On line continuous chemical synthesis of ferrate(VI): Enhanced yield and removal of pollutants

This paper presents a new process to synthesize ferrate(VI) (Fe VI O 4 −2 ) continuously through the oxidation of ferric ion (Fe 3+) by hypochlorite (OCl - ) under alkaline condition. Synthesis was performed under different experimental conditions ([OH - ] = 5.0 – 16.0 M, and T = 20 – 45 °C) to obtain optimum yield of ferrate(VI). Under the most favorable condition (i.e., ([Fe 3+ ] = 0.10 M, [OCl - ]: [Fe 3+ ] = 10.0, [OH - ] = 10.0 M, and T = 40 °C), the yield of ferrate(VI) in the newly designed reactor increased by about 11% in 60 min compared to conventional reactor (or increased in [FeO 4 2- ] from 4.0 × 10 −2 M to 4.5 × 10 −2 M). The rapid mixing under flow condition in the closed coil of the new reactor improved the reaction efficiency and yield. When [Fe 3+ ] was varied in the range from 0.10 to 0.20 M in the reactor under the same condition, the optimum concentration of Fe 3+ was at 0.16 M, which increased the concentration of FeO 4 2- to 6.8 × 10 −2 M. Applying ultrasound power density (5.0–25.0 W/L) in the reaction process further increased the yield by about 12% (or increased [FeO 4 2- ] from 6.8 × 10 −2 M without ultrasound to 7.6 × 10 −2 M at 15.0 W/L). Overall, operating the newly designed reactor under ultrasound could increase the concentration of synthesized ferrate(VI) from 4.0 × 10 −2 M to 7.6 × 10 −2 M. At pH 7.0, the prepared ferrate(VI) completely removed atrazine (ATZ), sulfachloropyridazine (SCP), ibuprofen (IBP), and naproxen (NAP)) in water.