Red-mud treatment using oxalic acid by UV irradiation assistance

Red-mud is the residue from the Bayer process, in which the iron minerals should be removed before red-mud is used to produce refractory materials. The iron minerals in red-mud were extracted by oxalic acid solution. The content of Fe (calculated in Fe2O3) in red-mud was reduced from 17.6% to less than 1% after being treated by 1 mol/L oxalic acid solution at 75 °C for 2 h. The Fe(III) oxalate solution obtained was then irradiated by UV light, resulting in the precipitation of Fe(II) oxalate. Under UV photocatalysis, more than 90% of Fe(III) oxalate in the extracted solution was transformed into the precipitation of Fe(II) oxalate crystallite (β-FeC2O4·2H2O). The filtrate from the Fe(II) oxalate precipitate filtration could be reused in the next cycle. The mechanism of UV photocatalysis precipitation was also discussed.