Flocculation by polyelectrolytes

Chen, L.A., Carbonell, R.G. and Serad, G.A., Recovery of proteins and other biological compounds using fibrous materials II. Flocculation by polyelectrolyte addition, J. Chem. Technol. Biotechnol., 74, 740,1999. 

The adsorption of polymers to the surface of particles leads to the two fundamental mechanisms of flocculation by polyelectrolytes. These are commonly referred to as the electrostatic or charge patch mechanism and the bridging mechanism and may act individually or, in some instances, simultaneously. 

From this work, it is concluded that 1. the ion exchange of latex to remove adsorbed emulsifier and solute electrolyte may cause flocculation of the latex particles, particularly those of small particle size 2. all three mechanisms proposed for the flocculation are probably operative, but the destabilization because of emulsifier removal and the flocculation by polyelectrolytes leached from the ion-exchange resin account for most of the flocculation ... 

This type of mechanism is likely to be partly operative in systems containing inorganic electrolytes as, for example, in the case of aluminium species. Some polyelectrolytes may also induce flocculation by charge neutralisation but the adsorbed polymer may also be able to bridge from one particle surface to another ( polymer bridging ). 

LA Mer, V. K. Disc. Faraday Soc. 42 (1966) 248. Filtration of colloidal dispersions flocculated by anionic and cationic polyelectrolytes. 

Organic polymeric coagulants and flocculants (or polyelectrolytes) are polymers of repeating monomer units held together by covalent bonds and are available in many hundreds of permutations, in such a variety of molecular weights, ionic charges, physical form, etc., that it has become the province of experts in this field to determine the precise product or combination of products most suitable for any specific purpose. 

Petzold G, Schwarz S, Lunkwitz K (2003) Higher efficiency in particle flocculation by using combinations of oppositely charged polyelectrolytes. Chemical Engineering and Technology 26 48... 

Charge neutralization (simple and/or patch) is often the mechanism for flocculation by low molecular-weight polyelectrolytes. 

Regulation of the physico-chemical properties of colloid dispersions by polyelectrolytes is of great interest from the theoretical and practical points of view [89]. A consideration of the peculiarities of absorption of polyelectrolytes on disperse particles can be of help to clarify some aspects of kinetics and mechanism of flocculation, elemental acts of flocculation, as well as to provide the se-... 

Typical synthetic water soluble flocculants are polyelectrolytes that are most often based upon copolymers of acrylamide or substituted derivatives. Acrylamide monomer is obtained industrially by the catalytic hydration of acrylonitrile and occurs in both crystaUine form and in aqueous solution. The 50% aqueous form is the preferred form for polymerisation systems in which water can be tolerated. Acrylamide has a very fast propagation rate and a high exothermic heat of polymerisation. 

Kasper, D.R. (1971) Theoretical and Experimental Investigations of the Flocculation of Charged Particles in Aqueous Solutions by Polyelectrolytes of Opposite Charge. PhD Thesis, California Institute of Technology, Pasadena. 

The three mechanisms for the flocculation of latex particles upon ion exchange described earlier are 1. depositioh of anionic latex particles on the surface of the cationic resin beads 2. the removal of emulsifier from the surface of particles which have too-few residual surface groups to give stability 3. the flocculation of latex particles by polyelectrolytes leached from the ion-exchange resin. 

Emulsions may be flocculated by the addition of polymers. Excluding those cases where the addition of a polymer affects the van der Waals or electrostatic forces directly (e.g. the addition of polyelectrolytes), the process of polymer-induced flocculation may proceed by two mechanisms, bridging or depletion. These are depicted schematically in Figure 4.3. 

The bonding of P EG was confirmed by gravimetry, IR and conductometric titration of carboxyl groups. Freeze-dried nanocrystals could be redispersed in water or organic solvents and showed strongly increased stability towards flocculation with polyelectrolyte. 

The natural process of bringing particles and polyelectrolytes together by Brownian motion, ie, perikinetic flocculation, often is assisted by orthokinetic flocculation which increases particle coUisions through the motion of the fluid and velocity gradients in the flow. This is the idea behind the use of in-line mixers or paddle-type flocculators in front of some separation equipment like gravity clarifiers. The rate of flocculation in clarifiers is also increased by recycling the floes to increase the rate of particle—particle coUisions through the increase in soUds concentration. 

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