Efficient solid-liquid separation of fine tailings is essential for improving water recovery and tailings management in mineral processing. In this study, the combined effects of flocculant dosage and water chemistry on sedimentation, floc size evolution, and pressure filtration behavior of sulfide iron ore tailings were investigated. A representative tailings sample from a concentrator, characterised by XRF, XRD, and SEM-EDS, was treated with a commercial anionic polyacrylamide-based flocculant using pure water and plant process water. Sedimentation performance was evaluated using interface height and supernatant turbidity; floc size evolution was monitored by laser diffraction; and pressure filtration tests were conducted at 7 bar using filter chambers with thicknesses of 25, 32, and 40 mm. The results showed that the addition of the flocculant significantly improved settling and clarification compared with the unconditioned suspension. A dosage of 30 g/Mg produced the most compact sediment bed and the most shear-resistant flocs, while increasing the dosage to 60 g/Mg further reduced supernatant turbidity, particularly in process water. At 120 g/Mg, excessive polymer addition partially restabilized the suspension and increased floc breakage, resulting in higher supernatant turbidity. Pure water consistently promoted faster settling, whereas process water provided better clarification at intermediate dosages, consistent with obtained zeta potential measurements indicating electrical double-layer compression and cation-mediated aggregation. Pressure filtration tests showed that increasing chamber thickness increased cumulative filtrate recovery, reaching 32.30% for the 40 mm chamber, while final cake moisture remained similar for all chamber configurations. Overall, 30 g/Mg was identified as the optimum flocculant dosage, providing the best balance between settling, sediment consolidation, floc stability, and filtration performance. These findings show that recycled process water can be used effectively without compromising dewatering performance.