- The kinetics of polymer-induced flocculation in an agitated suspension has been investigated. A typical floc growth pattern under continuous polymer addition has been observed: initially, the floc size increases steadily; then the growth rate gradually decreases until a limiting "equilibrium" floc size is reached. A model has been formulated based on the assumption that floc growth results from the simultaneous agglomeration and breakage of flocs.
Flocculation experiments performed in concentrated (3 wt. % solids) suspensions revealed that both the rate of agglomeration and breakage increase, although not in direct proportion, with increasing rate of polymer addition. This results in higher initial floc growth rate and final limiting floc size. Increased agitation speed does not change the rate of agglomeration but does increase the rate of breakage which therefore results in a lower final limiting floc size. For dilute suspensions, however, the limiting floc size is essentially independent of the rate of polymer addition and agitation speed. The suspension pH has an effect on the agglomeration rate because the surface charge conditions are changed by pH adjustment. The rate of agglomeration is low when the surface is highly charged and vice versa.
Polymer adsorption has been investigated. The initial state of dispersion of the suspension has a prominent effect of the polymer adsorbed. When suspensions are initially unstable, the amount of polymer adsorption is extremely low probably due to limited surface area and accelerated flocculation. For unstable suspensions, high agitation speeds and low rates of polymer addition result in high polymer adsorption. When suspensions are initially stable the physical conditions have a negligible effect on adsorption. Oppositely charged particle surfaces and polymers lead to enhanced adsorption; when the charges are similar adsorption is suppressed and may even be completely prevented for low molecular weight polymers.
The feasibility of using high molecular weight polymeric flocculants as binders in non-clay ceramic systems has been studied. It has been shown that green strength is closely correlated to the amount of polymer adsorption, and not the amount of polymer addition. Green strength comparable to that achieved using conventional binders has been obtained at a significantly lower level of polymer dosage.
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- Dissertation Note:
- Ph.D. The Pennsylvania State University 1988.
- Source: Dissertation Abstracts International, Volume: 50-03, Section: B, page: 1088.
Adviser: Richard Hogg.
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