Generation, transformation and inhibition mechanism of hazardous waste flue coated materials during copper smelting process.

During the pyrometallurgical process of copper, the hard nodular substances formed in the flue system can easily disrupt the smelting operation and cause various types of environmental pollution. This study investigated the formation mechanism, and phase transformation of flue coating materials (FCMs) during copper smelting through multi-scale characterization and thermodynamic simulation, and proposed corresponding suppression measures. The results show that, driven by the oxygen potential gradient and sulfur condensation, the FCMs follow the pathway of "volatilization migration - encapsulation - sulfation", leading to the accumulation of toxic metal compounds. The spatial evolution of phases from metallic Cu/CuFe2O4 in the vertical flue to sulfates/sulfides in the horizontal flue was quantitatively elucidated. The application results of the new suppression strategy show that raising the bottom temperature of the vertical flue from the original 1220---1320 ℃ can reduce the total mass of the dangerous range hood by 35% - 45%. Adding 1---5% CaO can reduce the accumulation of FCMs by 30---40% by forming a porous structure that is easy to move, while adding 1---5% MgO can lower the formation rate of new FCMs by 25---35% by promoting a stable spinel framework. The proposal of the new suppression measures can reduce the additional energy consumption caused by furnace shutdown, cooling, manual slag removal and reheating start-up for an annual 300,000-ton oxygen-enriched top-blown copper smelting enterprise by approximately 400 tons of standard coal each year.