Study on the removal of fulvic acid in water by potassium ferrate-enhanced iron–manganese co-oxide film and its mechanism.

The previous studies have shown that iron–manganese co-oxide film (MeO_x) could simultaneously remove ammonium, manganese ion and bisphenol A. In this study, the removal of fulvic acid (FA) was explored by adding potassium ferrate (K₂FeO₄) to heighten the catalytic activity of MeO_x. After adding about 3.0 mg/L potassium ferrate, the elimination efficiency of 7.0 mg/L FA by the MeO_x increased from 20 to 50%. The effects of temperature and ammonium on the elimination of FA were investigated. Higher temperature (above 22 °C) and higher ammonium concentration (above 2.0 mg/L) caused a decrease in FA removal. Most of FA combined with the ferric hydroxide colloid produced by K₂FeO₄ in water to form macromolecular groups, and they were subsequently absorbed and covered on the surface of MeO_x. Scanning electron microscope showed that more viscous flocs appeared on the surface of MeO_x, and the film thickness became thicker. Electron energy-dispersive spectrometer analysis revealed a notable increased in the C–O element ratio and a significant decreased in the Mn–Fe element ratio on the surface of MeO_x. From Fourier transform infrared spectroscopy, the content of transition metal carbonyl compounds increased in the surface of MeO_x. XPS analysis confirmed that the presence of Fe₃O₄, FeO, Mn₂O₃ and Mn₃O₄ along with functional group substances of FA attached on the surface of MeO_x. The removal mechanism of FA was studied. [ABSTRACT FROM AUTHOR]