Atrazine degradation by aqueous ferrate( <scp>vi</scp> ) activated with sulfite <i>vs.</i> thiosulfate: performance, products, and pathways

Sulfur-reductants (<i>e.g.</i>, 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 <i>s</i>-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 (<i>e.g.</i>, 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 <i>via</i> 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)) <i>vs.</i> Fe(vi)/thiosulfate systems (Fe(iv) alone). These insights advance understanding of the novel Fe(vi)/sulfur-reductants systems, and promote their potential applications.