Quantitative analysis in alkaline aluminate solutions by Raman spectroscopy

A detailed investigation has been made of the analysis of concentrated alkaline aluminate solutions (synthetic Bayer liquors) by Fourier transform (FT) Raman spectroscopy. Satisfactory determinations of Al(OH)₄ ^–, SO₄ ^2– and CO₃ ^2– were achieved at industrially-relevant concentrations. Possible extensions to a number of other inorganic and organic anions of interest to the alumina refining industry were demonstrated. No significant interferences were observed except for a small but readily correctable contribution of a minor SO₄ ^2– mode at ∼615 cm^–1 to the Al(OH)₄ ^– envelope centred at ∼620 cm^–1. Hydroxide (OH^–) could not be determined with the present FT instrument, due to the low detector sensitivity at high wavenumbers, but might be possible with other spectrometers. Successful extension of the analyses to industrial Bayer process solutions is briefly discussed.