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

Abstract

(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.

Temperature controlled surface hydrophobicity and interaction forces induced by poly (N-isopropylacrylamide)

“…For this reason, the presence of PNIPAM on silica surfaces causes a small decrease in the magnitude of the negative zeta potential of the silica surfaces, with the magnitude of the zeta potential becoming smaller with increasing polymer molecular weight. This is consistent with adsorption studies performed by Li et al [15], which showed that the adsorption density of PNIPAM onto silica surfaces significantly increases with the increase in polymer molecular weight. The adsorption measurements have also shown that at temperatures below the LCST, PNIPAM does adsorb onto silica surfaces, but to a much lesser extent than at higher temperatures.…”

“…4). The repulsive force can instead be attributed to steric repulsion, resulting from a low level of adsorption of fully extended and hydrated PNIPAM molecules [14,15,28]. Contact angle measurements have shown that the presence of PNIPAM on silica surfaces slightly increases their hydrophobicity (see Fig.…”

“…The ability of PNIPAM to undergo controlled transitions from hydrophobic to highly hydrophilic has sparked considerable interest in its suitability as a surface modification reagent in minerals processing. A large number of studies have found PNIPAM to be a highly successful agent for facilitating mineral aggregation and consolidation [9][10][11][12][13][14][15], however questions remain regarding PNIPAM-induced aggregation mechanisms. In typical settling operations, flocculation occurs as a result of polymer bridging between mineral particles, which causes them to form aggregates [16].…”

Probing the stability of sterically stabilized polystyrene particles by centrifugal sedimentation

“…In addition to van der Waals attraction, it has been proposed that the poorly soluble polymeric stabilizers on the particle surface induce an additional 'hydrophobic' attraction. The 'hydrophobic' attraction was first 35 presented by Klein,38,39 who observed the presence of an attractive force in a poor organic solvent for two approaching polymeric coated surfaces. This observation was also seen recently by the Franks group 40 during their temperature investigation of the hydrophilic/hydrophobic nature of poly(N-40 isopropylacrylamide) (PNIPAM) in order to manipulate interparticle interactions.…”

Flocculation of flotation tailings using thermosensitive polymers

“…He used zircon suspension and methylcellulose as the thermosensitive agent. Identical conclusions were made in other papers Li et al, The aggregation via standard flocculation runs in four steps (Gregory, 1993). In the first step a polymer is added to the solution and they are mixed.…”