Chlorine-mediated electrochemical oxidation process for highly efficient removal of thallium from saline wastewater

Thallium (Tl), an unconventional and highly toxic metal, is increasingly recognized as a significant contaminant in wastewater. One promising strategy to enhance Tl removal is the electrocatalytic oxidation of Tl(I), yet the contribution of chloride ions—prevalent in wastewater from metallurgical and smelting industries—has often been overlooked in such processes. Herein, this study introduces a novel chlorine-mediated electrochemical oxidation system, coupled with a coagulation process, designed to efficiently treat thallium-contaminated saline wastewater. The dimensionally stable anode (Ti/TiO 2 -RuO 2 -IrO 2 , DSA) demonstrates exceptional electrocatalytic chlorine evolution and efficient oxidation of Tl(I), with a kinetic rate constant of 0.131 min −1 , which is 21.8 times faster than that of a carbon cloth anode (0.006 min −1 ) in the presence of Cl − ions. Under optimized conditions of 5 mM Cl − ions at pH 3.0, over 98.3 % of Tl(I) was removed within 30 min. After coagulation treatment, the total Tl removal efficiency reached 98.5 %, in stark contrast to the mere 18.0 % achieved without the pre-electro-oxidation step. Mechanistic analysis revealed that the reactive chlorine species (Cl•) plays a more significant role in the oxidation of thallium (Tl) compared to the hydroxyl radicals. Notably, the system exhibits excellent recyclability (up to 35 cycles) and stable performance in the presence of various competing ions and actual wastewater, even under unsteady-state continuous-flow conditions. These findings offer valuable insights into chlorine-mediated electrocatalytic oxidation coupling with coagulation processes for thallium removal, providing guidance for practical applications in purifying thallium-contaminated industrial wastewater.