Removal of Rhodamine B under visible irradiation in the presence of Fe⁰, H₂O₂, citrate and aeration at circumneutral pH.

A new Vis-Fe(0)-H(2)O(2)-citrate-O(2) system comprising zero-valent iron, hydrogen peroxide, citrate anion and aeration at circumneutral pH under visible irradiation was studied. 21 μmol L(-1) of Rhodamine B (RhB) was chosen as the substrate to be tested. Experiments were conducted under conditions of 2.9 mmol L(-1) of H(2)O(2), 12.6g of Fe(0) and 1.0 mmol L(-1) of citrate at pH 7.5. Results showed that, in 1h reaction, 54% of RhB was removed with corresponding 26% of COD reduced. Meanwhile, the amount of released dissolved irons from Fe(0) surface was found to be at a very low level as <5.4 μmol L(-1). Extinguishing tests with isopropanol suggested that RhB oxidation by hydroxyl radicals was the main process taken place in Vis-Fe(0)-H(2)O(2)-citrate-O(2) system, which accounted for 75% of substrate removal in 3h reaction. Control and factor influencing experiments showed that the prohibitive extents of individual factor importance on RhB removal followed a decreasing order of Fe(0)>H(2)O(2)>citrate>Vis>O(2). This study showed an excellent system that could remove refractory organic compounds from water in laboratory researches, and also provided a good idea to reduce secondary contamination by dissolved irons in future investigations.