Objective
Objectives
The production of alumina by the Bayer process involves three main steps: digestion of bauxite, precipitation of aluminum trihydrate (gibbsite, Al2O3.3H2O) from the resulting solution and calcining of the gibbsite at 980 - 1200oC to produce alumina. The calcination step absorbs 3 GJ/t alumina or 25% of the total Bayer process. The objective of the current project is to develop a highly innovative modification of the Bayer process, whereby aluminum monohydrate (boehmite, Al2O3.H2O) rather than the trihydrate will be the product of the precipitation stage. This will result in significant energy savings, estimated to 1.8 GJ/t alumina or 60% over the current practice at 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.
Technical Approach
Initially chemical modeling of the system H2O-Na2O-Al will be carried out and the stability area of boehmite and gibbsite as well as the solubility of boehmite in sodium hydroxide solutions will be determined as a function of temperature and alkali concentration.
Based on the above, the precipitation of boehmite from aluminate liquors will be studied experimentally; the effect of a number of parameters such as precipitation temperature and time, concentrations, quantity and quality of seed, on the physical properties of the product and on the extent of the reaction will be investigated in detail.
A mathematical model will then be developed to describe the precipitation of boehmite combining thermodynamic and kinetic equations with material, energy and population balances. This model will be incorporated into a simulator and used to develop the optimum processing flow-sheet for the precipitation section. A preliminary technological and economical evaluation of the proposed process will then be carried out in comparison with the existing gibbsite process.
Expected Achievements and Exploitation
The output of this project will be a modification of the precipitation section of the Bayer process whereby aluminum monohydrate (boehmite, Al2O3.H2O) rather than trihydrate (gibbsite, Al2O3.3H2O) will be precipitated. This will result in energy savings of 1.8 GJ/t alumina; for an average size smelter producing 1.000.000 t alumina/year, this represents savings of 1.8x106 GJ/year. Because of this huge energy savings potential, it is expected that the proposed Bayer process modification will be applied to all new smelters; it is also possible that the incentive will be high enough so that it will be adopted by existing smelters as well, with the appropriate modifications in the precipitation section.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: https://op.europa.eu/en/web/eu-vocabularies/euroscivoc.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: https://op.europa.eu/en/web/eu-vocabularies/euroscivoc.
- natural sciences chemical sciences inorganic chemistry alkali metals
- natural sciences mathematics applied mathematics mathematical model
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Programme(s)
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Funding scheme (or “Type of Action”) inside a programme with common features. It specifies: the scope of what is funded; the reimbursement rate; specific evaluation criteria to qualify for funding; and the use of simplified forms of costs like lump sums.
Coordinator
15780 ATHENS
Greece
The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.