Thallium (Tl) poses a significant pollution risk due to its high volatility during clinker calcination. Thermodynamic calculations and multi-stage monitoring have revealed that, despite sulfur suppression, over 90% of Tl volatilised as thallium chloride at 900°C due to chlorine. Volatilised Tl migrated with gas, condensing in cooler zones, enriching Tl in mill-outlet raw meal. The recycling of Tl-enriched dust from the suspension preheater boiler and bag filter further intensified the Tl enrichment in the kiln-feed raw meal. As this enriched material reached the two-stage cyclone, it re-adsorbed and condensed Tl from the gas and reintroduced Tl back into the high-temperature zone again, forming an internal ‘volatilisation-condensation’ cycle. After calcination, only 0–27.85% of input Tl resided in the clinker, while the bypass system released merely 1.31–6.66%. Crucially, the bag filter efficiently intercepted volatile Tl, preventing detectable Tl emissions from kiln gas. Therefore, despite high volatility, the internal cycle, effective dust capture and dust recycling led to closed-loop circulation and enrichment of most Tl within the system, preventing environmental release. In addition, co-processing Tl-containing solid waste amplified the imbalance between Tl input and output, leading to greater internal circulation and enrichment within the kiln system, without significantly altering clinker Tl content or emissions.
Wang et al. (Sat,) studied this question.