Speciation Analysis and Advanced Removal of Thallium from Washing Wastewater of Sintering Machine Head Ash
Sintering ash washing wastewater from steel plants is characterized by high salinity, high chloride content, high thallium load, and coexistence of multiple metals, posing significant treatment challenges. This study employed thermodynamic simulation to elucidate the speciation and transformation of thallium in such wastewater, and systematically investigated a combined process of sulfide precipitation coupled with coagulation-flocculation. The results showed that at pH 9–10, thallium predominantly existed as Tl+. Under oxidizing conditions, the stable complex anion [TlCl4]− dominated at pH < 8.1, while at pH > 8.1, a mixed system of solid Tl2O3 and dissolved TlClO3 coexisted. Under optimized conditions (pH 12, 2.0% thallium removal agent, 1.0% multi-effect auxiliary agent), the thallium concentration in the wastewater decreased from an initial 9.58 mg·L−1 to 4.31 μg·L−1, meeting the stringent discharge limit of ≤5 μg·L−1. Concurrent removal of Cu, Zn, and Cd was achieved. The primary removal mechanism was sulfide precipitation, with lattice substitution between Tl+ and K+ serving as an auxiliary pathway. This study provides a practicable technical route for advanced treatment of high-chloride, high-thallium industrial wastewater.