Recovery of sodium from bauxite residue by pressure filtration and cake washing

•Filtration and washing of bauxite residue in a vertical filter press were studied.•A sodium recovery of 98% was obtained at a wash ratio of 1.4.•Dissolution of Na increased with the temperature, Δp and the wash ratio.•The classic cake washing sequence was shown to be most effective.•The selected washing sequence had an effect on the uniformity of cake washing.

Bauxite residue, the main waste fraction of alumina production, is extremely hazardous to the environment, as well as to human health. After the recovery of the pregnant liquor, the washed and thickened bauxite residue is typically pumped as thick slurry to a residue disposal area. The use of filter presses for the final washing, in order to further enhance the recovery of alkali and aluminum, together with effective deliquoring, may be beneficial in many cases. In this study, a vertical filter press (A = 0.1 m2) was used for the filtration and washing of industrial bauxite residue. The effectiveness of various washing sequences, as well as variation in the local washing results in the filter cakes, was compared. The results show that Na recovery of 98% can be obtained at a wash ratio as low as 1.4. It was also observed that not only the wash ratio is important: temperature and pressure have a significant effect on the dissolution of Na.