Chemical pretreatment enhances vacuum filtration of slime-rich iron ore tailings

Efficient dewatering of iron ore tailings is critical for safer tailings management via dry stacking in Brazil. Typical tailings streams comprise a coarse, siliceous fraction from reverse cationic flotation and an ultrafine slime fraction (<10 μm) generated during desliming before flotation. In industrial practice, both fractions are thickened with anionic polyacrylamides and blended before vacuum filtration at a pressure differential of approximately 0.9 bar. For feeds containing ∼ 10–30 wt% ultrafine particles, this configuration typically produces filter cakes with 16–20 wt% moisture, above the 12–14 wt% target generally required for geotechnically stable dry stacking. This study evaluates chemical pretreatment strategies to improve the vacuum filtration process/performance of typical Brazilian slime-rich iron ore tailings. Conditioning with cationic tannin and/or high-molecular-weight cationic polyacrylamides markedly enhanced dewatering, enabling residual cake moistures of 12–14 wt% for feeds containing up to 30 wt% ultrafine particles. Under optimised conditions (pH 8.0; 55 wt% solids), cationic polyacrylamide achieved 12.5 wt% cake moisture, with a cake formation time of ∼ 10 s, cake thickness of 24 mm, and permeability of ∼ 300–500 mD (vs ∼ 225 mD for the untreated reference). Scanning electron microscopy indicated that cationic conditioning increased cake porosity and was consistent with the observed permeability gains. Overall, cationic-flocculant pretreatment offers a practical route to meet dry-stacking moisture targets for slime-rich iron ore tailings under moderate vacuum pressures, addressing a persistent issue in Brazilian operations.