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Effect of molecular weight of poly(N-isopropyl acrylamide) temperature-sensitive flocculants on dewatering

Authors

  • Haihong Li,

    1. Australian Mineral Science Research Institute, Chemical and Biomolecular Engineering, University of Melbourne, Victoria, 3010, Australia
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  • John-Paul O'Shea,

    1. Australian Mineral Science Research Institute, Chemical and Biomolecular Engineering, University of Melbourne, Victoria, 3010, Australia
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  • George V. Franks

    Corresponding author
    1. Australian Mineral Science Research Institute, Chemical and Biomolecular Engineering, University of Melbourne, Victoria, 3010, Australia
    • Australia Mineral Science Research Institute, Chemical and Biomolecular Engineering, University of Melbourne, Victoria, 3010, Australia
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Abstract

The influence of molecular weight (MW) and dose of Poly(N-isopropyl acrylamide) (PNIPAM) (temperature-sensitive flocculant) on sedimentation rate, sediment density, and supernatant clarity of silica suspensions was investigated. The addition of PNIPAM 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. © 2009 American Institute of Chemical Engineers AIChE J, 2009

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