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Miranda de Castro, M., Wischnewski, R., Corrêa, L.G. and Filho, J.R.A.

Alunorte uses dry stacking based on the technology of Giulini (Schepers & Haerter 1975) for bauxite residue storage. The residue is washed and filtered in drum filters. A high solids content of 64 wt.-% is achieved and specific soda loss is low with less than 6 kg per ton of alumina. Effluent water from the RDA is cleaned and neutralized. The existing concept has a low environmental impact and the advantage of no water returning to the Bayer process.

This paper presents the study of a new concept to move from dry stacking to dry disposal for the next implementation phase of Alunorte's residue disposal area (RDA). A key element is the use of filter presses for residue washing and filtration. It will be possible to increase the residue solids content to about 80 wt.-%. This will result in a number of advantages, such as maximizing the residue storage capacity, increasing lifetime of the RDA, cost reduction and disposing a significantly lower amount of liquid. The environmental performance is kept and specific water consumption for residue washing will be reduced.

Tests which were performed at Alunorte demonstrate the viability of the concept. Field tests with pilot-scale filter presses gave good results. Process simulation was used to quantify process impacts resulting from the replacement of drum filters with filter presses. The water balance of the refinery, the risk of higher organics concentrations in the plant liquor and potential impacts on precipitation productivity are discussed.