Simultaneous removal of lead, cadmium, and norfloxacin by Calcite/PMS system: Performance and mechanisms

This work investigated the performance and mechanisms of calcite activating peroxymonosulfate (PMS) for the simultaneous elimination of lead (Pb(II)), cadmium (Cd(II)), and norfloxacin (NOR). At an initial pH = 7, 1.0 g/L calcite, and 0.5 mM PMS, the removal of Pb(II), Cd(II), and NOR was 97.5%, 96.0%, and 98.1%, respectively. The results of EPR, quenching, and chemical probe quantification experiments revealed that singlet oxygen (1O2) derived from calcite activating PMS dominated NOR degradation. Meanwhile, surface complexation and carbonate precipitation were identified as the main mechanisms in the removal of Pb(II) and Cd(II) by ATR-FTIR and different ionic strength experiments, respectively. Kinetic analysis and XPS results indicated that the solid phase Pb(IV) generated through surface complexed Pb(II) oxidized by PMS facilitated the NOR degradation. The NOR degradation pathway along with biological toxicity assessment was also presented through HPLC-MS and ECOSAR software. This study provides the prospects of using natural carbonate minerals to activate PMS for treating the combined contamination of antibiotics and heavy metal ions, and also provides a new understanding of the removal of organic substances in the presence of heavy metal ions.