Impact of Bauxite quality on process efficiency of Alumina refinery

Hi Friends,

We are aware that the total bauxite reserves in the World is about 39,950 Million tonnes based on the exploration of bauxite carried out so far and estimated annual production of Bauxite for metallurgical as well as non-metallurgical applications in the World is about 215 Million tonnes per annum (Mtpa). Thus we have adequate bauxite reserves to sustain the successful operation of existing Alumina refineries of the World for over 185 years from now. Outcome of past exploration study raise our confidence level on ongoing exploration work to provide us ample resources to take care of expansion of existing plants and addition of new capacity all over the World. In present post, we will concentrate ourselves to analyse the impact of bauxite quality on process efficiency figures thereby economic viability of Alumina refinery in any part of the globe. Thus, bauxite quality plays vital role in achieving improved process efficiency figures as described in subsequent paragraphs. 

• Bauxite having module (ratio of total Al₂O₃ and total SiO₂) more than 8 with minimum alumina content of 40% and maximum silica content of 5% is considered acceptable for its processing by commercially proven Bayer's process. Module less than 6.5 is considered uneconomical.
• Out of total silica present in Bauxite, reactive silica content generally varies from 50% to 80% of total silica. High reactive silica causes high soda loss on account of high chemical soda loss. 
• High quartz content causes additional soda loss at digestion above 250 degree C as above this temperature non-reactive silica (Quartz) gets converted to reactive silica and forms sodalite as well as cancrinite complexes.
• Presence of high organic carbon and high P2O5 content will badly affect the productivity and product purity.
• Low Fe2O3 content  and high Goethite to Haematite ratio are not desirable in Bauxite as these factors directly  affect the settling rate of bauxite residue in settlers and washers badly affecting the residue washing efficiency ultimately causing high soda loss with washed residue.

These are the major impacts of poor quality of Bauxite on efficiency figures of Alumina refinery. Please put your views / suggestions / remarks / comments, if any.



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Kunwar Rajendra