Hydrometallurgy alumina

Impurity control and residue management

Page 5 of 7

Most alumina refineries have two major problems associated with impurities: the formation of crystalline scale deposits and soluble impurities (both organic and inorganic) in the Bayer liquor.


Scale forms in almost every part of an alumina refinery.

Scale deposits can vary from sand-like accretions to cement-like layers consisting of settled red mud solids from bauxite processing.

A person in orange protective coveralls standing next at a steel pipe which containing a tick layer of orange scaley deposits inside.

An example of scale build-up in a pipe in an alumina refinery.

Our researchers offer a fundamental understanding of scale nucleation. This is essential for developing control mechanisms to prevent the formation and growth of scale, and effective strategies for scale removal.

Their expertise includes:

  • in situ x-ray diffraction of scaling simulations
  • nanoscale surface analysis
  • kinetics of scale formation.

Organic impurities

Organic impurities in alumina production diminish the yield of the process and cost the industry of the order of $500 million per annum in Australia alone.

Our researchers offer a deep understanding of the reaction mechanisms of organic impurities and response to oxygen/catalysts. The team has also developed a specialised wet oxidation facility to investigate organic impurities.

Located at CSIRO’s Waterford site in Western Australia, the wet oxidation facility is used to:

  • examine fundamental chemistry involved in oxidising organic mixtures at high pressure and temperature
  • measure hydrogen and volatile organic compound production.

Residue management

Bauxite residue is a highly alkaline by-product arising from the Bayer process to produce refined alumina from feed bauxite ore. 

The characteristics of bauxite residue are primarily a result of the treatment of the bauxite by the application of sodium hydroxide (caustic soda), heat and pressure, as well as lime and other chemical additives. Thickening processes and any pre-disposal caustic recovery or neutralisation treatments can further alter the residue. 

The chemical and physical characteristics of residue requires sophisticated impoundment engineering to minimise environmental impact, and can also cause closure and rehabilitation (such as re-establishing vegetation) difficulties.

The ultimate solution to the problem lies with finding avenues for bauxite residue utilisation in other areas of the economy.

Our research is focused on fully understanding residue characteristics in such a way that its direct environmental impact can be minimised and future uses for the residue can be found.

Our researchers offer residue research and characterisation expertise in the following areas:

  • mineralogical description of bauxite residues 
  • physical description: particle size, bulk density, surface area
  • understanding of toxic metal association, speciation, adsorption  and reactivity
  • acid neutralising capacity (ANC) and pH behaviour
  • soda behaviour
  • surface charge effects
  • fundamental chemistry of leaching and neutralisation.