Enabling safe dry cake disposal of bauxite residue by deliquoring and washing with a membrane filter press

Dry cake disposal is the preferred technique for the disposal of bauxite residue, when considering environmental issues together with possible future utilisation of the solids. In order to perform dry cake disposal in an economical way, the deliquoring of the residue must be carried out efficiently, and it is also important to wash the obtained solids well to minimise the amount of soluble soda within the solids. The study presented in this article aims at detecting the most important variables influencing the deliquoring and washing of bauxite residue, performed with a horizontal membrane filter press and by determining the optimal washing conditions. The results obtained from pilot-scale experiments are evaluated by considering the properties of the solids, for instance, the residual alkali and aluminium content, as well as the consumption of wash liquid. Two different cake washing techniques, namely classic washing and channel washing, are also used and their performances compared. The results show that cake washing can be performed successfully in a horizontal membrane filter press, and significant improvements in the recovery of alkali and aluminium can be achieved compared with pressure filtration carried out without washing, or especially compared with the more traditionally used vacuum filtration.