Speciation Analysis and Advanced Removal of Thallium from Washing Wastewater of Sintering Machine Head Ash

• • At optimized conditions (pH 12, 2.0% thallium removal agent, 1.0% multi-effect auxiliary agent), thallium concentration was reduced from 9.58 mg·L−1 to 4.31 μg·L−1, achieving a removal efficiency of 99.955% and meeting the ≤5 μg·L−1 discharge standard (GB 13456-2012). • • Thermodynamic simulation revealed that at pH 9–10, Tl+ is the dominant species; under oxidizing conditions, [TlCl4]− forms at pH < 8.1, while at pH > 8.1, Tl2O3(s) and TlClO3(aq) coexist, guiding pH control for optimal removal. • • The combined sulfide precipitation-coagulation-flocculation process simultaneously removed Cu, Zn, and Cd, addressing the challenge of multi-metal coexistence in high-salinity wastewater. • • The identification of KxTlyCl phases confirms lattice substitution between Tl+ and K+ as an auxiliary removal mechanism, enhancing understanding of thallium immobilization in complex matrices.