lkali Metal ferrates; bio-superoxidants : synthesis and application in wastewater treatment

Abstract

This study aims to optimize the conditions of ferrate (VI) production using both dry and electrochemical methods. The electrochemical synthesis was performed in a two- compartment cell using chitosan membranes, while the dry synthesis used a double-walled cell. Key parameters such as current density, temperature, electrolyte concentration, electrolysis time, and electrode type were optimized for both membranes. For the dry method, particle size, drying time and temperature (for both the precursor and the ferrate (VI) product), reaction time and temperature, and washing number were also evaluated. Optimal conditions for ferrate (VI) synthesis were established for both electrochemical and dry methods. Using the chitosan membrane, the best electrochemical conditions were 210 minutes of electrolysis at 30 °C, with a current density of 60 mA/cm² in 24 M NaOH and 0.12%C electrodes, yielding 0.19 M ferrate (VI).For the dry method, the optimal process used iron sulfate particles sized 160–200 μm, pre- dried at 90 °C for 10 minutes, reacted at 30 °C for 60 minutes, followed by drying at 100 °C for 15 minutes and triple methanol washing. This achieved a maximum ferrate (VI) purity of 98.85%.The resulting product was characterized quantitatively and qualitatively using UV– Vis, XRD, FTIR, SEM, TGA, CV and chromite titration. The characterization findings reveals that the synthesized product with both method is ferrate (VI). The UV–Vis analysis revealed characteristic absorption peaks within the typical range of 500–510 nm, the XRD pattern and SEM images confirms an orthorhombic structure, and the FTIR spectra show a distinct peak of Fe-O bond. The synthesized ferrate was subsequently applied in wastewater treatment, demonstrating significant and promising efficiency in the removal of key pollutants. Under optimal ferrate, concentrations rang of [0.08-0.12] %, the removal rates reached up to 94% for COD, 98% for BOD₅, 91% for nitrate, 97.22% for nitrite, 95.8% for ammonium, and 100% of bacterial removal.