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(PNIPAM) (temperature-sensitive flocculant) on sedimentation rate, sediment density, and supernatant clarity of silica suspensions was investigated. The addition of PNI-PAM resulted in rapid sedimentation (T [ critical solution temperature, CST) and low sediment moisture (T \ CST). Higher MW polymers resulted in more effective flocculation and sediment consolidation. At 10 ppm, PNIPAM (3.6 million Da) produced 20 m/h settling rate and 48 vol % solids sediment density, whereas 0.23 million Da polymer produced 0.1 m/h settling rate. PNIPAM produces effective flocculation and consolidation by cycling the interparticle interactions between repulsion and attraction as temperature is cycled around the CST. The change in temperature produces a hydrophilic/hydrophobic transition of the polymer, influencing adsorption onto the surface and the inter-particle forces. Conventional polyacrylamide flocculants (not influenced by temperature), cannot be used to produce both rapid sedimentation and dense sediments.

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Temperature responsive charged block-copolymers of poly(N-isopropylacrylamide) (PNIPAM) have been used in the solid-liquid separation of alumina mineral particles from aqueous solution. The effects of temperature, polymer charge-sign and fraction of charged segment have been investigated. Batch settling and adsorption studies showed that rapid sedimentation results for suspensions with polymers of opposite charge-sign to the particle surface-charge (counterionic) at 50 °C. Cooling the suspensions after flocculation at 50 °C was found to increase the final solids volume fraction of the sediment beds formed through a mechanism related to partial desorption of polymer and the reduction of the hydrophobic attraction. Suspension stability results after dosing with polymers of similar charge-sign to the particle surface-charge (co-ionic) at both 25 and 50 °C. Increasing the amount of polymer charge increased the influence of polymer charge-sign on the adsorption and solid-liquid separation behavior. The performance of the charged block copolymers are compared to that of the random charged copolymer and neutral homopolymer PNIPAM structures.