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The objective of the current project was the development of a highly innovative modification of the Bayer process, whereby aluminium monohydrate (boehmite, Al2O3.H2O) rather than the trihydrate is the product of the precipitation stage. This modification will result in significant energy savings during the calcination stage because (a) the enthalpy of dehydration of boehmite to alumina is lower by 1.1 GJ/t alumina compared to that of gibbsite, and (b) the quantity of material to be calcined will be reduced by 20% per t alumina, as only one rather than three moles of water are associated to one mole of alumina. The energy saving in calcination of boehmite is estimated to be 34.8 kg/t of alumina for fuel oil and 7.2 kWh/t of alumina for electricity. This corresponds to 40-50% less fuel or electricity consumption compared with gibbsite calcination for the same alumina production. For a typical Bayer process plant with a capacity of 1.000.000 tpa alumina, this represents energy savings of 35000 t of fuel oil per year.

In the present project the condition of boehmite precipitation from aluminate liquors have been studied in detail. A theoretical model predicted boehmite solubility in caustic solutions has been developed and also validated by the experimental data of boehmite solubility in such solutions. Detail kinetic analysis of experimental data has been carried out and a kinetic equation has been established. This equation has been incorporated into a new simulator and used to develop the optimum processing flow sheet for the precipitation section. Finally, a technological and economical evaluation of the new process has been carried out to. The main results of the research performed are the folowing:
- Boehmite is precipitated from supersaturated sodium aluminate solutions at atmospheric conditions in the presence of boehmite seed.
- The % yield of the new boehmite precipitation process is very close to this achieved in the current gibbsite precipitation pr

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