Atrazine degradation by aqueous ferrate(vi) activated with sulfite vs. thiosulfate: performance, products, and...

Sulfur-reductants (e.g., sulfite and thiosulfate) can enhance ferrate (Fe(vi)) oxidation toward organic contaminants, which has recently attracted increasing attention. This work presented a systematic and comparative study on the oxidation performance, products, and pathways of atrazine (ATZ, one of the most widely used s-triazine herbicides) by Fe(vi)/sulfite and Fe(vi)/thiosulfate systems. Both systems achieved efficient ATZ degradation with the optimal efficiency at neutral pH, and the efficiency was affected by reagents dosage and co-existing components (e.g., Cl^-, NO₂ ^-, natural organic matter). Five oxidation products of ATZ were produced in Fe(vi)/sulfite and Fe(vi)/thiosulfate systems, and their formation was quantified. ATZ degradation was initiated via electron transfer, resulting in dealkylation, alkylic-oxidation, and dechlorination-hydroxylation. Specifically, the molar ratio of two primary products (atrazine amide (CDIT) and deethyl-atrazine (DEA)) was calculated. In Fe(vi)/sulfite system, the [CDIT]/[DEA] value varied in the range of 0.04-0.82, depending on solution chemistry. Comparatively, the ratio obtained in Fe(vi)/thiosulfate system kept relatively constant at ∼0.2 under various conditions, coinciding with that reported in pure Fe(iv) oxidation. This discrepancy was attributed to the difference of reactive oxidants involved in Fe(vi)/sulfite (SO₄˙^- and Fe(v)/Fe(iv)) vs. Fe(vi)/thiosulfate systems (Fe(iv) alone). These insights advance understanding of the novel Fe(vi)/sulfur-reductants systems, and promote their potential applications.