Hydrometallurgy alumina

Silica mineral reactions

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In lateritic bauxites, silica exists in two forms – as kaolinite clay and quartz.

Under low temperature Bayer digest conditions (150 °C), clay readily dissolves whereas quartz only dissolves at high temperatures (greater than ~200 °C). 

At high temperatures, and in the absence of lime, dissolved silica re-precipitates as sodalite and some cancrinite.

The addition of lime results in the formation of more cancrinite and hydrogarnets.

Bauxite in two hands.

CSIRO research will unlock bauxite deposits currently thought to be uneconomic to process.

Collectively the compounds formed from the dissolution and re-precipitation of bauxite silica is known as desilication products (DSPs).

DSPs are a major cost for alumina producers as they reduce the caustic soda available in the Bayer liquor used in the digestion process. However they do have an up-side, reducing inorganic impurities like chloride, sulphate and carbonate, thus increasing liquor productivity.  

Influencing the formation of desilication products

The type of DSP formed is dependent on reaction temperature and the composition of the liquor from which it is formed. We have a thorough understanding of the formation of DSPs and the effect they have on process performance.

Our team offers expertise in:

  • pre-treatment processes to reduce the input of silica into the process 
  • processes that modify Bayer liquor in order to reduce silica transformation or result in less disruptive forms of DSP 
  • processes to recover soda from DSP.