Conventional, polymeric flocculants which are widely used in flocculation and dewatering of clay mineral tailings are mostly completely hydrophilic polymers and therefore have the drawback that the flocs trapped large amount of water and produce low solid content (e.g. 20-25 wt%) sediments. One of the non-conventional polymers of significant interest in recent year is thermosensitive poly(N-isopropylacrylamide) (PNIPAM) which undergoes phase-transition from hydrophilic coiled state to the hydrophobic globule state upon raising the temperature above the lower critical solution temperature (LCST, ~32 ºC) in aqueous system.

In the present works, the influence of suspension temperature, PNIPAM molecular weight (MW: 0.81 - 2.02 × 10⁶ Da), different dosing methods and sonication on flocculation and dewatering behaviour of talc suspensions is investigated. PNIPAM addition to suspension pre-heated to 50 ºC gave a fast settling rate (e.g. 5-9 m/h) but turbid supernatant. For PNIPAM dosed at 22 ºC then slowly heated up to 50 ºC, the initial settling rates increased gradually with increasing temperature, accompanied by good supernatant clarity. An abrupt increase in settling rate (from 1 m/h to 8 m/h) was displayed by PNIPAM polymer around the LCST. Settling behaviour improved dramatically with increasing polymer MW. Improvement of ≈ 3-8 wt% in consolidation was achieved upon pulp sonication for 30 min, leading to floc densification. Flocculant dewatering optimization studies provide useful information in the development and novel application of temperature responsive flocculants.