Characterisation of red mud by UV–vis–NIR spectroscopy

The characterisation of red mud has been studied by diffuse reflectance spectroscopy in the UV–vis–NIR region (DRS). For the first time the ferric ion responsible for the bands has been identified from electronic spectroscopy. It contains valuable amounts of oxidised iron (Fe3+) and aluminium hydroxide. The NIR peak at around 11,630 cm−1 (860 nm) with a split of two components and a pair of sharp bands near 500 nm (20000 cm−1) in the visible spectrum are attributed to Fe3+ ion in distorted sixfold coordinations. The observation of identical spectral patterns (both electronic and vibrational spectra) of red mud before and after seawater neutralisation (SWN) confirmed that there is no effect of seawater neutralisation on structural cation substitutions such as Al3+, Fe3+, Fe2+, Ti3+, etc.