Thallium flow network in a zinc hydrometallurgy system and evaluation of thallium fate pathways from a collaborative...

Thallium (Tl) is a highly toxic rare element, and zinc hydrometallurgy is a main anthropogenic source of Tl pollution in the environment. A comprehensive understanding of Tl metabolism throughout the entire process is critical for effective control and management. This study established a process-level substance flow analysis (SFA) model for Tl in the zinc hydrometallurgy system, incorporating both main and auxiliary processes, to systematically analyze Tl flow and distribution characteristics. Two key Tl fate pathways-purification residue (PR) and high-fluorine-chlorine dust (HFCD)-were evaluated for environmental risks, transfer costs and benefits. And a multi-criteria decision-making (MCDM) approach was employed to prioritize the two fate pathways under different policy-driven scenarios from a techno-enviro-economic collaborative perspective. Results revealed that under identical system inputs, Tl was mainly introduced via mixed zinc concentrates (97.79% of the total Tl input mass in the zinc hydrometallurgical process) and predominantly enriched in PR (86.07% with an enrichment ratio of 547.50 relative to the mixed zinc concentrates) or HFCD (82.33% with an enrichment ratio of 441.60 relative to the mixed zinc concentrates). And policy scenarios influenced pathway preferences: under baseline and pollution-control-oriented scenarios, the HFCD fate pathway emerged as the superior option, whereas the PR fate pathway slightly excelled in the resource-recovery-oriented scenario. These findings provide useful and theoretical insights for decision-makers in zinc hydrometallurgy enterprises to prioritize Tl fate pathways, and promote a balanced integration of technological feasibility, economic practicality and environmental sustainability in Tl enrichment regulation.