THE ELECTROCHEMICAL MANAGEMENT OF SCALE BUILD UP IN BAYER SOLUTIONS: FROM THE LABORATORY TO THE FIELD

von Moger, W. and Holloway, L.

The formation of scale in the Bayer process is a well know challenge to the alumina industry. Research focused on the nature of scale formation in Bayer process liquors has found the bulk scale formations in the Bayer process are most commonly sodium aluminosilicate and alumina hydroxide scales, with the main phases of sodalite, cancrinite and gibbsite. These scale formations can bond very well to the steel surfaces in pipes and tanks throughout the Bayer process, and can accumulate to form thick layers of scale. Due to the strong bonding between accumulating scale and the underlying steel a combination of chemical and mechanical cleaning may be employed to combat scale accumulation. The nature of this cleaning can also be hazardous to employees conducting the cleaning or working in nearby areas, increasing the importance of technologies that allow for reductions in the frequency and/or duration of scheduled cleaning.

Electrochemical scale management (ECSM) technology has been successfully used in the paper pulping industry for over 25 years. Early applications of ECSM focused primarily on plants utilising the kraft process to convert wood chips into pulp; a process which uses a highly alkaline mixture of sodium hydroxide and sodium sulphide. Over the past 10 years considerable effort has been made into adapting this technology for application in the Bayer process.

This paper presents the findings from the fundamental research conducted over that 10 year period through to the results from the latest field applications. The results presented include;

  • The electrochemical characterisation of the Bayer process from both real life and synthetic solutions using potential dynamic scans.
  • Scanning electron microscopy analysis of scale formation on steel electrodes under the application of an electrochemical signal.
  • The assessment of ECSM and the risks of inducing stress corrosion cracking.
  • Evidence of the significant reduction in scale accumulation where ECSM has been applied in the field.