries already throw away by the tonne.

How coal and steel waste became useful 

The team, led by Prof Sunipa Bhattacharyya from the Department of Ceramic Engineering, along with research scholars Susant Mohapatra and Sourav Ranjan Satpathy, developed a wastewater-based ceramic adsorbent using fly ash, Ground Granulated Blast-Furnace Slag (GGBS), and kaolin clay. 

Fly ash comes from coal combustion in thermal power plants, while GGBS is generated during steelmaking. Both pile up in enormous quantities and are notoriously hard to dispose of safely, a challenge other Indian innovators have tackled by turning fly ash into bricks for affordable housing.

What makes the choice of materials clever is that fly ash and GGBS are abundant and chemically suited to the job. 

India produced over 340 million tonnes of fly ash in 2024-25. Fly ash and slag also contain silica and alumina,........

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