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

Abstract

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.