Catalytic Degradation of Sulfamethazine by Ferrate(VI)-Activated Calcium Sulfite: Performance and Mechanism

Calcium sulfite (CaSO3) is introduced as a solid-phase sulfite source with slow-release characteristics to overcome the drawbacks of highly soluble sulfite in conventional S(IV)-based advanced oxidation processes (AOPs). In this work, we establish a catalytic Fe(VI)/CaSO3 system for the efficient degradation of sulfamethazine (SMT). The system operates through a catalytic cycle wherein ferrate(VI) activates sulfite to generate sulfate radicals (SO4•−) and hydroxyl radicals (•OH) as the primary reactive oxygen species (ROS), with concomitant involvement of high-valent iron species (Fe(V)/Fe(IV)) and singlet oxygen (1O2). The catalytic mechanism, involving electron transfer and radical chain reactions, is elucidated by EPR spectroscopy, radical quenching experiments, and probe tests. The Fe(VI)/CaSO3 system achieves 98.6% SMT removal within 20 min and exhibits broad-spectrum activity against various organic pollutants. The catalytic performance remains robust over a wide pH range and in the presence of coexisting ions and natural organic matter. This study highlights the potential of ferrate(VI)-activated calcium sulfite as a promising catalytic AOP platform for water treatment.