Mercury mobility in byproducts of sinter plants by sequential fractionation

• Significant variations in Hg total and Hg diss concentrations were observed among dust samples from Plants A, B, and C. • Plant A, using activated carbon for flue-gas cleaning, showed the highest Hg total concentrations (400–600 µg/g). • Sequential extraction revealed high variability in inert and mobile Hg fractions, with some samples exhibiting highly water-soluble Hg. • Dusts with >85 % total solubility due to water-soluble salts pose a significant environmental risk of Hg release. • Pre-treatment strategies, such as immobilization or HgS precipitation, are essential for reducing Hg emissions and ensuring waste stability. Mercury (Hg) is a global pollutant, present in air, water and soil, with natural and anthropogenic sources. Industrial processes, particularly steel production, release Hg into the environment, but with specific adsorbent materials used in air pollution control devices (APCD), it could be removed from the flue-gas, finally posing significant waste management challenges. This study examined Hg concentrations in adsorbent materials from the flue-gas of different sinter plants, assessing the potential Hg mobility when disposed in landfills through sequential fractionation. The study was conducted as a laboratory work. The results revealed significant different Hg concentrations in the byproducts of APCD. The byproducts exhibited a solubility of over 90 %, which result in the high concentrations of Na + , Cl - , K + and SO₄ 2- present in the byproducts. Higher Hg concentrations (400–600 µg/g) were found in samples from facilities using activated carbon, while facilities without activated carbon had lower concentrations (75 µg/g and 1.0 µg/g). The different Hg concentrations between the devices investigated based in the raw materials and their origin. Sequential extraction revealed that a substantial Hg fraction in the byproducts were water-soluble, acid-soluble, reducible and oxidizable, making it mobile. Compared to other byproducts from APCD the byproducts in this study had a higher solubility, making leaching a potential pre-treatment step before landfilling. The leachates were characterized, and dissolved Hg concentrations were too high to be safely discharged into a waterbody.