Flocculation by polymers

In order to generate information on the mechanism of flocculation by polymers it is, however, necessary to correlate flocculation with various system properties, particularly adsorption. Thus, if particle/polymer-polymer/particle contact is the aggregation mechanism, the flocculation responses should be expected to continuously increase with surface coverage. On the other hand, if particle/polymer-particle contact is predominant and if the polymer adsorption is essentially irreversible, maximum flocculation might be expected under submonolayer conditions. In order to determine the nature of this relationship for the present systems, selected flocculation responses are plotted in Figures 8 and 9 as a function of surface coverage for the nonionic and the anionic polymer respectively. The assumptions involved in the computation of the surface coverage are to be noted at this point ... 

The increase in the rheological parameters, ri0> G0 and 1(5 with reduction in surface coverage points towards an increase in particle interaction. This could be the result of either flocculation by polymer "bridging" (which is favourable at coverages <0.5) or as a result of coagulation due to the van der Waals attraction between the "bare" patches on the particles. In the absence of any quantitative relationship between interaction forces and rheology, it is clearly difficult... 

Figure 7.7 Diagramatic representation of flocculation by polymer bridging.

J. Gregory and L. Xing, Influence of Rapid Mix Conditions on Flocculation by Polymers in Dispersion and Aggregation Fundamentals and Applications, B.M. Moudgil and P. Somasundaran (eds.). Engineering Foundation, New York, 1994, pp. 427-441. 

A polymer molecule may also simultaneously adsorb onto both surface, hence causing flocculation by polymer-bridging mechanism [8], Figure 3.2 shown this behavior. 

Y. Otsubo Elastic percolation in suspensions flocculated by polymer bridging. Langmuir 6, 114-118 (1992)... 

An interesting illustration is found in the production of aluminium from the mineral bauxite. After grinding the ore. the AljOg Is dissolved by alkali to give aluminate. The insoluble ore particles left behind are flocculated by polymer and thus separated. Hien the aluminate is acidified again, and the colloidal AI2O3 is concentrated by flocculants and further used for the production of aluminium. 

Often stabilization and destabilization may occur in the same system. At high polymer concentrations the system may be strongly stabilized whereas at low concentrations the dispersion may flocculate. In the latter case, a distinction can be made between (a) adsorption flocculation (. ., flocculation by polymer only) and (b) sensitization (i.e.y in addition to polymer some electrolyte is needed to ensure complete flocculation). 

Colloidal aggregates may be formed by different mechanisms. For instance, particles surrounded by an electrical double layer coagulate either in the primary or secondary minimum by the addition of salt. Polymer-coated particles may flocculate by polymer bridging or by changing the composition of the medium such that the polymer coats become insoluble. 

J Gregory. Flocculation by polymers and polyelecirolytes. In Th F. Tadro.s. ed. Solid/liquid dispersions. London Academic Press, 1987. chapter 8,... 

Gregory J, Barany S (2011) Adsorption and flocculation by polymers and polymer mixtines. Adv Colloid Interface Sci 169 1... 

Oily sludge with flocculation by polymer alone 25 to 40%. 

Suspensions Flocculated by Polymer Bridging and Cross-linking... 

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