Comparison of Hydroxylamine Hydrochloride and Hydrogen Peroxide in Activated Fe(VI) for Fracturing Flowback Fluid Treatment: Efficiency, Mechanism, and Toxicity Analysis

Ferrate(VI) oxidation is an effective approach for organic wastewater treatment. However, its application in fracturing flowback fluid with high salinity and complex contaminants requires further investigation. In this study, two distinct Fe(VI) activation strategies, hydroxylamine hydrochloride and hydrogen peroxide, were applied to enhance contaminants oxidation in fracturing flowback fluid. The results showed HA facilitated Fe(IV)/Fe(V) generation by electron transfer, whereas exogenous H₂O₂ enhanced ·OH generation. Both Fe(VI) activated systems improved pollutant degradation compared with Fe(VI) alone. Under optimal conditions, Fe(VI)-H₂O₂ system dominated by ·OH exhibited better organic removal (TOC removal 46.0%, UV₂₅₄ removal 66.6%, and the BOD₅/COD value (the B/C) 0.436) than Fe(VI)-HA system dominated by Fe(IV)/Fe(V) (TOC removal 33.7%, UV₂₅₄ removal 61.5%, and the B/C 0.332). The organic species number in the Fe(VI)-H₂O₂ system was reduced by nearly half than Fe(VI)-HA, and the system can completely remove the alcohols, acids, and ether substances. In addition, toxicity tests showed that in high salinity wastewater (Cl^- and salinity concentration of 5498.9 and 10332.0 mg/L), both HA and H₂O₂ activated Fe(VI) strategies can decrease the acute toxicity and phytotoxicity. Overall, both HA and H₂O₂-activated Fe(VI) oxidation are feasible for treating fracturing flowback fluid, with H₂O₂-activated Fe(VI) oxidation exhibiting higher efficacy.