Every year, approximately 170 M tonnes of bauxite residue is produced globally from the Bayer alumina refining process. The residue, red mud, consists of ultra-fine particles and is extremely alkaline, posing an environmental hazard when stored as a liquid. Filtration to high solids content reduces the risk but is challenging for red mud, which forms compressible and impermeable filter cakes. Conventional filtration technologies are constrained by throughput and achievable moisture content, require regular cloth washing and replacement, and are typically batch operated. This work evaluates High Pressure Dewatering Rolls (HPDR), which is a continuous and cloth-less filter using a 30 μm screen, as an alternative mechanical dewatering technology for red mud.

An experimental program was undertaken to characterise the red mud sample and determine its filtration performance in the HPDR relative to a conventional filter. Particle sizing using light scattering and SEM image analysis confirmed an ultrafine particle suspension (D[3,2] = 3.05 µm). Filtration and sedimentation testing were used to determine compressibility and permeability functions across a broad solids concentration range, allowing prediction of solid-liquid performance. Shear yield stress measurements were used to quantify the susceptibility of red mud to mechanical shear. Red mud was filtered in the HPDR under controlled operating conditions, assessing achievable solids concentration, filtrate quality, and throughput as functions of roller speed, hydraulic pressure, and roll speed differential.

The HPDR successfully filtered red mud to very high corrected cake solids (71 wt%) without the use of flocculants, significantly higher than conventional filtration at ~ 1 MPa (59-60 wt%). Specific solids [...] compared to the conventional filter due to the smaller cake formation pressure. Filtrate solids were relatively high for the HPDR since there was no flocculation but remained [...]. Lower roller speeds and speed differentials of 10 to 20% were found to enhance [...]

Overall, the results demonstrate that HPDR technology can deliver [...] for ultra-fine, compressible tailings such as red mud, particularly where shear-induced dewatering mechanisms can be exploited. The findings provide practical guidance on material selection, operating windows, and key limitations relevant to the industrial deployment of HPDR as a complementary or alternative tailings de