The chemical analysis of Bayer liquor is a critical requirement for the control of the Bayer process. Knowledge of these parameters is needed to keep Bayer liquors within set limits, which maximise the efficiency of unit processes such as bauxite digestion, aluminium hydrate crystallisation, and causticisation. A ground breaking infrared-based method for Bayer liquor analysis which requires no titrations, liquor dilution or additional reagents has been successfully trialled over a number of months in several alumina refinery laboratories. The method is fully automated and capable of analysing a range of liquor components including alumina, total caustic, total alkalinity, total organic carbon (TOC) and oxalate, along with a range of other organic and inorganic compounds.
Liquor samples from across the entire Bayer process were analysed daily by both currently used routine analysis methods and infrared. The total alumina, total caustic, total alkalinity, TOC and sodium oxalate results from one refinery were compared. The results from the infrared-based system were effectively the same as those obtained from the current routine methods of analysis, except far more detail was available using the trialled commercial infrared-based system. Correlation coefficients between the infrared-based system and routine titrations were typically greater than 0.999 for the alumina, total caustic and total alkalinity results. For the TOC and sodium oxalate results, correlation coefficients were typically greater than 0.995. The analysis time for the infrared-based measurements is substantially shorter than current methods. No fouling of the infrared analyser was observed over the course of the trial. The use of infrared for liquor analysis will undoubtedly provide major benefits to the alumina industry.